Dissertations / Theses on the topic 'Urban rain water tanks'

Denna fältstudie kommer att undersöka betydelsen av regnvattenanvändning som vattenförsörjnings alternativ. Hur kan hållbara innovativa lösningar tas fram för att lösa vattenförsörjningen på Sri Lanka? Efter lidandet av mer än 30 års inbördeskrig och efter de omfattande skadorna från tsunamin 2004, står nu Sri Lanka inför många utmaningar rörande landets återuppbyggnad. Tillgången till vatten är den viktigaste grundläggande förutsättningen för ett fungerande samhälle. I landets torra zon är det långa perioder av torka då vattenkällor sinar och inget naturligt vatten finns att tillgå. Detta trots att det under monsunen kommer tillräckligt med regn för att täcka vattenbehovet om det skulle samlas på ett optimalt sätt. Avrinningskoefficienten är här mer än 60% outnyttjat regnvatten. I ett flertal lyckade projekt har man samlat regnvatten i RWH system för senare användning. Människor i dessa områden saknar kranvatten eftersom detta område ej är täckt av vattenförsörjningsnätet. Detta gör att dessa människor har en positiv inställning till att ha RWH system..I den våta zonen, och då speciellt i Colombos stadsmiljö som denna studie handlar om, är situationen annorlunda. Här har de flesta invånare kranvatten. Det kommunala kranvattnet är högt subventionerat av regeringen vilket gör att kostnaden är låg för användarna samt ökar vattenkonsumtionen. Invånarna känner inget ansvar för vattenresurserna eftersom den gemena uppfattningen är att det är en evig källa. Majoriteten av hushållen ser inget skäl till att installera RWH på grund av den låga lönsamheten. Trots att det finns ett förordnande att det ska ingå ett RWH system, så följs inte detta. Saknande av uppföljningsplikt anges som orsak av vatten styrelsen. Kostnaden för att behandla och leverera vatten till invånarna är väldigt hög och är mycket energi krävande. Det finns ett behov av enorma investeringar för att rusta upp och bygga ut både vattenverken och vattennätet för att klara av att möta det växande invånarantalet i Colombo området. Ett annat problem är att 40% av hushållen i Colombo saknar avloppsanslutning. De leder sitt avloppsvatten direkt eller efter en septi-tank ut i jorden eller havet.Om medvetenheten kring dessa frågor ökar, samt att förhållandet mellan kranvattnets kostnad och RWH justeras med ändringar i subventionerna, kunde en hållbar lösning på vattensituationen med såväl ekonomiska som miljövinster ske.Resultatet av denna studie är att RWH får ses som ett komplement när det gäller vattenförsörjningen för hushållens del. Fokus bör istället ligga på industrier, sjukhus, skolor, kommunala byggnader och andra byggnader med stora vattenbehov och med de största möjligheterna att uppnå optimalt resultat.Studien visar också på en hållbar lösning på avloppshanteringen. Den visar DWWT och dess fördelar.
The field study will investigate the importance of Rain Water Harvesting (RWH) as a water supply option. How can sustainable innovative solutions be developed to solve the water problem of Sri Lanka? Suffering from more than 30 years of civil war and damages after being struck by the tsunami 2004, Sri Lanka faces many challenges to recover and rebuilt the country. The access to water is the most important need for a civilization´s existence. In the dry zones of the island people suffer from long drought periods with dried up wells and no natural sources for water. However the rainfall during the monsoon, even in these areas, is more than enough to provide the water needs if properly collected, thus the run-off coefficient is more than 60%. Several projects with rain water harvesting in so called RWH systems have been implemented with success. Because these areas are not covered by the water supply net and therefore have no tap water, the people are very positive to having the RWH system. In the wet zones and especially in the urban environment of Colombo the situation is different. Here most of the people have treated pipe-borne tap water. The metered tap water is highly subsidized by the government which makes the cost low for the users and increases the water consumption. The citizens do not feel a responsibility to be careful with resources since the common opinion is that water is a never ending source. The majority of the households find no reasons for installing a RWH system because it´s low economic profits. Even if there is a legislation that demands all new buildings should have a RWH system not many households have installed these systems. However the cost to deliver and treat this water is very expensive for the government and demands a lot of energy. Huge investments need to be done in both the treatment plants and the pipe-line net to meet the growing population in Colombo area. Another problem is that 40% of the households today in Colombo have no sewage connection but lead their wastewater directly or after a septic tank into the ground or the sea. If the awareness regarding these concerns could be improved and the conditions between tap water costs and RWH be adjusted with changes in the subsidized system, a sustainable solution to the water situation in Colombo with both economic and environmental benefits could be found. The result from the case study is a recommendation about installing RWH as a complimentary source of water for the households. And investments in RWH systems should be focused to industries, hospitals, schools, municipal buildings and other public buildings with a high water demand and with the best possibilities for optimal results. Further the case study treats a sustainable solution to the sewage situation. It shows the Decentralized waste water treatment plant (DWWT) and its advantages.

