Dissertations / Theses on the topic 'Flash flood'

A major area targeted for hydrometeorological forecast service improvements is in flash flood forecasting. Verification data show that general public service products of flash flood forecasts do not provide enough lead time in order for the public to make effective response. Sophisticated users of flash flood forecasts could use forecast probabilities of flash flooding in order to make decisions in preparation for the predicted event. To this end, a systematic probabilistic approach to flash flood forecasting is presented. The work first describes a deterministic system which serves as a conceptual basis for the probability system. The approach uses accumulated rainfall plus potential rainfall over a specified area and time period, and assesses this amount against the water holding capacity of the affected basin. These parameters are modeled as random variables in the probabilistic approach. The effects of uncertain measurements of rainfall and forecasts of precipitation from multiple information sources within a time period and moving forward in time are resolved through the use of Bayes' Theorem. The effect of uncertain inflows and outflows of atmospheric moisture on the states of the system, the transformation of variables, is resolved by use of convolution. Requirements for probability distributions to satisfy Bayes' Theorem are discussed in terms of the types and physical basis of meteorological data needed. The feasibility of obtaining the data is evaluated. Two alternatives for calculating the soil moisture deficit are presented--one, an online automatic rainfall/runoff model, the other an approximation. Using the soil moisture approximation, a software program was developed to test the probabilistic approach. A storm event was simulated and compared against an actual flash flood event. Results of the simulation improved forecast lead time by 3-5 hours over the actual forecasts issued at the time of the event.

A flash flood is a flood that follows the causative storm event in a short period of time. The term “flash” reflects a rapid response, with water levels in the drainage network reaching a crest within minutes to a few hours after the onset of the rain event, leaving extremely short time for warning [Creutin and Borga, 2003; Borga et al., 2008]. Flash floods are localized phenomena that occur in watersheds of few hundred kilometres or less, with response times of a few hours or less [Creutin and Borga, 2003; O’Connor and Costa, 2004]. Such basins respond rapidly to intense rainfall because of steep slopes and impermeable surfaces, saturated soils, or because of human (i.e., urbanization) or fire-induced alterations to the natural drainage. Causative events are generally excessive storms, but can also be the sudden release of water impounded by a natural jam (i.e., formed by ice or rock, mud, and wood debris) or human-made dam or levee. This thesis focuses on flash flood events associated with heavy rainfall. Europe experienced several catastrophic flash floods in the last decades. Data concerning a number of these floods occurred during the last 15 years have been reported in Marchi et al. (2010). Examination of these data and references therein shows that: Flash floods occur in any of the hydroclimatic regions of Europe, even though three regions appear to be characterized by high flash flood potential: Mediterranean, Alpine Mediterranean, and Inland Continental Europe; Heavy rainfall accumulation is a necessary but not sufficient condition for flash floods, since hydrology critically controls flash-flood-triggering. Without hydrological analysis, it is impossible to evaluate the flood potential of storms, particularly in the fringe of the flood/no flood threshold; Flash flood hazard is related to both stream response (flood) and landscape response (landslide and erosion). The intense erosion and solid transport associated with these extreme events add to the hazard and strongly influence the quality of soils, waters and ecosystems. The twofold consequence of the above observations is that forecasting of flash-floods: Depends critically on meso-scale storm forecasting, with a specific attention to the processes leading to slow movement of the precipitation system; Necessitates real time hydrological modelling, with a specific attention to the runoff generation processes over a wide range of scales. Although they are seldom all deployed at the same time, the technical requirements for a hydrometeorological flash flood forecasting system include: A numerical weather prediction (NWP) model, capable to provide short-range Quantitative Precipitation Forecasts (QPF); A remote sensing based (radar, satellites) precipitation detection system, for storm monitoring and for the possible initialization and conditioning of the NWP model, and A hydrological-hydraulic forecasting model, capable to forecast the stream response from the rain input. These requirements are similar to those of more common riverine flood forecasting systems. However, some features characterise flash flood forecasting with respect to riverine flood forecasting and point out to their larger uncertainty. These are: The short lead time, which implies both the integration of meteorological and hydrologic forecast, and the difficulties of using data assimilation procedures based on real time observed discharges to reduce uncertainty in hydrologic predictions; The need to provide local forecasts, which means that, on one hand, the rainfall must be monitored and forecasted on a wide range of space/time scales, and, on the other hand, every tributary of a monitored basin can be considered as a potential target for flood warning. Estimation of extreme rainfall rates by weather radar at the appropriate time and space scales is the cornerstone of flash flood analysis and forecasting. A large body of research work has greatly improved in the last two decades radar technology and algorithms for rain quantification. This work has shown that well maintained conventional radar systems can estimate rainfall at ground level provided that a number of precautions are taken, and in particular: The siting of the instrument and its scanning protocol must be carefully selected and analysed; The quality of the instrument must be routinely checked; The signal processing must take into account the physics of the instrument as well as the properties of the atmospheric and ground targets. A downstream control of the radar rainfall processing can rely on rain-gauge measurements at ground level using a variety of methods. When these precautions are taken, different studies have shown that radar-based rainfall estimates are reliable and may be used as input in rainfall-runoff models for flood modelling and forecasting [Borga et al., 2000; Delrieu et al., 2005; Borga et al., 2002]. These very positive results must not be hiding some weaknesses: Most of these results never had the opportunity to be coherently validated over a significant number of flash floods events. The use of specific experiments or of limited operational radar data sets is insufficient to test complex combinations of algorithms, especially if high rain intensities are of interest. Very few results have been translated into operational hydrologic applications. This thesis aims to investigate the use of weather radar for the purpose of understanding the hydrometeorological mechanisms leading to flash floods, and then for flash flood forecasting. The outline of the thesis work is as follows. Chapter 1 provides a literature review of the rainfall estimation by weather radar for flash flood-generating storms. Chapter 2 describes a number of procedures for the rainfall estimation at the ground during flash flood events in mountainous catchments. A metric for the analysis of the rainfall field spatial patterns is proposed in Chapter 3, in the context of the analysis of a number of Romenian flash floods. This metric is used for the analysis of two flash flood events, respectively occurred in 2003 in the Eastern Italian Alps (Chapter 4) and in Western Slovenia (Chapter 5). Major conclusions from the work are reported in Chapter 6.
Una piena improvvisa è una piena che segue l’evento precipitativo che la ha causata entro un breve periodo di tempo. Il termine “improvvisa o flash” riflette una risposta rapida, con il picco di piena che si verifica nella rete di drenaggio nel volgere di alcuni minuti fino a poche ore dopo l’inizio dell’evento di pioggia. Questo fatto lascia intendere quanto poco tempo ci sia per l’allerta [Creutin and Borga, 2003; Borga et al., 2008]. Questo tipo di bacini rispondo rapidamente ad una precipitazione intensa a causa di pendii ripidi e superfici impermeabili, terreni saturi, o a per fattori determinati dall’uomo (vedi per esempio l’urbanizzazione) o a causa di alterazioni del drenaggio naturale del terreno dovuto ad incendi. Gli eventi scatenanti le piene improvvise sono generalmente precipitazioni che portano all’eccesso di drenaggio, ma questo tipo di piene possono anche essere scatenate dal rilascio improvviso di acqua trattenuta da impedimenti naturali (per esempio formati da ghiaccio e roccia, fango e detriti di legno) o di tipo artificiale come dighe e argini. Questa tesi si concentra su eventi di piena improvvisa associati a precipitazioni intense. L’Europa ha conosciuto diverse inondazioni catastrofiche negli ultimi decenni. I dati relativi un certo numero di queste inondazioni che si sono verificate nel corso degli ultimi 15 anni sono riportati da Marchi et al. (2010). Dall’analisi di questi dati e di queste fonti risulta che: Una piena improvvisa si può verificare in qualsivoglia regione idroclimatica dell’Europa, anche se tre regioni sembrano essere caratterizzate da una grande incidenza di di piene improvvise: l’area Mediterranea, quella Alpino-Mediterranea, e quella Continentale; Una gran quantità di pioggia accumulata è una condizione necessaria ma non sufficiente al verificarsi di una piena improvvisa, dal momento che l’idrologia controlla in modo decisivo l’innesco della piena improvvisa. Senza un’analisi di tipo idrologico, risulta impossibile valutare la probabilità che una data precipitazione scateni una piena, in praticolare in termini di una soglia oltre la quale si verifica la piena; La pericolosià delle piene improvvise è collegata sia alla risposta del fiume (la piena) che alla risposta del terreno (fenomeni di tipo franoso ed erosivo). L’intensa erosione ed il trasporto solido associati a questi fenomeni estremi si aggiungono alla pericolosità ed influenzano in modo significativo la qualità dei terreni, delle acque e degli ecosistemi. La duplice conseguenza delle osservazioni appena fatte è che la previsione di piene improvvise: Dipende in modo determinante dalle previsioni delle precipitazioni che si sviluppano alla meso-scala, con una attenzione specifica ai processi che frenano la circolazione del sistema di precipitazione; Richiedone modelli idrologici che lavorino in tempo reale, con una particolare attenzione ai processi du generazione del deflusso a vasta scala. Anche se raramente sono tutti utilizzati contemporaneamente, i requisiti tecnici per un sistema di previsione idrometeorologica per le piene improvvise comprendono: Un modello numerico di previsione (NWP2), in grado di fornire previsioni quantitative di pioggia a corto raggio (QPF3); Un sistema di rilevamento in remoto per la pioggia (radar, satellite), per il monitoriraggio dei fenomeni temporaleschi e la possibilie inizializzazione e condizionamento del modello NWP, e Un modello di previsione idrologico-idraulico, in grado di prevedere la risposta del corso d’acqua all’input pioggia. Tali requisiti sono simili a quelli più comuni utilizzati per la previsione delle alluvioni dei sistemi fluviali. Tuttavia, alcuni elementi caratterizzano la previsione delle piene improvvise rispetto alla previsione delle alluvioni e ne sottolineano la grande incertezza. Questi sono: Il breve periodo durante il quale questi processi si sviluppano, che implica sia l’integrazione di un sistema di previsione di tipo meteorologico e idrologico, che la difficoltà nell’utilizzo di procedure di assimilazione di dati basate sull’osservazione in tempo reale delle portate al fine di ridurre l’incertezza nelle previsioni idrologiche; La necessità di fornire previsioni a scala locale, il che significa da una parte che la pioggia deve essere monitorata e prevista su una vasta scala spazio-temporale, all’altra che ciascun tributario del bacino monitorato può essere considerato come un bersaglio potenziale per un allarme di piena. La stima di fenomeni precipitativi estremi tramite l’utilizzo del radar meteorologico alla appropriata scala spazio-temporale è una pietra miliare dell’analisi e della previsione delle piene improvvise. Una grande branca della ricerca in questo campo ha favorito un notevolmente migliorato, negli ultimi due decenni, delle tecnologie radar e degli algoritmi per la stima di pioggia. Questo lavoro ha dimostrato che anche utilizzando sistemi radar convenzionali si possono ottenere stime di precipitaziona a livello del suolo, a condizione che vengono adottate una serie di precauzioni, in particolare: L’ubicazione dello strumento e del suo protocollo di scansione devono essere attentamente selezionati ed analizzati; La qualità dello strumento deve essere sottoposta a controlli ordinari; L’elaborazione del segnale deve tener conto della fisica dello strumento così come delle proprietà atmosferiche e dei bersagli di terra. Un controllo a valle del trattamento delle precipitazioni radar può essere fatto tramite misurazioni da pluviometro a livello del suolo utilizzando una varietà di metodi. Quando si sono prese queste precauzioni, diversi studi hanno dimostrato che le stime di precipitazione basate su radar meteorologico sono affidabili e possono essere utilizzate come input di modelli afflussodeflusso per la modellazione e la previsione delle piene [Borga et al., 2000; Delrieu et al., 2005; Borga et al., 2002]. A fronte di questi risultati molto positivi non devono però essere nascosti alcuni punti deboli: La maggior parte di questi risultati non hanno mai la possibilità di essere coerentemente convalidati su un numero significativo di eventi di piena improvvisa. L’utilizzo di esperimenti specifici o di una banca dati limitata di dati radar è insufficiente a testare la combinazione complessa degli algoritmi utilizzati, specialmente se si è interessati ad intensità di pioggia elevata. Un numero molto limitato di risultati positivi è stato tradotto in applicazioni idrologiche operative. Questa tesi si propone di esaminare l’uso del radar meteorologico ai fini della comprensione dei meccanismi idrometeorologici che portano alla formazione di piene improvvise, e quindi alla loro previsione. L’organizzazione del lavoro di tesi è la seguente. Il Capitolo 1 fornisce una revisione della letteratura sul tema della stima di precipitazione tramite radar meteorologico per le precipitazioni che causano la formazione di piene improvvise. Il Capitolo 2 descrive una serie di procedure per la stima delle precipitazioni al suolo durante gli eventi di piena improvvisa in bacini montani. Una metrica per l’analisi spaziale del campo di pioggia viene proposta nel Capitolo 3, nel contesto dell’analisi di una serie di piene improvvise verificatesi in Romania. Questa metrica è utilizzata per l’analisi di due eventi di piena, accaduti rispettivamente nel 2003 nelle Alpi Italiane friulane e nella parte ovest della Slovenia (Capitolo 5). Le conclusioni principali del lavoro di tesi sono riportate nel Capitolo 6.

ABSTRACT: “Flash flood analysis and modelling in mountain regions” Flash flood are rare and localized phenomena, triggered by meteorological event with a pronounced spatial variability, with a precipitation gradient, at event scale, up to 20-50 mm/km. The consequences of these features is that the scientific and operational communities working on flash flood analysis have to deal with an impressive lack of data. Even a dense raingauge network may not be able to represent spatial variability of rainfall patterns associated with convective storms that trigger flash floods. Radar rainfall estimations, when correctly elaborated, are able to represent spatial patterns, but quantitative precipitation volume estimations need to be validated. In addition, concerning discharge data, the majority of the upstream and larger catchments affected by flash floods are not gauged and stream gauges, where present, are often damaged, so that peak discharge distribution along main and secondary river network is even less known than precipitation fields. This study aims at covering the gap between needed and available data for flash flood event analysis, combining different methodologies. An Intense Post Event Campaign (IPEC) may be very useful to collect peak discharge estimations and time sequence of the flood in ungauged sections. Simplified hydrological model, based on rough runoff excess computation and set velocity propagation, can be used to cross validate quantitative distributed precipitation data from weather radar and peak discharge estimations collected during an IPEC. More complex and detailed model may help to improve the knowledge about flash flood associated phenomena, like debris flow. Another objective of this thesis is to investigate the role of rainfall spatial variability in flash flood triggering. First a standard procedure to describe the variability catchment scale is needed. It will be so possible to study the relationship between rainfall input distribution and flood propagation dynamics. Then a simplified hydrological model is used to investigate the role of spatial variability in precipitation patterns: systematic studies are carried to describe the accuracy of rainfall volumes at basin scale and the effect of spatial variability within the basin. Often the studies about flash flood dynamics are slow down or stopped because no measured data are directly to hand, or, if so, because they are not considered sufficiently accurate. This work shows the possibility to combine together data with an assured degree of uncertainty, the only available or collectable existing data, and processed them with simple statistical and hydrological tools to obtain a more precise knowledge about past flash floods. The remainder of this dissertation is organised as follows. Chapter 1 “Introduction”. The work starts with the aim to define what a “flash flood” is, underlying the importance to characterize such event according spatial and temporal proprieties. From this definition it follows that a generic flood can be classified according its own spatial and temporal proprieties and located in a specific point of a segment delimitated by the two ideal cases of “flash flood” and “flood at large scale”. Chapter 2 “Literature review”. Spatial and temporal characterization lead to describe typical features of flash flood in different climates. Meteorological conditions able to trigger this kind of events are described and analyzed, with particular care about convective cells system organized in mesoscale structures. Finally some literature examples are reported to show different possible approach and to underline usual uncertainty when dealing with flash flood. Chapter 3 “Materials an methods”. This chapter summarizes and describes the tools used in this thesis to carry on flash flood analysis. 3.1 Weather radar data are used to describe rainfall spatial distribution and obtain quantitative estimations of rainfall patterns. Data acquiring and processing are described and most common errors are summarized along with most common procedures and algorithms to avoid and correct them. It is finally shown how merging radar and conventional raingauge network information can provide a more exhaustive description of rainfall fields, with quantitative estimation. This data processing is very useful for further characterization and analysis of past flash flood events. 3.2 Post event surveys are presented as an essential tool to collect the richest possible documentation. Measure campaigns are valorised to obtain qualitative and quantitative description of past floods. The goal is to complete the spatial and temporal precipitation knowledge and dynamic description, focusing on discharge estimation along hydrological network in term of peak values and timing. 3.3 Hydrological models can be routed for a better comprehension of flood dynamics at event scale. Two hydrological models, then used for flash flood analysis, are described in detail. The first one is applied at large event scale and starts from a distributed precipitation input. Hortonian runoff generation is applied punctually and superficial flood propagation is computed basing on fixed hillslope and channel velocity. The second model is built to be applied at very small catchment scale and simulate infiltration and transport processes for surface and subsurface flow through uniform hypothesis equations. Chapter 4 “Analysis of past flash flood events”. Some specific post flood analysis are collected in three section. 4.1 Five flash flood events occurred in Romania are analysed with HYDRATE European project contribution. This study shows that even if the conventional hydrometeorological data are poor, weather radar information and hydrological modelling can help in understanding specific past flood dynamics. 4.2 HYDRATE project was also involved in the analysis of a flash flood occurred in Slovenia in September 2007, including radar processing and post event surveys. It is shown how this approach, characterize by time and cost significant efforts, is a precious tool to collect data and information for a detailed description that would be not possible through traditional hydrometeorological network. 4.3 A detailed model is used to describe surface and subsurface flow dynamics during the debris flow occurred in two small subcatchments in Fella river valley (North Est of Italy), hit by a flash flood on August 29, 2003. The study mainly consists on liquid and solid mass balance during the different phases of the event. Chapter 5 “Spatial variability in flash flood events”. An analysis on rainfall spatial distribution is carried with the same tools on two different basin interested by flash flood event. The studies includes a fist detailed analysis on rainfall spatial variability within selected subcatchments at different scales: spatial variability is described through time distance calculated in base of hydrological network. Then a simplified hydrological model is used to investigate spatial aggregation effects on mean areal rainfall and peak discharge value at subcatchment scale. 5.3 For Fella river basin (in Friuli Venezia Giulia region), ten subcatchments from 10.5 and 623km² are choosen. 5.4 For Cervo River (Piomente region, North West Italy) the study is applied to three flood events characterized by different rainfall spatial variability, and focused on four subcatchments (from 75 to 983km²). Chapter 6 “Conclusions”. Are here reported and summarized the main observations coming from the specific studies describe in the two previous chapters as long as recommendation for future research.
RIASSUNTO: “Analisi e modellazione di piene improvvise in zone montane” Le piene improvvise sono fenomeni rari e localizzati, causati da eventi meteorologici caratterizzati da una spiccata variabilità spaziale, con gradienti di precipitazione che possono raggiungere, a scala di evento, i 20-50 mm/km. La conseguenza di ciò è che la comunità scientifica e gli enti operativi interessati nell’analisi dei fenomeni di piena si relazionano quotidianamente con una carenza di dati. Anche una fitta rete di pluviometri non è in grado di rappresentare la variabilità spaziale dei campi di precipitazione associati a fenomeni convettivi che innescano piene improvvise. Le stime di precipitazione ottenute attraverso il radar meteorologico, opportunatamente elaborate, sono in grado di rappresentare i pattern spaziali, ma i valori di volumi di pioggia necessitano di essere validati. Inoltre, per quanto riguarda i dati di portata, la maggior parte dei bacini colpiti da piene improvvise non sono strumentati e gli strumenti, dove presenti, risultano spesso danneggiati, cosicché la conoscenza della distribuzione delle portate al picco, lungo la rete idrologica principale e secondaria, è persino più approssimativa di quella della distribuzione spaziale della precipitazione. Questo studio si prefigge di colmare la distanza tra i dati disponibili e quelli richiesti per un’analisi a scala di evento con riferimento a fenomeni di piena improvvisa. Un’approfondita campagna di rilievi post evento (in inglese Intense Post Event Campaign, IPEC) può risultare estremamente utile per raccogliere le stime di portate al picco e la sequenza cronologica dello svilupparsi della piena in sezioni non monitorate. Modelli idrologici semplificati, dotati di metodi elementari per la separazione dei deflussi e predeterminate velocità di propagazione, possono essere utilizzati per una validazione incrociata tra una descrizione quantitativa della distribuzione di precipitazione ottenuta attraverso il radar meteorologico e le stime di portate al picco raccolte durante un IPEC. Modelli più complessi e dettagliati possono migliorare il livello di conoscenza riguardo fenomeni associati alle piene improvvise, come le colate detritiche. Un altro obiettivo di questa tesi è quello di investigare il ruolo della variabilità spaziale della precipitazione nei fenomeni di piena improvvisa. In primo luogo è necessario impostare una procedura che permetta di caratterizzare tale variabilità all’interno di un particolare bacino idrografico, mettendo in relazione la distribuzione degli apporti meteorici con le modalità di propagazione della piena. In secondo luogo si vuole indagare, attraverso l’applicazione di modelli idrologici semplificati, il ruolo della risoluzione spaziale della precipitazione. A questo fine è necessario separare due aspetti: l’accuratezza della stima dei volumi piovuti a scala di bacino e l’influenza della variabilità spaziale all’interno del bacino stesso. Spesso gli studi che si concentrano sulle dinamiche delle piene improvvise sono rallentati o resi impossibili per il fatto che nessun dato misurato risulta utilizzabile così come disponibile, oppure perchè i dati di partenza non sono ritenuti sufficientemente accurati. Questo lavoro si prefigge di mostrare come sia possibile, partendo dai soli dati esistenti, disponibili o recuperabili, caratterizzati da un certo grado di incertezza, passare attraverso un’elaborazione tramite semplici strumenti statistici e idrologici al fine di ottenere una conoscenza più precisa riguardo passati eventi di piena improvvisa. Si riporta una breve descrizione del contenuto dei capitoli della tesi, che sarà elaborata in lingua inglese. Capitolo 1 “Introduction”. Introduzione alla tematica che comprende una definizione del termine “piena improvvisa”, convenendo sulla necessità di caratterizzare tali eventi in termini di proprietà spazio-temporali. Si nota che, a partire da questa definizione, è possibile classificare una generica piena in un punto di un segmento ai cui estremi ci sono i casi ideali di “piena improvvisa” e “piena a larga scala”. Capitolo 2 “Literature review”. Partendo dalla caratterizzazione spazio temporale si descrivono le caratteristiche tipiche delle piene improvvise nei diversi tipi di clima, si individuano le condizioni meteorologiche in grado di innescare tali fenomeni, quali le celle convettive organizzate in strutture di mesoscala. Si riportano, infine, alcuni esempi di studi in letteratura che mostrano diverse tipologie di approcci e che sono indicativi dell’incertezza in cui si è soliti lavorare quando si approfondiscono questi temi. Capitolo 3 “Materials an methods”. In questo capitolo vengono presentati i principali strumenti comuni a tutte le analisi di fenomeni di piena improvvisa presentati in questa tesi. 3.1 L’utilizzo del radar meteorologico per studiare, dal punto di vista quantitativo, la distribuzione spaziale della precipitazione. Vengono approfondite la modalità di acquisizione del dato, sottolineando le possibili fonti di errore ed i metodi più comuni per ovviare a questi inconvenienti. Viene anche mostrato come l’utilizzo combinato di radar e tradizionali pluviometri renda più completa la caratterizzazione della precipitazione ai fini di un analisi di una piena improvvisa. 3.2 Le indagini post evento, necessarie per raccogliere la maggior documentazione possibile, sono valorizzate al fine di una ricostruzione, anche qualitativa, delle dinamiche caratteristiche di una specifica piena. Queste, attraverso diverse metodologie, devono aiutare a descrivere la struttura spazio temporale della precipitazione e la stima di portata, distribuita lungo la rete idrica, in termini di valore al picco e di tempistica 3.3 L’uso della modellistica idrologica applicata ad una miglior comprensione delle dinamiche a scala di evento. In particolare vengono descritti i due modelli idrologici utilizzati. Il primo, da applicare a larga scala, parte da un input di precipitazione spazialmente distribuito e, attraverso un meccanismo hortoniano di separazione dei deflussi applicato puntualmente, propaga la piena in base a fissate velocità di versante e di canale. Il secondo, da applicare a bacini di piccolissima dimensione, simula i processi di trasporto superficiale e sottosuperficiale integrando le note equazioni di moto uniforme. Capitolo 4 “Analysis of past flash flood events”. Vengono qui presentate alcune analisi di eventi, distinte in tre sezioni. 4.1 Analisi di cinque eventi di piena improvvisa avvenuti in Romania nell’ambito del progetto europeo HYDRATE. Da questo studio risulta che, pur in presenza di scarsi dati provenienti dalle tradizionali fonti di monitoraggio idro-meteorologico, l’informazione proveniente da radar meteorologico e la modellistica idrologica possono aiutare nella ricostruzione delle dinamiche dell’evento preso in considerazione. 4.2 Analisi di una piena improvvisa avvenuta in Slovenia nel settembre 2007 per la quale, attraverso il progetto HYDRATE si è condotta un indagine post evento. La ricchezza di questo approccio, pur dispendioso in termini di tempo, mostra un possibile percorso per recuperare le maggior informazioni possibili per eventi di piena che non sono ricostruibili solo attraverso le normali reti di monitoraggio idrometeorologico. 4.3 Analisi attraverso un modello dettagliato di deflusso superficiale e sottosuperficiale della colata detritica avvenuta in due piccoli sottobacini nella valle del fiume Fella, colpita da una piena improvvisa il 29 agosto 2003. Lo studio consiste essenzialmente nel bilancio di massa liquido e solido durante le diverse fasi dell’evento. Capitolo 5 “Spatial variability in flash flood events”. Questa analisi sulla distribuzione spaziale della precipitazione è stata condotta con le medesime metodologie in due diversi bacini. Gli studi comprendono un primo approfondimento della variabilità spaziale della precipitazione all’interno di sottobacini di diversa estensione: la variabilità è descritta in funzione del reticolo idrografico del bacino preso in considerazione. Successivamente, attraverso un modello idrologico semplificato, si è valutata l’influenza della variabilità spaziale della precipitazione analizzando gli effetti dell’aggregazione spaziale in termini di precipitazione media su bacino e di portata al picco simulata. 5.3 Per l’analisi nel bacino del fiume Fella (FVG), colpito da una piena improvvisa il 29 agosto 2003, si sono scelti dieci sottobacini di dimensione variabile tra i 10.5 e i 623km². 5.4 Nel caso del fiume Cervo (Piemonte) lo studio ha riguardato tre eventi di piena con diversa variabilità spaziale della precipitazione e si è concentrato su quattro sottobacini (tra i 75 e i 983km²). Capitolo 6 “Conclusions”. Vengono riassunte le principali osservazioni ricavate dalle analisi descritte nei due capitoli precedenti e indicazioni per possibili future linee di ricerca.

