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1
Meigh, J. R. "Transport of bed material in a gravel-bed river." Thesis, University of East Anglia, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382828.
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Thoms, Martin C. "Channel sedimentation within urban gravel bed rivers." Thesis, Loughborough University, 1987. https://dspace.lboro.ac.uk/2134/10844.
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Fine substrate sediments are considered to be important in the management of urban river systems. Urban construction activities have been reported to increase sediment loads causing the temporary siltation of channel substrates within the urban area. Nevertheless fine sediment derived from urban areas frequently carry toxic material well in excess of background concentration levels. While the soluble phase of heavy metals and the importance of their association with suspended sediment has received considerable attention, longer term studies of fine urban river-bed sediments are limited. Furthermore studies of heavy pollutants in active stream sediments, below mine waste tips, have shown the channel substrate can provide a long term store for heavy metals in association with fine sediments. This thesis investigates the variety of impacts that urbanisation has upon the sedimentation of gravel bed rivers. A freeze coring technique and infIltration baskets have been used to study the textural-geochemical properties of fme matrix sediment and its development within an urban river-bed framework, within and below a number of contrasting urban catchments in the U.K. Complex urban hydrological and sedimentological regimes are shown to have a variable influence upon matrix sedimentation. The actual volume of matrix present within the urbanised substrate is influenced by the degree of urbanisation within the catchment. Furthermore this sediment is finer in size and associated heavy metal concentrations are well in excess of natural background levels. Although heavy metal levels do correlate slightly with textural characteristics, the presence of maximum concentrations at depth in the substrate indicate possible mobilisation of metals within the urbanised river-bed. The temporal behaviour of matrix development within an urbanised substrate is shown to differ from natural river-beds. Despite high suspended sediment concentrations the magnitude of the potential rate of supply is lower, by 50 percent, and dominated by organic material. This sediment also contains elevated heavy metal cocnentrations. This contrasts to the inorganic sediment ingress of natural river substrates. It is concluded that fine matrix sediments within urban gravel bed rivers should be at least of concern to public health engineers, water authorities and conservationists.
3
Gaskin, Janet. "Intensive aDcp Survey of a Gravel-Bed River Confluence." Thesis, University of Ottawa (Canada), 2010. http://hdl.handle.net/10393/28738.
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An intensive survey of the high angle asymmetric gravel-bed confluence of the Fraser River Main Channel with Minto Side Channel, downstream of a mid-channel island, was conducted using an acoustic Doppler current profiler (aDcp) during the freshet in June, 2008 at a combined discharge of 7 500 m 3/s. The confluence was characterized by a vertical mixing interface, with the Minto high velocity core being advected downwards in the upstream part of the scour zone; weaker helical flow is evident in the main channel flow as it confines the strongly helical left bank flow. Apparent bed velocity generally followed the thalweg, with the highest values near 0.15 m/s occurring at the edges of the scour zone and along the elongated bed step. In plotted spatial distributions, the areas of high primary bed velocity matched areas of high shear velocity and/or strongly upward vertical flow velocity.
4
Markham, Andrew James. "Flow and sediment processes in gravel-bed river bends." Thesis, Queen Mary, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308275.
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Ashworth, Philip John. "Bedload transport and channel change in gravel-bed rivers." Thesis, University of Stirling, 1987. http://hdl.handle.net/1893/2555.
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Spatial and temporal variations in channel morphology, near-bed velocity, shear stress, bedload transport rate, pebble tracer movement, and bedload and bed material size distribution were measured in seven different channel patterns in two gravel-bed rivers in the Scottish Highlands (the Dubhaig and Feshie) and a proglacial stream in Norway (the Lyngsdalselva). The results showed that there were discernible links between the channel processes and changes which were consistent for all river types. 169 shear stress estimates from velocity profiles with changing discharge showed that Keller's (1971) velocity-reversal hypothesis holds true in different channel patterns of gravel-bed rivers and can be extended to include subunits of the pool/riffle cycle. At discharges near bankfull there is a decrease in the flow strength and amount of bedload movement from the poolhead down to the pooltail (and then riffle). On a broader scale 72 Helley-Smith bedload samples and the movement of over 3700 pebble tracers showed that the entrainment of different size fractions from heterogeneous bed material is inefficient and is overpredicted by the traditional bedload transport equations. Empirical analyses showed that when the armour is mobile/broken large and small particles have almost equal mobility as first proposed by Parker et al. (1982) and Andrews (1983). However for the majority of flow conditions the armour is static and entrainment is selective to a greater or lesser degree depending on the availability of appropriate-sized sediment at the surface and from bank erosion. The magnitude and direction of flow strength and bedload transport helps to explain the location and mode of channel development as revealed by repeated levelling and mapping. The accelerating convergent/decelerating divergent cells of flow alter the channel morphology in predictable ways. The positions of these cells can change with increasing discharge as the channel becomes generally, rather than locally, competent to move coarse sediment. The rates of bank erosion and volumetric scour and fill decreased from the active multi-braided system through to the stable straight channel type.
6
Movafagh, Kerman Soheil. "Mapping three-dimensional velocity in a large gravel-bed river." Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27894.
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Three-dimensional images of the boundary, water surface elevation, and velocity vectors in a wandering gravel-bed reach of Fraser River, British Columbia, are prepared. Data were collected through intensive surveying of a 6 km reach using an Acoustic Doppler Current Profiler (ADCP) and Real Time Kinematic GPS (RTK-GPS) mounted on a boat. Nominal channel width was 500 m, and diagonal sections were spaced an average of 120m apart. Using Matlab, binary data in ADCP raw data files are extracted and converted to ASCII format to be usable by Surfer, Tecplot, and other programs. Measured vertical velocities for each single ping ensemble are corrected for boat motion using simultaneous instantaneous change in GPS rover altitude recorded in the navigation data files. Using Surfer, water surface elevation and bottom boundary elevation are interpolated to 25m x 25m grids and combined together to form the boundary of a volume grid. The ASCII files are reformatted in Excel to produce water surface and channel boundary images in Tecplot. The three-dimensional velocity field is interpolated using kriging, and vorticity is calculated based on the velocity field. The error velocity is calculated as well. The high velocity follows the thalweg and reveals the coherence of the interpolated velocity field and the validity of the method. The three-dimensional velocity field and vorticity are analyzed to assess the cause of high bank erosion and sediment transport observed at a particular location. Erosion at this site appears to be related to complicated flow at a channel confluence and 3D vortices produced by flow separation around a riprap nickpoint.
7
Clayton, Jordan Arthur. "Sediment transport and channel form in gravel-bed river meanders." Diss., Connect to online resource, 2005. http://wwwlib.umi.com/dissertations/fullcit/3178363.
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Wild, Michelle Anne. "Growth dynamics of braided gravel-bed river deltas in New Zealand." Thesis, University of Canterbury. Dept of Civil and Natural Resources Engineering, 2013. http://hdl.handle.net/10092/8456.
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This research has been undertaken to further our knowledge of decade-to-century timescale braided, gravel-bed river delta growth dynamics. The study included: a review of available literature; field studies; the development of microscale models for two study deltas; and the development of a simple numerical model incorporating movement of braided river channels across a delta topset (varying the location of sediment delivery to the delta).
Results from the microscale modelling showed that successful physical modelling requires well-defined fixed boundaries and, ideally, good historical aerial photography for the estimation of the model time scale. A complex braided gravel-bed river delta system composed of two merging deltas entering a deep, low-energy receiving basins was able to be successfully modelled to provide valuable information on delta growth dynamics. However, a microscale model of a delta prograding into shallow receiving basins, with a large supply of fine sediment, was more difficult to calibrate and assess (partly due to limited field data), and was considered less reliable.
The simple rule-based numerical model ‘DELGROW’, developed to simulate a braided river system entering a deep, low-energy body of water, requires a known sediment supply rate, as well as information on the braided river topography, submerged delta foreset, and lakebed bathymetry. Unlike simple 1-d width-averaged geometric models, DELGROW takes into consideration barriers (e.g. islands) as well as relatively complex converging braided river delta configurations. By changing the sediment supply, or modifying the river system, the response of the river system to various scenarios can also be assessed.
Microscale models and DELGROW appear to realistically simulate decade-to-century timescale growth of braided gravel-bed river deltas entering a deep, low-energy, receiving basin. Both of these modelling methods initially use the supplied sediment to try and eliminate any riverbed irregularities (e.g. low areas), before continuing to advance and deposit sediment in a more evenly-distributed manner, whilst taking into consideration irregularities due to barriers, and asymmetric sediment sources such as merging deltas. Neither model can reliably predict locations of bank erosion, or channel avulsions that divert flow and sediment outside of the fixed model boundaries.
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Harris, T. R. J. "Gravel-bed stability and water quality variation in a lowland stream." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283968.
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Milan, David John. "Sand and gravel transport through a riffle-pool sequence." Thesis, University of Newcastle upon Tyne, 2000. http://hdl.handle.net/10443/3146.