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The capitalist city summarizes, in the heterogeneity of its localities, the processes of social inequalities and issues like access to built environments, the economical situation of its population, as well as the effects of the ongoing public policies. The city of Sao Paulo, a metropolis of global characteristics, has developed serious social debts throughout its history. During the raining season, Sao Paulo city becomes the scenery of constant social and economical impacts towards the losses caused by flooding. This fact is associated, among other reasons, to a meaningful soil occupation and its consequent impermeabilization, plus the flooding areas occupation river margins and valleys. At the late 90 s, the city started having a type of anti-flood measure, called piscinões , great rain water reservoirs whose aim is to hold the water back in situations of higher rain rates. This fact is strongly settled by the construction of Pacaembu s underground reservoir. However, the spreading of this kind of anti-flood measure, especially in Stream Cabuçu de Baixo micro basin, located in the northwest area of the city, left margin of River Tietê, hasn t had the same success, for some of the existing gaps between the two areas measures result in social dissatisfaction and they threat being a public health issue. This work, therefore, studied two anti-flood measures in two different places: the first in a noble area, and the other in the outskirts of the city. The result showed that the dynamics of managing and maintenance of Pacaembu s reservoir is different from the one existent in the reservoirs of Stream Cabuçu de Baixo, indicating a different action of the authorities concerning the handling of urban rain water and the society interests on the whole
A cidade capitalista resume, na heterogeneidade de seus espaços, os processos de desigualdade social, de acesso ao ambiente construído, das condições econômicas de sua população, bem como os efeitos das políticas urbanas em curso. A cidade de São Paulo, metrópole de características globalizadas, carrega as marcas de graves débitos sociais que se desenvolveram ao longo de sua história. Nos períodos de precipitações, a cidade de São Paulo torna-se cenário de constantes impactos sociais e econômicos frente aos prejuízos causados pelas inundações. Esse fato está associado, entre outros motivos, a uma expressiva ocupação e impermeabilização do solo e à ocupação das áreas de risco de enchentes as várzeas e fundos de vales. A partir do final da década de noventa a cidade passou a utilizar como medida de combate às inundações os chamados piscinões , grandes reservatórios cuja finalidade é conter os picos de escoamento nos eventos de chuvas. Este fato está fortemente marcado pela construção do reservatório subterrâneo do Pacaembu. Entretanto, a pulverização da utilização deste dispositivo, em específico na Micro Bacia do Córrego Cabuçu de Baixo, localizada na zona noroeste da cidade, margem direita do Rio Tietê, não têm sido acompanhada pelo mesmo sucesso, algumas lacunas existentes resultam no descontentamento por parte da sociedade e no risco de tornar-se um problema de saúde pública. Esta pesquisa, portanto, utilizou o estudo de duas intervenções em locais distintos: a primeira em uma área nobre e outra na periferia da cidade. O resultado apontou que a dinâmica de gestão e manutenção do reservatório do Pacaembu, é bastante distinta daquela encontrada nos reservatórios da Bacia do Cabuçu de Baixo, indicando uma ação diferenciada do Poder Público frente a questão do manejo de água pluviais e aos interesses da sociedade como um todo

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There are many centuries that the rain, in the city, is not understood as life ; it incorporates road and health infrastructure, confined to gutters, manholes, underground galleries, returning to people perception like floods. Nowadays, the understanding about eco-systemic relationships brings new models for managing urban storm water, in the way of bioclimatic architecture, designing with nature, with contemporary principles of environmental comfort in the cities, i. e., sustainable urban development. The speech is ready; how to transfer theory into practice is one of the objectives of this work. Some places in the world have adopted this paradigm and developed methodology for public and private actions, according to a model called the green infrastructure system. Professionals in individual works also believe in that path, contributing with creative design, showing the model potential. By this principle, every place has its unique design, according to its physical territory and the cultural characteristics of its society. Considering that joint urban operations are the most advanced in urban policy for development, in Brazil, do they incorporate the urban sustainability principles brought by the green infrastructure model? That is what will be analyzed, in reference to the Água Espraiada Joint Urban Operation, in São Paulo.