An empirical method is developed for constructing likelihood functions required in a Bayesian probabilistic flash flood forecasting model using data on objective quantitative precipitation forecasts and their verification. Likelihoods based on categorical and probabilistic forecast information for several forecast periods, seasons, and locations are shown and compared. Data record length, forecast information type and magnitude, grid area, and discretized interval size are shown to affect probabilistic differentiation of amounts of potential rainfall. Use of these likelihoods in Bayes' Theorem to update prior probability distributions of potential rainfall, based on preliminary data, to posterior probability distributions, reflecting the latest forecast information, demonstrates that an abbreviated version of the flash flood forecasting methodology is currently practicable. For this application, likelihoods based on the categorical forecast are indicated. Apart from flash flood forecasting, it is shown that likelihoods can provide detailed insight into the value of information contained in particular forecast products.

Flash flooding in the semi-arid United States poses a significant danger to life and property. One effective way to mitigate flood risk is by implementing a rainfall-runoff model in a real-time forecast and warning system. This study investigated the feasibility of using the mechanistic, distributed semi-arid rainfall-runoff model KINEROS2 driven by high resolution radar rainfall input estimates obtained from the NEXRAD WSR-88D DHR reflectivity measurements in such a system. The original procedural paradigm-based KINEROS2 Fortran 77 code with space-time looping was recoded into an object-oriented Fortran 90 code with time-space looping for this purpose. The recoded form is now applicable to large basins, is easily future-extensible, and individual modules can be incorporated into other models.Sources of operational uncertainty in the above system were investigated for their influence over several events within a sub-basin of the USDA-ARS Walnut Gulch Experimental Watershed. Uncertainties considered were in the rainfall estimates, the model parameters, and the initial conditions. The variance-based Sobol' method of global sensitivity analysis conditioned on the observed streamflow showed that the uncertainty in the modeled response was heavily dominated by the operational variability of biases in the radar rainfall depth estimates. Sensitivities to KINEROS2 parameters indicates the need for improved representation of semi-arid hillslope hydrology in small basins, while pointing to specific influential, but poorly identified model parameters towards which field investigations should be directed. The significant influence of initial hillslope soil moisture showed the requirement of a sophisticated inter-storm model component for a continuous forecasting model.A synthetic study data was used to further explore the phenomena seen in the above real data study, of behavioral modifier set inconsistency across all events and of irreducibility in the spatial modifier ranges. The former was found to be attributable to wide uncertainty ranges in the sources of uncertainty, and the latter to the high distributed model non-linearity with associated interactions. These contribute towards a high predictive uncertainty in operational forecasting.Overall, the GLUE-based predictive uncertainty method with behavioral classification and accommodation of wide operational source uncertainty ranges is recommended as a simple and effective setup for operational flash flood forecasting.

The dangerous hazard posed by flash flooding to upland communities is likely to increase due to climate change. The flood risk management policy approach has become predominant since the 1990s, with an emphasis on the public awareness of, and responses to, flood risks; however, the unpredictable nature of upland flash flooding means that responses to such hazards are uncertain. This thesis uses an integrated analysis of social and physical science datasets to study responses by local residents and the Environment Agency to flash flooding, using a case study of a major upland flood in North Yorkshire. Responses to flash flooding within upland communities were found to be mostly present as changes to individual behaviour and awareness. However, physical, damage reducing modifications were limited. Flash flood hazard perception was found to be linked to knowledge and experience of local flooding. Major flash flood events occurring in areas which have not experienced other recent floods are unlikely to increase perceptions or provoke responses. Although local awareness of changing weather patterns was found, supporting analyses of rainfall records, local flood risks were frequently framed in the context of river management, rather than climate change. The implementation of policy changes and responses to flash flooding by the Environment Agency will prove difficult at the local level, due to the nature of attitudes and perceptions encountered at the local level, including important differences in the perception of the flash flood hazard between local residents and representatives from nationwide organisations. Encouraging property-level modifications following flash floods, in accordance with national policies, is very difficult. In order to increase local perceptions of the flash flood hazard, the use of participatory work, focusing on long-term awareness raising and the sharing of locally held flood knowledge may be beneficial, alongside the support of existing resilience in upland communities.

This study was conducted at the mountainous catchment part of Batinah Region of the Sultanate of Oman called Al-Awabi watershed which is about 260km2 in area with about 40 Km long Wadi main channel. The study paper presents a proposed modeling approach and possible scenario analysis which uses 1D - hydraulic modeling for flood routing analysis; and the main tasks of this study work are (1) Model setup for Al-Awabi watershed area, (2) Sensitivity Analysis, and (3) Scenario Analysis on impacts of rainfall characteristics and transmission losses. The model was set for the lower 24 Km long of Al-Awabi main channel (Figure 13). Channel cross-sections were the main input to the 1D-Hydraulic Model used for the analysis of flash flood routing of the Al-Awabi watershed. As field measurements of the Wadi channel cross-sections are labor intensive and expensive activities, availability of measured channel cross-sections is barely found in this study area region of Batinah, Oman; thereby making it difficult to simulate the flood water level and discharge using MIKE 11 HD. Hence, a methodology for extracting the channel cross-sections from ASTER DEM (27mX27m) and Google Earth map were used in this study area. The performance of the model setup was assessed so as to simulate the flash flood routing analysis at different cross-sections of the modeled reach. And from this study, although there were major gap and problems in data as well as in the prevailing topography, slope and other Hydro Dynamic parameters, it was concluded that the 1D-Hydraulic Modelling utilized for flood routing analysis work can be applied for the Al-Awabi watershed. And from the simulated model results, it was observed that the model was sensitive to the type of Boundary Condition chosen and taken, channel cross sections and its roughness coefficient utilized throughout the model reach.

Au XXIe siècle, la prévision de l'aléa hydrométéorologique et des impacts associés aux crues rapides demeurent un défi pour les prévisionnistes et les services de secours. Les mesures structurelles et / ou les avancées des systèmes de prévision hydrologique ne garantissent pas, à elles seules, la réduction des décès lors de ces phénomènes d'inondation rapide. La littérature souligne la nécessité d'intégrer d'autres facteurs, liés aux processus de vulnérabilité sociaux et comportementaux, afin de mieux prendre en compte les risques encourus par les populations lors de ces épisodes extrêmes. Cette dissertation conduit une analyse théorique couplés à ceux de une analyse des accidents historiques mortels afin d'expliquer les interactions qui existent entre les processus hydrométéorologiques et sociaux responsables de l'apparition de vulnérabilités humaines lors de crues rapides aux États-Unis. Des données d'enquêtes liées aux crues rapides sont examinées afin d'élaborer un système de classification des circonstances du décès (en voiture, à l'extérieur, à proximité d'un cours d'eau, dans un camping, dans un bâtiment ou en mobile-home). L'objectif est d'établir un lien entre la conception des vulnérabilités et l'estimation des pertes humaines liées à ces catastrophes naturelles. "Random forest" est utilisé et est basé sur un arbre de décision, qui permet d'évaluer la probabilité d'occurrence de décès pour une circonstance donnée en fonction d'indicateurs spatio-temporels. Un système de prévision des décès liés à l'usage de la voiture lors des crues rapides, circonstance la plus répandue, est donc proposé en s'appuyant sur les indicateurs initialement identifiés lors de l'étude théorique. Les résultats confirment que la vulnérabilité humaine et le risque associé varient de façon dynamique et infra journalière, et en fonction de la résonance spatio-temporelle entre la dynamique sociale et la dynamique d'exposition aux dangers. Par exemple, on constate que les jeunes et les personnes d'âge moyen sont plus susceptibles de se retrouver pris au piège des crues rapides particulièrement soudaines(par exemple, une durée de près de 5 heures) pendant les horaires de travail ou de loisirs en extérieur. Les personnes âgées sont quant à elles plus susceptibles de périr à l'intérieur des bâtiments, lors d'inondations plus longues, et surtout pendant la nuit lorsque les opérations de sauvetage et / ou d'évacuation sont rendues difficiles. Ces résultats mettent en évidence l'importance d'examiner la situation d'exposition aux risques en tenant compte de la vulnérabilité dynamique, plutôt que de se concentrer sur les conceptualisations génériques et statiques. Ce concept de vulnérabilité dynamique est l'objectif de modélisation développée dans cette thèse pour des vulnérabilités liés aux véhicules. À partir de l'étude de cas sur les crues rapides survenues en mai 2015, et en analysant principalement les états du Texas et de l'Oklahoma, principaux états infectés par ces évènements,le modèle montre des résultats prometteurs en termes d'identification spatio-temporelle des circonstances dangereuses. Cependant, des seuils critiques pour la prédiction des incidents liés aux véhicules doivent être étudiés plus en profondeur en intégrant des sensibilités locales non encore résolues par le modèle. Le modèle établi peut être appliqué, à une résolution journalière ou horaire, pour chaque comté du continent américain. Nous envisageons cette approche comme une première étape afin de fournir un système de prévision des crues rapides et des risques associés sur le continent américain. Il est important que la communauté scientifique spécialisée dans l'étude des crues éclairs récoltent des données à plus haute résolution lorsque ces épisodes entrainement des risques mortels, et ce afin d'appuyer la modélisation des complexités temporelles et spatiales associées aux pertes humaines causées par les futures inondations soudaines
In the 21st century the prediction of and subsequent response to impacts due to sudden onset and localized flash flooding events remain a challenge for forecasters and emergency managers. Structural measures and/or advances in hydrological forecasting systems alone do not guarantee reduction of fatalities during short-fuse flood events. The literature highlights the need for the integration of additional factors related to social and behavioral vulnerability processes to better capture risk of people during flash floods. This dissertation conducts a theoretical analysis as well as an analysis of flash flood-specific historic fatalities to explain complex and dynamic interactions between hydrometeorological, spatial and social processes responsible for the occurrence of human life-threatening situations during the "event" phase of flash floods in the United States (U.S.). Individual-by-individual fatality records are examined in order to develop a classification system of circumstances (i.e., vehicle-related, outside/close to streams, campsite, permanent buildings, and mobile homes). The ultimate goal is to link human vulnerability conceptualizations with realistic forecasts of prominent human losses from flash flood hazards. Random forest, a well-known decision-tree based ensemble machine learning algorithm for classification is adopted to assess the likelihood of fatality occurrence for a given circumstance as a function of representative indicators at the county-level and daily or hourly time steps. Starting from the most prevalent circumstance of fatalities raised from both the literature review and the impact-based analysis, flash flood events with lethal vehicle-related accidents are the subject to predict. The findings confirm that human vulnerability and the subsequent risk to flash flooding, vary dynamically depending on the space-time resonance between that social and hazard dynamics. For example, it is found that younger and middle-aged people are more probable to get trapped from very fast flash floods (e.g., duration close to 5 hours) while participating in daytime outdoor activities (e.g., vehicle-related, recreational). In contrary, older people are more likely to perish from longer flooding inside buildings, and especially in twilight and darkness hours when rescue and/or evacuation operations are hindered. This reasoning places the importance of situational examination of dynamic vulnerability over generic and static conceptualizations, and guides the development of flash flood-specific modeling of vehicle-related human risk in this thesis. Based on the case study of May 2015 flash floods with a focus in Texas and Oklahoma, the model shows promising results in terms of identifying dangerous circumstances in space and time. Though, critical thresholds for the prediction of vehicle-related incidents need to be further investigated integrating local sensitivities, not yet captured by the model. The developed model can be applied on a daily or hourly basis for every U.S. county. We vision this approach as a first effort to provide a prediction system to support emergency preparedness and response to flash flood disasters over the conterminous U.S. It is recommended that the flash flood disaster science community and practitioners conduct data collection with more details for the life-threatening scene, and at finer resolutions to support modeling of local temporal and spatial complexities associated with human losses from flash flooding in the future

The height of an overflow dam must be designed low enough to prevent the reservoir water level from exceeding a flood plain during flooding conditions. Because of this constraint, much of the available water storage area is wasted and the available pressure head for power generation will be less than maximum during normal conditions. Crest control gates alleviate this problem by providing a variable spillway height. The Flash Gate Board is a passive automatic crest control gate. Its purpose is to regulate flood water while providing increased water pressure for power generation or for additional water storage for a municipality. The governing equations for the Flash Gate Board system are derived and used to formulate models of the system. Computer simulations are used to examine the system response in a variety of operating conditions. The results of these simulations are presented and discussed. The results include an investigation which developed an optimum gate height to maximize the potential of the Flash Gate Board. An experimental model was developed to verify analytical results and to provide additional insight. Conclusions from the study, recommendations for future work, and modifications for a trouble-free design are discussed.
Master of Science

Flash flood is among the most hazardous natural disasters, and it can cause severe damages to the environment and human life. Flash floods are mainly caused by intense rainfall and due to their rapid onset (within six hours of rainfall), very limited opportunity can be left for effective response. Understanding the socio-economic characteristics involving natural hazards potential, vulnerability, and resilience is necessary to address the damages to economy and casualties from extreme natural hazards. The vulnerability to flash floods is dependent on both biophysical and socio-economic factors. This study provides a comprehensive assessment of socio-economic vulnerability to flash flood alongside a novel framework for flash flood early warning system. A socio-economic vulnerability index was developed for each state and county in the Contiguous United States (CONUS). For this purpose, extensive ensembles of social and economic variables from US Census and the Bureau of Economic Analysis were assessed. The coincidence of socio-economic vulnerability and flash flood events were investigated to diagnose the critical and non-critical regions. In addition, a data-analytic approach is developed to assess the interaction between flash flood characteristics and the hydroclimatic variables, which is then applied as the foundation of the flash flood warning system. A novel framework based on the D-vine copula quantile regression algorithm is developed to detect the most significant hydroclimatic variables that describe the flash flood magnitude and duration as response variables and estimate the conditional quantiles of the flash flood characteristics. This study can help mitigate flash flood risks and improve recovery planning, and it can be useful for reducing flash flood impacts on vulnerable regions and population.