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This study focuses upon flow hydraulics, sediment transport and riffle-pool maintenance on the River Rede, Northumberland, UK. Analysis of bed structure indicate pools to be coarser than riffles, suggesting these to be zones of maximum tractive force at high flow. Tractive force reversal can be demonstrated using a combination of velocity, shear stress and gravel tracer data, and is therefore advocated as a mechanism for maintaining the riffle-pool form. Three dimensional flow structures are likely to increase the likelihood of reversal in pools situated on bends, which may not always be detected using one-dimensional measures of flow hydraulics. Magnetic tracing and basket trapping techniques were used to provide an insight into rates of movement, accumulation, initial motion criteria and routing, of sand. Sand is transported selectively and is mobilised at between 11-22 Nm⁻². Deposition of sub 2mm material is prevalent on morphological high points (bars/riffle margins), although greatest quantities were routed through morphological lows. Freeze core evidence shows limited intragravel storage. Gravel tracer movements showed evidence of size selective entrainment overall, however hiding effects were also found to be evident at two scales; 30-50mm and 110-140mm (for riffles) and 20- 90mm and 11O-140mm for pool. Slope exponents for log-log relations between scaled grain size (D/D₅₀) versus dimensionless shear stress (Өc) of ≈-0.9 suggest that hiding strongly influences sediment transport. Stream power estimates from pgQs demonstrate a higher threshold for motion for gravel in pools (132 Wm⁻²) compared with riffles (127 Wm⁻²). Differences in initial motion criteria (8e) between riffles and pools were found to be significant (p<0.05), indicating pool sediments to be less mobile than riffle, despite pool sediments being less compact. Reduced mobility of pool bedload sediment results from clasts being sheltered by immobile lag gravel found in the pool. It appears therefore that mobility differences between riffles and pools, related to bed structure, does not explain riffle-pool maintenance on the Rede. Scaled travel distance (L/L₅₀s) for tracers in the reach as a whole showed a convex-up relationship with scaled grain size (D/D₅₀s), demonstrating that for tracer grains progressively coarser than the surrounding D₅₀ surface grains, travel distance drops off rapidly, whereas grains progressively finer than the surrounding clasts, travel further but at a less rapid rate. Furthermore, virtual velocity (V*) of tracer grains showed a positive dependence upon D/D₅₀s. Gravel tracer movement provided important insights into riffle-pool maintenance. Transfer of material through the Rede riffle-pool sequence appeared to be influenced by flow magnitude and duration. For low magnitude high frequency flows below 25% bankfull, intra-unit movement was found to predominate. Medium magnitude and frequency flows (up to 50% bankfull) appeared capable of inter-unit transport; scour from pool troughs and deposition on pool exit slopes I riffle heads, movement of material from riffles to bar edges and from bar to bar. For higher magnitude low frequency flows up to bankfull, there was less scour from pools, and a dominance of bar-to-bar sediment transfer. Limited evidence of sediment routing and deposition in pools suggest these to be scour / sediment source zones only, with supply originating from the bed and outer bank. These data demonstrate the importance of different flow magnitude and frequency in creating / maintaining different areas of the riffle-pool structure.
11
Lamparter, Gabriele Johanna. "Modeling fine sediment behavior in gravel-bed rivers." Thesis, University of Exeter, 2014. http://hdl.handle.net/10871/18441.
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Fine-grained sediment accumulation in the interstices of gravel beds is a key factor in degrading riverine habitats. However, interstitial deposits are highly dynamic and are not sufficiently understood. This work enhances the understanding of interstitial fine sediment deposition by investigating interstitial storage and ingress, flow, suspended sediment and gravel bed character. Furthermore, this work introduces a numerical suspended sediment deposition model with the power to predict patterns of interstitial ingress. The investigation of interstitial deposition were carried out on two levels. Both data orginating from flume experiments and from three locations of the River Culm, Devon, UK was collected. The experimental data showed the significant influence of small scale variations in flow and bed character and their influence on interstitial ingress. The field investigation showed clear differences in interstitial fine-grained sediment for the different river reaches and an overall higher interstitial ingress compared to recent published data. The numerical model development was realised in a two-step approach. First, the model was coded and calibrated for the flume scale processes and, second, an upscaled reach scale model was devolped for the field data. This reach scale suspended sediment deposition model included flow information, for which depthaveraged two dimensional hydrodynamic models were developed with the software Delft3D. The overall explanatory power of the model at this state is not satisfactory with regards to local deposition distribution. A separate chapter discusses the possible causes and implications of this short coming for further research from a data aquisition and modelling perspective.
12
Wittenberg, Lea. "Structural patterns and bed stability of humid temperate, Mediterranean and semi-arid gravel bed rivers." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391270.
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Emerson, Samuel D. "The role of bed shear stress in sediment sorting patterns in a reconstructed, gravel bed river." Thesis, San Jose State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10128515.
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The role of bed shear stress in bed surface grain size sorting was investigated on a reconstructed reach of the Merced River in the Central Valley of California. Pebble count data were collected at the inside, middle, and outside of ten bends in April 2015 and compared to data from pebble counts conducted in previous years. Output from a previously developed 2D flow model (FaSTMECH) was compared to critical shear stresses calculated from median grain-size data. Comparison of pebble count results from 2002 through 2015 showed that there was no temporally consistent pattern of coarsening or fining along the study reach; however, the bed surface coarsened between 2002 and 2015. Pebble count data from April 2015 revealed a distinct spatial distribution of grain sizes with a larger median grain size (D50) at the outside of bends and a smaller D50 at the inside of bends. Regression analyses performed on pebble count data from point bars revealed statistically significant downstream changes in surface grain size on two of the seven bars. Analysis of shear stress data showed a weak relationship between the modeled bed shear stress (τb) and the calculated critical shear stress (τcr ). The weak relationship between τb and τcr indicated that bed shear stress was not solely responsible for the grain size sorting in the study reach. It is likely that the observed grain size sorting patterns resulted from helical secondary flows at the bends.
14
Reid, Simon Christian. "Coarse sediment delivery and transfer within an upland gravel-bed river environment." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414171.
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Demir, Tuncer. "The influence of particle shape on bedload transport in coarse-bed river channels." Thesis, Durham University, 2000. http://etheses.dur.ac.uk/4375/.
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This thesis investigates the influence of bed material shape on sediment transport in gravel-bed rivers. The approach involves a combined series of field and laboratory experiments. Magnetic tracing experiments were carried out at three experimental sites in two Pennine gravel-bed streams. The specific aim of these experiments was to quantify the selective transport of different shapes of coarse river gravel and determine their spatial sorting within a natural stream channel. A total of 900 tracers in three size groups (32- 64 mm, 64-128 mm and greater than 128 mm) and four shape classes (spheres, blades, rod and discs) were prepared for each of the three sites. In die laboratory, tilting table experiments were carried out to clarify the mechanistic behaviour of different particle shapes, sizes and orientations on a variety of artificial and naturally formed bed roughnesses. Using strobe-light photography visualization experiments were undertaken with natural and artificially-moulded gravel-size particles of differing shape, size and weight in order to investigate the influence of shape on settling, grain impact, initial motion and transport paths of gravel-size particles. Results of the magnetic tracing experiments showed that there was both size and shape selectivity in bedload transport. Preferential movement occurred in die small and medium particle size classes with tracers concentrated along the channel thalweg. Sphere-shaped particles were transported the greatest distance and in greatest numbers. Rods also moved preferentially, while discs showed a lesser degree of transport and blades hardly moved at all. Results from the tilting table experiments highlight the importance of roundness as well as particle form and particle orientation in continuing thresholds of entertainment. In terms of size, friction angle was found to depend on the ratio of the diameter of the test particle to be moved to that it rests upon (d/D). Shape and orientation were found to be important parameters influencing friction angles. On a given bed roughness and for a constant size non-spherical test particles showed greater friction angles than spherical ones. A very clear difference was found in friction angle distibutions between sphere, transverse rod and other flat-shaped particles, namely, blades with parallel and transverse orientations, disc, and rod with parallel orientations. Visualisation experiments indicated that shape is an important particle characteristic that has a significant effect on settling rates and also the mode of near bed transport. These effects increase with greater particle sizes. The departure of a particle from a sphere leads to a decrease in its settling velocity, Experiments, across a range of test sizes showed that when compared to a sphere of equivalent weight and density, sphere and rod-shaped particles tend to settle the fastest and move by rolling. Discs and blades showed slower settling rates and, in most instances, moved by sliding. Experiments carried out with irregularly-shaped, natural particles show greater variability in settling behaviour and irregular patterns of motion. For every size group, sphere and rod shaped particles have lower critical angles of initial motion flian blade and disc-shapes. Regardless of shape, greater bed roughness, or decreasing particle size results in an increase in the critical angle for motion.
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Moretto, J. "Linking River Channel Forms and Processes in Gravel Bed Rivers: Time, Space, Remote Sensing and Uncertainty." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423802.
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The “modern” fluvial morphology, is the results of a series of events characterized by both natural and human dynamics. Recognizing the process responsible for particular morphology is not a simple analysis, it can be more difficult or impossible if the data collected have too low resolution or too high uncertainty in relation to the spatial and temporal scale assessed.
This work aims to analyse and optimize different data and collection methods, derived from different time, space and resolution scales, with a good equilibrium between time-consuming and results at low uncertainty.
Different gravel bed reaches were analysed as study area: Brenta, Piave, Tagliamento River (Italy) and Feshie River (Scotland).
Three geomorphic analyses were applied at different spatial and temporal scale. A planimetric approach through a multitemporal analysis over the last 30 years on the Brenta River. A volumetric approach through a revised colour bathymetry; hybrid digital terrain models (HDTM) building and comparison of different digital elevation models (DoD) was used to study relevant flood events that occurred in the North-East Italian rivers (Brenta, Piave and Tagliamento). A highly detailed resolution, derived from Terrestrial Laser Scanner (TLS) to study its uncertainty, was applied on the Feshie River and to some laboratory experiments.
Results show that on the Brenta River, lower active channel narrowing happened from 1981 to 1990 even if relatively important floods occurred. The active channel was likely at its minimum extent due to still relevant human impacts. Partial recovery of the active channel width was detected from 1990 to 2011 due to less gravel mining and human pressure.
The proposed methodology for producing high-resolution Digital Terrain Models (DTMs) in wet areas has an uncertainty comparable to LiDAR (Light Detection And Ranging) data in dry areas. The bathymetric model calibration only requires a dGPS survey in the wet areas contemporary to aerial images acquisition. Detailed and automatic erosion - deposition analyses starting from a DoD are possible thanks to the “principal erosion deposition analyser” script developed.
Density, angle of incidence and laser intensity seem to be the most uncertain influencing factors in DTMs building from TLS point clouds. A new TLS filter developed provides semi-automatic point cloud classifications to filter the vegetation.