A chuva, nas cidades, deixou por muitos séculos de ser entendida como vida e passou a incorporar a infraestrutura viária e sanitária, confinada a sarjetas, bueiros, galerias subterrâneas, retornando à percepção da população sob a forma de enchentes. Com a compreensão que se tem hoje sobre as relações ecológico-sistêmicas, novos modelos de gestão das águas pluviais urbanas surgem, consonantes com a arquitetura bioclimática, com a linha de pensamento de desenho com a natureza, com os preceitos contemporâneos do conforto ambiental nas cidades, ou seja, do desenvolvimento urbano sustentável. O discurso está pronto; como transferir a teoria para a prática é um dos objetivos deste trabalho. Alguns lugares no mundo já adotam tais paradigmas e vêm desenvolvendo metodologia para ações públicas e privadas, segundo um modelo denominado sistema de infraestrutura verde. Profissionais em obras individuais também apostam nesse caminho, contribuindo com projetos criativos, mostrando o potencial do modelo. Por esse princípio, cada lugar tem seu projeto único, seja pelas condições físicas de seu território, seja pelas características culturais de sua sociedade. Considerando-se que as operações urbanas consorciadas são o instrumento mais avançado como política urbana em prol do desenvolvimento, no Brasil, até que ponto elas incorporam os preceitos de sustentabilidade urbana trazidos pelo modelo de infraestrutura verde? É o que se analisará, tomando como referência a Operação Urbana Consorciada Água Espraiada, em São Paulo.

L’objectif de cette thèse est de caractériser les Rejets Urbains par Temps de Pluie (RUTP) et leur flux au niveau des exutoires d’eaux pluviales de trois sous-bassins majeurs de l'agglomération orléanaise. Pour cela des prélèvements ponctuels d’eau ont été effectués et un modèle conceptuel a été utilisé. Les trois sous-bassins : La Corne (463 ha), l'Egoutier (2080 ha) et Ormes (2256 ha) ont des occupations du sol différentes.D’une manière générale, la conductivité, la demande chimique en oxygène (DCO), la demande biochimique en oxygène (DBO5 et la DBO28), le carbone organique dissout (COD), l'azote total(NT), et les concentrations en anions et cations majeurs étaient plus élevés par temps sec que par temps de pluie indiquant un effet de dilution par les précipitations. Il a été mis en évidence un mélange des eaux pluviales avec des eaux usées dans le sous bassin d’Ormes. L’occupation des sols et les activités anthropiques influencent de manière significative la qualité du ruissellement. Par exemple, dans le sous-bassin de l’Egoutier, la présence d’une zone imperméable (industries et habitations) importante (40% de la surface) est responsable d’une augmentation des paramètresDBO5, DBO28, COD et NT.Les flux aux exutoires des différents paramètres de qualité de l’eau ont été évalués et comparés à ceux issus des quatre principales stations d’épuration (STEP) et à ceux de la Loire. La charge destrois sous-bassins urbains représente environ 166,61% de la charge des quatre STEP. Les trois sous bassins ont un faible impact sur la Loire en termes de flux annuels (environ 1,62% pour les MES par temps de pluie).Deux versions d’un modèle conceptuel dit d'accumulation/lavage-transport ont été évaluées pour estimer les flux de ruissellement des polluants ; la version classique et une version modifiée dans laquelle le paramètre accumulation des polluants a une forme logarithmique. Les performances des modèles étaient acceptables pour les MES et la DCO. Les coefficients de corrélation étaient supérieurs à 90% pour le sous bassin de l’Egoutier, par exemple. Pour les éléments traces métalliques en phase particulaire, la corrélation avec l’expérience était bonne également. D’une manière générale, lorsqu'un flux mesuré était inférieur à 1 kg.ha-1, les modèles n’étaient plus applicables.Des premiers essais de simulation de la qualité et la quantité de RUTP ont été effectués à partir de MIKE URBAN, qui équipe les deux logiciels de modélisation MOUSE et SWMM. Les hydrogrammes ont indiqué que le débit maximum obtenu avec SWMM était toujours inférieur à celui obtenu avec MOUSE. La qualité de l’eau (masse de MES) était toujours plus fortement impactée par le lessivage des MES dans le modèle MOUSE que dans SWMM.Ce travail constitue la première étape du travail d'évaluation de RUTP pour l'Agglomération orléanaise. Il constitue une base solide pour un futur programme de surveillance continue