Effective prediction of localized flash flood regions for an approaching rainfall event requires an in-depth knowledge of the land surface and stream characteristics of the forecast area. Flash Flood Guidance (FFG) is currently formulated once or twice a day at the county level by River Forecast Centers (RFC) in the U.S. using modeling systems that contain coarse, generalized land and stream characteristics and hydrologic runoff techniques that often are not calibrated for the forecast region of a given National Weather Service (NWS) office. This research investigates the application of embedded geographic information systems (GIS) modeling techniques to generate a localized flash flood model for individual small watersheds at a five minute scale and tests the model using historical case storms to determine its accuracy in the FFG process. This model applies the Soil Conservation Service (SCS) curve number (CN) method and synthetic dimensionless unit hydrograph (UH), and Muskingum stream routing modeling technique to formulate flood characteristics and rapid update FFG for the study area of interest. The end result of this study is a GIS-based Flash Flood Forecasting system for ungaged small watersheds within a study area of the Blacksburg NWS forecast region. This system can then be used by forecasters to assess which watersheds are at higher risk for flooding, how much additional rainfall would be needed to initiate flooding, and when the streams of that region will overflow their banks. Results show that embedding these procedures into GIS is possible and utilizing the GIS interface can be helpful in FFG analysis, but uncertainty in CN and soil moisture can be problematic in effectively simulating the rainfall-runoff process at this greatly enhanced spatial and temporal scale.
Master of Science

Improving the capacity to make predictions in ungauged basins is one of most difficult challenge for the scientific community (see for example the current initiative Prediction Ungaged Basins (PUB) launched by the International Association of Hydrological Sciences, IAHS). Whatever hydrological models are used, in view of the tremendous spatio-temporal heterogeneity of climatic and landscape properties, extrapolation of information, or knowledge, from gauged to ungauged basins remains fraught with considerable difficulties and uncertainties, especially in the light of the generally poor understanding of where water goes when it rains, what flow path it takes to the stream, and the age of the water that emerges in the channel. The PUB problem is the key concept of this thesis and it is analysed from several point of view. Methodologies able to observe, model and predict the hydrological response at the regional scale are proposed.

Flash floods caused by localized thunderstorms are a natural hazard of the semi -arid Southwest, and many communities have responded by installing ALERT flood forecasting systems. This study explored a rainfall- runoff modeling approach thought to be appropriate for forecasting in such watersheds. The kinematic model KINEROS was evaluated because it is a distributed model developed specifically for desert regions, and can be applied to basins without historic data. This study examined the accuracy of KINEROS under data constraints that are typical of semi -arid ALERT watersheds. The model was validated at the 150 km2, semi -arid Walnut Gulch experimental watershed. Under the conditions examined, KINEROS provided poor simulations of runoff volume and peak flow, but good simulations of time to peak. For peak flows, the standard error of estimate was nearly 100% of the observed mean. Surprisingly, when model parameters were based only on measurable watershed properties, simulated peak flows were as accurate as when parameters were calibrated on some historic data. The accuracy of KINEROS was compared to that of the SCS model. When calibrated, a distributed SCS model with a simple channel loss component was as accurate as KINEROS. Reasons for poor simulations were investigated by examining a) rainfall sampling errors, b) model sensitivity and dynamics, and c) trends in simulation accuracy. The cause of poor simulations was divided between rainfall sampling errors and other problems. It was found that when raingage densities are on the order of 1/20 km2, rainfall sampling errors preclude the consistent and reliable simulation of runoff from localized thunderstorms. Even when rainfall errors were minimized, accuracy of simulations were still poor. Good results, however, have been obtained with KINEROS on small watersheds; the problem is not KINEROS itself but its application at larger scales. The study also examined the hydrology of thunderstorm -generated floods at Walnut Gulch. The space -time dynamics of rainfall and runoff were characterized and found to be of fundamental importance. Hillslope infiltration was found to exert a dominant control on runoff, although flow hydraulics, channel losses, and initial soil moisture are also important. Watershed response was found to be nonlinear.

The frequent occurrence of natural disasters; especially flash floods, are resulting the significant threats to many countries around the world. The truth that cannot be ignored, is that the effects of flash floods on the developing countries’ societies and economies are massive, compared with developed countries. Petra region; which is located in Jordan, is exposed to flash flood risks, which led to losses in lives, public and private properties. While the frequencies and impacts of flash floods might not be controlled easily, the need for more effective early warning systems has become extremely important. United Nations International Strategy for Disaster Reduction (UNISDR) and many researchers assumed that if an effective tsunami early warning system had been in place in the Indian Ocean region on 26 December 2004, thousands of lives would have been saved. Accordingly, Petra Region’s communities have experienced the impacts of flash floods in recent years due to absence of early warning systems and the lack of knowledge among communities about flash flood risks. These problems provide the context and demonstrate the significance of this study. Research aims to develop a responsive Flash Flood Early Warning System Guidance (FFEWSG) to enhance resilience in Petra Region. This research takes the social constructivism (interpretivism) stance in the continuum of philosophy and adopts a case study research strategy with qualitative method of research techniques. The research data collection was conducted in three phases. During the first phase, pilot semi structured interviews were conducted among people in Petra Region while the second phase focused on collecting the data from disaster affected communities, and disaster experts using semi-structured interviews. The third phase gathered information from Petra Development and Tourism Region Authority (PDTRA) documents. Data was analysed using content analysis. The research investigated flash floods in developed and developing countries; reviewed previous reports of flash flood events in Petra Region and how they affect the study area; and current early warning systems related to flooding. The research recommended a flash flood early warning system that could empower the local governmental institutions to mitigate flash flood impacts and enhance the resilience in Petra Region. It is expected that the research will add significant empirical evidence on the elements of the guidance within early warning system for flash flood, and will provide a useful tool in Petra Region for stakeholders, particularly for the government or the implementing agencies, helping to ensure the success of reducing the flash flood risks by the development of FFEWSG.

As one of the most devastating natural hazards, flash floods are responsible for major and abrupt geomorphic effects in the fluvial system as well as significant loss of life and socio-economic damages. Flash floods are characterized by strong spatio-temporal rainfall variability and therefore show variations in discharge and energy expenditure: associated geomorphic effects depend on geological controls on channel geometry and sediment characteristics, as well as on variations in flood intensity. Geomorphic effects usually take the form of erosional and depositional modification of the pre-flood channel. The central question of this thesis is to evaluate why flash floods of similar magnitudes and intensities sometimes produce dissimilar geomorphic results. The use of peak instantaneous hydraulic flow parameters such as discharge, velocity, shear stress, and stream power to quantify geomorphic changes has commonly been non-deterministic. This thesis aims at investigating how factors such as channel geometry, substrate, and flood magnitude and duration can interact and influence geomorphic effectiveness of high magnitude floods. A combined analysis of data from post-flood surveys and hydrological modelling permitted a comprehensive hydro-geomorphic investigation of seven major flash flood that occurred between 2007 and 2014 in different hydro-climatic regions in central and southern Europe. High peak discharge coupled with long flow duration ensured significant geomorphic impacts in Mediterranean basins. Values of stream power are generally consistent with observed geomorphic changes in the studied cross sections. However, bedrock channels show the highest values of energy expenditure but no visible erosion, whereas major erosion has been observed in alluvial channels. The trends in semi-alluvial channels urge the recognition of local or event-specific conditions that increase the resistance of channel bed and banks to erosion. Short flow duration caused major sedimentological effects but limited channel widening in most semi-alluvial channels. Eight rivers that were highly affected by three of the studied flash floods were selected for detailed analysis and modelling of the contiguous downstream variability in stream power. Power functions adequately interpreted the systematic downstream increase in peak discharge, whereas contrary to the usual exponential function, a quadratic function better interpreted the high downstream variability in channel gradient. The performance of the resulting empirical models for cross-sectional stream power and unit stream power were essentially influenced by channel gradient. The availability of high-resolution pre- and post-flood satellite images allowed assessment of channel changes along seven of these channels. Statistical analysis indicated that hydraulic forces alone are not adequate to interpret the rate of channel widening, which is primarily influenced by the degree of channel confinement. Together with lateral confinement, unit stream power better predicted channel widening in steep channels, whereas cumulative energy expenditure was relatively better for moderate channel reaches. The use of different erosion-resistance thresholds to quantify the geomorphological changes of riverbeds supports the conclusion that the determination of these changes is much more difficult than to determine the hydraulic variables involved.
Le piene improvvise (flash flood) sono fra i processi naturali più devastanti e sono responsabili di rilevanti e subitanei effetti morfologici, nonché della perdita di vite umane e di gravi danni economici. Le piene improvvise sono caratterizzate dalla forte variabilità spazio-temporale delle precipitazioni innescanti, cui consegue una forte variabilità delle portate e della potenza della corrente. Gli effetti geomorfologici delle piene improvvise dipendono sia dal controllo che l’assetto geologico esercita sulla geometria del canale e sulle caratteristiche del sedimento, sia dall’intensità della piena. Gli effetti geomorfologici delle piene improvvise si manifestano attraverso processi sia erosivi che deposizionali che determinano variazioni nell’assetto del canale rispetto alle condizioni antecedenti l’evento. La questione centrale di questa tesi è valutare perché piene improvvise di simile intensità producano talvolta effetti morfologici nettamente differenti. L’uso dei valori istantanei massimi di variabili di tipo idraulico, quali la portata, la velocità, lo sforzo tangenziale e la potenza della corrente, si è spesso rivelato non conclusivo nel quantificare i cambiamenti morfologici. Questa tesi mira a studiare come fattori quali la geometria del canale, il substrato, l’intensità e la durata dell’evento possano interagire e influenzare l’azione morfologia delle piene improvvise. Un’analisi combinata, basata rilievi post-evento e sulla modellazione idrologica, ha consentito di caratterizzare sette importanti eventi di piena improvvisa verificatisi fra il 2007 e il 2014 in diverse regioni dell’Europa centrale e meridionale. Nei bacini mediterranei gli elevati valori delle portate di picco, uniti alla durata relativamente lunga degli eventi, hanno determinato le condizioni favorevoli a significativi impatti geomorfologici. I valori della potenza della corrente sono generalmente coerenti con i cambiamenti morfologici osservati. Inoltre, i canali in roccia mostrano i valori di dispendio energetico più elevati ma senza erosioni apprezzabili, mente ingenti fenomeni di erosione sono stati osservati in canali alluvionali. Gli andamenti dei processi geomorfologici nei canali semi alluvionali richiedono il riconoscimento di situazioni locali che aumentano la resistenza del letto del canale e delle sponde all’erosione, o di condizioni specifiche di un particolare evento. Piene di breve durata causano talvolta abbondante trasporto solido, peraltro non associato a significativi allargamenti del canale nella maggior parte degli alvei semi-alluvionali. Otto corsi d’acqua, individuati fra quelli maggiormente interessati da tre delle piene studiate sono stati scelti per ulteriori analisi e per la modellazione della variazione longitudinale dei valori della potenza della corrente. Funzioni di potenza interpretano adeguatamente l’aumento verso valle delle portate di picco, mentre funzioni quadratiche si sono dimostrate più soddisfacenti delle relazioni esponenziali comunemente utilizzate per rappresentare la variazione longitudinale della pendenza dell’alveo. Le prestazioni dei modelli empirici per la variazione longitudinale della potenza della corrente per unità di larghezza dell’alveo (unit stream power) evidenziano il fondamentale controllo esercitato dalla pendenza dell’alveo. La disponibilità di immagini satellitari ad elevata risoluzione riprese prima e dopo gli eventi oggetto di studio ha permesso di valutare le modifiche del canale lungo sette di questi canali. Analisi statistiche hanno indicato che le sole variabili idrauliche non sono sufficienti per interpretare il tasso di allargamento del canale, che è principalmente influenzato dal grado di confinamento del canale stesso. Insieme al confinamento laterale, la potenza della corrente per unità di larghezza dell’alveo appare un valido predittore dell’allargamento in alvei ad elevata pendenza, mentre l’energia complessiva della corrente calcolata per l’intero evento fornisce prestazioni migliori nell’interpretare la variabilità dell’allargamento dell’alveo in canali a pendenza moderata. L'uso di differenti soglie di resistenza all’erosione per quantificare i cambiamenti geomorfologici degli alvei supporta la conclusione che la determinazione di tali cambiamenti è molto più difficile della determinazione delle variabili idrauliche coinvolte.

This study presents an integrated approach to estimating the risk of flash floods in arid wadis. Flash floods impact seriously on the infrastructure and development of Egyptian desert towns, such as Marsa Alam, and their surrounding areas. The study developed a method using the example of the wadi El-Alam, which has an area of approximately 407 km2. The method has three stages. First, the construction of a Digital Elevation Model from which morphometric properties of the brain were calculated. In particular, representing the flat areas and the sharp junctions between badland slopes and the adjacent wadi system (which generally characterised arid landscapes), were among the major issues facing this study. Second, the derivation of land cover from satellite remote sensing data which were rigorously pre-processed with the aid of aerial photographs and fieldwork measurements. Third, the application of a hydrological model, incorporating the basin morphometry and land cover data, to transform rainfall into runoff and route the floodwater through the sub-catchments of the wadi. The hydrological model system (HMS) was run to simulate discharge at the main wadi outlet (where the town of Marsa Alam is located) and at each sub-basin intersecting the Idfu-Alam highway that runs through the wadi. From these results, sites vulnerable to flash flood and their risk classes were identified. The sites judged to have the highest flood hazard along the highway were exactly the sites damaged in the 1991 flash flood. Thus, as an outcome of this study, the first digital database that includes information on land cover, geomorphology and hydrology of wadi El-Alam was developed. This database can be used to highlight regions vulnerable to flood damage.

Various models have been applied in the analysis of hydrologic conditions in different watershed areas. The whole spectrum of models available as tools for natural resource managers is because the use of modeling techniques are limited for specific areas and/or purposes. Constraints and limitations have to be realized in order to properly select a model that answers the needs of a certain locality, for a stated goal. It is the purpose of this paper to review existing hydrologic models, and in the process, select the most promising for application in the southwestern part of Saudi Arabia for the purpose of designing flood control and warning systems. The six models under investigation are the SCS Method, SCS TR-20, Stanford, USDA HL-74, HEC-1 and ANSWERS. Based on the scope and limitations of each model, as well as certain restrictions found within the area of study, it became evident that the SCS models are the most appropriate. This became more apparent having considered the type of data input the models require that can be provided for in the study area, as well as the simplicity of the models and scale of application.

The North American Monsoon System (NAMS) is a significant weather and climate phenomenon that brings critical rainfall to the southwestern United States and northwestern Mexico. As a result of the North American Monsoon Experiment, and research efforts surrounding the field campaign, the understanding of the NAMS has increased considerably over the last 15 years. In addition questions concerning potential flash flood causing mechanisms of the NAMS have not been thoroughly investigated. This dissertation is comprised of two papers that collectively address the aspects of the literary understanding of the NAMS as we know it today and conduct an investigation into the complex interactions between various weather systems that may influence the NAMS. In the first paper, a review of the major research of the NAMS literature since the last comprehensive review 15 years ago is conducted. The results of his review are assessed for where our understanding has been improved and where future research needs to be guided for purposes of the second paper. Based upon the results from the literature review, the second paper focuses on identification of inverted troughs and gulf surges based upon lower- and mid-level atmospheric parameters for purposes of assessing the impacts on National Weather Service Storm Report flash flood dates. This research contributes to the synthesis of the current knowledge of the NAMS in general and to the specific regional impacts that do occur during periods of heavy precipitation over the NAMS region for purposes of improving meteorological predictability of flash flooding. The results can (1) gauge our understanding of the NAMS literature to date and (2) improve meteorological forecasts through the recognition of synoptic and sub-synoptic patterns related to the NAMS that are most likely to cause flash floods.

Eastern Kentucky is a 35-county region that is a part of the Cumberland Plateau of the Appalachian Mountains. With mountaintop removal and associated land cover change (LCC) (primarily deforestation), it is hypothesized that there would be changes in various atmospheric boundary layer parameters and precipitation. In this research, we have conducted sensitivity experiments of atmospheric response of a significant flash flood-producing rainfall event by modifying land cover and topography. These reflect recent LCC, including mountaintop removal (MTR). We have used the Weather Research and Forecasting (WRF) model for this purpose. The study found changes in amount, location, and timing of precipitation. LCC also modified various surface fluxes, moist static energy, planetary boundary layer height, and local-scale circulation wind circulation. The key findings were the modification in fluxes and precipitation totals. With respect to sensible heat flux (H), there was an increase to bare soil (post-MTR) in comparison to pre-MTR conditions (increased elevation with no altered land cover). Allowing for growth of vegetation, the grass simulation resulted in a decrease in H. H increased when permitting the growth of forest land cover (LC) but not to the degree of bare soil. In regards to latent heat flux (LE), there was a dramatic decrease transitioning from pre-MTR to post-MTR simulations. Then with the subsequent grass and forest simulations, there was an increase in LE comparable to the pre-MTR simulation. Under pre-MTR conditions, the total precipitation was at its highest level overall. Then with the simulated loss of vegetation and elevation, there was a dramatic decrease in precipitation. With the grass LC, the precipitation increased in all areas of interest. Then forest LC was simulated allowing overall slightly higher precipitation than grass.

