No description available.

No description available.

This research describes the testing, development and application of an established hydro-geomorphic numerical model (CAESAR) over different time scales (170-2000 years) to simulate at hourly time resolution, the changes in the hydrological and sediment regime of the Petit lac d’Annecy catchment in response to changes in system drivers. Two thousand year long model runs in five different morphological settings were simulated, the results suggest that intrinsic system behaviour such as storage-release, hillslope-channel coupling and supply-capacity relationships may well exert larger controls on sediment discharge patterns over this timescale than climate or land use drivers. Hypothetical scenarios to investigate the geomorphic implications of a snow-free pre-alpine region over the last 2000 years show that there would be around 1.4 times more sediment discharge, with the annual hydrological regime radically altered with increased flooding throughout the year, particularly in winter months and a lack of a sustained discharge peak in the ‘melt’ months. This has implications for the projected environmental changes over the coming decades. The simulated effects of increased precipitation, reduced forest cover and snow-free conditions, in combination, point to increased amounts of coarse sediment discharge within the channels. Broad estimations show that a 20% reduction in forest cover or snow-free conditions can result in an additional 1m of sediment moving through the system and accumulating in the lake with potentially large impacts on flooding, in-channel fauna, benthic-dwelling lake fauna, aquatic macrophysics and water quality and water availability for storage and local power generation.

No description available.

No description available.

No description available.

This thesis documents the rates and patterns of contemporary and recent overbank deposition along the lower reaches of the River Calm, S. E. Devon, England. Two temporal perspectives are adopted: (i) short-term rates based on contemporary flood events, using sediment traps, the sampling of in-channel suspended sediment and qualitative field observation of inundation processes; and, (ii) recent (over the past 35 years) rates of vertical accumulation, using the caesium-137 technique. These techniques also enable lateral and downstream trends to be identified. Longer-term implications are also addressed using a simple lithofacies classification of alluvial sections, supplemented by historical evidence of channel change and anthropogenic impact along the study reach. Overbank deposition rates are generally low along the study reach, averaging 0.7 mm year-1 (using estimates of suspended sediment conveyance losses), 0.4 mm year-1 (sediment traps) and 0.5 mm year-1 (caesium-137 studies). In general, the highest deposition rates are associated with the levee, depressions and breaches. Deposition rates, however, are temporally and spatially highly variable, being dependent upon the microtopographic relief and vegetation of the floodplain, the mode of inundation, and the extent of retention pondage. Anthropogenic impact on the floodplain is also noted, in particular the role of ditches in distributing floodwaters across the floodplain and the compartmentalisation effect of barriers to flow. These have important implications for the rates of overbank deposition and the sedimentological characteristics of deposits. The role of scour remobilisation of sediment is also assessed. The spatial detail afforded by the caesium-137 technique has been used to identify areas of the floodplain which may be locally susceptible to scour. This study highlights the potential for lowland floodplains undergoing regular flooding to suffer contamination from radionuclides and other pollutants, and leads to an improved understanding of the spatial and temporal rates and trends in deposition and sedimentological characteristics of overbank deposits on the floodplain of a suspension load-dominant river system.

No description available.

The delivery of suspended sediment from drainage basins has frequently been quantified in mass terms by use of the suspended sediment budget approach, which identifies sources, storage and output of mobilised sediment. This thesis investigates the particle size characteristics of the sediment associated with the key components of the suspended sediment budgets of four drainage basins in Devon, U. K. to determine whether particle size selectivity occurs in the delivery of suspended sediment from the hillslopes to the basin outlet. Attention focused on pasture land because previous studies had indicated that this was the dominant source of suspended sediment and that arable fields and channel banks were relatively insignificant in these catchments. Samples of sediment were mobilised from pasture hillslopes using a field-portable rainfall simulator; samples of suspended sediment were collected from the river channel during storm events either manually, by automatic pump samplers or by using rising limb siphon samplers; suspended sediment deposited on the channel bed was sampled using bed traps and by resuspending sediment deposited on the river bed during low flows; and sediment deposited on the floodplain during overbank flooding was collected using Astroturf mat traps or by sampling surface material. Samples were collected to investigate both temporal and spatial variability in grain size behaviour. All sediment samples were pretreated to remove organic matter and their chemically dispersed (absolute) particle size composition was measured using a Coulter LS 130 laser granulometer. The particle size composition of transported/deposited sediment was compared with that of the samples from potential sources to determine whether particle size selectivity had occurred. Where possible, measurements of the natural in situ particle size distribution (effective particle size) were also undertaken by quick return of samples to the laboratory for immediate measurement without pre-treatment using the laser granulometer. Particle size selectivity was found to have occurred in the mobilisation of sediment from the hillslope pasture land sources. Seasonal variations were identified in the particle size characteristics of both sediment mobilised from the hillslopes and suspended sediment samples. Spatial variations were identified in the particle size composition of sediment deposited on the floodplain. These seasonal and spatial variations reflect the particle size selectivity of detachment, transport and deposition processes which is in turn influenced by the aggregation or flocculation (effective particle size) of the sediment.

Στόχος της εργασίας ήταν η λιθοστρωματογραφική ανάλυση των ιζημάτων, η αναγνώρι- ση των Περιβαλλόντων Ιζηματογένεσης και η εξέλιξη τους στην πάροδο του χρόνου σε έναν τεκτονικά παραγόμενο ποταμόκολπο όπως ο Αμβρακικός κόλπος. / The subject of this study is the lithostratigraphic research and recognition of sedimentary environments of the sediments of Amvrakikos Gulf.