The objective of this thesis was to characterize urban runoff water at the level of stormwater outletson three major urban sub-basins of the Orléans agglomeration, covering land areas ranging in size from463 to 2257 ha and with contrasted land use. 11 individual rain events were sampled at runoff outletsbetween April 2015 and June 2017 and 10 campaigns were also carried out in dry weather.In general, it was observed that the conductivity, chemical oxygen demand (COD), biochemicaloxygen demand (BOD5 and BOD28), dissolved organic carbon (DOC), total nitrogen (NT), anions andmajor cations were found to be higher in dry weather conditions than in rainy weather. These resultsindicate a dilution effect due to precipitation.A mixture of rainwater and wastewater was also identified in the sub-basin of Ormes. Land use andhuman activities in the sub-basin studied were found to significantly influence the quality of the resultedrunoff from rainfall events. For example, in the Egouttier sub-basin 2, the presence of a large imperviouszone (industrial and residential, 40% of the surface area) was responsible for an increase in the parametersBOD5, BOD28, COD and NT.The flows at the outlets of the different water quality parameters were evaluated and compared withthose from the four main wastewater treatment plants (WWTP) and those from the Loire. The estimatedloads of the three sub-urban basins accounts for approximately 166.61% of the load of the four WWTP.The three sub-basins have a small impact on the Loire in terms of annual flows (about 1.62% for wetweather case).Two versions of a conceptual model of accumulation / washoff were evaluated to estimate pollutantrunoff; the classical version and a modified version in which the pollutant accumulation parameter has alogarithmic form. The performances of the models were found acceptable for the MES and the COD. TheNash-Sutcliffe (NS) coefficients were found as 0.84 and 0.85 for the two versions at the Egouttier subbasin.For trace elements in particulate phase, the correlation with the experimental measured value wasfound good as well. In general, when a measured flow was less than 1 kg.ha-1, the modified model was nolonger applicable.The first simulation tests of the quality and quantity of urban runoff were carried out with MIKEURBAN, which equips both MOUSE and SWMM modeling software. For water quantity, the hydrographsindicated that the maximum flow obtained with SWMM was always lower than that obtained with MOUSE.For water quality, TSS mass was still more strongly impacted by the leaching of TSS in the MOUSE modelthan in the SWMM model.This work can be considered as the first step of the evaluation work of RUTP for the Orléansagglomeration. It provides a solid foundation for a future monitoring program

A pesquisa objetiva a composição de cenários de planejamento para o Plano Diretor utilizando-se de medidas de recuperação ambiental através de uma bacia selecionada. São avaliadas simulações hidrológicas através: a) da implantação de: medidas de reúso de águas pluviais com microreservatórios instalados no lote, b) da arborização urbana, c) do reservatório de detenção, d) do coeficiente de permeabilidade, e outras medidas para micro e macro-drenagem. A metodologia utiliza uma base regional para espacializar através de bacias embutidas (MENDIONDO E TUCCI, 1997) a classificação de uso e ocupação do solo para os anos: 1962, 1972 e 1998. Os resultados oferecem diretrizes para novos empreendimentos, loteamentos urbanos e políticas públicas. A situação de passivo ambiental da bacia justifica o estudo em micro-bacias urbanas embutidas. As simulações envolvem cenários retrospectivos de 40 anos, atual e prospectivos de 15 anos com e sem Plano Diretor. Os critérios adotados resultam para o planejamento ambiental melhorias na carga de poluição hídrica e prevê a recuperação de suas funções hidrológicas e ambientais. Inclui-se uma análise de incertezas a partir dos diferentes estados de condições de umidade antecedente que afetam o valor de CN. A partir destes resultados, recomenda-se avaliar novos cenários de planejamento, instrumentação de monitoramento para bacias sem dados que visem o estudo aplicado do aproveitamento de águas pluviais no lote associado às incertezas das previsões hidrológicas dessas bacias sem dados, conforme o programa PUB - Predictions in Ungauged Basins (SIVAPALAN et al, 2003)
The research aims to compose planning scenarios for Master Plan using measures of environmental recovering to control of urban drainage at the scale of an ungauged basin selected. Hydrologic simulations are assessed by the implementation of several measures as: a) indirect impacts of rain water use system in the urban lot, b) urban arborization, c) detention reservoir, d) permeability coefficient and complementary measures at micro and macro drainage. The methodology uses regionally-based nested basins (MENDIONDO e TUCCI, 1997) with a classification of land-use in years: 1962, 1972 and 1998. Results will offer directive to new urban achievements and water policies. Environmental passive situations (diagnosis) at the basin scale justify experimental studies in nested urban micro-basins. The simulations involve retrospective scenarios through 40 years, present state (1998) and prospective scenarios of 15 years with and without master plan. Criteria adopted result in best management practices (BMP’s) in water pollution and foresee recovery of hydrologic environmental functions. Analysis of uncertainties of hydrologic estimations to different antecedent moisture conditions through the CN parameter is also presented and discussed. From these results it is recommended to assess new planning scenarios that aim experimental study, thereby looking forward to proposing new concepts of rain water use, i.e. by using micro reservoir at domiciliary lot. These scenarios are to be depicted into the hydrologic uncertainties at basins without data especially addressing the PUB program - Predictions in Ungauged Basins (SIVAPALAN et al, 2003)