Els treballs d’aquesta tesi es centren geogràficament en el sector del NE de Catalunya, i concretament entre el cap de Creus i la frontera amb França. Es tracta d’una zona amb conques torrencials petites però en les que s’originen inundacions amb una certa freqüència i sovint amb danys importants. Comprèn 11 conques distribuïdes en els termes municipals de Portbou, Colera, Llançà, la Selva de Mar i el Port de la Selva. Les conques presenten unes diferències entre si, però també moltes similituds, ja que es troben en una àrea amb pluges abundants en períodes curts de precipitació. Tenen també un pendent del perfil longitudinal molt brusc, amb els cims de capçalera al voltant dels 600 m. En conseqüència s’originen avingudes sobtades o rierades (flash flood). Geològicament es tracta d’una àrea bastant homogènia, en la que la major part del territori correspon a esquistos i pissarres paleozoïques (cambroordovicianes). Hi ha un petit retall granític en el sector meridional del tram mig de la conca de Llançà. Al fons de les valls els sediments al·luvials han originat les formes recents de tipus terrassa, que aporten informació al respecte de la dinàmica hídrica dels torrents. Hi ha zones recobertes per materials antròpics de recent aportació amb diferents finalitats. Les finalitats es van basar en la cerca del coneixement de la dinàmica dels torrents, de cara a la identificació i determinació de les zones vulnerables als perills d’inundació. Dins d’aquest marc es buscava determinar la freqüència i la magnitud de les inundacions, correlacionant-les amb les característiques geomorfològiques i antròpiques del sistema fluvial. Posteriorment els objectius es van ampliar amb l’anàlisi de la incertesa ja que aparegué aquest problema, de manera general en temàtiques del medi natural i també en la mateixa zona d’estudi. Així es va plantejar determinar el perquè es produeixen aquestes incerteses (aleatòria i epistèmica) i posteriorment mirar de reduir-les. D’aquí va sorgir la necessitat d’innovar i millorar la metodologia d’identificació i cartografia de zones inundables. També es va abordar el problema del canvi climàtic. Com a base del treball es va escollir el “Mètode geomorfològic integrat d’identificació i cartografia de zones inundables” o “Mètode geomorfològic integrat”. Els primers passos de la recerca van ser l’elaboració de la cartografia geomorfològica integrada, de la qual se n’ha derivat la cartografia d’inundabilitat de cada conca. Aquestes cartografies han estat informatitzades mitjançant el programa ArcGIS, i es presenten, a escala 1:3000, en el Volum 2 d’aquest treball, i classificats per conques, començant pel N (la frontera) i acabant pel SE (cap de Creus). Els treballs de camp han estat complementats amb la recollida de dades històriques referents a esdeveniments succeïts en el passat. Amb l’aplicació del Mètode geomorfològic integrat, i a rel de l’aparició de la incertesa abans descrita, es va anar a buscar innovacions i a plantejar la problemàtica de manca de dades prou generals mitjançant l’anàlisi de tipus multiconca-multifunció. Amb el “Mètode geomorfològic integrat” es van identificar, cartografiar i analitzar els elements indicadors de zones inundables, especialment les terrasses, de les quals, en totes les conques, se'n van diferenciar dues: la T0 o llera i la T1 o superior. Les incerteses que aparegueren en l’anàlisi es centraven especialment en els càlculs dels cabals dels torrents en moments punta, però també en les determinacions dels períodes de retorn Tr de les inundacions. Les incerteses es donen, essencialment, a causa de: a) la insuficiència de dades que permetin els càlculs dels cabals i les distorsions derivades de la seva aplicació; b) la insuficiència de dades pluviomètriques; c) la insuficiència de dades en el registre històric; d) la desigualtat en la distribució de la població; e) la imperfecta predicció dels episodis d’inundació a causa de la mida de les conques; i f) la rapidesa i variabilitat de la resposta hidrològica, que fan que el temps d’actuació davant la crescuda sigui molt reduït. Pel que fa a les tipologies de zones inundables, s’ha estudiat les normatives d’àmbit europeu, estatal i autonòmic, amb la finalitat d’aplicar-les a la zona d’estudi. Aparegueren problemes d’aplicabilitat, ja que es basen en el funcionament de grans rius. Els resultats de les conques extenses i de crescuda relativament lenta no encaixaven amb els de les conques petites que tenen avingudes brusques de tipus “flash flood”. Tampoc coincidien en els períodes de retorn ni amb les zonificacions de “Zona Fluvial”, “Sistema hídric” i “Zona Inundable”. És a partir de la cartografia geomorfològica integrada i de tota la resta d’informacions que s’ha arribat a establir una classificació qualitativa de la inundabilitat: alta, mitja i baixa. És la classificació que queda recollida en la cartografia d’inundabilitat, complementada amb altres elements d’interès que hi van relacionats (zona protegida, línies de circulació preferent, punts crítics, etc.). En relació al canvi climàtic s’han buscat referències per poder preveure comportaments en futurs escenaris. S’ha buscat indrets amb possibilitats d’estudiar registres sedimentaris de materials granulomètricament fins i de naturalesa orgànica que permetessin datacions. L’anàlisi multiconca-multifunció, s’ha basat en dos aspectes principals: la magnitud de les precipitacions, i les dades històriques dels efectes de les inundacions. Ha permès la quantificació de les freqüències d’inundació, prenent els períodes dels quals es disposa de més informacions i que són més representatives. S’ha obtingut un promedi de 3 anys de temps de separació entre inundacions o període de retorn. El concepte d’inundació es considera, aquí, que les aigües desbordin de la llera del torrent ocupada per la terrassa inferior T0, i passin a ocupar l’àrea de la terrassa superior T1. En aquest concepte no es té en consideració el gruix d’aigua desbordada ni la magnitud dels efectes ni dels danys ocasionats. De tot el conjunt de treballs, ha sigut possible la formulació de conclusions referents a: - les possibilitats de zonificació de les àrees inundables, - la reducció dels factors d’incertesa característics de les conques - la introducció de millores en el Mètode geomorfològic integrat d’identificació i la cartografia de les zones inundables - la determinació de la freqüència de les inundacions mitjançant l’anàlisi multiconca-multifunció, basat en dos aspectes principals: la magnitud de les precipitacions, i les dades històriques dels efectes de les inundacions Nota: L’estructura d’aquest treball de tesi doctoral desglossa les dades en dos volums. El primer volum comprèn la totalitat dels textos, i el segon només la cartografia: la geomorfològica integrada i la d’inundabilitat, classificades per conques i amb les corresponents llegendes de simbologies gràfiques.
The study area is located in NE Catalonia, Spain, between Cap de Creus and the border with France. The area consists of eleven small basins distributed over the municipalities of Portbou, Colera, Llançà, La Selva de Mar and El Port de la Selva. These basins are prone to devastating flash floods and display differences as well as similarities given that the area is characterised by high intensity short duration rainstorms. The slope of the longitudinal profile of the basins is abrupt and the watershed attains approximately 600 m. Geologically, the area is homogeneous, consisting of palaeozoic schists and slates (cambro ordovician). A small part of the southern sector of the middle of the Llança basin is composed of granite. Recent alluvial terraces are located at the bottom of the valleys and provide valuable insights into stream dynamics. Parts of the study area are covered with diverse materials as a result of human intervention. The aim of the thesis is to improve our understanding of stream dynamics in order to identify the areas that are prone to flood hazards. An attempt was made to determine the frequency and magnitude of floods by correlating them with the geomorphological and anthropogenic characteristics of the fluvial system. Subsequent aims arose given the special characteristics of the study area, which required an analysis of uncertainty (random and epistemic). Special emphasis was placed on innovating and improving the methodology of identification and mapping of flood prone areas. Climate change was also addressed. The “Integrated geomorphological method of identification and mapping of flood hazard areas” or “Integrated geomorphological method” was used. The study consists of two parts. The first part of the study is focused on the integrated geomorphological mapping and the second part is devoted to flood hazards from which the flood hazard map for each basin was derived. These maps were computerized using ArcGis software and are at 1:3000 scale. The basins from the N (the border with France) to the E (Cap de Creus) are classified in volume 2 of the thesis. Field work was complemented by historical data of past events. The multibasin-multifunction analysis was performed to address the uncertainties that resulted from using the integrated geomorphological method. The Integrated geomorphological method enabled us to identify, map and analyse all the features providing evidence of flood prone areas especially fluvial terraces of which two were differentiated in each basin: T0 or lower terrace and T1 or upper terrace. The uncertainties of analysis affected the calculation of peak discharges and the determinations of flood frequency. These uncertainties were attributed to a) paucity of data which resulted in distortions or in the impossibility of discharge calculations, b) scarcity of rainfall data, c) insufficient historical records, d) irregular distribution of population in the basins, e) inaccurate prediction of floods because the size of the basins and f) speed and variability of the hydrological response, which considerably reduces the time for action before the flood. European, national and regional norms and zoning were studied in an effort to make a hazard classification of the flood prone areas. Problems of applicability arose because the norms are based on dynamics of large rivers. The results of the large rivers with relatively slow floods were not consistent with those of small basins that generate flash floods. These results did not coincide with those of return periods nor with the regional zoning of “Zona fluvial”, Sistema hídric” and Zona inundable” in Catalonia. The integrated geomorphological mapping together with all other data enabled us to classify qualitatively flood hazards into: high, medium and low. This classification is presented in the flood hazard mapping and is complemented by other related information (protected zone, preferential flow lines, critical points, etc.). Climate data that could predict future scenarios were obtained. It was not possible to find sedimentary records of fine grained organic sediments to enable dating. The multibasin-multifunction analysis was based on two sets of data: the magnitude of rainfall associated with flooding and historical data of floods. This enabled us to quantify the frequency of flooding by selecting the periods with more data and those that were more representative. A gap of 3 years between flooding or return period was obtained. The concept of flooding considered in the study is as follows: water overflows the lower terrace (T0) and occupies the area of the upper terrace (T1). This concept considers neither the magnitude of overflow nor the damage caused. In the light of our findings, the following conclusions may be drawn: - possibility of zoning flood prone areas - reduction of uncertainty that is characteristic of these basins - improvement in the Integrated geomorphological method of identification and mapping of flood hazard areas - determination of flood frequency by multibasin-multifunction analysis based on two main data: magnitude of rainfall and historical data (effects of floods). NB This doctoral thesis consists of 2 volumes. The first contains the text and the second includes the maps (integrated geomorphological maps and flood hazard maps) classified by basins, and the corresponding legends.

Enxurradas e inundações apresentam-se como fenômenos naturais que têm potencial de causar grandes perdas e danos à população. Estes poderiam ser reduzidos ou evitados a partir de políticas públicas de não ocupação de áreas suscetíveis ou metodologia de alerta diante da possível ocorrência destes eventos adequada. Os eventos de inundação e enxurrada são consequências de uma interação de condições físicas do terreno e de condições meteorológicas. A geomorfologia fluvial se utiliza, portanto, dos parâmetros morfométricos como ferramenta importante na descrição quantitativa das características físicas do terreno. O objetivo deste trabalho é correlacionar os dados morfométricos, extraídos a partir de dados SRTM (Shuttle Radar Topographic Mission) de sete bacias hidrográficas da Região Hidrográfica do Guaíba/Rio Grande do Sul, a episódios de inundação e enxurrada, considerando a incidência destes eventos no inventario pela Defesa Civil no período de 1991 a 2010. O modelo digital de elevação utilizado, o SRTM, possui resolução de 90m, de onde foram extraídas as variáveis analisadas neste estudo. Os resultados foram então correlacionados com os diferentes padrões de escoamento superficial das sete bacias hidrográficas. Buscando análises comparativas o estudo dividese na análise areal, linear e hipsométrica de cada um dos recortes; além de uma breve descrição das características de chuva e de uso e ocupação da área de estudo. Os resultados da análise areal, em todas as suas variáveis, mostraram-se inadequados para a tentativa de relacionar a ocorrência do evento aos seus resultados. Já os resultados obtidos pelas variáveis da análise linear mostraram-se mais eficientes na identificação de áreas de enxurrada, enquanto que a análise hipsométrica reflete melhor os episódios de inundação. Este fator de erro está provavelmente associado a dois fatores distintos: a heterogeneidade das áreas trabalhadas, por vezes generalizando regiões heterogêneas, por outras vezes supervalorizando características físicas de determinadas áreas. Além disso, credita-se erro associado aos problemas de metodologia do inventário base utilizado, este apresentando falhas no que tange a possível ausência de dados ou diferenças na obtenção e classificação dos diferentes tipos de evento. A compartimentação das bacias estudadas, visando obter recortes mais precisos e homogêneos para as diferentes áreas e uma revisão e aperfeiçoamento do inventário são apresentados como sugestões futuras para o refinamento dos resultados obtidos visando encontrar correlação entre as características morfométricas do terreno e os episódios de inundação e enxurrada.
Floods and flash floods are presented as natural phenomena that have the potential to cause major damages to the population. These could be reduced or avoided from public policies of no occupation of susceptible areas or appropriate methodology warning about the possible occurrence of the events. The events of flash flooding and flood are consequences of an interaction of an interaction of physical conditions of the terrain and weather conditions. The fluvial geomorphology uses morphometric parameters as an important tool in the quantitative description of the physical characteristics of the land. The objective of this work is to correlate the morphometric data , extracted from SRTM ( Shuttle Radar Topographic Mission ) data from seven watersheds of the Guaiba River Basin / Rio Grande do Sul , the episodes of flooding and flash flood, whereas the incidence of the incidence of these events in inventory by the Civil Defense from 1991 to 2010. The digital elevation model used, the SRTM has a resolution of 90m, where from the variables analyzed in this study were extracted. The results were then correlated with different patterns of runoff f rom seven river basins analyzed. Seeking benchmarking study is divided into areal, linear and hypsometric analysis; and a brief description of the characteristics of rain, and use and occupation of the study area were also presented. The results of areal analysis, in all its variables, proved inadequate to the attempt to relate the occurrence of the event and its results. The results obtained by the linear analysis variables were more effective in identifying areas of flash flood, while the hypsometric analysis reflects the best episodes of flooding. This error factor is probably related to two distinct factors: the heterogeneity of areas worked, sometimes generalizing heterogeneous regions, other times overestimating physical characteristics of certain areas. Also is credited to the problems of error associated inventory methodology used base, this presenting failures regarding the possible absence of data or differences in collection and classification of different types of event. The partitioning of the basins studied , aiming at obtaining more accurate and homogeneous cutouts for the various areas and a review and improvement of the inventory are presented as suggestions for future refinement of the results aimed at finding correlations between morphometric characteristics of the terrain and episodes of flooding and flash floods.

This work describes the derivation of a set of statistics, termed spatial moments of catchment rainfall, that quantify the dependence between rainfall spatial organization, basin morphology and runoff response. These statistics describe the spatial rainfall organisation in terms of concentration and dispersion along the flow distance coordinate. These statistics were derived starting from an analytical framework, and related with the statistical moments of the flood hydrograph. From spatial moments we also created an index quantifying catchment scale storm velocity. This index measures the overall movement of the rainfall system over the catchment, reflecting the filtering effect of its morphology. We also extended spatial moments to the hillslope system, developing a framework to evaluate the relevance of hillslope and channel propagation in the flood response to spatially variable rainfall fields. Data from six flash floods occurred in Europe between 2002 and 2007 are used to evaluate the information provided by the framework. High resolution radar rainfall fields and a distributed hydrologic model are employed to examine how effective are these statistics in describing the degree of spatial rainfall organisation, which is important for runoff modelling. The size of the study catchments ranges between 36 to 2586 km2. The analysis reported here shows that spatial moments of catchment rainfall can be effectively employed to isolate and describe the features of rainfall spatial organization which have significant impact on runoff simulation. Rainfall distribution was observed to play an important role in catchments as small as 50 km2. The description timing error was further improved by the inclusion in the framework of hillslope propagation. This development allows to compare scenarios of hillslope conditions, to evaluate the sensitivity of single basins or the effect of catchment scale. The analysis of catchment scale storm velocity showed a nonlinear dependence with basin scale. The values of velocity observed were however rather moderate, in spite of the strong kinematic characteristics of individual storm elements, and did not play a relevant effect on the flood analyzed.
Questo lavoro presenta una serie di statistici, denominati "momenti spaziali di pioggia a scala di bacino", che permettono di quantificare la relazione tra l’organizzazione spaziale della pioggia, la morfologia del bacino e la forma dell’idrogramma di piena. Tali statistici descrivono la posizione e la dispersione della pioggia su un assegnato bacino idrografico. La trattazione include la derivazione di una serie di relazioni che consentono di stabilire un rapporto fra detti statistici di pioggia ed i momenti temporali dell’onda di piena. La formulazione complessiva del lavoro consente di isolare e quantificare l’effetto della variabilità spaziale della pioggia sulla struttura della risposta di piena, e di creare un indice di velocità del sistema di pioggia. Questo indice considera l'iterazione tra morfologia del bacino e spostamento della pioggia, quantificando l'influenza sull'idrogramma. I momenti spaziali stati poi ampliati alla propagazione su versante, sviluppando degli statistici per valutare l'importanza della propagazione di canale e di versante sulla risposta nella riposta di un bacino ad una pioggia distribuita. Dati relativi a sei eventi estremi di piena improvvisa verificatisi in diverse regioni Europee sono utilizzati per illustrare il significato degli statistici e le relazioni con la forma dell'idrogramma. Stime di pioggia da radar ed un modello idrologico distribuito sono utilizzati per valutare l'efficacia degli statistici nel cogliere l'organizzazione delle piogge che ha un'influenza sulla simulazione di piena. Lo studio mostra che i momenti spaziali di pioggia a scala di bacino possono essere efficaci nel cogliere questa organizzazione. Nelle piene improvvise analizzate la distribuzione della pioggia ha un effetto rilevante anche per bacini di circa 50 km2. La descrizione dell'errore temporale dell'idrogramma è ulteriormente migliorata dalla considerazione dell'effetto del versante. Questo sviluppo permette inoltre di confrontare condizioni di versante diverse, di valutare la suscettibilità di singoli bacini o l'effetto in relazione alla scala dei bacini. L'analisi della velocità di spostamento a scala di bacino mostra una relazione non lineare con le dimensioni del bacino. I valori di velocità osservati sono comunque moderati, nonostante la forte velocità di spostamento delle singole celle convettive, e non hanno avuto un ruolo rilevante nell'evento analizzato.

The final thesis is focused on assessing the current state of hydrological system in the watershed area Jankovice stream and on draft proposal of food protection measures of the village Jankovice. In the first part of the thesis, there is documented the current situation Jankovice stream, its appreciation and draft measures for a improvement the current state. In the following part, there is the elaboration of the sediment transport balance in the stream. In the last part of the final thesis, there is documented the current state Jankovice stream in the village Jankovice and the stream regulation is designed for the purpose of flood protection of the village.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
Numa contemporaneidade na qual as estatísticas apontam o incremento dos chamados desastres naturais em todo o mundo, sobretudo em nações como o Brasil, onde o crescente adensamento populacional nas cidades faz delas as áreas preferenciais para a realização das catástrofes, especialmente quando marcadas pela desigualdade social e pela baixa capacidade institucional de prevenção e gerenciamento desses fenômenos. A presente pesquisa faz uma interpretação geográfica do evento de inundação brusca ocorrido na cidade de Areal – RJ no dia 12 de janeiro de 2011, diretamente vinculado à catástrofe socioambiental que se processou na Região Serrana do estado naquela data. A partir da experiência vivenciada pelo próprio autor como testemunha e vítima do desastre em Areal, o trabalho registra como o evento se processou no tempo e no espaço e discute numa proposta integradora as condicionantes físicas e socioinstitucionais relacionadas ao fato da cidade ter tido a quase totalidade de sua área urbana fortemente impactada pela inundação. Dentre as condicionantes analisadas ressalta-se a presença e a operação da barragem Morro Grande, um reservatório para aproveitamento hidrelétrico a montante e próximo da área urbana do município. Duas paisagens são consideradas na interpretação, a da bacia hidrográfica do rio Piabanha e a da área urbana do município de Areal, cidade localizada no curso médio do rio que dá nome à bacia. As interações natureza-sociedade na geração do desastre, o mapeamento da área urbana afetada no evento de 2011, a análise da capacidade político-institucional de resposta à crise e o ordenamento urbano de Areal no engendramento de riscos são aspectos averiguados na pesquisa. Com base na proposta de Libaut (1971), a metodologia obedeceu quatro etapas seqüenciadas e empregou técnicas de trabalho de campo, entrevistas e mapeamento da área inundada. A pesquisa conclui que o evento na cidade foi de grande porte, deflagrado por um contexto de exceção na dinâmica flúvio-meteorológica regional, mas amplificado por fatores ligados à própria espacialidade local.
At the present times, the statistics are aiming to the increase of those called “global nature disasters”, particularly in nations like Brazil where the population of small and big cities are in constant development which contribute in addition to, the weakness of the administration and management of the prevention of disasters like the one that occurred at the city of Areal- RJ on January 12, 2011. The present work made a geographical interpretation of that event that might be the cause for that sudden flood that covered the city, located near at the highlands region of Rio de Janeiro. From that self-experience as a witness and victim the author, present a friendly proposition to discuss the construction and operation of the Morro Grande, located near that urban area and used as a Hydroelectric Reservoir to the enhancement of the region. At this point there are multiple factors to be analyzed like the area between the rivers, the urban area, the interaction nature-society, description of the area affected, the capacity political-institutional to respond to these type of events. This work is in according with Libaut (1971), this work follow the four steps and technical of work on the field. Interviews and description of the area object of this work. The paper concludes that the event in the city was large, triggered by an exception in the context of river dynamics and regional weather, but amplified by factors related to spatiality own site.

Distributed models of the land surface are essential for global climate models because of the importance of land-atmosphere exchanges of water, energy, momentum. They are also used for high resolution hydrologic simulation because of the need to capture non-linear responses to spatially variable inputs. Continued improvements to these models, and the data which they use, is especially important given ongoing changes in climate and land cover. In hydrologic models, important aspects are sometimes neglected due to the need to simplify the models for operational simulation. For example, operational flash flood models do not consider the role of snow and are often lumped (i.e. do not discretize a watershed into multiple units, and so do not fully consider the effect of intense, localized rainstorms). To address this deficiency, an overland flow model is coupled with a subsurface flow model to create a distributed flash flood forecasting system that can simulate flash floods that involve rain on snow. The model is intended for operational use, and there are extensive algorithms to incorporate high-resolution hydrometeorologic data, to assist in the calibration of the models, and to run the model in real time. A second study, which is designed to improve snow simulation in forested environments, demonstrates the importance of explicitly representing a near canopy environment in snow models, instead of only representing open and canopy covered areas (i.e. with % canopy fraction), as is often done. Our modeling, which uses canopy structure information from Aerial Laser Survey Mapping at 1 meter resolution, suggests that areas near trees have more net snow water input than surrounding areas because of the lack of snow interception, shading by the trees, and the effects of wind. In addition, the greatest discrepancy between our model simulations that explicitly represent forest structure and those that do not occur in areas with more canopy edges. In addition, two value-added Land Cover products (land cover type and maximum green vegetation fraction; MGVF) are developed and evaluated. The new products are good successors to current generation land cover products that are used in global models (many of which rely on 20 year old AVHRR land cover data from a single year) because they are based on 10 years of recent MODIS data. There is substantial spurious interannual variability in the MODIS land cover type data, and the MGVF product can vary substantially from year to year depending on climate conditions, suggesting the importance of using climatologies for land cover data. The new land cover type climatology also agrees better with validation sites, and the MGVF climatology is more consistent with other measures of vegetation (e.g. Leaf Area Index) than the older land cover data.