The geomorphic approaches presented provide an adequate topographical description of the rivers to explore channel adjustments due to natural and human causes at different spatial and temporal scales. The study represents a valuable tool for any fluvial engineering, river topography description, river management, ecology and restoration purposes.La “moderna” morfologia fluviale, è il risultato di una serie di eventi caratterizzati da differenti dinamiche, naturali ed antropiche. Riconoscere i processi responsabili di una particolare morfologia, può divenire complesso se i dati disponibili presentano bassi livelli di risoluzione o eccessiva incertezza in funzione della scala temporale e spaziale analizzata. Questo lavoro si è focalizzato ad analizzare ed ottimizzare differenti tipi di dati e metodologie di rilievo in differenti tratti fluviali a fondo ghiaioso dell’Italia Nord-Orientale e della Scozia: Fiume Brenta, Piave e Tagliamento (Italia) e Fiume Feshie (Scozia). Tre differenti metodologie geomorfometriche sono state applicate a diverse scale spaziali e temporali. Un approccio planimetrico attraverso un’analisi multitemporale degl’ultimi 30 anni in un tratto del Fiume Brenta. Un approccio volumetrico attraverso una rivisitata applicazione di batimetria da colore, con costruzione di modelli digitali del terreno “ibridi” (HDTM) e comparazione di modelli di elevazione (DoD) per lo studio di un intenso evento di piena, avvenuto nei fiumi italiani considerati. Rilievi in laboratorio e nel Fiume Feshie ad alta risoluzione, tramite laser scanner terrestre (TLS), sono stati eseguiti per studiarne l’incertezza ed individuare metodologie di classificazione spaziale delle nuvole di punti. I risultati, mostrano che dal 1981 al 1990 nel Fiume Brenta persiste ancora un processo di restringimento dell’alveo attivo. L’impatto umano è ancora presente. L’alveo attivo presenta la sua minima estensione. Dal 1990 al 2011, sembra che un parziale recupero della larghezza dell’alveo attivo sia in atto. Minor pressione da estrazione di ghiaia e da impatto umano, caratterizzano questo periodo. La metodologia proposta per produrre DTM ad alta risoluzione in presenza di aree bagnate ha dimostrato un’incertezza comparabile con il LiDAR nelle aree secche. La calibrazione dei modelli batimetrici, richiede un rilievo dGPS nelle aree bagnate in “contemporaneo” con l’acquisizione delle foto aeree. Grazie allo script sviluppato (PrEDA), sono possibili più dettagliate e automatiche analisi dell’erosione e della deposizione. Densità, angolo di incidenza ed intensità laser sembrano essere i fattori che maggiormente influenzano l’incertezza nella realizzazione di modelli di elevazione da TLS. Il filtro sviluppato per nuvole TLS è in grado di fornire semi-automatici filtraggi della vegetazione. Gli approcci geomorfometrici presentati, forniscono adeguate descrizioni topografiche dei sistemi fluviali; utili ad esplorare aggiustamenti dei canali dovuti a cause naturali o antropiche in differenti scale spaziali e temporali. Lo studio proposto, può rappresentare un valido supporto alla topografia in ambito fluviale, alla progettazione di interventi di ingegneria fluviale, ad una adeguata gestione fluviale, considerando aspetti ecologici e di riqualificazione fluviale.
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Picco, Lorenzo. "Long period morphological dynamics in regulated braided gravel-bed rivers: comparison between Piave River (Italy) and Waitaki River (New Zealand)." Doctoral thesis, Università degli studi di Padova, 2010. http://hdl.handle.net/11577/3426981.
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Aim of this research has been to make an analysis of long and medium term morphological dynamics that may affect the regulated gravel-bed braided rivers as the Piave river (Italy) and the Waitaki river (New Zealand).
The Piave river (drainage area around 4000km2), is one of the largest rivers in the north-east of Italy, the study reach is, mainly, 37 km long, and represent the intermediate course of the river within the mountain district. In addiction were been study different sub-reaches until a minimum of around 1,5 km long.
The Waitaki river (drainage area around 11000 km2), is a large gravel-bed river draining the eastern slope of Southern Alps, South Island, New Zealand, has been analyzed along a 13 km long subreach.
The flow regime and the sediment supply of these rivers have been considerably altered by hydroelectric dams, flow diversions and, along the Piave river, gravel mining. In addiction, river dynamics have been affected by the construction of stream-bank protection structures.
To document these changes, an historical analysis was performed using aerial photographs, cross section survey data and a LiDAR dataset.
Morphological features that were examine included planform configuration, active corridor extension, channel width, channel top depth, flow area, number of channels and bed elevation.
Vegetation features that were examine included, instead, areal island cover extension and different vegetation class extension.
The results indicate as remarkable changes occurred during the study period.
In both river there was a marked tendency to the diminution in the number of channels and in the active corridor extension, just subsequently to the main flood events is possible see an increase in the active corridor extensions.
Along the Piave river was possible see a marked tendency to narrowing and channel incision during the last 80 years.
The island, along both rivers, tend to encroachment and maturation for many years, occupying the active corridor. The island extension could decrease just after considerably flood events (RI > 10 years) or thanks to many close flood events. Regarding islands, has been possible see their tendency to joining with perifluvial vegetation, in consequence of long no-flood periods.Obbiettivo della presente ricerca è quello di eseguire un’analisi di lungo e medio periodo sulla dinamica della morfologia fluviale riguardante fiumi a canali intrecciati a fondo ghiaioso, sottoposti a regolazione dei regimi idrici, come il fiume Piave (Italia) e il fiume Waitaki (Nuova Zelanda). Il fiume Piave (area del bacino di circa 4000 km2), è uno dei principali fiumi del nord-est d’Italia; il tratto analizzato ha una lunghezza di circa 37 km e si trova nella parte centrale del bacino montano. Inoltre, sono stati studiati diversi sottotratti fino ad un minimo di 1.5 km di lunghezza. Il fiume Waitaki (area del bacino di circa 11000 km2) è il più importante fiume delle Nuova Zelanda per valori di portata, scorre dal versante est delle Alpi del Sud dell’isola del Sud della Nuova Zelanda; il tratto analizzato ha una lunghezza di circa 13 km. Il regime delle portate e l’apporto di sedimenti di questi due fiumi sono stati considerevolmente alterati dalla presenza di dighe per la produzione di energia idroelettrica e dalla presenza di opere trasversali e di difesa spondale. Per studiare le variazioni che si sono succedute nel tempo si è eseguita una ricostruzione storica con l’ausilio di fotografie aeree, dati storici di rilievi topografici e un set di dati LiDAR. Le caratteristiche che si sono analizzate sono l’estensione dell’alveo attivo, la larghezza massima dei canali, la profondità massima dei canali, l’area bagnata dei canali, il numero di canali e le caratteristiche altimetriche del letto del fiume. Si sono, anche, condotte analisi sulla variazione e la dinamica della vegetazione presente in alveo, attraverso la misurazione dell’area delle isole fluviali e l’estensione delle diverse tipologie di vegetazione presente nell’area perifluviale. I risultati ottenuti indicano come nel corso degli anni considerati vi siano stati delle variazioni considerevoli. In entrambi i fiumi c’è stata una marcata tendenza alla diminuzione dei numeri di canali e dell’estensione de corridoio attivo, solamente a seguito di eventi di piene rilevanti è stato possibile osservare un aumento dell’estensione del corridoio attivo. Lungo il corso del fiume Piave è stato possibile osservare una marcata tendenza all’incisione del canale durante gli ultimi 80 anni. Le isole fluviali tendono a maturare e stabilizzarsi per molti anni, occupando così il corridoio attivo. L’estensione delle isole diminuisce solamente a seguito di eventi di piena con tempi di ritorno marcati (> 10 anni), oppure a seguito di eventi che si succedono frequentemente, anche se di intensità minore. Infine si è potuto notare una tendenza delle isole fluviali a fondersi con la vegetazione perifluviale circostante, limitando ancor più l’estensione del corridoio attivo.
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Brown, Anthony Alan. "The self-regulation of a gravel river bed subject to upstream sediment supply." Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287564.
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The aims of this work are to improve the understanding of the way in which a river system approaches equilibrium during and after sediment transporting events and by using experimental data and hypothetical models to gain an insight into mixed grain sized transport and its connection with local bed morphology. Large scale flume experiments were undertaken in a trapezoidal channel where a mixed grain sized river bed is subjected to a variety of imposed sediment loads. The river system was allowed to adjust naturally to the imposed conditions while flow and bed conditions were frequently monitored. Changes to both flow and bed occur at many scales and the superimposition of these changes adds to the complexity of the interpretation of hydraulic and bed data. Three experiments are reported in which the sediment influx differ. One in which no material is added. One in which a feed rate is established equal in magnitude to 50% of the initial transport rate for the equivalent non-fed case. In the third experiment the feed rate is doubled to 100% of the initial transport rate in the degradation experiment. The imposed load is continued for approximately 75% of the duration of the run or until a dynamic equilibrium transport rate is evident within the reach. The river channel is analysed at two distinct scales; grain scale and reach scale. Conclusions about the relative influence of grain and form effects are drawn on the basis of detailed surface texture information and reach scale measurements of the bed surface. A hypothetical model is proposed to show that the transport activity during a degradation experiment can be qualitatively linked to a wave like translation of grain dislodgement through the channel.
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Sohag, Mumtaz. "Sediment tracing, bed structure and morphological approaches to sediment transport estimates in a gravel-bed river : the River South Tyne, Northumberland, UK." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358970.
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Stout, Jacob B. "Trout Habitat in an Altered Gravel-Bed River with an Augmented Flow Regime." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7589.
Full textAbstract:
The Diamond Fork River, and it’s tributary Sixth Water Creek, has been highly altered in terms of shape, function, and ecologicaly due to large, trans-basin flows additions to the system for irrigation starting in the early 1900s. Flows were exceptionally large for 80 years, after which they were reduced in 2004. Larger than natural flows during the low flow season were then added to the river in an effort to improve ecosystem health and recreational fishing opportunities. Since the prescription additional flow during low flow seasons, the river channel has undergone further change, most noticeably in the form of narrowing. With the channel change that has occurred over the past decade, it has been suggested that the additional flows, which augment baseflows, are too large and that key habitat elements, particularly pools, are lacking throughout the river.
We evaluated trout habitat throughout the altered reaches of the Diamond Fork River and Sixth Water Creek which are still subject to flow additions. We used a model to estimate the number of fish a reach can support at a given flow in order to evaluate which flow produces the highest quality trout habitat. We found that the current summer baseflows of 80 cfs for the lower Diamond Fork and 32 cfs for Sixth Water Creek are less than desirable and that flows less than 40 cfs for the lower Diamond Fork and flows between 20 cfs and 30 cfs for Sixth Water Creek would increase the quality of trout habitat.