Le souci constant de diminuer l'impact des rejets urbains par temps de pluie a conduit les aménageurs à s'intéresser à la composition et à la variation de la pollution induite par les eaux de ruissellement sur des bassins versants urbanisés. Plusieurs études ont montré que la pollution, souvent évaluée par la mesure de la quantité de matières en suspension, est une fonction croissante de plusieurs facteurs climatologiques, dont les principaux sont la pluie et la durée du temps sec précédent l'épisode pluvieux. Afin de mieux évaluer la relation qui existe entre la pollution et le couple de variables constitue de la durée du temps sec précédent un épisode pluvieux et des variables représentatives de la pluie suivante, une étude statistique a été entreprise sur le bassin versant urbanisé de la commune d'Entzheim. Une première étape porte sur l'étude du comportement de variables aléatoires représentatives de la pluie d'une part, et de la durée de temps sec d'autre part, ces deux séries étant issues de données recueillies sur 10,25 années. Les ajustements ont été testés au moyen des lois utilisées classiquement en hydrologie. Une deuxième étape de cette étude a conduit à un traitement de données de pollution sur un échantillon de 38 individus. L’analyse statistique a permis de définir les paramètres du couple temps sec/pluie les plus influents dans la production de pollution et d'établir des régressions linéaires. L’ajustement de modèles globaux sur les données de pollution, comparé à ces dernières, offre des modèles susceptibles d'être transposés à d'autres bassins et pour lesquels il est possible de déterminer une période de retour pour chaque événement tout en ne connaissant que peu de paramètres. La troisième étape établit les lois de fréquence des couples temps sec/pluie et les compare à celles obtenues pour la pollution lors de la deuxième étape. L’objectif est de définir une loi simple entre les fréquences, de façon à encadrer rapidement la période de retour d'un événement de pollution

Intense but short-term cloudbursts may cause severe flooding in urban areas. Such short-term cloudbursts mostly are of convective character, where the rain intensity may vary considerably within relatively small areas. Using uniform design rains where maximum intensity is assumed over the whole catchment is common practice in Sweden, though. This risks overestimating the hydraulic responses, and hence lead to overdimensioning of stormwater systems. The objective of this study was to determine how the hydraulic response to cloudbursts is affected by the spatial variation of the rain in relation to the catchment size, aiming to enable improved cloudburst mapping in Sweden. Initially, the spatial variation of heavy rains in Sweden was investigated by studying radar data provided by SMHI. The distribution of rainfall accumulated over two hours from heavy raincells was investigated, based on the assumption that the intensity of convective raincells can be approximated as spatially Gaussian distributed. Based on the results, three Gaussian test rains, whose spatial variation was deemed a representative selection of the radar study, were created. In order to investigate how the hydraulic peak responses differed between the Gaussian test rains and uniform reference rains, both test and reference rains were modeled in MIKE21 Flow model. The modelling was performed on an idealised urban model fitted to Swedish urban conditions, consisting of four nested square catchments of different sizes. The investigated hydraulic peak responses were maximum outflow, proportion flooded area and average maximum water depth. In comparison with spatially varied Gaussian rains centered at the outlets, the uniform design rain with maximum rain volume overestimated the peak hydraulic response with 1-8%, independent of catchment size. Uniform design rains scaled with an area reduction factor (ARF), which is averaging the rainfall of the Gaussian rain over the catchment, instead underestimated the peak response, in comparison with the Gaussian rains. The underestimation of ARF-rains increased heavily with catchment size, from less than 5 % for a catchment area of 4 km2 to 13 - 69 % for a catchment area of 36 km2. The conclusion can be drawn that catchment size ceases to affect the hydraulic peak response when the time it takes for the whole catchment to contribute to the peak response exceeds the time it takes for the peak to be reached. How much the rain varies over the area which is able to contribute to the peak response during the rain event, can be assumed to decide how much a design rain without ARF overestimates the peak responses. If the catchment exceeds this size, an ARF-scaled rain will underestimate the peak responses. This underestimation is amplified with larger catchments. The strong pointiness of the CDS-hyetograph used in the study risks underestimating the differences in hydraulic peak responses between the test rains and a uniform rain without ARF, while the difference between test rains and uniform rains with ARF risks being overestimated.