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A pesquisa aborda as consequências das fortes precipitações que aconteceram em Pelotas o que levou a ocorrência de uma grande enxurrada em 28 e 29 de janeiro de 2009. O recorte espacial da pesquisa é a bacia hidrográfica do Arroio Quilombo, Pelotas/RS, localizada em sua maior parte na zona rural de Pelotas e uma pequena área no município de Canguçu e outra pequena área no Município de Arroio do Padre. O recorte temporal é do inicio do século XX até o ano de 2009, data da enxurrada que atingiu a bacia hidrográfica do Arroio Quilombo (BHAQ), deixando consequências bastante significativas. As enxurradas podem ser consideradas como um desastre natural, tanto pela sua intensidade, quanto pelas suas consequências. Nesse sentido o referencial teórico trata da questão dos desastres naturais, a fim de se compreender alguns conceitos que geram certa confusão, é o caso dos termos: enxurradas, enchentes, inundações e alagamentos. Nesse sentido a revisão teórica que se apresenta, vem em busca de sanar esses e outros conceitos. Sendo assim, essa pesquisa tem como objetivos: Compreender os fatores que levaram à ocorrência da enxurrada de 28 e 29 de janeiro de 2009 na BHAQ, bem como as transformações geomorfológicas consequentes; Realizar uma revisão teórica sobre a temática dos desastres naturais, geomorfologia, transformações geomorfológicas, uso e cobertura da terra, enxurradas e as suas consequências; Realizar um resgate histórico das inundações no município de Pelotas, bem como um breve histórico das enxurradas na Bacia Hidrográfica do Arroio Quilombo; Realizar um estudo morfométrico da Bacia do Arroio Quilombo; Verificar o uso e cobertura da terra na BHAQ; Investigar sobre as transformações da paisagem após as inundações na bacia hidrográfica do Arroio Quilombo e Identificar e mapear as consequências geomorfológicas e os danos ao patrimônio provocados pelas cheias de 2009. A pesquisa mostrou que a enxurrada de 2009 não foi o único evento de grande intensidade a atingir a bacia do Arroio Quilombo. Porém, a bacia hidrográfica do Arroio Quilombo não apresenta condicionante a enxurradas, e que a enxurrada de 2009 não ocorreu em toda bacia, porém atingiu de forma intensa a baixa bacia do Arroio Quilombo, deixando algumas consequências como perdas de animais, de lavoura, materiais e infraestruturais. As entrevistas realizadas mostraram que as alterações geomorfológicas mais significativas ocorreram fora dos limites da BHAQ.
This research addresses the consequences of heavy rainfall that occurred in Pelotas, which led to a great flash flood on the 28th and 29th January 2009. The area of research is the Quilombo Creek Watershed, Pelotas municipality, in the State of Rio Grande do Sul. Most of the Watershed is located in the rural zone of the Pelotas municipality, but also has a small section in the Canguçu municipality and another small section in the Arroio do Padre municipality. The time frame starts at the beginning of the twentieth century until 2009, when the flash flood hit the Quilombo Creek Watershed, leaving very significant consequences. Flash floods can be considered as a natural disaster, both for their intensity and their consequences. Thus, the theoretical background deals with the issue of natural disasters in order to understand some flood concepts that frequently create confusion in Portuguese: “enxurradas”, “enchentes”, “inundações” and “alagamentos”. This way the presented theoretical background tries to solve this confusion and other conceptual problems. This research has the following objectives: understand the factors that triggered the flash flood of the 28th and 29th January 2009 in the Quilombo Creek Watershed, as well as the consequent geomorphological changes; expose a theoretical background about natural disasters, geomorphology, geomorphological changes, land use and land cover, flashfloods and their consequences; carry out a historical review of the floods in the Pelotas municipality as well as a historical review of the floods in the Quilombo Creek Watershed; carry out a morphometrical study of the Quilombo Creek Watershed; observe the land use and land cover in the studied area; study the landscape changes and identify the damage done to the patrimony in the area of study after the 28th and 29th January flash flood. This research shows that the 2009 flash flood was not the only high intensity event to touch the Quilombo Creek Watershed. However, the studied watershed does not present natural conditions that would trigger flash floods, and the 2009 flash flood does not affect the entire Watershed in the same way. It intensely hit the lower part of the watershed creating consequences such as animal loss, land crop loss and material loss. The interviews showed that the most significant geomorphological changes occurred outside the boundaries of the studied watershed.

The thesis concerns different arguments of research, but strictly related between them. All the activities of research were carried out simultaneously during the period of study. The aim is to provide a more accurate rainfall estimation in mountainous areas, improving the capability to detect intense events leading to flash floods Another object is to investigate the role of rainfall spatial variability in flash flood triggering. Flash floods are caused by heavy precipitation over small area (usually not bigger than 500 km2), and have a timescale that normally does not exceed 12 hours. What makes flash flood very dangerous is their sudden nature. They cause great damages to the human activities. In order to reduce their effects and to get a real-time system monitoring, it is necessary to have an instrument that allows to have a spatial resolution of the data, that the conventional weather stations network not guarantees. For these reasons in recent decades had a strong diffusion the meteorological radar; this tool allows to locate the precipitation and to calculate the intensity of rain in real- time, with a resolution that no other instruments might reach. The meteorological forecasters use this instrument to provide short-time forecasts, named nowcasting (1-3 hours). For such short interval time the mathematical models are useless, and the only instruments that support the forecasters are the data from satellite and the rain maps from the radar. Radar data are unfortunately affected by several sources of error; between them the main important are the occlusion, the ground clutter, the attenuation, the vertical variation of the reflectivity. By using double-polarimetric radar operating at low wavelenght (X-band radar) is possible to reduce the effects of these errors, acquiring more accurate data than the ones provided by the traditional tool. A part of this work of thesis aims to assess if the eventual introduction of this new technology (double polarimetric radar operating at low wavelengths) in the Alpine area might ensure more accurate rain estimation. This instrument were tested during the summer of 2007 in Folgaria, and it was used in different conditions to monitorate the events over several hydrological basins. On the same area are available the data collected by two C-band radar, one managed by the Provincia Autonoma of Trento, and the other one by the Veneto Region. The aim of the study is to evaluate the advantages/disadvantages of these different technologies, and finally to set if by using this X-band polarimetric radar, would be possible to get a better description of the rainfall patterns, and to improve the predictability of flood events. The meteorological precipitations detected in real-time works as input for the hydrological models, that operate a simplification of the real processes to obtain a discharge hydrograph for different closing sections. The accuracy of the input data allows to improve the flood predictability and to reduce the catastrophic impacts that these event have on human activities. Within the present work the efforts have been focused in understanding the dynamics underlying the generation of a flood hydrograph; systematic studies were carried out to describe the accuracy of rainfall volumes at basin scale and the effect of spatial variability within the basin. The analysis focused on the flash flood event that affected the Weisseritz Region (Saxony) in the summer of 2002. Some statistics were applied that allow to put in direct relation the rainfall distribution, the shape of the basin, and their influence on the hydrograms at the closing section. Particularly, in a place with the characteristics of the pre-Alpine area, orography strongly influences the rainfall distribution. The events are mostly concentrated in the basins that are affected by a great increase of the precipitation with the altitude. The meteorological radar often describes only partially the precipitation in the mountain regions, because the beam, along its propagation path, can be occluded by orography. It often happens then, that the weather stations are located in the valleys, where the majority of the population lives, and where it is easier for the person assigned to control their working. For this reason, particularly in the last year of the studies, the efforts have been mainly focused in detecting some methodologies that might allow to estimate correctly the lapse rate of the precipitation (even in places where there are no rainfall measurements i.e. high mountains), and the total volumes of rain. The methodology uses the data collected by the tradition weather network, and allows to calculate rainfall maps for the whole territory The remainder of this dissertation is organised as follows: Chapter 1 → Short description of the main topics selected. Bibliography on the different arguments. Methodology applied to study flash flood events; what has been dome to mitigate the effects of these catastrophic events, and how to improve in understanding their dynamics. Chapter 2 → The meteorological radar. Data acquiring and processing. Most common errors. The double-polarimetric radar. The measure campaign of Folgaria: short description of the basin object of the analysis and events selected. Procedures and algorithms to correct the data. Different algorithms used and comparison. Analysis of the results and some statistics calculated by merging radar data and conventional raingauge network. Significant advantages incoming from this new technology. Chapter 3 → The Hydrological model KLEM. Characteristic of the model and simplifications. An hydrological event in the Weisseritz: short description of the characteristics of the basin and of the flash flood event of the summer of 2002. The application of the hydrological model. The role of rainfall spatial variability in flash flood triggering .Statistics to describe the relationship between the variability catchment scale and the rainfall distribution. Comments and conclusions Chapter 4 → Alto Adige: brief description of the territory and development of a methodology of spatialisation from the rainfall data. Underestimation of snowfall. Calculation of the rain maps. Verification of the results, comparing the estimated rainfall and the flow rates for different closing sections throughout the Province. The introduction of some additional weather stations of Austria, and its effect in achieving a more accurate estimate of the precipitation lapse rate. Possible future developments
La presente attività di ricerca abbraccia tematiche diverse tra loro, ma allo stesso tempo fortemente interconnesse. Esse sono state sviluppate simultaneamente nel corso dell’ attività di ricerca. L’ obiettivo finale è fornire una stima più accurata dei campi di pioggia in un territorio ad orografia complessa come quello pre-alpino, per poter migliorare la capacità previsionale di eventi di piena improvvisi. Si vuole inoltre valutare l’influenza che il movimento dei campi di pioggia ha nel generare l’idrogramma di piena finale, e metterlo in relazione al tipo di bacino e alla sua morfologia. Gli eventi di piena improvvisi (flash flood) si generano quando intense precipitazioni si riversano in un breve lasso temporale su un territorio circoscritto; essi. non superano la durata di 6-12 ore e coinvolgono bacini non superiori ai 500 km2. Data la loro improvvisa formazione essi producono notevoli disagi e danni anche ingenti. Per poter mitigare i loro effetti, e per poter arrivare a monitorare in ogni istante quello che succede sul territorio, è importante avere uno strumento che consenta di ottenere in tempo reale stime di pioggia con una risoluzione spaziale che la tradizionale rete pluviometrica non riesce a garantire. Per questo motivo nel corso degli ultimi decenni ha avuto una forte diffusione il radar meteorologico; questo strumento permette di localizzare e misurare le precipitazioni in tempo reale, consentendo di calcolare mappe di pioggia con una risoluzione spazio-temporale che nessun altro tipo di strumento consente di ottenere. I meteorologi utilizzano il radar meteorologico per formulare previsioni a brevissimo termine (1-3 ore), comunemente definite nowcasting. Per intervalli temporali così limitati difatti i modelli matematici, generalmente utilizzati per formulare le previsioni per i giorni successivi, sono insufficienti, e gli unici strumenti che possano supportare i previsori sono i rilevamenti dati dal satellite e dal radar. Le misure rilevate dai radar sono però soggette a diverse forme di errore che possono alterare la qualità delle misure. Tra questi vale la pena citare l’occlusione, il ground clutter, l’attenuazione e la variazione del profilo di riflettività con la quota. L’impiego di radar a doppia polarizzazione operanti nel campo delle basse lunghezze d’onda (radar in banda X) consente di ridurre l’effetto di questi errori, rispetto al tradizionale radar meteorologico. Parte del lavoro di tesi è volto a valutare se l’introduzione di questi strumenti innovativi (radar a doppia polarizzazione) possa garantire nell’area pre-alpina misure dei campi di pioggia più accurate. A tale scopo ci si avvale delle misure rilevate nel corso dell’estate del 2007 da un radar a doppia polarizzazione installato sull’altipiano di Folgaria (Trento). Su tale area operano, accanto a una fitta rete di pluviometri disseminati alle varie quote, due radar doppler in banda C appartenenti al sistema nazionale (uno gestito dalle Province di Trento e Bolzano, l’altro di proprietà della Regione Veneto). Si vuole pertanto valutare la qualità delle misure associate alle diverse tecnologie, e in pratica testare se un' eventuale introduzione di questi radar (doppio polarimetrici) garantirebbe in territorio montano una migliore descrizione dei fenomeni di precipitazione e una maggiore tutela nei confronti di fenomeni alluvionali improvvisi. Le misure di pioggia vengono rilevate in tempo reale e vengono fornite ai diversi modelli idrologici, che le utilizzano per formulare una previsione dell’idrogramma di piena finale, relativo alle diverse sezioni di chiusura di interesse. Si capisce quindi come la possibilità di disporre di misure quanto più precise e rappresentative permetta di dare come input ai modelli valori più rappresentativi e di conseguire una buona capacità previsionale, migliorando la capacità predittiva di questi eventi catastrofici. All’ interno del percorso di ricerca parte degli sforzi sono stati volti a migliorare le conoscenze di come lavorano questi modelli idrologici, e a comprendere se il movimento dei campi di pioggia durante l’evento abbia una reale influenza sull’andamento dell’idrogramma. Si vuole quindi capire se per un dato bacino è sufficiente avere una stima dei volumi complessivi di precipitazione caduti, oppure è importante conoscere la distribuzione e il movimento dei campi di pioggia per ottenere simulazioni più accurate. All’interno del presente lavoro si è cercato di capire quali dinamiche siano sottese alla generazione di un idrogramma di piena, e si è cercato di sviluppare una metodologia che consenta di valutare per ogni singolo bacino quale influenza abbia la dinamica dell’evento nel generare la piena finale. Si è a tale scopo analizzato un evento specifico (evento di piena del 2002 che ha interessato il bacino del Weisseritz in Sassonia), e sono stati sviluppati alcuni statistici che consentono di metter in relazione la distribuzione dei campi di pioggia e l’effetto che essi producono nella generazione dell’idrogramma dio piena finale. In particolare in un territorio come quello pre-alpino l’orografia influenza fortemente la distribuzione delle precipitazioni. Gli eventi più significativi si concentrano nei bacini in cui la particolare orografia determina un forte incremento delle precipitazioni con la quota, Il radar meteorologico non sempre riesce a descrivere correttamente l’andamento delle precipitazioni nei territori montani, in particolare in quei bacini in cui il fascio risulta occluso. Capita poi sovente che le stazioni meteorologiche siano concentrate nel fondovalle ove risiede la maggior parte della popolazione e dove è più agevole il controllo dal personale qualificato. Per questo motivo, in particolare nell’ultimo anno dell’attività di ricerca, gli sforzi sono stati maggiormente indirizzati a sviluppare altre tecniche che consentano di stimare correttamente i volumi complessivi di pioggia, anche nei punti in cui non sono disponibili misure pluviometriche, e quindi in particolare in alta montagna. Lo studio si propone di partire dai dati di precipitazioni rilevati dalla tradizionale rete pluviometrica . e di sviluppare una metodologia di spazializzazione, che consenta di ottenere delle mappe di pioggia continue e rappresentative per tutto il territorio. La struttura dell’elaborato di tesi si presenta così articolata: Capitolo 1 → Fornisce una breve inquadratura dell’argomento prescelto. Viene fornita una rapida illustrazione dello stato dell’arte, delle metodologie che vengono applicate per studiare eventi di piena improvvisi, di cosa viene fatto per mitigarne gli effetti, e degli studi che vengono condotti per migliorare la comprensione di questo tipo di eventi. Capitolo 2 → Il radar meteorologico. Principi di funzionamento. Principali forme di errore. Il radar doppio polarimetrico. L’esperimento di Folgaria: breve descrizione del bacino monitorato e eventi selezionati. Procedure di correzione applicate ai dati. Confronto tra i diversi algoritmi di calcolo. Analisi dei risultati ottenuti e calcolo di indici statistici, ottenuti confrontando tra loro i dati radar e i dati pluviometrici. Significativi vantaggi che un eventuale introduzione di questo tipo di strumenti consentirebbe di ottenere. Capitolo 3 → Il modello idrologico KLEM. Schema di funzionamento e semplificazioni adottate. Il caso del Weisseritz: breve descrizione del bacino e dell’evento di piena dell’estate del 2002. Applicazione del modello idrologico. Influenza spaziale delle precipitazioni nella generazione dell’idrogramma di piena .Sviluppo di alcuni statistici che permettono di mettere in relazione tra loro l’andamento delle precipitazioni all’interno del bacino, e la morfologia stessa del bacino. Commenti e conclusioni. Capitolo 4 → Alto Adige: breve descrizione del territorio e sviluppo di una metodologia di spazializzazione delle precipitazioni, partendo dai dati pluviometrici. Sottostima delle precipitazioni nevose. Calcolo delle mappe di pioggia. Verifica dei risultati ottenuti, confrontando tra loro le precipitazioni stimate, e le portate misurate, in prossimità delle diverse sezioni di chiusura disseminate nel territorio provinciale. Effetto dell’ introduzione di alcune stazioni meteorologiche austriache, per conseguire una stima più precisa dell’incremento di precipitazione con la quota. Possibili sviluppi futuri.

Depuis 25 ans, plus de 200 personnes ont perdu la vie dans le Sud de la France suite à une inondation (Vaison-la-Romaine en 1992, Aude en 1999, Gard en 2002, Var en 2010...). La sauvegarde des populations est affichée comme une priorité des pouvoirs publics, pourtant nous manquons encore d'une caractérisation globale de la vulnérabilité des personnes face aux phénomènes hydrométéorologiques. Ce travail de thèse postule que la mortalité liée aux catastrophes naturelles n'est pas fortuite. Elle reflète des vulnérabilités structurelles et conjoncturelles. L'analyse fine des circonstances de décès et du profil des victimes met en évidence les facteurs qui déterminent la mortalité face à de tels phénomènes et aide à mieux cibler la prévention. Ce travail s'appuie en grande partie sur la constitution d'une base de données géoréférencée pour la période 1988-2011 collectant les lieux, les circonstances et le profil des victimes. La zone d'étude couvre la France Méditerranéenne soumise aux crues " torrentielles " dans un triangle allant des Pyrénées-Orientales à l'Ardèche et au Var. L'analyse permet de remettre en perspective les préjugés d'une vulnérabilité " supposée " (femmes, enfants, personnes âgées...) sur lesquels porte de façon " réflexe " la prévention. Pour les inondations majeures (plus de dix décès) qui totalisent les 2/3 du bilan humain, les décès à domicile sont prépondérants. Les circonstances de décès laissent apparaitre une vulnérabilité subie liée à l'exposition des personnes (par exemple dans un bâti inadapté) ou une vulnérabilité structurelle liée à la capacité des personnes à résister à l'eau. A l'inverse, pour les petits évènements, moins meurtriers mais récurrents, se dégage une vulnérabilité plus " active " qui se traduit par des comportements à risque, conscients ou inconscients, notamment liés aux déplacements. La troisième partie de la thèse envisage les leviers de prévention aptes à réduire ces bilans humains. Une bonne connaissance des circonstances de décès et des facteurs expliquant la mortalité liée aux crues méditerranéennes permet d'évaluer l'efficacité et l'efficience des mesures de gestion du risque et laisse entrevoir des potentialités de " décès évitables " en ciblant les mesures de prévention adéquates.