We also evaluated the size and number of pools throughout the system and identified that pools are generally lacking both in size and number relative to standard requirements for trout success. We documented that as the channel narrowed, the number of pools/deep water disappeared. The lack of sediment and the limited number of flows capable of moving sediment were identified as key causes of the channel simplification and loss of pool habitat. Crucial components of future pool formation and maintenance are i) active sediment availability and ii) frequent sediment mobilizing flows. If the baseflow regime were to be lowered, we predict that the channel would narrow, which would increase the effectiveness of floods, increase mobility of sediment, and overall increase pool habitat. This research, as part of a larger, interdisciplinary project, lays the foundation for proposing new flows for the Diamond Fork River that targets ecological goals identified by stakeholders as well as providing information for future habitat restoration projects.
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Lane, Stuart Nicholas. "Monitoring and modelling morphology, flow and sediment transport in a gravel-bed stream." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336765.
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Frings, Roy. "From gravel to sand : downstream fining of bed sediments in the lower river Rhine /." Utrecht : Koninklijk Nederlands Aardrijkskundig Genootschap, Faculteit Geowetenschappen, Universiteit Utrecht, 2007. http://www.loc.gov/catdir/toc/fy0804/2008400397.html.
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Petrie, John Eric. "The Accuracy of River Bed Sediment Samples." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/30957.
Full textAbstract:
One of the most important factors that influences a stream's hydraulic and ecological health is the streambed's sediment size distribution. This distribution affects streambed stability, sediment transport rates, and flood levels by defining the roughness of the stream channel. Adverse effects on water quality and wildlife can be expected when excessive fine sediments enter a stream. Many chemicals and toxic materials are transported through streams by binding to fine sediments. Increases in fine sediments also seriously impact the survival of fish species present in the stream. Fine sediments fill tiny spaces between larger particles thereby denying fish embryos the necessary fresh water to survive. Reforestation, constructed wetlands, and slope stabilization are a few management practices typically utilized to reduce the amount of sediment entering a stream. To effectively gauge the success of these techniques, the sediment size distribution of the stream must be monitored.
Gravel bed streams are typically stratified vertically, in terms of particle size, in three layers, with each layer having its own distinct grain size distribution. The top two layers of the stream bed, the pavement and subpavement, are the most significant in determining the characteristics of the stream. These top two layers are only as thick as the largest particle size contained within each layer. This vertical stratification by particle size makes it difficult to characterize the grain size distribution of the surface layer. The traditional bulk or volume sampling procedure removes a specified volume of material from the stream bed. However, if the bed exhibits vertical stratification, the volume sample will mix different populations, resulting in inaccurate sample results. To obtain accurate results for the pavement size distribution, a surface oriented sampling technique must be employed. The most common types of surface oriented sampling are grid and areal sampling. Due to limitations in the sampling techniques, grid samples typically truncate the sample at the finer grain sizes, while areal samples typically truncate the sample at the coarser grain sizes. When combined with an analysis technique, either frequency-by-number or frequency-by-weight, the sample results can be represented in terms of a cumulative grain size distribution. However, the results of different sampling and analysis procedures can lead to biased results, which are not equivalent to traditional volume sampling results. Different conversions, dependent on both the sampling and analysis technique, are employed to remove the bias from surface sample results.
The topic of the present study is to determine the accuracy of sediment samples obtained by the different sampling techniques. Knowing the accuracy of a sample is imperative if the sample results are to be meaningful. Different methods are discussed for placing confidence intervals on grid sample results based on statistical distributions. The binomial distribution and its approximation with the normal distribution have been suggested for these confidence intervals in previous studies. In this study, the use of the multinomial distribution for these confidence intervals is also explored. The multinomial distribution seems to best represent the grid sampling process. Based on analyses of the different distributions, recommendations are made. Additionally, figures are given to estimate the grid sample size necessary to achieve a required accuracy for each distribution. This type of sample size determination figure is extremely useful when preparing for grid sampling in the field.
Accuracy and sample size determination for areal and volume samples present difficulties not encountered with grid sampling. The variability in number of particles contained in the sample coupled with the wide range of particle sizes present make direct statistical analysis impossible. Limited studies have been reported on the necessary volume to sample for gravel deposits. The majority of these studies make recommendations based on empirical results that may not be applicable to different size distributions. Even fewer studies have been published that address the issue of areal sample size. However, using grid sample results as a basis, a technique is presented to estimate the necessary sizes for areal and volume samples. These areal and volume sample sizes are designed to match the accuracy of the original grid sample for a specified grain size percentile of interest. Obtaining grid and areal results with the same accuracy can be useful when considering hybrid samples. A hybrid sample represents a combination of grid and areal sample results that give a final grain size distribution curve that is not truncated. Laboratory experiments were performed on synthetic stream beds to test these theories. The synthetic stream beds were created using both glass beads and natural sediments. Reducing sampling errors and obtaining accurate samples in the field are also briefly discussed. Additionally, recommendations are also made for using the most efficient sampling technique to achieve the required accuracy.Master of Science
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Rempel, Laura L. "Physical and ecological organization in a large, gravel-bed river and response to disturbance." Thesis, University of British Columbia, 2004. http://hdl.handle.net/2429/37993.
Full textAbstract:
Along the 80-km gravel reach between Hope and Mission, Fraser River has a wandering
morphology that includes secondary channels, gravel bars, and islands that together support a diverse
and productive ecosystem. The wandering morphology is produced, in part, by annual sediment
deposition within the reach. Sediment deposition, however, is perceived as a threat to flood security
and gravel mining is proposed as a profitable solution to flood risk. This thesis presents a hierarchical
habitat classification for the gravel reach, which provided a spatial framework to, first, examine
habitat associations of benthic invertebrates and fish and, second, evaluate the physical and ecological
responses to habitat disturbance by gravel mining.
At the highest level of the classification, the river is divided into 5 sub-reaches (104 m scale)
that vary in morphological expression and sediment gradational tendency. The intermediate level
specifies gravel bar units (103 m scale) each consisting of a riffle, gravel bar, and adjacent pool.
Nested within gravel bars are physically distinct habitat units, which represent the finest level of the
classification (101- 102 m scale). Results demonstrated that the assemblages of invertebrates and fish
associated with habitats are moderately distinct and differentiated along a hydraulic gradient
corresponding to velocity. However, the congruence between habitat structure and the structure of
aquatic communities was weakened by large spatial and temporal variability in the distribution and
abundances of many species. This variability was predicted to afford the invertebrate and fish
community resilience to physical disturbance.
The second component of this study examined the effect of disturbance by gravel mining
from an exposed bar in 2000. Physical changes immediately after mining were substantial as the pre
existing cobble surface was replaced by loose gravel and sand. Two subsequent freshets transformed
the site into a topographically complex area with similar substrate texture as before mining, although
sediment replenishment to the site was negligible. Habitat availability at flows <3000 m3 s-1
increased and habitat quality was comparable with reference sites. A third above-average freshet
replenished 31% of the removal volume and restored average bar surface elevation to within 9 cm of
the pre-scalped surface. Physical changes elicited a significant reduction in invertebrate density
immediately after mining, however, the impact lasted less than one freshet cycle. No change in fish
density as a result of mining was found, although statistical power to detect an impact was low and
fish sampling was carried out at flows <5700 m3 s-1. These results support the expectation that the
invertebrate and fish community in the gravel reach has resilience to disturbance from a single gravel
removal provided that site recovery by way of sediment transport and replenishment occurs.Arts, Faculty of
Geography, Department of
Graduate
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Butler, Justin Barrie. "High resolution photogrammetric monitoring and analysis of the structure of gravel-bed river surfaces." Thesis, University of Cambridge, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368098.
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Oakey, Robert James. "The use of tracers to determine coarse-bedload transport in a gravel-bed river." Thesis, Lancaster University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414592.
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Waterhouse, Emma Kate. "Interactions between coarse sediment transfer, channel change, river engineering and flood risk in an upland gravel-bed river." Thesis, Durham University, 2008. http://etheses.dur.ac.uk/2056/.
Full textAbstract:
Coarse sediment transfer in upland gravel-bed river systems is often neglected in the design and operation of river management schemes. Yet, it is increasingly attributed to problems within upland environments including bank erosion and enhanced flood risk. Developing a sufficient understanding of coarse sediment transfer and channel change requires strategic field monitoring. Predicting future channel change and flood risk under varying management options requires numerical modelling. This thesis employs a combined field monitoring and numerical modelling approach to explore the relationship between coarse sediment transfer, lateral channel change, river engineering and flood risk. Intensive field monitoring is used to understand sediment transfer and channel change. Methods include repeat cross-sectional resurvey, bank erosion pins and bank-top surveys, and sediment impact sensors. These data are used to illustrate the spatial and temporal variability of in-channel sedimentation and rates and mechanisms of bank erosion. When analysed further, these data explain patterns of sedimentation and demonstrate implications of coarse sediment accumulation for flood risk. The data are then used in the development and application of a quasi two-dimensional model of channel change. The model couples a one-dimensional sediment routing model with a lateral adjustment component to simulate patterns of downstream fining alongside vertical and lateral channel changes. By using a split channel approach, asymmetrical width adjustments are simulated based on critical shear stress thresholds. Lateral differences in bed elevation and curvature are used to distribute shear stress across the channel. Simulations are run to explore scenarios including changing the flow regime, removing bank protection and implementing a river engineering scheme on a reach with high sedimentation and bank erosion problems. The results highlight the potential impact that poor river management can have on upland rivers, demonstrating enhanced bank erosion upstream and greater sedimentation downstream of the engineered reach. The accumulation of sediment results in increased flood risk.
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Parsons, Helena. "An analysis of landscape diversity on the floodplain of a Scottish wandering gravel-bed river." Thesis, University of Stirling, 2000. http://hdl.handle.net/1893/1222.