Intensiva men kortvariga skyfall kan orsaka omfattande översvämningsproblematik i urbana områden. Trots att sådana kortvariga skyfall oftast är av konvektiv karaktär, där regnintensiteten kan variera avsevärt inom relativt små områden, används idag uniforma designregn där maxintensitet antas över hela avrinningsområdet. Detta riskerar att leda till en överskattning av hydrauliska responser, och följaktligen överdimensionering av dagvattensystem. Denna studie syftar till att utreda hur den hydrauliska responsen av skyfall påverkas av regnets spatiala variation, i relation till avrinningsområdets storlek. Ytterst handlar det om att möjliggöra förbättrad skyfallskartering i Sverige. Initialt undersöktes den spatiala variationen hos kraftiga regn i Sverige, genom en studie av radardata tillhandahållen av SMHI. Utbredningen av regnmängd ackumulerad över två timmar från kraftiga regnceller undersöktes utifrån antagandet att intensiteten hos konvektiva regnceller kan approximeras som spatialt gaussfördelad. Baserat på resultatet skapades tre gaussfördelade testregn vars spatiala variation ansågs utgöra ett representativt urval från radarstudien. För att undersöka hur de hydrauliska responserna skiljer sig åt mellan de gaussfördelade testregnen och uniforma referensregn, modellerades såväl test- som referensregn i MIKE 21 Flow model. Modelleringen utfördes på en idealiserad stadsmodell anpassad efter svenska urbana förhållanden, bestående av fyra nästlade kvadratiska avrinningsområden av olika storlekar. De hydrauliska responser som undersöktes var maximalt utflöde, maximal andel översvämmad yta samt medelvärdesbildat maximalvattendjup, alltså toppresponser. Jämfört med spatialt varierade gaussregn centrerade kring utloppen överskattade ett uniformt designregn med testregnens maximala volym de hydrauliska toppresponserna med 1-8 %, oberoende av avrinningsområdets storlek. Uniforma designregn skalade med area reduction factor (ARF), vilken medelvärdesbildar gaussregnets nederbörd över avrinningsområdet, underskattade istället toppresponsen jämfört med gaussregnen. ARF-regnets underskattning ökade kraftigt med avrinningsområdets storlek, från mindre än 5 % för ett avrinningsområde på 4 km2, till 13 - 69 % för ett avrinningsområde på 36 km2. Slutsatsen kan dras att avrinningsområdets storlek upphör att påverka den hydrauliska toppresponsen, då tiden det tar för hela avrinningsområdet att samverka till toppresponsen överstiger tiden till denna respons. Hur mycket regnet varierar över det område som under regnhändelsen hinner samverka till toppresponsen, kan antas avgöra hur mycket ett designregn utan ARF överskattar toppresponserna. Överstiger avrinningsområdet denna storlek kommer ett ARF-regn att underskatta toppresponserna, och underskattningen förstärks med ökande avrinningsområdesstorlek. Den kraftiga temporala toppigheten hos den CDS-hyetograf som användes i studien riskerar att underskatta skillnaderna i hydraulisk topprespons mellan testregnen och ett uniformt regn utan ARF, medan skillnaden mellan testregn och uniforma regn med ARF istället riskerar att överskattas.

Short duration intense rainfall causes an increase in rainfall derived infiltration and inflow (RDII) in aging sewer networks, which leads to Sanitary Sewer Overflows (SSOs). This, in turn, causes various detrimental impacts, both on human health and the environment. This research aims to quantify the benefits of Water Sensitive Urban Design (WSUD) approaches to mitigate the negative impacts of rainfall induced SSOs. In this context, this research develops a generalised framework for assessing and mitigating the impacts of intense rainfall on the performance of the sanitary sewer network. The first part of the developed framework involves detailed hydraulic modelling to evaluate the performance of the sewer network. The second part deals with the development of SSO mitigation strategies based on popular WSUD approaches. This study also demonstrates the application of the developed framework for a case study catchment in Melbourne, Australia. A detailed hydraulic modelling to analyse the performance of the case study sewer network during a wet (2010) and a dry year (2008) has been presented. The hydraulic performance analysis found that the system experienced 23 ML of sewer overflow volume in 2010 as compared to 3.42 ML in 2008. Towards mitigating the negative impacts of SSOs, this study has implemented two commonly used WSUD approaches, namely rainwater tanks and rain gardens for the case study sewer network. A detailed hydraulic modelling has been undertaken with rainwater tanks and rain gardens (individually and in combination) for the wet year 2010. It was observed that rainwater tanks (individually) could lead to a maximum reduction in SSO volume by 33% when compared to the base case overflow volume of 23 ML. A higher reduction in SSO volume up to a maximum of 45% was observed when rain gardens were implemented in conjunction with rainwater tanks. Such an analysis will benefit the urban water authorities to develop sustainable WSUD based mitigation strategies for controlling SSOs in their sewer system. Thus, the study will be beneficial for the community and the environment.