Anticiper les inondations constitue un enjeu majeur pour les communes exposées aux crues car c’est sur cette anticipation que repose l’ensemble de la chaîne d’alerte, garante de la sécurité des personnes et des biens. Si un système de suivi du risque de dommages liés aux crues est disponible pour un cinquième du réseau hydrographique français, les petits cours d’eau composant les quatre cinquièmes restants ne font pas partie du dispositif de suivi temps réel du ministère en charge de l’écologie, appelé « Vigicrues ». Or il s’agit également des cours d’eau les plus concernés par le phénomène de crues rapides, pour lesquelles l’anticipation joue un rôle crucial en gestion de crise. Voilà pourquoi début 2017, Vigicrues a été complété par un service automatique d'avertissement des crues appelé Vigicrues Flash. Ce système permet de fournir en temps réel une information sur l’intensité de la crue des cours d’eau pour 10 000 communes françaises.Même si ce nouveau service constitue un réel progrès pour les communes jusqu’alors dépourvues de système d’anticipation, la méthode AIGA qui constitue le cœur de Vigicrues Flash possède certaines limites. L’une d’entre elles, est le fait que la méthode n’avertit que sur le niveau de rareté de la crue, sans tenir compte des enjeux présents. Or, pour générer un avertissement efficace, il est nécessaire de prendre en compte les conséquences potentielles de cette crue. Cette thèse a donc pour but de permettre l’estimation anticipée des dommages liés aux crues rapides, en particulier sur les bassins non jaugés. Pour cela, nous proposons une méthode d’estimation du risque de dommages fondée d’une part sur la qualification de l’intensité de l’aléa crue par la méthode AIGA et d’autre part sur la prise en compte de la vulnérabilité du territoire. Cette dernière a été construite à partir d’une approche bottom-up innovante, directement auprès de gestionnaires du risque. Le croisement de ces deux types d’informations a permis de fournir une première caractérisation du risque de dommages liés aux inondations sous la forme d’un indice de risque dynamique.En adaptant des tests de performances issus de la météorologie, nous avons pu évaluer notre indice par rapport à la méthode AIGA seule. Des informations sur les dommages déjà existantes (les arrêtés « CATNAT » issus de la BD GASPAR) ou spécifiquement collectées (la BD DamaGIS constituée pour cette thèse à partir d’informations présentes notamment sur les réseaux sociaux) constituent nos données de validation. Notre évaluation a porté sur 12 communes dans les Alpes-Maritimes, 69 dans le Gard et 28 dans le Var, et s’est faite de deux manières complémentaires : d’une part une évaluation en continue et exhaustive à partir des arrêtes CATNAT pris pour nos communes sur toute la période 1998-2016 ; et d’autre part une évaluation événementielle, mais à l’échelle infra-communale.Nos résultats montrent que le passage de la caractérisation de l’aléa à celle du risque améliore nettement la pertinence des avertissements émis, surtout à l’échelle infra-communale. Les dommages y sont mieux détectés, avec un taux moindre de fausse alertes. Cette thèse ouvre donc de réelles perspectives d’amélioration de la chaîne de l’alerte actuelle, permettant de mieux organiser la réponse des services de secours et de gestion de crise face à l’annonce de dommages potentiels liés aux crues rapides
Anticipating floods is a major challenge for communities at risk of flooding as the entire warning system – responsible for the safety of people and goods - relies on this anticipation. There is an existing monitoring system “Vigicrues” for flood damage for a fifth of the river network in France. But for four-fifths of this network, made of small rivers, no monitoring is available. Yet those rivers are the most affected by flash floods which especially require anticipation for crisis management purposes. This is why at the beginning of 2017, the Vigicrues system for flood monitoring has been completed with a new flood warning system called Vigicrues Flash. This system provides automatic information in real-time on flood severity of ungauged basins for 10 000 French communities.Even if this new system is a real innovation for communities with no monitoring at all, the AIGA method which is used in Vigicrues-Flash has some limits. The first one is that the warnings are only based on the assessment of flood severity. But estimating flood severity is not enough to issue efficient flood warnings. To be able to do so, taking into account potential flood losses is essential. The main goal of this work is to enable an anticipated estimation of flood related damage, especially for ungauged basins. We offer a method to assess the risk of flood related damage based on flood severity assessed by the AIGA method and a territorial vulnerability assessment. This last one has been built on a bottom-up approach developed with crisis managers. Putting together this data has enabled a first assessment of the risk of flood risk damage as a dynamic risk index.By adjusting performance testing used in the meteorology field, we have been able to evaluate our risk index and to compare the results with the AIGA method. In order to do so, we have used existing damage data (CATNAT from the GASPAR database) as well as a specific multisource database (using notably social media data) which has been put together as part of this study (DamaGIS). The evaluation process has been tested for 12 communities in the Alpes-Maritimes, 69 in the Gard and 28 in the Var department. Two types of evaluation have been performed: a first comprehensive one continuously with CATNAT data on the 1988-2016 period; and another one per flood event at a finer scale.Our results show that moving from hazard assessment to risk assessment has significantly increased the relevance of the warnings and mostly at a smaller scale than the community one. Though, there is a better detection of flood related damage as the false alarm rate has been significantly reduced. This PhD work offers promising prospects to improve the current French warning system for floods and enable a more efficient emergency response

Les crues rapides sont considérées parmi les catastrophes naturelles les plus dangereuses en raison de leur imprévisibilité et la rapidité de leurs dynamiques spatio-temporelles. Même si ces évènements touchent généralement des petites étendues spatiales, elles causent un nombre important de victimes. Les différentes analyses des impacts des crues rapides pointent la mo- bilité quotidienne comme un facteur principal augmentant l’exposition et la vulnérabilité des individus : près de la moitié des victimes sont des automobilistes surpris par les submersions des routes durant leurs trajets quotidiens. C’est dans ce contexte que plusieurs travaux ont été conduits afin de développer des outils de prévision des coupures des routes par submersion dans le département du Gard, fréquemment exposé à des évènements hydro-météorologiques extrêmes. Ces études ont permis d’identifier les points de coupure, situés aux niveaux des intersections routes/rivières, vulnérables aux crues rapides et de développer des méthodes d’estimation du risque de submersion des routes.Cette thèse s’inscrit dans la continuité de ces travaux dans le but de quantifier et de caractériser l’exposition des individus aux crues rapides durant leurs mobilités. Pour cela, nous avons contribué au développement de MobRISK : un modèle de simulation de l’ex- position des automobilistes aux submersions des routes lors d’évènements de crues rapides. Une première application de MobRISK est présentée dans le but d’évaluer l’exposition d’une population d’un zone d’étude, située au nord-ouest du Gard, à l’évènement de crue rapide des 8-9 Septembre 2002.Les résultats de ce cas d’étude ont permis d’identifier un décalage entre les dynamiques temporelles du trafic simulé au niveau des points de coupure et des niveaux de submersion de ces points. Ce décalage temporel a probablement constitué un facteur de réduction du nombre de victimes sur la route. La combinaison des estimations de submersion des routes avec le trafic simulé a permis de localiser les routes qui ont présenté le plus de danger pour les automobilistes lors de cet évènement. Ensuite, l’évaluation de l’exposition individuelle aux submersions routières a permis d’identifier les profils socio-démographiques des automobilistes les plus exposés constitués majoritairement de jeunes actifs de sexe masculin.Enfin, différents scénarios de comportements en situation de crise ont été construits et tes- tés à travers l’intégration des décisions d’adaptation des déplacements face aux perturbations environnementales. La comparaison des effets des scénarios de comportements a permis de souligner le rôle important des règles adoptées dans les prises de décision et dans l’évaluation du danger dans la réduction l’exposition des automobilistes.Au final, cette thèse souligne les potentialités et les performances de MobRISK comme un outil innovant et prometteur pour la simulation de l’exposition sociale aux crues
Flash floods are considered as ones of the most dangerous natural hazard due to their rapidness and suddenness that leave little time for exposed people to protect themselves. Although the relatively small spatial extension of those events, several studies showed strong human impacts regarding the number of affected people. Recently, daily mobility is pointed at as important social factor increasing individual exposure and vulnerability to flash flooding : almost half of the victims are motorists trapped while travelling on flooded roads. Therefore, several studies have been conducted for assessing roads’ sensitivity to flooding in the Gard area, frequently exposed to sever flash flood events.This thesis goes a step further by integrating social dimension in order to quantify and analyze road users’ exposure to flash flood during their itineraries. It contributes to the development of MobRISK : A simulation model for assessing motorists’ exposure to roads submersion by integrating individual travel-activity patterns and behavioral adaptation regarding weather disruptions. In order to assess population exposure to September 2002 flash flood event, we conducted an application of MobRISK in a study area located in the north-ouest of the Gard department.The results show that risk of flooding is mainly located in principal road links with considerable traffic load. However, a lag time between the timing of roads’ submersion and persons crossing these roads contributes to reduce the potential vehicle-related fatal accidents. It is also found that socio-demographic variables have significant effect on individual exposure and that young working males are the most exposed persons to road flooding. Finally, different behavior scenarios are built and tested by integrating individual travel adaptation decisions regarding perceived weather disruptions. The comparison of motorists’ exposure for each scenario highlights the important role of risk attitudes and threat evaluation processes on reducing population exposure.Thus, the proposed model demonstrates the benefits of considering spatiotemporal dy- namics of population exposure to flash flood and presents an important improvement in exposure assessment methods. Such improved characterization of road users’ exposure can present valuable information for flood risk management services and emergency planning

In this research work, an analysis is first undertaken on the hazard regarding people exposed to floods in urban areas. Several experiments with people were carried out in order to determine the stability limit to pedestrians, with physical characteristics previously established, crossing through a water flow. This study was complemented by including surveys on the tested people regarding their feelings during the tests. The aim was to evaluate the adequacy of the tests and more especially to figure out the stability feelings of every person under different hydraulic conditions (water depths and velocities). Vehicles are essential components related to impacts in cities when importants floods occurs, considering that direct tangible damages (impacts either on the vehicles themselves or on other urban structures), indirect tangible damages (traffic interruption) and indirect intangible damages (impacts on pedestrians) may be caused by important flash flood events. After losing the stability vehicles are swept away by the water flow as if they were huge debris. Therefore, it is essential to have suitable tools to evaluate the stability of different types of vehicles (shapes and weights) under different hydraulic conditions (water depths and velocities). Herein, tools to evaluate the stability of vehicles exposed to floods are provided, which have been developed carrying out experimental tests using a sample of vehicles with different scales. Together with the conducted experimental studies, several three-dimensional simulations were carried out. Hardly-measurable variables were obtained due to those simulations which allowed analysing the phenomenon in more depth. The critical friction coefficient was estimated for a tested subject, based on the forces obtained through the conducted simulations. A numerical validation of the proposed experimental threshold was performed for one of the tested vehicles. It opens a wide research field in the pedestrians and vehicles stability studies based on the employment of numerical tools. Lastly, a case study is presented where hazard and risk criteria based on the conducted stability experiments are applied. A new methodoly for the economic damages estimation for vehicles when those are exposed to flooding is presented and applied as well within the case study. In summary, experimental results are presented here, complemented with numerical simulations, and are applied together into a real case, thereby providing valued information according to the final target, flood risk management in urban areas.
En este trabajo de investigación se ha analizado en primer lugar la peligrosidad a la que se ven expuestas las personas durante eventos de inundación en zona urbana, estudiando los límites de estabilidad de éstas, cuando cruzan a través de una corriente de agua, a partir de ensayos experimentales con personas de ciertas características escogidas previamente. Éste estudio se ha complementado con encuestas realizadas a las personas ensayadas, de forma que se pueda evaluar la idoneidad de los ensayos y sobretodo la sensación de estabilidad que presentaba cada sujeto ensayado para las diferentes condiciones hidráulicas (calados y velocidades) a las que se veían sometidos. Los vehículos son componentes esenciales en las afectaciones producidas en una ciudad ante importantes inundaciones ya que pueden producir daños directos tangibles (viéndose afectados los propios vehículos o colisionando sobre otros elementos urbanos), daños indirectos tangibles (derivados de la interrupción del tráfico) y daños indirectos intangibles (afectaciones a personas). Éstos, al perder la estabilidad, terminan siendo grandes escombros arrastrados por el agua, con lo cual resulta imprescindible disponer de herramientas para evaluar su estabilidad ante diferentes condiciones hidráulicas (calados y velocidades) y para diferentes tipologías de vehículos (formas y pesos). En este documento se ofrecen herramientas para evaluar la estabilidad de los vehículos, habiéndose llevado a cabo ensayos experimentales con vehículos de diferentes características a escalas que permitian ser ensayados en un canal de 0.6 m de ancho. En combinación con los estudios experimentales, se llevan a cabo simulaciones numéricas tridimensionales con las que se obtienen resultados (fuerzas actuantes) difícilmente medibles en laboratotio. Es posible estimar el coeficiente de rozamiento que produjo una inestabilidad de un sujeto ensayado en laboratorio, así como validar numéricamente el umbral de estabilidad de un vehículo ensayado. Se abre un amplio campo de investigación basado en herramientas numéricas para el análisis de la estabilidad de personas y vehículos. Por último se presenta un caso de estudio en el que aplican criterios de peligrosidad y riesgo basados en los estudios experimentales de estabilidad para peatones y vehículos. Se propone y se aplica una metodología para estimar los daños ocasionados a vehículos, derivados de una cierta inundación. En definitiva, en este trabajo de investigación se presentan resultados fundamentados experimentalmente, complementados con simulaciones numéricas y aplicados conjuntamente a un caso real, que aportan información de gran valor para el objetivo final, la gestión del riesgo de inundaciones en zonas urbanas.

The present work analyzes the hydrologic conditions leading to the triggering of debris flows in an alpine region. The overall analysis has been split in two parts: the first part of the analysis has been carried out at a regional and decadal scale to improve our knowledge of rainfall thresholds for debris-flow occurrences, of the uncertainty related to rainfall estimation at debris-flow initiation sites, and of the main morphometric characteristics of debris-flow triggering locations; in the second part a focus has been devoted to the analysis of the hydrologic response of some watersheds for a selection of events with the help of detailed input information, both topographic and hydrological. The study area is upper Adige River basin (Northern Italy), which occupies a distinctive hydrometeorological niche, characterized by high frequency of orographic thunderstorms. The first part of the thesis analyzes the debris-flow triggering issue at regional and decadal-scale (2000-2010). A morphometric characterization of debris-flow triggering locations has been carried out in terms of slope-area analysis. The characterization was carried out dividing considered debris flows in classes of rainfall duration, rainfall intensity and considering also the potential relation with the different geologic settings. Another issue under investigation is related to rainfall threshold estimation (from raingauges network) for debris-flow occurrence and the uncertainty related to this estimation. First, a set of rainfall thresholds has been derived adopting a frequentist approach. The rainfall estimation procedure used for threshold identification was based on two major sources: records from the nearest gauge and an Inverse Distance interpolation of all the available records at regional and decadal scale. Thresholds have been analyzed considering all the available points and also trying to group debris-flow occurrences according to seasonal occurrence, different storm characteristics and homogeneous geologic setting. The level of uncertainty related to rainfall threshold estimation has been analyzed in detail The estimation problem is especially severe for the location of the debris flows, with raingauges that are commonly located at low elevation (e.g., in the valley floors) and debris flows that originate at high elevations, in the head part of the mountain catchments. The rainfall estimation procedure used for the uncertainty assessment, is the one based on the nearest raingauge, which is used as a proxy to estimate the rainfall that has resulted in debris flows. The objective is to investigate the impact of the uncertainty inherent in the estimation of rainfall on the definition of a threshold for possible debris-flow occurrence, and on the operational use of the threshold for prediction purposes. These effects are likely to depend on two factors: the space-time rainfall variability and the distances between the debris-flow locations and the raingauges on both the horizontal and the vertical planes. Three main problems are considered: (i) the effect of the rainfall sampling problem on the estimation of the parameters of the threshold model, (ii) the effect of applying a number of procedures to filter the rainfall information on the threshold model estimation, and (iii) the examination of the impact of the precipitation sampling problem on the performance of the threshold as a predictor of debris-flow occurrence. These aspects are examined here based on a simulation experiment. The methodology examines the intensity-duration thresholds derived from a set of raingauge locations that is assumed to represent debris flow/landslide points (DFR) and an equivalent set of raingauges assumed to have the role of closest available measurement (MR). A set of reference rainfall thresholds is used to identify the rainfall events at DFR that “triggered debris flows (i.e. exceed the threshold). For these same events, the corresponding rainfall thresholds are derived from MR observations. Comparison between the rainfall thresholds derived from DFR and MR, revealed that uncertainty in rainfall estimation has a major impact on estimated intensity-duration thresholds. Specifically, results showed that thresholds estimated from MR observations are consistently underestimated. Evaluation of the estimated thresholds for warning procedures, showed that while detection is high, the main issue is the high false alarm ratio, which limits the overall accuracy of the procedure. Overall performance on debris-flow prediction was shown to be good for low rainfall thresholds and poor for high rainfall thresholds examined. Finally different interpolation techniques have been applied to a set of gauges close to the DFR to assess the eventual improvement brought by the interpolation procedure. Results on this showed that interpolation can improve estimates specifically in the case of poor DFR-MR correlation, while in the other cases, especially considering intense and/or localized storms, the benefits of considering interpolated value in respect to only one near gauge is not so significant. In the second part of the thesis the hydrometeorological and hydrological controls of these events are examined through analyses of three storm systems occurred on October 3-4, 2006, June 20-21 2007 and September 3-4, 2009. The first storm system generated a moderate flash flood along the main streams with almost no debris flows in the tributaries, the second triggered a large number of debris flows and was characterized by a minor runoff response for the major streams, and the third resulted in both a relevant flash flood response and widespread debris flows. These events have been examined by using per-event calibrated radar rainfall data, providing an important input for the evaluation of a distributed hydrological model, and by using a database reporting location and information related to the events. Raingauge and streamflow data, debris flow spatial information and observations are used along with the distributed model to analyze the hydrological and geomorphic responses to these rainstorms. The striking contrast in flood and geomorphic responses between the three floods is related to contrasts in the antecedent moisture conditions and in the space-time structure of the triggering storm. Rainfall-runoff modeling has permitted estimating discharge and runoff volumes in a number of small ungauged catchments in which debris-flow volumes had been assessed by means of post-event surveys. The computation of sediment concentration by volume using model-estimated water runoff has resulted in realistic values. The relations between water peak discharge and debris-flow volumes show higher correlation coefficients than those involving morphometric variables and rainfall amounts.
Il presente lavoro ha analizzato le condizioni idrologiche associate all’innesco di colate detritiche in una regione alpina. L’analisi è stata suddivisa in due rami principali: la prima parte è stata effettuata a scala regionale e decennale (2000-2010) per approfondire le tematica delle soglie pluviometriche per l’innesco di colate e delle incertezze legate alla determinazione della pioggia nelle zone di innesco delle colate detritiche. Si è cercato, inoltre, di caratterizzare, dal punto di vista morfometrico, le zone di innesco delle colate stesse. Uno studio approfondito è stato dedicato successivamente all’analisi della risposta idrologica di alcuni bacini, per tre eventi di piena avvenuti fra il 2006 ed il 2009. L’area di studio è l’intera Provincia Autonoma di Bolzano (Alto Adige, Nord Italia). Tale area occupa una nicchia idrometereologica peculiare, caratterizzata da un’elevata frequenza di fenomeni temporaleschi con forzante orografica, che, specialmente nel periodo estivo, possono attivare colate detritiche e piene improvvise. La caratterizzazione morfometrica dei siti di innesco è stata effettuata esaminando l’area contribuente e la pendenza locale dei punti stessi. La caratterizzazione è stata effettuata dividendo il dataset in classi di durata di precipitazione, introducendo ulteriori filtri sull’intensità di pioggia e considerando anche la relazione con la litologia. Un’altra questione in esame è legata alla stima di soglie pluviometriche per l’innesco di colate detritiche unitamente all’incertezza legata a questa stima. In primo luogo, un insieme di soglie pluviometriche è stato derivato mediante un approccio frequentista. La procedura di stima di precipitazione per l’identificazione della soglia è basata su due fattori principali: dato del pluviometro più vicino e una interpolazione (Inverse Distance) di tutti i dati orari disponibili a scala regionale e decennale. Le soglie sono state analizzate prendendo in considerazione tutti i punti disponibili ed anche cercando di raggrup-pare i fenomeni di colata in base alla stagionalità, alle diverse caratteristiche dell’evento meteorico ed in base a zone geologicamente omogenee. Il livello di incertezza relativo alla stima di soglie di pioggia è stato analizzato in dettaglio. Il problema della stima di risulta essere particolarmente importante proprio a causa della posizione delle zone di innesco di colate detritiche, con pluviometri che sono comunemente situati a bassa quota (e.g., nei fondovalle) e colate detritiche che hanno origine ad altitudini elevate, nella parte di testata di bacini montani. La procedura di stima di precipitazioni adottata per la valutazione dell’incertezza, è quella basata sull’utilizzo del pluviometro più vicino, che viene considerato come proxy per stimare la pioggia innescante sul sito di colata. L’obiettivo è quello di studiare l’impatto dell’incertezza insita nella stima delle precipitazioni sulla definizione di una soglia per l’innesco di colate detritiche, e l’uso operativo della soglia per scopi di previsione. Due sono le condizioni che maggiormente influenzano l’icertezza di stima: la variabilità spazio-temporale delle precipitazioni e le distanze tra le zone d’innesco ed i relativi pluviometri più prossimi sia sul piano orizzontale che sul piano verticale. Tre sono gli effetti principali considerati: (i) l’effetto del campionamento delle precipitazioni sulla stima dei parametri del modello di soglia, (ii) l’effetto dell’applicazione di una serie di procedure per filtrare le informazioni di precipitazione sul modello di stima della soglia, e (iii) l’incidenza del campionamento della precipitazione sulle performance della soglia come predittore di accadimento di colate. Questi aspetti vengono esaminati mediante una simulazione condotta a scala regionale. La metodologia adottata esamina le soglie di intensità-durata mediante la selezione di una serie di pluviometri che si assumono rappresentare un sito di innesco di colata, denominati DFR, ed una serie di pluviometri prossimi a questi (in rapporto 1:1), denominati MR, che vengono usati per stimare la precipitazione sul sito DFR. Una serie di soglie pluviometriche di riferimento viene utilizzate per identificare gli eventi di precipitazione che “innescano” colate de- tritiche su DFR (cio` eventi che superano la soglia). Per questi stessi eventi, le corrispondenti soglie pluviometriche sono derivate da osservazioni MR. Il confronto tra le soglie pluviometriche derivate da DFR e MR, ha rivelato che l’incertezza nella stima di precipitazione ha un impatto importante sulle soglie di intensità-durata. In particolare, i risultati hanno mostrato che le soglie stimate dalle osservazioni MR presentano stime in difetto. La valutazione delle soglie stimate per procedure di allarme, ha mostrato che, mentre la probabilità di rilevamento è alta, il problema principale è l’elevato rapporto di falsi allarmi, che limita la precisione complessiva del procedimento. Le performance generali sulla previsione di colate detritiche si sono dimostrate buone per soglie pluviometriche moderate e scarse per soglie elevate. Infine, diverse tecniche di interpolazione sono state applicate ad una selezione di pluviometri prossimi al DFR per valutare l’eventuale miglioramento portato dagli interpolatori. I risultati hanno dimostrato che l’interpolazione può migliorare le stime, in particolare i miglioramenti più significativi si sono notati nei casi di correlazione debole tra DFR e MR, mentre per gli altri casi ed in particolare considerando eventi intensi e/o localizzati, i benefici derivanti dal considerare i valori interpolati rispetto al valore del pluviometro più prossimo non sono così significativi. Nella seconda parte della tesi viene esaminata la forzante idrometeorologica ed idrologica relativa all’innesco di colate, attraverso l’analisi dei tre eventi meteorici avvenuti il 3-4 ottobre 2006, 20-21 giugno 2007 e 3-4 Settembre 2009 per capire come la variabilità meteorologica si rifletta nelle diverse risposte dei bacini. Il primo evento ha generato infatti piene improvvise di modesta intensità lungo le aste torrentizie principali con quasi nessuna colata registrata nei corsi d’acqua secondari, il secondo ha innescato un gran numero di colate in bacini secondari ed è stato caratterizzato da una risposta idrica minore nei collettori principali, il terzo ha visto sia piene improvvise importanti che colate detritiche diffuse. Tali eventi sono stati studiati utilizzando dati di pioggia calibrati da radar sul singolo evento, fornendo un input importante per la calibrazione di un modello idrologico distribuito, ed utilizzando inoltre informazioni derivanti dall’analisi di un ampio database di fenomeni di instabilità (incluse le colate detritiche) che copre l’intero territorio provinciale e che viene mantenuto costantemente aggiornato. L’integrazione di dati radar e da rete pluviometrica, dati di portata, informazioni spaziali e volumetriche sugli eventi di colata assieme ad osservazioni sul campo sono usati, unitamente al modello idrologico distribuito, per analizzare le risposte idrologiche e geomorfologiche agli eventi innescanti. Il forte contrasto in termini di risposta idrica ed effetti morfologici fra le tre piene risulta legato a differenze nelle condizioni di umidità antecedenti e nella struttura spazio-temporale degli eventi innescanti. La modellazione afflussi-deflussi ha permesso la stima e di portate al picco e di volumi di deflusso in una serie di piccoli bacini non strumentati in cui i volumi depositati dalle colate sono stati stimati mediante indagini post-evento. Il calcolo della concentrazione volumetrica di sedimento eseguito utilizzando i risultati dell’approccio di modellazione scalato ai bacini da colata ha portato a valori realistici. Le relazioni tra portate al picco e volumi mobilizzati dalle colate mostrano coefficienti di correlazione più elevati di quelli che considerano le variabili morfometriche ed i volumi di precipitazione.