Full textAbstract:
This thesis examines landscape diversity within alluvial valley floors using the case study of a Scottish wandering gravel-bed river. The thesis aims are two-fold; firstly to investigate the spatial and temporal patterns of valley floor landscape diversity within semi-natural environments, and secondly to develop a methodology for quantifying alluvial valley floor landscape diversity in space and time. The diversity analysis involves quantifying the spatial patterns of geo-, pedo- and biodiversity (flora) within floodplain zones which have been exposed to approximately 100 years of recovery since flood embankment abandonment along the most active reaches of the river. In addition historical records including aerial photographs, maps and narrative accounts were used to assess the temporal patterns of the diversity of landscape patches and how they have changed through time using a series of landscape indices. The analysis thus accounts for the role of river channel change in producing a complex mosaic of land cover types within alluvial valley floors. The spatial analysis revealed that landscape diversity tends to be greater in the perpendicular orientation to the main channel, i.e. along an aquatic-to-terrestrial environmental gradient. The temporal analysis results revealed that the landscape over the last 50 years has changed from being dominated by few relatively large isodiametric patches to a landscape dominated by small irregular shaped patches. Thus although landscape patch richness has increased along with an increase in land cover types through time, the landscape patches have also become more fragmented. The major outcomes of the research are the deriving of quantitative results of the spatial and temporal patterns of floodplain landscape diversity, an evaluation of the role of channel dynamics in creating the diverse mosaic of land cover types, the identification of the environmental controls and supporting floodplain habitats of a number of rare species and a proposed methodology for assessing landscape diversity to be validated on other river systems.
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Wathen, Simon John. "The effect of storage upon sediment transfer processes in a small Scottish gravel-bed river." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/3844.
Full textAbstract:
A detailed morphological approach is used to determine the effect of storage location upon sediment mobility, providing partial explanation for previously reported non systematic characteristics of sediment transfer. Data were collected over a period of 2 years from a small river in the Highlands of Scotland. Sediment transfer fluxes and volumetric storage were measured using an integrated data collection programme utilising 990 magnetic tracers and 225 cross sections spaced at c1 m intervals over two contrasting reaches (A and B). Scaled tracer fluxes were monitored between 6 numerically defined storage types (very active, active, semi active, stable, inactive and dormant). Storage characteristics were determined using response time, defined as the time at which cumulative output from a store exceeds sediment in storage. Activity progressively declined from very active to inactive stores, the exact magnitude being a function of local morphology, particularly the presence of fixed bars. Inter store exchanges of sediment were assessed using descriptive matrices categorised into individual types according to transfer and storage proportions. A relative dimensionless shear stress scale used to differentiate the storage conditions responsible for the occurrence of each matrix type indicated that transfer in reach A is a function of hydraulic conditions, grain size and storage, in reach B grain size is the only dominant factor. These controlling factors were subdivided into peak stage, duration, relative and absolute grain size, morphology and burial and assessed with reference to fractional transfer distances. The relative importance of each factor to transfer depends upon storage location and the incidence of morphological change. Comparison between tracer and volumetric fluxes provides explanation for sediment transfer distributions and allows assessment of morphological controls upon channel pattern maintenance. The results from this study were summarised in two conceptual models describing downstream and within reach sediment transfer.
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Shintani, Christina. "Comparing Photogrammetric and Spectral Depth Techniques in Extracting Bathymetric Data from a Gravel-Bed River." Thesis, University of Oregon, 2016. http://hdl.handle.net/1794/20517.
Full textAbstract:
Recent advances in through-water photogrammetry and optical imagery indicate that accurate, continuous bathymetric mapping may be possible in shallow, clear streams. This research directly compares the ability of through-water photogrammetry and spectral depth approaches to extract water depth for monitoring fish habitat. Imagery and cross sections were collected on a 140 meter reach of the Salmon River, Oregon, using an unmanned aerial vehicle (UAV) and rtk-GPS. Structure-from-Motion (SfM) software produced a digital elevation model (DEM) (1.5 cm) and orthophoto (0.37 cm). The photogrammetric approach of applying a site-specific refractive index provided the most accurate (mean error 0.009 m) and precise (standard deviation of error 0.17 m) bathymetric data (R2 = 0.67) over the spectral depth and the 1.34 refractive index approaches. This research provides a quantitative comparison between and within bathymetric mapping methods, and suggests that a site-specific refractive index may be appropriate for similar gravel-bed, relatively shallow, clear streams.
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Srymanske, Roy H. "When Does A Stream Gain The Ability To Create Its Own Channel? A Field Study In Northwest Georgia On The Conasauga River." Digital Archive @ GSU, 2013. http://digitalarchive.gsu.edu/geosciences_theses/57.
Full textAbstract:
Rivers are said to be self-shaping when a stream is able to create its own morphological features. This occurs when bankfull Shields stress (τbf*) is greater than reference Shields stress (τr*). Shields stress in the channel is affected during upstream progression by the height and width of the water decreasing, the slope becoming steeper, and the bed material becoming coarser. Bankfull Shields stress decreased progressing upstream while reference Shields stress increased due to increased slope. The self-shaping portions of the Conasauga occur in areas where the relative roughness of the bed material is fully submerged or greater than 5. Once the relative submergence is no longer fully submerged the stream channel no longer produces enough bankfull Shields stress to overcome the reference Shields stress. This occurs about midway through the study. This study allows better classification of streams using Shields stress and better understanding of channel processes for hydrologic engineering.
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Ashley, William F. "Large-scale coherent flow structures in a natural braided reach section of a gravel-bed river." Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5674.
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Emery, Joanne Claire. "Characteristics and controls of gravel-bed riffle-pool sequences for habitat assessment and river rehabilitation design." Thesis, University of Birmingham, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410577.
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Walther, Suzanne Corinna. "Remote measurement of gravel-bed river depths and analysis of the geomorphic response of rivers to canals and small dams." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/11069.
Full textAbstract:
xviii, 128 p. : ill. (some col.)This dissertation investigates the potential impacts of canals and small dams on gravel-bed rivers and methods for documenting those impacts. First, I evaluate the potential for mapping channel depths along the McKenzie River, OR, using 10 cm resolution optical aerial imagery with a hydraulically-assisted bathymetry (HAB-2) model. Results demonstrate that channel depths can be accurately mapped in many areas, with some imagery limitations. The HAB-2 model works well in the majority of the river (R 2 =0.89) when comparing modeled to observed depths, but not in areas of shadow, surface turbulence, or depths >1.5 m. Next, I analyze the relative effects of a small dam and two diversion canals on sediment distribution along bars of the lower McKenzie River. The typical pattern of downstream fining is disrupted at each feature and several tributaries, particularly in the "reduced water reaches" below canal outtakes. Most modeled discharge values necessary to mobilize bar sediments fall at or below the 2-year flood return interval, with the remaining at or below the 5-year flood return interval, generally reflecting the D 50 values at each bar (20-115 mm). The third analysis investigates the potential to document geomorphic impacts of small dams in Oregon at ecoregion extents using air photos and publically available data sets. This analysis highlights data disparity with respect to the collecting agency's mission and the difficulty of using remote sensing for small dams. Though the imagery was not useful in evaluating small dam impacts due to resolution and feature size, the data were useful in mapping the small dam distribution across Oregon and each ecoregion. Sixty-one percent of Oregon land is located in the catchment of at least one small dam and the greatest number of dams per area is in the Willamette Valley ecoregion. Overall, this research suggests that, while the application of these techniques must be improved, our ability to observe, study, and understand rivers is enhanced by remote sensing advancements and the combined use of these methods in river restoration and management. This dissertation includes previously published and co-authored material.
Committee in charge: W. Andrew Marcus, Chairperson; Patricia F. McDowell, Member; Dan G. Gavin, Member; David W. Hulse, Outside Member
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Brenna, Andrea. "Estimate of bed material transport in large gravel-bed rivers using the virtual velocity approach and the morphological method." Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425899.
Full textAbstract:
Estimating the bed material transport in large gravel-bed rivers represents a challenging task. Among the alternatives to achieve estimates of such key process, the virtual velocity approach represents one of the most promising possibilities. The research aims at improving the virtual velocity approach and at evaluating the reliability of its transport estimates using an independent and robust procedure as the morphological method applied at the same dam-regulated study sector of the Parma River (Italy). After field and remote sensing data collection, we performed the coarse sediment transport calculations using the two selected approaches and compared the estimates obtained at the same river cross-sections. Since the two methods provided remarkably similar transport results over the period April 2016 - April 2017, the virtual velocity approach can be considered as a viable tool for achieving reliable bed material load estimates in large gravel-bed rivers.La stima del trasporto del materiale grossolano costituente il letto dei corsi d’acqua ghiaiosi di grandi dimensioni rappresenta un’attività complessa. Fra le diverse possibilità per conseguire tale obiettivo il metodo della “velocità virtuale” costituisce una delle opzioni più promettenti. Il presente lavoro di ricerca mira al miglioramento di tale approccio e alla valutazione dell’affidabilità delle stime da esso fornite utilizzando quale termine di confronto i risultati forniti dall'applicazione di un robusto “metodo morfologico” applicando entrambi le metodologie al medesimo settore studio posto a valle di una diga che regola il flusso del Torrente Parma (Italia). A seguito della raccolta di dati in campo e attraverso tecniche di telerilevamento è stato eseguito il calcolo del trasporto solido grossolano mediante le due metodologie selezionate e sono state confrontate le stime ottenute in corrispondenza di quattro sezioni-studio. I risultati ottenuti risultano essere significativamente simili per il periodo Aprile 2016 - Aprile 2017, permettendo di concludere che il metodo della velocità virtuale rappresenta un’alternativa affidabile per stimare il trasporto solido grossolano in corsi d’acqua ghiaiosi di grandi dimensioni.
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Powell, Rebecca. "Geomorphological connectivity and sensitivity examined in a recently degraded gravel-bed stream: implications for river-floodplain rehabilitation." Thesis, Rhodes University, 2017. http://hdl.handle.net/10962/53722.