Cape Town, South Africa, falls within a winter rainfall region, making it difficult to assess the feasibility of rain- and stormwater harvesting. The reason for this is because the region’s high water demand period coincides with the low rainfall summer season, thereby limiting the availability of this alternative water resource when most needed. During this study, rainwater harvesting for toilet flushing purposes, collected from roof surfaces, was practically assessed by means of inserted flow meters at a pilot study site in Kommetjie, Cape Town. The combined and single system roof- and land surface runoff yields and savings of commercial buildings within the Kommetjie business area, were also theoretically assessed by making use of a mathematical roof- and land surface runoff model specifically developed during this study. The statistical testing of the hypotheses statements relating to the pre- and post-harvesting savings at the pilot study building, compared against the average actual municipal water usage, were performed. Hypotheses testing were also performed in order to compare the theoretical rain- and stormwater runoff yields for the commercial business area against the average actual municipal water consumption. The conclusions drawn from this study indicated that valuable potable water, as well as related financial savings, can be achieved within a winter rainfall region, thereby making rain- and stormwater harvesting a feasible option for commercial businesses in Cape Town.
Environmental Sciences
M.Sc. (Environmental Management)

Increasing global mean temperature or global warming has the potential to affect the hydrologic cycle. In the 21st century, according to the UN Intergovernmental Panel on Climate Change (IPCC), alterations in the frequency and magnitude of high intensity rainfall events are very likely. Increasing trend of urbanization across the globe is also noticeable, simultaneously. These changes will have a great impact on water infrastructure as well as environment in urban areas. One of the impacts may be the increase in frequency and extent of flooding. India, in the recent years, has witnessed a number of urban floods that have resulted in huge economic losses, an instance being the flooding of Mumbai in July, 2005. To prevent catastrophic damages due to floods, it has become increasingly important to understand the likely changes in extreme rainfall in future, its effect on the urban drainage system, and the measures that can be taken to prevent or reduce the damage due to floods. Reliable estimation of future design rainfall intensity accounting for uncertainties due to climate change is an important research issue. In this context, rainfall intensity-duration-frequency (IDF) relationships are one of the most extensively used hydrologic tools in planning, design and operation of various drainage related infrastructures in urban areas. There is, thus, a need for a study that investigates the potential effects of climate change on IDF relationships. The main aim of the research reported in this thesis is to investigate the effect of climate change on Intensity-Duration-Frequency relationship in an urban area. The rainfall in Bangalore City is used as a case study to demonstrate the applications of the methodologies developed in the research Ahead of studying the future changes, it is essential to investigate the signature of changes in the observed hydrological and climatological data series. Initially, the yearly mean temperature records are studied to find out the signature of global warming. It is observed that the temperature of Bangalore City shows an evidence of warming trend at a statistical confidence level of 99.9 %, and that warming effect is visible in terms of increase of minimum temperature at a rate higher than that of maximum temperature. Interdependence studies between temperature and extreme rainfall reveal that up to a certain range, increase in temperature intensifies short term rainfall intensities at a rate more than the average rainfall. From these two findings, it is clear that short duration rainfall intensities may intensify in the future due to global warming and urban heat island effect. The possible urbanization signatures in the extreme rainfall in terms of intensification in the evening and weekends are also inferred, although inconclusively. The IDF relationships are developed with historical data and changes in the long term daily rainfall extreme characteristics are studied. Multidecedal oscillations in the daily rainfall extreme series are also examined. Further, non-parametric trend analyses of various indices of extreme rainfall are carried out to confirm that there is a trend of increase in extreme rainfall amount and frequency, and therefore it is essential to the study the effects of climate change on the IDF relationships of the Bangalore City. Estimation of future changes in rainfall at hydrological scale generally relies on simulations of future climate provided by Global Climate Models (GCMs). Due to spatial and temporal resolution mismatch, GCM results need to be downscaled to get the information at station scale and at time resolutions necessary in the context of urban flooding. The downscaling of extreme rainfall characteristics in an urban station scale pose the following challenges: (1) downscaling methodology should be efficient enough to simulate rainfall at the tail of rainfall distribution (e.g., annual maximum rainfall), (2) downscaling at hourly or up to a few minutes temporal resolution is required, and (3) various uncertainties such as GCM uncertainties, future scenario uncertainties and uncertainties due to various statistical methodologies need to be addressed. For overcoming the first challenge, a stochastic