Small catchments with fast hydrological responding geomorphology are commonly prone to Flash Floods, which have to be predicted on the basis of meteorological forecast and radar nowcasting, rather than continuously monitoring river water levels. Moreover, real-time rainfall observations at high resolution in time and space are required to understand the watershed processes involved. However small catchments are generally scarcely instrumented and only a sparse rain gauge network is available. This work analyze different flood forecasting techniques and investigates their applicability on some small catchments located in the east side of southern central Sardinia, where only a small number of rain gauges is available. The first part of the work investigates the sensitivity and accuracy of hydrological processes simulation of flooding events, using rain gauge networks of different density with a statistical approach, by means of a long synthetic rainfall dataset simulated at high resolution in time and space. Analyses on a set of 12 basins of different sizes, ranging from 15 up to 1800 km2, are performed on the hydrological response of two simplified rainfall-runoff models: a lumped and a distributed model. Results highlight a strong dependence of model performance with the event severity, and show that even in very small basins and regardless of the model approach implemented, to guarantee satisfying hydrological simulations, more rain gauges than those generally available are required. A final comparison with a real case, although restricted to very few rain gauges, seems to confirm the outcomes of the synthetic approach. In the second part of the work, different Flash Flood forecasting techniques are tested on two small basins (sizing 121 and 53 km2) provided with long observations at the rain gauges and hydrometric stations. These techniques are classified in two main forecasting approaches: RTCM (Rainfall Thresholds based on Conceptual Models) e RFTDM (Runoff and Frequency Thresholds based on Distributed Modelling). RTCM are strictly deterministic and provide rainfall thresholds for the entire basin through simple operational curves, obtained by applying different event-based lumped models in inverse mode, and taking into account only initial soil moisture content and event duration. These techniques are operationally easy and could be rapidly transferred to other catchments. Meanwhile they provide fairly good forecasting performances when base flow is rather low, even if an high false alarm rate is usually exhibited. RFTDM rely on a physically based distributed model which simulates continuously all hydrological basin processes: in this work tRIBS (TIN based Real Time Integrated Basin Simulator) is applied for its efficiency and computational speed. In particular two different approaches are proposed: Direct method, in which the model is part of a forecasting chain running continuously in real-time and simulating directly maximum floods on the basis of meteorological forecasts; Statistic method, through flood frequency analyses (FFA) on observed and simulated discharges, provides probabilistic flood predictions comparing occurrence frequencies rather than discharges. Results highlight a significant reduction of false alarms with respect to the RTCM, preserving good prediction skills in different operational conditions. Meanwhile, compared with the direct method, the expected forecasting improvement using statistic method has not detected, regardless of the probability distribution chosen for FFA. It’s important to note that Statistic method, notwithstanding the laborious setting, allows to creating alert maps for flash flooding. Outcomes suggests to pay particular attention when using alert maps produced by few rain gauges due to distortions induced through rainfall field sampling.

L'objectif de la thèse est d'améliorer la compréhension des processus hydrologiques lors des événements de crues éclair. Se basant sur un modèle existant (MARINE), l'étude se concentre sur les processus internes au sol. Une étape préliminaire permet, à partir de l'analyse des données, de confirmer l'activité du socle rocheux durant les crues éclair. Une analyse structurelle de MARINE est réalisée, afin de connaître la sensibilité des flux de subsurface aux choix structurels. Une nouvelle modélisation, plus robuste et intégrant explicitement une représentation des roches altérées, est mise en place. Supposant des chemins préférentiels à l'interface sol/roche, le modèle donne une bonne reproduction des bassins sédimentaires. Sur les bassins granitiques, il sous-estime les récessions et, en conséquence, les éventuels seconds pics de crue, montrant la nécessité de représenter des flux significatifs sur ces bassins, y compris dans la zone altérée
The purpose of this thesis is to improve the knowledge of hydrological processes during flash flood events using rainfall-runoff modelling. The project focuses on hydrological processes occurring into soil and subsoil horizons. A preliminary data analysis corroborates the activity of the weathered bedrock during flash floods. The hydrological response, simulated by the MARINE model, is then investigated to detect the sensitivity of subsurface flow processes to model assumptions. It leads to several modifications of the model structure in order to make it more robust. Moreover a two-layered soil column is implemented to explicitly integrate the activity of the weathered bedrock into the model. Assuming preferential path flows at the soil-bedrock interface, the model performs well on sedimentary watersheds, but underestimate recession curves and second flood peaks on granitic ones, showing the need to simulate as well significantcontribution from the weathered bedrock

Floods and Drought are some of the most catastrophic natural disasters for humanity, averaging 1 to 5 billion dollar of annually damage for flood events and 6 to 8 billion dollars respectively for drought events. To avoid this phenomena risk management science has grown in the last years and allows us to assess the risk and the possible benefits if some specific measures are implemented (e.g. mitigation / adaptation measures). A methodology for Non-Structural Measures (NSM) implementation in risk assessment has been developed for flood event management. Likewise, an uncertainty analysis has been done in order to identify the variation of the possible results in the risk assessment. An analysis has been done based on the Expected Annual Damage (EAD) to determine the optimal return period of design of a structural measure. A new indicator has been proposed based on this analysis: The Optimal Expected Annual Damage indicator (OEAD). In the present document the results of pluvial flood risk assessment are described. These results include structural and non-structural measures based on a developed methodology for Arenys de Munt basin, which belongs to the region of Catalonia in Spain. To include non-structural measures in risk assessment, mitigation coefficients where built in the methodology, and are described in the methodology. Also, steps for the optimization of their possible implementation are defined. This research shows that potential economic losses are decreasing with the construction of structural measures from approximately 6.6 M€ to 3 M€ (box culvert of €14Million), and in combination with the implementation of non-structural measures this could even decrease to 0.7 M€ if the non-structural measures are implemented (for 500 year return period event). Related potential casualties results decrease from approx. 11 casualties to 8 and even as low as 2 casualties respectively if non-structural measures are implemented (for 500 year return period). This, demonstrate that non-structural measures are a way to follow in the flood risk mitigation. For drought events, a new methodology has been developed in order to relate quantitative potential economic losses for rainfed crops with "Meteorological Drought". In the same, a method for the hazard (through the Palmer index) and vulnerability assessment was developed. The susceptibility of a particular crop due to a drought event was linked with a classification of the phenological stages according two seasons: the sowing and harvesting season. The case study was focus on the Llobregat basin, in which both, hydrometeorological and crop statistics data series were available. Results illustrate that the Llobregat basin has suffered at least 2 important periods of drought (2000/2001 and 2005/2006) during the length of the considered 16 year crop production record statistics. These periods of drought caused potential economic losses of approximately 40.13 M€ and 55.84 M€ in the geopolitical subdivision called "Comarcas" of the Llobregat basin. The related methodology, demonstrates coherence in the detection of "important" drought events, and in the quantification of individual potential losses per crop type, which shows that crops, like olives (classified in category woody crop type) are more resistant to drought than vegetables (tomato, lettuce chard etc.). Finally, in addition to the presented methodology the potential losses of crop efficiency curves are proposed, as indicators for agricultural drought risk assessment.
Les inundacions i les sequeres són alguns dels desastres més catastròfics per a la humanitat, promitjant anualment al voltant d'1 a 5 x 10³ milions de dòlars i 6 a 8 x 10³ milions de dòlars en pèrdues econòmiques respectivament. Per combatre aquests fenòmens, la ciència de la "gestió del riscs" ha anat desenvolupant al llarg dels últims anys, permetent-nos quantificar el risc i els possibles beneficis en el cas que algunes mesures siguin implementades (tals com mesures de mitigació/adaptació etc.). En el present document es presenta una metodologia per a la quantificació del risc considerant la implementació de mesures no-estructurals (NSM). Així mateix, es va desenvolupar una anàlisi d'incertesa per identificar les fonts de variància sobre els resultats en el càlcul del risc. Amb l'indicador EAD (Expected Annual Damage), es va realitzar una anàlisi per determinar el període de tornada òptima en el disseny de mesures estructurals, com a resultat del mateix, es proposa un nou indicador: l "Optimal Expected Annual Damage" (OEAD). En el present document s'exposen els resultats per a la quantificació del risc pluvial. Aquests resultats inclouen mesures estructurals i no-estructurals d'acord amb la metodologia desenvolupada per a la conca d'Arenys de Munt a Catalunya-Espanya. Per incloure en el càlcul del risc a les mesures no-estructurals, es van desenvolupar coeficients de mitigació els quals són explicats dins de la metodologia. Igualment, es defineixen els passos a seguir per a l'optimització en la implementació d'aquestes mesures. En aquesta investigació, s'il·lustra que les pèrdues potencials econòmiques disminueixen si una mesura estructural és implementada (canalització per Box Culvert de 14 M€), des de 6.6 M€ a 3 M€ (T=500 anys), i si s'implementen mesures no-estructurals en combinació amb la mesura estructural, les pèrdues potencials poden disminuir-se fins a 0.7 M€ per al període de tornada de 500 anys. Sobre les pèrdues potencials de vides humanes, la mitigació obtinguda segueix el mateix comportament que les pèrdues potencials econòmiques, disminuint des d'11 possibles víctimes a 8 amb la mesura estructural i a 2 en combinació amb la mesura no estructural. Pel fenomen de la sequera, es va desenvolupar una metodologia per relacionar la "Sequera Meteorològica" amb les pèrdues potencials econòmiques en cultius de secà. En la mateixa, es proposa un mètode per a la quantificació de la perillositat (mitjançant els índexs de Palmer) i la vulnerabilitat. La susceptibilitat d'un cultiu de secà a un esdeveniment de sequera (vulnerabilitat) es va relacionar fent una classificació d'acord a dos estats fenològics: l'època de sembra i de recol·lecció. El cas d'estudi es va enfocar a la conca del riu Llobregat-Espanya, de la qual es va disposar d'informació hidrometeorològica i de les estadístiques de producció de diferents tipus de cultius de secà. De l'anàlisi realitzada sobre la conca, es va observar que al llarg dels 16 anys d'estadístiques en els cultius, van ocórrer dos períodes importants de sequera (2000/2001 i 2005/2006). Aquests períodes de sequera van deixar respectivament pèrdues potencials econòmiques d'aproximadament 40.13 M€ i 55.84 M€ per a les comarques associades a la conca del riu Llobregat. La metodologia desenvolupada, demostra eficàcia en la detecció d'esdeveniments importants de sequera, així mateix, il·lustra una coherència en la quantificació de les pèrdues individuals en els tipus de cultiu, en les que cultius com l'oliva (classificat com a cultiu llenyós), demostra més resistència a la sequera respecte a altres cultius com l'enciam, tomàquets etc.. Finalment, com a complement a la metodologia desenvolupada, es proposa a les corbes de pèrdua d'eficiència de cultiu, com a indicadors per a la gestió del risc de sequeres en cultius de secà.

Ce travail de recherche vise à caractériser les propriétés hydrodynamiques des sols des Cévennes, une zone de moyenne montagne du sud de la France connue pour être sujette à des crues à cinétique rapide, appelées « crues éclair ». Il s'agit donc de déterminer les paramètres relatifs à la conductivité hydraulique et à la rétention en eau du modèle de Mualem-van Genuchten, leur variabilité spatiale à l'échelle du versant ou du petit bassin, et les facteurs qui expliquent cette variabilité spatiale. Il s'agit également d'évaluer la perméabilité du sous-sol constitué d'une roche plus ou moins altérée, et d'en déduire des informations sur les processus de saturation des sols pouvant être à l'origine de ruissellement.Les propriétés hydrodynamiques des sols et du sous-sol ont été estimées par modélisation inverse de la teneur en eau sols, à partir d'une station pilote sur le site de Sumène et d'un réseau de 50 stations de mesure répartis sur 4 versants granitiques (site de Valescure) et 2 versants schisteux (site de Tourgueille). La station pilote comprend 3 sondes de mesure installées à 20, 40, 60 cm de profondeur, et les stations installées sur les versants comprennent chacune 2 sondes de mesure installées à des profondeurs variables allant de 15 à 45 cm. Les teneurs en eau du sol ainsi que les précipitations ont été mesurées en continu au pas de temps 15 min sur les différents sites. La procédure de modélisation inverse est basée sur l'algorithme génétique multi-objectif NSGA-II. Cette procédure a été appliquée pour chaque station, en considérant que le sol d'épaisseur variable constitué de la superposition de 2 horizons, surmontant un troisième horizon figurant la roche altérée sous-jacente. Au total, quinze paramètres doivent être calibrés pour chaque station, et sont estimés à partir de périodes sélectionnées correspondant aux épisodes de pluie les plus importants. Les processus d'évapotranspiration ont été considérés comme négligeables au cours de ces épisodes. L'analyse des propriétés de rétention et de conductivité obtenues a mis en évidence la très forte conductivité hydraulique des sols étudiés, de l'ordre de 1000 à 2000 mm/h, et leur faible rétention en eau. Les teneurs en eau à saturation estimées s'échelonnent de 0.30 à 0.60 cm3.cm-3, traduisant une grande hétérogénéité locale. On retrouve cette forte variabilité pour l'estimation des profondeurs de sol qui varient de 31 à 120 cm. Pour l'horizon représentant le sous-sol, les perméabilités sont très contrastées, avec des valeurs de conductivités hydrauliques variant de quelques unités à plus d'une centaine de mm/h. Les stations présentant les sols les moins profondes et des sous-sols moins perméables génèrent des zones saturées qui se développent à la base du profil de sol, comme ça a été observé et simulé lors des épisodes pluvieux les plus intenses. Si les propriétés des sols apparaissent très variables d'une station à une autre et d'un versant à un autre, les résultats n'ont pas montré d'organisation particulière de cette variabilité spatiale. La position de la station sur le versant n'apparaît pas être déterminante pour les porosités, les profondeurs, les perméabilités et les rétentions en eau des sols ; les distributions de ces propriétés, calculées à l'échelle des différents versants, ne semblent pas reliées aux grands traits du paysage : géologie, orientation, végétation
This research work aims to characterize soil hydrodynamic properties of the Cévennes area, a low mountain region known to be prone to flash floods. We thus chose to estimate hydraulic conductivity and water retention properties of the Mualem –van Genuchten model and their spatial variability at the hillslope scale and between multiple hillslope profiles. The objectives are also to evaluate the weathered bedrock permeability, and consequently to enhance our understanding of the soil saturation processes.The soil and bedrock hydrodynamic properties were estimated by inverse modelling of soil moisture from a pilot station and a network of 50 stations distributed on 4 granitic hillslope and 2 schist hillslope. The pilot station was instrumented with 3 soil moisture sensors located at 20, 40 and 60 cm deep whereas the hillslope stations were instrumented with 2 soil moisture sensors located variably from 15 to 45 cm deep. Both soil moisture and precipitation were recorded with a 15 min time step for every station. The inverse modelling procedure is based on the multi-objective genetic algorithm NSGA-II. This procedure was used for every station considering a variably deep soil composed by 2 layers surmounting a 100 cm deep third layer representing the weathered bedrock. Fifteen parameters were calibrated for every station, and were estimated from small selected rainfall periods of 1 to 15 days corresponding to the major rainfall events during the monitoring period. Evapotranspiration has been considered as negligible during those events. The analysis of those retention and conductivity properties shows a very important hydraulic conductivity for the studied soils, ranging from 1000 to 2000 mm/h, and their low retention capacity. The soil saturated water content varies from 0.30 to 0.60 cm3.cm-3, which is a consequence of the important soil heterogeneity at the hillslope scale. We also find that heterogeneity on the estimation of soil depth which varies from 31 to 120 cm. For the weathered bedrock layer, we also found contrasted permeability varying from a few units to a hundred of mm/h. Stations with the shallowest soils and the less permeable bedrock presenting a saturation process at the soil/bedrock contact, as monitored and simulated during the most intense rainfalls. If the estimated soil hydrodynamic properties exhibit important variations at the hillslope scale from a station to another, results showed no specific spatial organization of this variability. The station's position on the hillslope is not decisive to estimate saturated soil moisture, soil depth, soil permeability or water retention capacity. The distribution of those properties, calculated for the 6 studied hillslope is not either correlated to the landscape general characteristic: geology, orientation, land cover