Full textAbstract:
The study of river complexity and sensitivity to future human land-use activities and climate change is a fast growing field within the discipline of fluvial geomorphology. Associated with this is a need to improve river rehabilitation and catchment management approach, design and effectiveness. This study aimed to investigate drivers of the recent geomorphological sensitivity of the Baviaanskloof River-floodplain, an upland system in South Africa, by integrating the concepts of geomorphological connectivity and Panarchy. The understanding generated was used to evaluate the approach of the State agency, Working for Wetlands (WfWet), to river-floodplain rehabilitation in the catchment.The concepts of geomorphological connectivity and Panarchy provide useful frameworks for understanding interactions between geomorphological processes and structure across scales of space and time. Geomorphological connectivity explains the degree to which water and sediment is linked in a river landscape, determined by the distribution of erosional and depositional landforms (Brierley et al. 2006; Fryirs et al. 2007a; Fryirs et al. 2007b). Panarchy attempts to explain lagged response to disturbances, non-linear interactions, and sudden shifts in system state, and has been applied largely to ecological systems. Panarchy theory, when combined with the concept of geomorphological connectivity, provides a guiding framework for understanding river complexity in greater depth. The first results chapter of this study investigated river long-term and recent geomorphological history, towards understanding the nature and timing of river geomorphological cycling between erosion and deposition. Optically Stimulated Luminescence dating of alluvial fan and floodplain sedimentary units was conducted, for analysis of river-floodplain long-term history (100s to 1 000s of years). Interviews with 11 local landowners, combined with analysis of historic aerial imagery and river-floodplain topographic surveys, provided a means of describing recent (last few decades) geomorphological dynamics. The results indicated that the Baviaanskloof is naturally a cut- and-fill landscape over scales of several hundred to thousands of years, characterized by the alternation between phases of high fluvial energy and alluvial fan expansion, and low energy conditions associated with floodplain accretion. Recent and widespread river-floodplain degradation was compressed into a short period of approximately 30 years, suggesting that one or more drivers have pushed the system beyond a threshold, resulting in increased water and sediment connectivity. The second results chapter investigated the role of human land-use activities and flooding frequency and magnitude, as drivers of recent river-floodplain degradation. Human impacts were investigated by describing land-use activities for the preceding 80 years, and relating these activities to changes in river-floodplain form and behavior. Temporal trends in flood events of different frequency and magnitude were investigated by analyzing rainfall data, integrated with landowner reports of flood-inducing rainfall magnitudes. The findings indicated that human land-use activities have been an important driver of recent river- floodplain degradation, through the enhancement of water and sediment connectivity across spatial scales of the catchment. Episodic and high magnitude floods synergized with human driven increased connectivity, precipitating stream power and geomorphological threshold breaches, resulting in a shift in river behaviour. The third results chapter investigated the influence of tributary-junction streams and fans on the geomorphological form, behavior and sensitivity of the Baviaanskloof River. Local- scale topographic impacts of tributary fans and streams were described using topographic surveys and geomorphological mapping techniques. Tributary streams form a major control on the behaviour of the river, by influencing the degree of coarse sediment connectivity with the main channel. Although tributary fans buffer the river from disturbances occurring in the wider catchment, they initiate topographic variations along the floodplain, influencing local-scale patterns of deposition and erosion along the river. The main river responds to water and sediment inputs from tributary junction streams by locally adjusting longitudinal slope, maintaining an overall constant slope of 0.0066 m/m. The response of the Baviaanskloof River to tributary junction fans and streams is however variable, and is fashioned by complex interactions between geomorphological and anthropogenic factors. The final two chapters of the thesis evaluate the findings of the study within the context of river-floodplain rehabilitation approaches in South Africa, and within the theoretical, philosophical and methodological context of the research. The first of these two chapters evaluates the approach of the WfWet programme to river-floodplain rehabilitation in the Baviaanskloof. The chapter indicates that the present practice of WfWet is to reinstate a pre-degradation state, which is not suited to the Baviaanskloof River-floodplain, since the river-floodplain has passed a geomorphological threshold, resulting in a new set of interacting processes and landforms. The author presents a conceptual model illustrating the existence of geomorphological adaptive cycles interacting across spatial and temporal scales, thereby attempting to explain a river Panarchy specific to the Baviaanskloof. From this conceptual model, a hierarchical rehabilitation framework, targeting geomorphological processes and structure situated at different spatial and temporal scales of the landscape is suggested. The final chapter discusses the implications of integrating the concepts of geomorphological connectivity and river Panarchy theory in studies of river complexity and sensitivity to geomorphological change. The author suggests that there is scope for further investigation of the application of the two concepts within the discipline of fluvial geomorphology, particularly with regard to developing quantitative approaches to measuring and describing connectivity and Panarchy.
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Pledger, Andrew G. "Foraging fish as zoogeomorphic agents : their effects on the structure and composition of gravel-bed river sediments with implications for bed material transport." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/16680.
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The plants and animals that inhabit river channels may act as zoogeomorphic agents affecting the nature and rates of sediment recruitment, transport and deposition. The impact of benthic-feeding fish, which disturb bed material sediments during their search for food, has received little attention, even though benthic feeding species are widespread in rivers and may collectively expend significant amounts of energy foraging across the bed. A series of experiments were conducted to investigate the impacts of benthic feeding fish on the structure and composition of gravel-bed river sediments, and the implications for bed material transport. An ex-situ experiment was conducted to investigate the impact of a benthic feeding fish (European Barbel Barbus barbus) on particle displacements, bed sediment structures, gravel entrainment and transport fluxes. In a laboratory flume, changes in bed surface topography were measured and grain displacements examined when an imbricated, water-worked bed of 5.6-16 mm gravels was exposed to feeding juvenile Barbel. For substrates that had been exposed to feeding fish and control substrates which had not, grain entrainment rates and bedload fluxes were measured under a moderate transport regime. On average, approximately 37% of the substrate, by area, was modified by foraging fish during a four-hour treatment period, resulting in increased microtopographic roughness and reduced particle imbrication. Structural changes caused by fish increased bed load flux by 60% under entrainment flows, whilst on average the total number of grains transported during the entrainment phase was 82% higher from substrates that had been disturbed by Barbel. An ex-situ experiment utilising Barbel and Chub Leuciscus cephalus extended this initial study by considering the role of fish size and species as controls of sediment disturbance by foraging. Increasing the size of Barbel had a significant effect on measured disturbance and bedload transport. Specifically, the area of disturbed substrate, foraging depth, microtopographic roughness and sediment structure all increased as functions of fish size, as did bedload flux and total transported mass. In a comparison of the foraging effects of like-sized Barbel and Chub 8-10 in length, Barbel foraged a larger area of the riverbed and had a greater impact on microtopographic roughness and sediment structure. Foraging by both species was associated with increased sediment transport, but the bed load flux after foraging by Barbel was 150% higher than that following foraging by Chub and the total transported mass of sediment was 98% greater. An in-situ experiment quantified the effects of foraging fish, primarily Cyprinids (specifically Barbel and Chub), on gravel-river bed sediment structures, surface grain-size distributions, sediment transport fluxes and grain entrainment in the River Idle, Nottinghamshire, UK. This was achieved by installing large experimental sediment trays seeded with food at typical densities. The experiments yielded data about 1) topographic and structural differences between pre- and post-feeding substrates using DEMs interpolated from laser scans, 2) modifications to surface and sub-surface grain-size distributions as a function of fish foraging and 3) differences in sediment entrainment from water-worked substrates exposed to feeding fish and control substrates, without fish. Small sections of the substrate trays were recovered in tact from the field and for substrates that had been exposed to feeding fish and control substrates which had not, grain entrainment rates and bedload fluxes were measured under a moderate transport regime in the laboratory. On average, approximately 74% of the substrate, by area, was modified by foraging fish during a twelve-hour period, resulting in increased microtopographic roughness and substrate coarsening which had significant implications for bed material transport during the steady entrainment flow. Together, results from these experiments indicate that by increasing surface microtopography, modifying the composition of fluvial substrates and undoing the naturally stable structures produced by water working, foraging can influence sediment transport dynamics, predominately by increasing the mobility of river bed materials. The implication of this result is that by influencing the quantity of available, transportable sediment and entrainment thresholds, benthic feeding may affect sediment transport fluxes in gravel-bed rivers. In addition, three discrete studies were performed alongside the core experiments described above. A quantitative examination of habitat conditions favoured by feeding Barbel was conducted in the River Idle (Nottinghamshire, UK) which served to supplement existing literature pertaining to Barbel ecology, and inform experimental design during the core experiments. Two further studies considered the potential importance of foraging as a zoogeomorphic activity in terms of spatial extent, at a variety of scales, thereby extending core experiments to larger spatial scales in-situ.
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Latulippe, Christian. "Morpho-sedimentary dynamics of pool-riffle sequences in a gravel-bed river : bedload transport reversal and pool-riffle maintenance." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=102671.
Full textAbstract:
Hydraulic and morpho-sedimentary differences between pools and riffles have always intrigued fluvial geomorphologists. Surprisingly, earlier explanations of pool-riffle morpho-sedimentology dynamic focus too exclusively on hydraulic patterns and neglect analysis of sediment transport. Understanding the mechanisms governing pool-riffle morpho-sedimentary dynamics, such as the sediment transport patterns represent a big challenge in fluvial geomorphology, considering the stochastic nature of bedload transport in gravel-bed rivers. The main objective of this thesis is to understand the two-dimensional relationship between hydraulic patterns, sediment transport patterns and morpho-sedimentary changes in pool-riffle sequences and to use these insights to understand how pool-riffle sequences maintain their form over time.This thesis is organized into four chapters. These chapters analyze hydraulic, sediment transport and morpho-sedimentary measurements collected on a riffle-pool-riffle sequence of the Des Coeurs river during seven controlled experimental floods. Chapter 2 tests the velocity reversal hypothesis (Keller, 1971), with results demonstrating that no velocity reversal was observed in the field, for peak flow up to 123% of the bankfull discharge. Chapter 3 demonstrates the existence of a bedload transport reversal: below 60% of bankfull discharge, sediment transport on the riffle exceeds transport in the pool; as discharge increased, more sediment was exported from the pool than imported, thereby maintaining the pool. Chapter 4 demonstrates that the bedload transport reversal is caused by the spatial heterogeneity of the sediment transport patterns (sediment supply, particle displacements and sediment sorting), which underlies the importance of developing two-dimensional bedload transport formulae. Chapter 5 tests the two-dimensional applicability of well-known bedload transport formulae developed in a one-dimensional environment. None of the formulae could be applied with accuracy in a two-dimensional environment. However, site-specific calibration considerably improves bedload transport rate and grain-size distribution prediction.
This thesis improves the understanding of the morpho-sedimentary dynamics of pool-riffle sequence; it argues that a purely hydraulic view of pool-riffle sequence is insufficient to understand their stability. It explains pool-riffle maintenance as a result of a bedload transport reversal caused by the spatial heterogeneity of the sediment transport patterns, and raises the importance of acquiring two-dimensional sediment transport data to improve two-dimensional bedload transport formulae.