rainfall generator is developed for spatial downscaling of GCM precipitation flux information to station scale to get the daily annual maximum rainfall series (AMRS). Although Regional Climate Models (RCMs) are meant to simulate precipitation at regional scales, they fail to simulate extreme events accurately. Transfer function based methods and weather typing techniques are also generally inefficient in simulating the extreme events. Due to its stochastic nature, rainfall generator is better suited for extreme event generation. An algorithm for stochastic simulation of rainfall, which simulates both the mean and extreme rainfall satisfactorily, is developed in the thesis and used for future projection of rainfall by perturbing the parameters of the rainfall generator for the future time periods. In this study, instead of using the customary two states (rain/dry) Markov chain, a three state hybrid Markov chain is developed. The three states used in the Markov chain are: dry day, moderate rain day and heavy rain day. The model first decides whether a day is dry or rainy, like the traditional weather generator (WGEN) using two transition probabilities, probabilities of a rain day following a dry day (P01), and a rain day following a rain day (P11). Then, the state of a rain day is further classified as a moderate rain day or a heavy rain day. For this purpose, rainfall above 90th percentile value of the non-zero precipitation distribution is termed as a heavy rain day. The state of a day is assigned based on transition probabilities (probabilities of a rain day following a dry day (P01), and a rain day following a rain day (P11)) and a uniform random number. The rainfall amount is generated by Monte Carlo method for the moderate and heavy rain days separately. Two different gamma distributions are fitted for the moderate and heavy rain days. Segregating the rain days into two different classes improves the process of generation of extreme rainfall. For overcoming the second challenge, i.e. requirement of temporal scales, the daily scale IDF ordinates are disaggregated into hourly and sub-hourly durations. Disaggregating continuous rainfall time series at sub-hourly scale requires continuous rainfall data at a fine scale (15 minute), which is not available for most of the Indian rain gauge stations. Hence, scale invariance properties of extreme rainfall time series over various rainfall durations are investigated through scaling behavior of the non-central moments (NCMs) of generalized extreme value (GEV) distribution. The scale invariance properties of extreme rainfall time series are then used to disaggregate the distributional properties of daily rainfall to hourly and sub-hourly scale. Assuming the scaling relationships as stationary, future sub-hourly and hourly IDF relationships are developed. Uncertainties associated with the climate change impacts arise due to existence of several GCMs developed by different institutes across the globe, climate simulations available for different representative concentration pathway (RCP) scenarios, and the diverse statistical techniques available for downscaling. Downscaled output from a single GCM with a single emission scenario represents only a single trajectory of all possible future climate realizations and cannot be representative of the full extent of climate change. Therefore, a comprehensive assessment of future projections should use the collective information from an ensemble of GCM simulations. In this study, 26 different GCMs and 4 RCP scenarios are taken into account to come up with a range of IDF curves at different future time periods. Reliability ensemble averaging (REA) method is used for obtaining weighted average from the ensemble of projections. Scenario uncertainty is not addressed in this study. Two different downscaling techniques (viz., delta change and stochastic rainfall generator) are used to assess the uncertainty due to downscaling techniques. From the results, it can be concluded that the delta change method under-estimated the extreme rainfall compared to the rainfall generator approach. This study also confirms that the delta change method is not suitable for impact studies related to changes in extreme events, similar to some earlier studies. Thus, mean IDF relationships for three different future extreme events, similar to some earlier studies. Thus, mean IDF relationships for three different future periods and four RCP scenarios are simulated using rainfall generator, scaling GEV method, and REA method. The results suggest that the shorter duration rainfall will invigorate more due to climate change. The change is likely to be in the range of 20% to 80%, in the rainfall intensities across all durations. Finally, future projected rainfall intensities are used to investigate the possible impact of climate change in the existing drainage system of the Challaghatta valley in the Bangalore City by running the Storm Water Management Model (SWMM) for historical period, and the best and the worst case scenario for three future time period of 2021–2050, 2051–2080 and 2071–2100. The results indicate that the existing drainage is inadequate for current condition as well as for future scenarios. The number of nodes flooded will increase as the time period increases, and a huge change in runoff volume is projected. The modifications of the drainage system are suggested by providing storage pond for storing the excess high speed runoff in order to restrict the width of the drain The main research contribution of this thesis thus comes from an analysis of trends of extreme rainfall in an urban area followed by projecting changes in the IDF relationships under climate change scenarios and quantifying uncertainties in the projections.