O aumento da ocorrência de desastres hidrológicos relacionados a inundações bruscas tem recebido maior atenção dos diversos órgãos em suas diferentes escalas, com o objetivo de reduzir ao máximo suas causas. Justamente por isso, as medidas não estruturais são medidas de extrema importância na prevenção de tais desastres. Uma dessas medidas deve ser o mapeamento de áreas de perigo de inundações. Portanto, o objetivo do presente trabalho foi propor e avaliar o perigo de inundações bruscas por meio de modelagem hidrogeomorfológica na bacia do arroio Forromeco-RS. Para isso, foi utilizado o modelo CAESAR-LISFLOOD, para representar os processos hidrológicos em escala de bacia e canal. Em escala de bacia foram gerados hidrogramas a partir da criação de chuvas de projeto para diferentes tempos de retorno (TR), considerando como base o maior evento registrado nessa bacia associado a um TR de 22 anos. Esses hidrogramas foram utilizados nas simulações em escala de canal para gerar os diferentes mapas de inundação em termos de profundidade e velocidade do fluxo da água. Para analisar as áreas de perigo de inundação, foram determinados os índices de perigo (IP) associados aos diferentes TR, a partir da profundidade e a velocidade d’água. Através das análises do resultado de IP foi criado o mapeamento final de perigo associado a três tempos de retorno (5, 22, e 100 anos). Além disso, estabeleceu-se três zonas para identificar os níveis de perigo, considerando o cenário mais crítico dos três mapas. Os resultados mostraram que a maior área inundada se encontra em alto perigo, ocupando 77% da área total, o que significa que as pessoas que moram nessa região estão em perigo tanto em casa, como fora delas. Ao mesmo tempo as construções estão em alta possiblidade de serem danificadas.
The increase in the occurrence of hydrological disasters related to flash floods has begun to be more important for several organs at different scales in order to reduce their magnitude and frequency as much as possible. Precisely because of it, non-structural measures are extremely important measures for preventing such disasters. One of these important measures might be the mapping of flood hazard areas. Therefore, the objective of the present work was to propose and evaluate the flash flood hazard by means of hydrogeomorphic modeling of the Forromeco river basin, Rio Grande do Sul state. Thus, the CAESAR-LISFLOOD model was used to represent the hydrological processes at basin and channel scale. At basin scale hydrographs were generated from the creation of hyetographs for different return periods (RP), considering the largest event recorded in this basin. These hydrographs were used in the channel scale simulations to generate the different flood maps in terms of depth and velocity of water flow. In order to analyze the flood hazard areas, the hazard indexes (HI) associated with the different RPs were determined from the depth and water velocity. Through the IP analysis, the final hazard mapping associated with three RPs (5, 22, and 100 years) was created. In addition, three zones were established to identify the hazard levels, considering the most critical scenario of the three maps. The results showed that the largest flood area is in high degree hazard, occupying 77% of the total area. It indicates that people are in danger both inside and outside houses. At the same time buildings are in high possibility of being damaged.

Alors qu’on attend beaucoup de lui, l’habitant, convoqué sous le terme de « citoyen » dans les dispositifs technocratiques, est pourtant une « entité » abstraite dont les dimensions psychosociologiques sont trop souvent sous-estimées. Néanmoins, l’adoption de comportements appropriés en cas d’événement est bel et bien lié à l’adéquation entre les ressources individuelles mobilisables et les mesures institutionnelles que l’individu est à même de s’approprier. Dès lors, cette thèse a pour but de mesurer plus finement les capacitations des habitants, en mobilisant notamment l’innovation sociale territorialisée face à un risque spécifique : les crues rapides pouvant se manifester dans le sud-est de la France. À cet effet, un protocole d’enquête s’appuyant sur l’interdisciplinarité (géographie des risques, psychologie environnementale et design social) et associant des données empiriques et expérimentales, a été mis en œuvre. Les entretiens réalisés (36 gestionnaires, 4 syndicats de rivières et 29 sinistrés) et les questionnaires (689) ont permis de mieux comprendre leur vision respective de la gestion des risques. Les gestionnaires sont lucides mais démunis face aux multiples failles des politiques publiques, tandis que des décalages importants existent entre les intentions comportementales et la connaissance des risques des habitants interrogés. Ces résultats ont ensuite permis de déployer un atelier créatif sur la commune de Sauve (Gard, France) qui a confirmé tout le potentiel d’appropriation par les habitants que peut avoir une démarche co-construite avec eux en amont. L’ensemble des éléments issus de ce travail amène à questionner la réalité de l’implication habitante et à identifier des leviers d’action pour faire évoluer l’approche stato-centrée encore privilégiée aujourd’hui, malgré le désengagement progressif de l’Etat-providence qui rajoute un degré supplémentaire de complexité
Although much is expected of them, inhabitants, referred to as “citizens” in technocratic programs, are still abstract “entities” with oft underestimated psychosocial underpinnings. Nonetheless, adopting the appropriate behaviours in the case of an event is related to a balance between actionable individual resources and the institutional measures individuals are able to take. As such, this thesis aims to measure inhabitants’ capacities with more finesse, namely by mobilising territorialised social innovation with regard to a specific risk: flash floods in south-east France. To this effect, an interdisciplinary survey was conducted (geography of risks, environmental psychology and social design) by associating empirical and experimental data. A series of interviews (36 managers, 4 river unions, 29 victims) and questionnaires (689) provided better understanding of their respective visions of risk management. Managers were lucid but powerless in the face of multiple flaws in public policy, whereas inhabitants displayed a large gap between their behavioural intentions and their risk-related knowledge. These results led us to conduct a creative workshop in Sauve (Gard, France) that confirmed the potential collective action from the start can have in terms of appropriation by inhabitants. The conclusions drawn from this work led us to question the reality of inhabitants’ involvement and to identify ways to encourage evolution of the state-centred approaches that are still preferred today, despite the progressive decline of the welfare state, which adds another degree of complexity

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.
Includes bibliographical references (leaf 25).
This thesis describes an automated monitoring station designed to detect flash floods occurring in the Rio Aguan river basin, Honduras. An Atmel microcontroller polls a series of sensors in the river, logging all data for later hydrological analysis and modeling. A high-power APRS radio is used to alert a central monitoring facility of impending floods. Careful component choices and power management allows the system to run for 100 days on a single deep-cycle marine battery or practically indefinitely using a supplemental solar panel.
by Joshua A. Weaver.
M.Eng.

Les crues éclair (i. E. Crues soudaines provoquées par des événements pluvieux orageux) constituent sans aucun doute le risque naturel le plus destructeur en France. Malgré la menace qu'elles représentent et les nombreuses questions qu'elles suscitent, elles n'ont pas fait l'objet par le passé d'études systématiques. Dans la première partie de ce document, une méthodologie d'analyse hydrologique post-événementielle a été mise au point et testée sur cinq études de cas. Les premiers résultats obtenus sont encourageants et relativement inattendus : a) les bassins versants réagissent avec retard aux épisodes de pluies intenses, b) les volumes d'eau de pluie retenus sur les bassins et ne participant pas à la crue sont importants (de 150 à 200 millimètres dans les études de cas traitées), c) le type d'occupation des sols ne semble pas jouer un rôle déterminant sur la réponse des bassins versants. La seconde partie de la thèse est consacrée à l'analyse théorique des lois de probabilité des débits de pointes de crues. Les possibilités offertes par l'approche qualifiée de semi-déterministe, consistant à coupler un modèle mathématique de genèse aléatoire de séries pluviographiques et un modèle ``pluie-débit'' sont explorées. Il apparaît que, compte tenu des propriétés de la relation pluie-débit, les distributions des débits pointes de crues (DDPC) n'appartiennent probablement à aucun des trois types de lois des valeurs extrêmes. Elles sont asymptotiquement contrôlées par la distribution des intensités moyennes maximales des événements pluvieux, mesurées sur une durée caractéristique du bassin versant
Flash floods (i. E. Floods produced by severe thunderstorms of limited areal extent) are certainly the most destructive natural hazard in France. They also give rise to numerous questions but no systematic studies have been conducted in the past on such events. In the first part of this document, a post flood investigation methodology is proposed and tested on five case studies. The first results obtained are hopeful and reveal some original aspects of the rainfall-runoff relationship during flash floods : 1) the watershed response to the intense storm bursts is late and relatively sudden, 2) a large amount of rainwater (150 to 200 millimeters in the present case studies) is retained on the catchments and does not contribute to the flood flow, 3) no significant effects of the land use type could be identified. The second part of the document, is devoted to the theoretical analysis of the flood peak distributions. The potential of the so called derived distribution methods consisting in coupling a stochastic rainfall simulator and a mathematical ``rainfall-runoff'' model is assessed. It appears that, due to the properties of the ``rainfall-runoff'' process, flood peak distributions (FPD) belong most probably to none of the three extreme value distibution types. The asymptotic behaviour of the FPD is controlled by the maximum rainfall intensities measured over a duration characteristic of the studied watershed

La bordure septentrionale du Vénézuela (bordure méridionale de la Plaque Caraïbe) correspond pour l’essentiel à un relais de grandes failles décrochantes actives, génératrice d’une marge escarpée et accidentée (Sud de la Mer Caraïbe, Fosse et Golfe de Cariaco, Fig. 1). Cette région est donc exposée à trois sources d’aléas naturels : 1) séismes et effets directs, 2) tsunamis (liés à ces failles, à l’activité plus lointaine des Arcs Antillais, ou à des glissements sous-marins), 3) glissements et coulées aériens, parfois liés à des événements climatiques brutaux (cf. flash flood de Vargas, Décembre 1999). Le deuxième et le troisième type de phénomènes affectent directement la sédimentation soit marine (littoral et plateforme) soit lagunaire ou lacustre. Par ailleurs, les dernières variations globales (rapides) du niveau marin ont subdivisé et structuré l’empilement sédimentaire.La partie récente de ces dépôts (env. 150 000 à 200 000 ans) a fait l’objet de deux campagnes préliminaires d’imagerie sismique à haute résolution, la première consacrée à la partie orientale (Golfe de Cariaco; Audemard et al., 2007 ; Van Daele et al., 2010) et la seconde au littoral central (entre Cabo Codera et la Golfe Triste, Fig. 2). Cette seconde mission sera complétée par une nouvelle acquisition d’imagerie et la prise de carottes courtes en mer et dans les lagunes côtières. L'interprétation des sections sismiques et l'analyse sédimentologique des carottes sera utilisé pour ce travail de thèse avec un double but : 1) reconstituer l’évolution générale de la sédimentation sur la marge, et l’influence des changements environnementaux globaux, 2) connaître la distribution géographique et dans le temps (pour une période d’au moins 100 000 ans) des phénomènes catastrophiques majeurs (séismes, tsunamis, flash floods) qui se sont intercalés dans cette sédimentation. L’impact possible de la superposition de phénomènes externes et sismo-tectoniques (cf. récent séismes de Tucacas pendant un épisode pluvieux) et la localisation des zones à risques pour les tsunamis, seront modélisés et discutés
The northern border of Venezuela (southern border of the Caribbean Plate) corresponds essentially to a relay of large active strike-slip faults, generating a steep and rugged margin (South of the Caribbean Sea, Pit and Gulf of Cariaco, Fig. 1). This region is therefore exposed to three sources of natural hazards: 1) earthquakes and direct effects, 2) tsunamis (related to these faults, to the more distant activity of the West Indies bows, or to submarine landslides), 3) slips and airflows, sometimes linked to sudden climatic events (see Vargas flash flood, December 1999). The second and third types of phenomena directly affect sedimentation, whether marine (littoral and platform), lagoon or lacustrine. In addition, the latest global (fast) changes in the sea level have subdivided and structured the sedimentary stack.The recent part of these deposits (about 150 000 to 200 000 years ago) was the subject of two preliminary high resolution seismic imaging campaigns, the first devoted to the eastern part (Gulf of Cariaco, Audemard et al. 2007, Van Daele et al., 2010) and the second at the central coast (between Cabo Codera and the Sad Gulf, Fig. 2). This second mission will be complemented by a new imaging acquisition and the taking of short cores at sea and in coastal lagoons. The interpretation of the seismic sections and the sedimentological analysis of the cores will be used for this work of thesis with a double aim: 1) to reconstruct the general evolution of the sedimentation on the margin, and the influence of the global environmental changes, 2) to know the geographical distribution and over time (for a period of at least 100,000 years) major catastrophic phenomena (earthquakes, tsunamis, flash floods) that have interbedded in this sedimentation. The possible impact of the superposition of external and seismo-tectonic phenomena (see the recent Tucacas earthquakes during a rainy episode) and the location of tsunami risk areas will be modeled and discussed

This paper analyzes the anatomical response of Pinus pinaster Ait. following wounding by flash floods. A total of 14 wood samples were taken from 14 different scarred trees located on the river banks of the Arroyo Cabrera torrent (Spanish Central System). In addition, 20 increment cores were collected from undisturbed and healthy P. pinaster trees to build a local reference chronology. For the injured trees, analysis focused on growth changes in early earlywood (EE) tracheids, namely on differences in (i) lumen size; (ii) cell-wall percentage and cell-wall thickness; (iii) radial length and tangential width of tracheids; as well as (iv) in the abundance of resin ducts in earlywood (EW) and latewood (LW) following wounding. Results indicate that tissues bordering flash-flood wounds are characterized by reduced growth rates and a decrease of EE tracheid lumen area by 51%. In addition, cell-wall percentage increases by 34% in the increment rings formed after the event and significant changes are observed in the radial length and tangential width of EE tracheids. Observations on resin ducts do not yield any significant results. Based on these anatomical parameters, detecting and dating past flash-flood events in growth rings is now possible for Mediterranean species, specifically P. pinaster.

Flash floods are one of the most devastating natural hazards, claiming numerous lives and tremendous economic losses. One of the main reasons for their catastrophic potential is the limited time available for precautionary measures, such as warnings or evacuations. Early warning systems (EWSs) play a key role for emergency managers to react in a timely manner to upcoming floods and effectively mitigate the impacts. This thesis explores possibilities to enhance the methods available for flash flood early warning and thus improve the operational decision support. While a variety of existing methods aims at the prediction of the hazard component of flash floods (e.g. the peak streamflow), an increasing number of EWS developers and end-users have recognised the potential of tools that automatically translate the flash flood hazard forecasts into the expected socio-economic impacts (e.g. the population affected). These so-called impact forecasts enable more objective and rapid decisions, ultimately leading to a more effective flood response. While for fluvial floods, impact forecasts have been available for several years and over various spatial scales, the existing approaches for flash floods have been limited to a small number of prototypes focusing on individual catchments or relatively small regions. These small-scale approaches can be useful for the coordination of local emergency measures, but their potential is limited for supporting the decisions of authorities operating over larger domains (e.g. regional, national, or international civil protection mechanisms). The main goal of this thesis has been to extend the available decision support by applying the concept of flash flood impact forecasting over large spatial scales. Two methods have been developed for estimating the impacts in real time, named ReAFFIRM and ReAFFINE. The two methods take into account that emergency services operating at different spatial scales require different kinds of real-time information to make informed decisions: ReAFFIRM provides detailed impact estimates in high resolution to support regional or national authorities in the coordination of location-specific emergency measures (e.g. evacuations), whereas ReAFFINE generates order-of-magnitude impact estimates with pan-European coverage that can be useful for end-users operating across regions or countries. The application of ReAFFIRM and ReAFFINE for a number of past flood events has demonstrated their capabilities to identify flash flood impacts in real time over the different spatial scales. The developed algorithms have a moderate computational cost and require only datasets that are available throughout the EU, which facilitates the real-time implementation of the methods and their integration into the operational procedures of end-users across Europe. An additional objective of this thesis has been to explore a more integrated perspective of flood early warning. Traditionally, EWSs are designed separately for the different physical processes that lead to flooding (i.e. individual systems for fluvial, pluvial, coastal, and flash floods). This means that the end-users need to monitor a number of separate flood forecasts with potentially even contradicting outputs. Especially during events in which different flood types coincide (so-called compound floods), this can be time-consuming and confusing. The decision support could be significantly simplified by automatically integrating the forecasts of different flood types into an overall compound flood forecast. This idea has been explored through the analysis of a recent catastrophic compound flood, for which the impact estimates from ReAFFIRM have been combined with those from a system designed for fluvial floods. The combined performance of the methods has shown to be superior to the individual performances, clearly demonstrating the potential of such integrated approaches for improving the decision support.
Las avenidas torrenciales son una de las amenazas naturales más devastadoras, causando numerosas víctimas y enormes pérdidas económicas. Los sistemas de alerta temprana (SAT) juegan un papel clave para que los servicios de emergencia puedan reaccionar de manera oportuna y mitigar con eficacia los impactos. Esta tesis explora diferentes posibilidades de ampliar los métodos disponibles para la alerta temprana de avenidas torrenciales, con el objetivo de mejorar la toma de decisiones de los servicios de emergencia. Una variedad de métodos se dedica a la predicción del componente de amenaza de las avenidas repentinas (e.g. los caudales máximos instantáneos). No obstante, un número creciente de desarrolladores de SAT y usuarios finales han reconocido el potencial de herramientas que traducen automáticamente estos pronósticos de amenaza en impactos socioeconómicos (e.g. la cantidad de población afectada). Estas predicciones de impacto permiten tomar decisiones más objetivas y rápidas, que conducen a una respuesta más eficaz ante las avenidas y sus consecuencias. Los estudios realizados para la predicción del impacto de avenidas torrenciales han sido limitados a unos pocos prototipos que se enfocan en cuencas individuales o regiones relativamente pequeñas que pueden resultar útiles para la coordinación de medidas de emergencia locales, pero su potencial es limitado para apoyar las decisiones de las autoridades que actúan en dominios más amplios (e.g. autoridades de protección civil regionales, nacionales o europeas). El objetivo principal de esta tesis ha sido extender el apoyo a la toma de decisiones disponible mediante la aplicación del concepto de previsión del impacto de avenidas torrenciales en grandes escalas espaciales. Para ello, se desarrollaron dos métodos para estimar los impactos en tiempo real: ReAFFIRM y ReAFFINE. ReAFFIRM proporciona estimaciones de impacto detalladas y en alta resolución para dar apoyo a las autoridades regionales o nacionales en la coordinación de medidas de emergencia específicas (e.g. evacuaciones), mientras que ReAFFINE genera estimaciones de impacto en órdenes de magnitud con cobertura paneuropea que resultan útiles para los usuarios finales que actúan en grandes dominios espaciales. El uso de ReAFFIRM y ReAFFINE para una serie de inundaciones pasadas ha demostrado su capacidad para identificar los impactos de las avenidas torrenciales en tiempo real y en diferentes escalas espaciales. Los algoritmos desarrollados tienen un coste computacional moderado y solo requieren datos que están disponibles en toda la UE, permitiendo su implementación e integración en los procedimientos operativos de varios usuarios finales en toda Europa. Un objetivo adicional de esta tesis ha sido explorar una perspectiva más integrada de la alerta temprana de inundaciones. Tradicionalmente, los SAT son diseñados por separado para los diferentes procesos físicos que pueden resultar en inundaciones. Esto significa que los usuarios finales deben monitorear una serie de pronósticos de inundaciones por separado con resultados que podrían resultar potencialmente contradictorios, especialmente durante eventos en los que coincidan diferentes tipos de inundaciones (también llamadas inundaciones compuestas). Lo anterior puede alargar los tiempos de respuesta, generar confusión y, en última instancia, impedir una respuesta de emergencia eficaz. El apoyo a la toma de decisiones podría ser simplificada significativamente y de manera automática mediante la integración de los SAT de diferentes tipos de inundaciones en un único pronóstico que las englobe. Esta idea se explora a través de la combinación de las estimaciones de impacto de ReAFFIRM con las de un sistema diseñado para inundaciones fluviales. El rendimiento de ambos métodos combinados ha demostrado ser superior al de cada uno de manera individual, indicando el potencial de combinar el pronóstico de impacto por inundaciones
Enginyeria civil