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Payne, Brigid. "Lateral instability and its effect on Atlantic salmon (Salmo salar) habitat in the wandering gravel-bed Rivière Nouvelle, Baie des Chaleurs, Québec." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23930.
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Lateral instability exerts considerable influence on the sedimentology, planform, and hydraulic characteristics of gravel-bed rivers. Because Atlantic salmon (Salmo salar) tolerate a narrow range of depths, velocities and substrate sizes, the quality and quantity of habitat available to salmon should vary with level of river instability. In the Riviere Nouvelle, a Gaspe river destabilized by deforestation and past channelization projects, the effect of lateral instability on habitat was variable. Fines content in riffle substrates did not show a significant relationship to local bank erosion rates, even where the rate was as high as 10 myr$ sp{-1}$ and the proportion of fines entering the channel was much higher than that found in riffles substrates (an excess of fines in potential spawning riffles reduces spawning success among salmonids). For juveniles, availability of hydraulically suitable habitat was largest where lateral instability resulted in aggradation of the river bed and development of a braided pattern. Hydraulic habitat availability was lowest where erosion patterns led to high planform curvature levels and to scouring of bed materials. In general, because of the relatively high power of the Riviere Nouvelle, structures or processes leading to diminishment of depths or velocities (e.g. aggradation) resulted in an increase in the amount of juvenile habitat available.
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Skalak, Katherine Joanne. "Fine-grained channel margin deposits in a typical gravel bed river spatial and temporal controls on the distribution, quantity, and residence time and implications for centennial-scale sediment and mercury cycling /." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 437 p, 2009. http://proquest.umi.com/pqdweb?did=1885693201&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Wishart, Duncan. "A combined catchment and reach-based assessment of historical channel planform change in a UK upland gravel-bed river." Thesis, Durham University, 2004. http://etheses.dur.ac.uk/2819/.
Full textAbstract:
River channel planform change in upland gravel-bed rivers has consequences for riparian land use, river habitats and flood hazards. Channel planform is predominantly determined by the balance between sediment supply and prevailing discharge regime which is governed by climate and land use, and anthropogenic channel modification. While the nature of channel response to individual factors is in some cases well documented, the complex interaction of theses variables and their relative significance requires further evaluation. This study assesses the nature and extent of historic (1856-1991) channel planform change in the upland catchment of the River Wear, Northern England. A nested research strategy is adopted consisting of catchment wide and reach-scale evaluations of channel planform change using archival maps and aerial photographs. The cause of channel changes is considered with reference to hydrological records (1800-present), catchment land use (metal mining) and accounts of river channel modification (gravel extraction). Comparative historic (reach-scale) and contemporary (trunk channel) data is provided from the upper reaches of the River Tees in Teesdale, Northern England. In the mid nineteenth century a pulse of sedimentation migrated through the upper Wear catchment resulting in the development of eight major sedimentation zones with channel braiding separated by confined single thread reaches. Increased sedimentation was related to a combination of high magnitude floods during the nineteenth century and enhanced sediment supply from extensive metal mining in tributary streams. A decline in flood frequency and magnitude coupled with the cessation of metal mining during the early twentieth century, led to a reduction of sediment supply and lateral channel instability in the catchment. This promoted gravel bar stabilisation through vegetation colonisation, reducing average channel width by 56%. In the sedimentation zones, gravel bar extent declined by up to 87% and this was accompanied by a change to a single thread planform. Gravel extraction operations during the mid-twentieth century lead to local instability and delayed the decline in gravel bar area. In contrast the contemporary channel of the upper Tees is still characterised by localised channel division, around both active gravel bars and vegetated islands. Differences between the two catchments demonstrate the importance of catchment specific controls such as bedrock control and anthropogenic channel interference. A large flood on 30 July 2002 provided significant insight into the mechanism of channel planform change. Substantial increases in gravel bar extents were recorded together with localised changes in flow routing. While local controls such as gravel extraction are significant over decadal time scales, catchment scale controls, primarily changes in the frequency of large floods; determine channel planform over centennial timescales. In order to discriminate ― between local and catchment controls, catchment wide assessments are required.
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Liu, Youcun. "Study on mass transport and hydraulics of gravel bed stream in a high mountain, the Urumqi River (Chinese Tianshan)." Paris, Institut de physique du globe, 2008. http://www.theses.fr/2008GLOB0008.
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Au cours des trois dernières décennies, les questions liées au transport des sédiments et la structure lit des rivières ont reçu une attention considérable. Les lois de l'écoulement et du mouvement des sédiments dans une rivière un lit de gravier sont un objectif important de recherche car ils permettent de caractériser la dynamique des flux de matière et l'évolution du lit d'une rivière. Un suivi in situ sur la rivière Urumqi (rivière à lit de gravier du nord-ouest de la Chine) a été réalisé de l'année 2004 à 2006. Les données acquises nous permettent la réalisation d'important progrès dans notre connaissance de la structure du lit et la dynamique précise de la charge de fond. Nous montrons que le protocole d'échantillonnage est d'une importance cruciale lorsqu'il s'agit de transport de sédiments en général et de charge de fond en particulier. Les données de terrain de grande envergure a été recueillies sur une gamme relativement étendue de débit,charriage et des conditions de pente du chenal. Ces données ont fourni l'occasion d'aller au delà des limites imposées par les corrélations classiques contrainte de cisaillement versus charge de fond, et nous a permis d'examiner en détail le comportement local du flux de gravier. La variation à court terme des taux de transport a été en outre étudiée. Une équation asymptotique "simple" de charriage est proposée, qui simplifie considérablement l'analyse de la charge de fond et ce malgré une structure de lit et une distribution granulométrique comple
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Mayoral, Helen. "Particle Size, Critical Shear Stress, and Benthic Invertebrate Distribution and Abundance in a Gravel-bed River of the Southern Appalachians." Digital Archive @ GSU, 2011. http://digitalarchive.gsu.edu/geosciences_theses/31.
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To determine the relationship between the abundance and density of benthic invertebrates, and the critical shear stress of individual grain sizes, a reach along Smith Creek, was divided into ten 2m x 2m quadrants. Within each quadrant, five randomly selected clasts for each grain size ranging from 2.26 to 25.6 cm were cleaned for benthic invertebrates. Wolman pebble counts for each quadrant were also conducted and used to determine the critical Shields stress per grain size fraction from the model given by Wiberg and Smith (1987) that explicitly accounts for particle hiding/sheltering effects in mixed-bed rivers. Particle entrainment values were then compared with estimated bankfull Shields stress values to determine sediment transport potential during bankfull flow. Invertebrate abundance was strongly positively correlated with critical Shields stress up to the 18.0 cm grain size, indicating a preference for certain grain sizes; while density was positively correlated with all grain sizes present.
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Rose, Teresa, and n/a. "AN INTERDISCIPLINARY STUDY INTO THE IMPACTS OF FLOW REGULATION ON AN UPLAND GRAVEL BED RIVERINE ENVIRONMENT: A TRIBUTARY CONFLUENCE IN THE SNOWY RIVER DOWNSTREAM OF JINDABYNE DAM, AUSTRALIA." University of Canberra. Cooperative Research Centre for Freshwater Ecology, 1999. http://erl.canberra.edu.au./public/adt-AUC20080917.153237.
Full textAbstract:
Inter-Basin-Water Transfers significantly reduce flow and sediment regimes to the
downstream ecosystem effecting differential channel adjustment at various locations. It
is not known how macroinvertebrates adjust to flow regulation, either spatially or
temporally, because research is lacking into how morphological adjustment affects
benthic habitat. Feedback mechanisms that initiate the adjustment process must first be
identified, then the effect on benthic habitat becomes apparent, thus, providing a link to
macroinvertebrate response.
Since regulation there has been a 95% reduction in flow volume, a complete downward
shift in both the flow duration and flood frequency curves and a 194% increase in flow
constancy compared to the pre- dam period. Furthermore, Jindabyne Dam traps 99.9%
of the total incoming sediment load.
Upstream of the tributary the dominant river response was accommodation adjustment
with subsequent contraction of the river channel. Associated feedback mechanisms
were ?armouring? and vegetation encroachment. Downstream of the tributary response
was more complex, with channel contraction through aggradation and specifically the
formation of a tributary mouth bar and fan, mid channel lobate bar, transverse bar and
in-channel bench. Associated feedback mechanisms were interactions between
vegetation and sediment; channel morphology, flow and sediment distribution; and
sediment distribution, flow and channel morphology. These processes have had site
specific and reach scale impacts on benthic habitat.
Macroinvertebrate response to flow regulation was habitat specific (riffle or edge) and
seemed to correspond to either site, or reach scale morphological adjustment, whereas,
flow constancy seemed to affect edge macroinvertebrates throughout both reaches.
Spatially, macroinvertebrates have not adjusted to the post- dam flow regime and
temporally, macroinvertebrates have not recovered 30 years after the closure of
Jindabyne Dam. How physical processes change habitats and how these impact on a
river?s ecology and at what scale, are important considerations in river management.
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Luce, James John. "Investigating the impact of moving sand during summer spates on the spatial distribution of stream periphyton biomass in a gravel-cobble bed boreal river." Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66695.
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The abrasive effects on periphyton biomass of saltating sand, that was transported over a stable gravel-cobble riverbed during summer flow events (spates), was studied on 35 riffles of an oligo-mesotrophic river in Quebec. A periphyton saltation abrasion model (PSAM) was developed from an existing bedrock erosion mechanistic model (Sklar and Dietrich 2004). The empirical PSAM models explained 56-59% of the variance in post-spate biomass on individual host-rocks following a low-magnitude, high-frequency spate. Periphyton biomass was curtailed on riffle rocks when sand transport rates exceeded 64-180 g m-1event-1 during spates. This perturbation threshold was confirmed by an in situ experiment that documented periphyton losses resulting from increasing rates of sand transport. Low profile substrates (2 cm) were scoured more thoroughly than high protruding substrates (6 cm), confirming the PSAM hypothesis that refuge potential increases with elevation above the stream bed relative to the mean sand saltation height. An analysis of spatial patterns of periphyton biomass across riffles confirmed the tendency for a spate-related refuge habitat between the edge of the varial zone (zone of frequent wetting and drying) and the thalweg (deepest point) of the channel. A hierarchical model (HPPM) that simulates how periphyton biomass is regulated by the flow of water and the flux of sand down a sedimentary link (segment of river along which grainsize and slope decreases systematically downstream) was developed and validated. Sedimentary links contained 3 channel types (hydrogeomorphic reaches, HGRs), each possessing significantly different morphological traits, ranging from straight-steep, cobble-bed reaches (High-HGR) at the upstream end, to low-gradient, sinuous gravel-bed reaches (Low-HGR) downstream. For low-magnitude spates (e.g. 0.85QMean_Annual), the most refuge (i.e. highest post spate biomass) was provided oLes effets abrasifs du sable en saltation sur la biomasse de périphyton, lorsqu'il est transporté au-dessus d'un lit de gravier et de galets stable durant les crues estivales, ont été étudiés sur 35 riffles d'une rivière oligomésotrophique québécoise. Un modèle d'abrasion du périphyton par saltation (PSAM) a été développé à partir d'un modèle mécanistique de l'érosion du soubassement. (Sklar et Dietrich, 2004). Les modèles PSAM empiriques expliquaient 56% à 59% de la variance de la biomasse après-crues sur les roches, suite à une période de crues de basse magnitude et de haute fréquence.La biomasse du périphyton sur les roches des riffles était limitée par une vitesse de transport du sable qui excédait 64-180 g m-1 événement-1 durant une période de crues. Ce seuil de perturbation a été confirmé par une expérience in situ, où nous avons observé les pertes de périphyton causées par des vitesses croissantes de transport du sable. Le substrat à profil-bas (2 cm) a eu des pertes plus importantes de périphyton relativement au substrat saillant (6 cm), ce qui confirme l'hypothèse PSAM que le potentiel du refuge augmente avec l'élévation au-dessus du lit. Une analyse de la distribution spatiale de la biomasse de périphyton dans les riffles a confirmé qu'une zone de refuge de crue existait entre les bords de la zone variable (zone fréquemment mouillée et séchée) et le thalweg du canal (le point le plus profond). Un modèle de perturbation hiérarchique de périphyton (HPPM) a été développé pour simuler l'influence du transport de l'eau et le flux du sable sur la biomasse de périphyton à travers un lien sédimentaire (section de rivière de plusieurs km de longueur, où la dimension des roches diminue systématiquement en aval). Les liens sédimentaires sont divisés en 3 échelles de refuge : des lits de galets droits et raides (haute HGR) en amont, aux li
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Parent, Alain Paul. "Scale models of gravel bed rivers." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28319.
Full textAbstract:
The combined studies of flow processes in a full size gravel-bed river and its associated small-scale model have demonstrated the applicability of the similitude concepts as well as the potential of scale models for quantitative research in fluvial geomor phology. This scaling investigation
considered the comparison of velocity profiles, shear stress measurements, flow structure and surface bed material samples. An extension of the strict comparison on a detailed level of field and laboratory processes in a specific case consisted in the proposition of a "generic model" framework according to which laboratory systems are viewed as part of the same family as field ones if some crucial conditions are satisfied. The pool-riffle sequence, used as a vehicle for the demonstration herein, is presented as a poorly Known but ubiquitous river phenomenon which would benefit from such research methodology. The laboratory study performed herein revealed the need for an appraisal of the variability of shear stress estimates in intermediate relative roughness flows such as field size gravel-bed rivers. Knowledge of elements of the history of the prototype (field) river was also demonstrated to be important for the appraisal of model performance.Arts, Faculty of
Geography, Department of
Graduate
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Jourdain, Camille. "Action des crues sur la dynamique sédimentaire et végétale dans un lit de rivière à galets : l'Isère en Combe de Savoie." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAU002/document.
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Au cours du XXe siècle, les lits de nombreuses rivières ont été sujets à l'installation de végétation alluviale. Dans le cas des rivières aménagées, cette tendance est souvent associée à des altérations géomorphologiques directes (extractions de granulats, endiguements, etc.) ainsi qu'à des modifications anthropiques de leur régime hydrologique et sédimentaire conduisant à une stabilisation du lit qui permet l'installation de la végétation. Cette végétation augmente le risque d'inondation en diminuant les vitesses d'écoulement et en augmentant les niveaux d'eau en crue. Par ailleurs la biodiversité est dégradée par la diminution des habitats pionniers caractéristiques de ces environnements. Manipuler artificiellement le régime hydrologique d'une manière qui pourrait limiter l'installation de végétation sur les bancs est une option considérée par les gestionnaires. Dans ce contexte, ce projet de thèse a pour objectif de comprendre les impacts des crues d'amplitude variable sur la destruction de végétation, et d'identifier les mécanismes associés. Le site d'étude sur lequel cette thèse se focalise est l'Isère en Combe de Savoie, une rivière à galets très aménagée des Alpes françaises.Dans le cadre de cette étude, la destruction de végétation a été étudiée à l'échelle du tronçon à partir d'une analyse des données hydrologiques, des photos aériennes, et des données topographiques disponibles pour la période 1996-2015. À l'échelle du banc, un suivi de terrain avant et après les événements hydrologiques marquants entre avril 2014 et septembre 2015 nous a permis d'étudier l'action des crues sur la mobilité sédimentaire et sur la végétation. Ces observations ont été complétées par une modélisation numérique bidimensionnelle de l'écoulement en crue.À l'échelle du tronçon (20 km), nous avons trouvé une corrélation très forte entre les volumes d'eau ayant transité dans le chenal sur une période donnée, et la destruction de végétation associée au cours de la période 1996-2015. Les débits associés à des temps de retour infra-annuels semblent permettre la destruction de végétation. Le mécanisme de destruction le plus efficace que l'on observe à cette échelle est l'érosion latérale ; les mécanismes prenant place à la surface des bancs sont très minoritaires. Cependant, les surfaces détruites sont modestes ; 3,4 % de la surface végétalisée est détruite annuellement en moyenne. À l'échelle du banc, la période de suivi de terrain a couvert une série de crues fréquentes (temps de retour < 1 an) et une crue de temps de retour 10 ans. Seule cette crue a partiellement détruit la végétation pionnière sur les bancs suivis. La destruction de végétation ligneuse jeune a eu lieu par le biais de quatre mécanismes : 1) déracinement par érosion de surface supérieure à 20 cm, 2) enfouissement sous une couche de sédiment grossiers supérieure à 30 cm, 3) déracinement par une combinaison d'érosion et de dépôt, et 4) érosion latérale en marge des bancs. La destruction de végétation est toujours associée à une mobilité sédimentaire importante.Ces résultats montrent qu'une crue très importante est nécessaire pour détruire la végétation par la mobilisation de la surface des bancs sur ce site. Par contraste, les débits forts mais non exceptionnels (temps de retour infra-annuel) sont en mesure de détruire la végétation par érosion latérale. Dans le cas de l'Isère en Combe de Savoie, il semble que l'utilisation de crues artificielles ne peut pas seule permettre de maintenir la largeur inter-digues libre de végétation. Pour la suite, on propose de s'intéresser à la destruction de végétation dans le contexte de la dynamique des bancs alternés plus ou moins végétalisés, en prenant en compte les apports et le transport des sédiments en plus de l'hydrologieMany rivers worldwide have seen vegetation establish within their beds throughout the 20th century. In the case of managed rivers, this trend is usually linked to direct geomorphological alterations (sediment mining, diking, etc.) as well as anthropic alterations of flow regime and sediment supply. These pressures have stabilized river beds, allowing vegetation to establish permanently. This vegetation increases the risk of flooding by decreasing flow velocities and increasing water levels. In addition, the associated reduction in availability of pioneer habitats characteristic of these stabilized environments typically degrades biodiversity. Managing hydrology in a way that would limit vegetation establishment on bars presents an interesting management option. In this context, our study was aimed at understanding the impacts of floods of varying magnitude on vegetation removal, as well as identifying and quantifying the underlying mechanisms. This work focused on the Isère River, a heavily managed gravel bed river located in the western French Alps.Vegetation removal was studied at the reach scale using hydrological data, aerial photographs, and topographic data available between 1996 and 2015. At the bar scale, field monitoring before and after floods from april 2014 to september 2015 allowed us to document the impact of floods on sediment mobility and vegetation. A 2D numerical model was used to document fine scale hydraulics.At the reach scale, we found a strong correlation between water volume flowing through the river channel and the amount of vegetation removal. Discharges with return intervals of less than one year seem to have an impact on vegetation removal. The main mechanism observed from aerial photographs was lateral erosion; surface processes were negligible in comparison. However, global vegetation removal was modest: since 1996, on average 3,4 % of vegetated area was removed annually. At the bar scale, our study period permitted monitoring of a series of high frequency floods (return interval < 1 year) and a 10-year food event. Only the largest flood partially removed pioneer vegetation from bars. Young vegetation removal occurred through four different mechanisms: 1) uprooting by surface scour > 20 cm, 2) burial under a thick layer of coarse sediments > 30 cm, 3) uprooting by a combination of surface scour and sediment deposition resulting in no net topographic change, and 4) lateral erosion of bars. Vegetation removal was always associated with significant sediment mobility.We conclude that on the Isere River a very important flood is required to remove vegetation by mobilizing bar surfaces. In contrast, high but not exceptional flows (return interval < 1 an) are capable of removing vegetation through lateral erosion. However, artificial floods alone are unlikely to maintain the full width of the channelized bed of the Isere River free of vegetation. In the future, vegetation removal needs to be studied in the context of alternate bar dynamics with or without vegetation. It seems necessary to consider sediment transport as well as hydrology to understand the overall dynamics of the bed
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Fripp, Jon Brooks. "Adhesive areal sampling of gravel bed streams." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-09052009-040310/.
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Hughes, Nicholas. "Heavy mineral distribution in upland gravel-bed rivers." Thesis, Loughborough University, 1992. https://dspace.lboro.ac.uk/2134/27944.
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The characteristics of gravel-bed river deposits vary according to the complex relationships between hydrological and sedimentological regimes that occur over a range of spatial and temporal scales. This thesis concerns the composition and distribution of fine-grained sediment in British upland rivers; the size fractions which are perhaps the most susceptible, as regards both quantity and quality, to human activity and yet which can yield important information regarding upstream geological characteristics.
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Broadhurst, Lucy. "Channel form flow resistance in gravel bed rivers." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267272.
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