This dissertation reports the results of a field based study examining sediment transport and bed mobility in a low-ordered, ephemeral watershed. Runoff and sediment transport concentrations were sampled at the watershed outlet to determine flow discharge and sediment flux during approximately 21 flow events, from 1998 - 2007. Sediment collected in flow was measured for grain-size distribution to determine if specific grain-size fractions behave differently while in transport. The coarse sediment yield was measured for mass and grain-size distribution at the watershed outlet for two years, 2005 - 2006. Further, the arrangement and composition of the channel bed material was comprehensively mapped using terrestrial-based photogrammetry for the years, 2005 - 2006. Results show that patterns of sediment transport are complex, controlled in part by flow hydraulics but also by other phenomena. Some of the variation in sediment transport is determined by grain-size. Grain-sizes with different sources within the watershed and that transported by different transport modes were observed to follow different patterns of transport. Also, the channel bed, which serves as the source for the coarse fraction of the sediment transport, was observed to change in grain composition during periods of flow. This tendency for the bed material to evolve in time likely affected the amount and composition of the sediment grains that were entrained from it.An additional objective of this dissertation was to determine how unique the observed patterns of sediment transport were to low-order ephemeral channels. Sediment transport and yield were modeled using bed load transport formulae designed to capture the physical mechanics of transport as observed in perennial streams. Results show that contemporary transport models predict transport within the field site with similar accuracy as that in many perennial systems but not well enough to rely on their predictions for many engineering applications.

Regulation of rivers by dams and reservoirs is a good example where anthropogenic impact could be considerable both in the local environment, but also has major implications upstream and downstream. This study was accomplished as a literature study of the river Nile, which is extremely important for water supply. The purpose of this study was to investigate the consequences of the construction of the Aswan High Dam, to obtain a consistent flow for water supply, irrigation and power generation in Egypt. Since Egypt has a very hot and dry climate large amounts of water in reservoir is lost to the Nubian aquifer system and by evaporation. The consequences from constructing the dam are considerable. It has led to the preventing of the annual flooding and a significant reduction in sediment load reaching the outer delta, which has led to an erosion of the delta front. The incoming waves create a current, mainly towards the east, carrying away the eroded material. In order to protect the delta front seawalls and breakwaters has been built. They have stopped the erosion of the areas behind them, but it has also led to the erosion of other areas. The issues in Egypt reflect the global crisis, mainly in delta areas, which prevail in regulated rivers. The biggest issue globally is the reduced sediment transport to the coast that causes land loss.

This thesis investigated the interaction of complex vegetation with wind flow and sediment transport at a creosote shrubland located in New Mexico and formed part of a larger on-going study to improve wind erosion modeling techniques. Directionally dependent roughness densities, λ, were computed and compared to mean wind speed ratios (WSRs) derived from anemometry data. A significant relationship existed among decreasing WSRs and increasing λ, indicating that shelter to the ground changed depending on the orientation of the wind. WSRs were larger on the west, more sparsely vegetated side, than in the east, demonstrating that distribution and plant size have a significant effect on near surface winds. Comparison of these data to a similar study completed in a mesquite coppice dune field demonstrated weaknesses in the roughness density parameter. These results have application for improving the understanding of interactions between wind flow and vegetation in complex rangeland environments.

This thesis concerns the computation of bed adjustments of equilibrium in alluvial meandering streams. It is assumed that the channel centerlines follow sine-generated curves, the banks are rigid, and the steady-state flow is turbulent and sub-critical. The flow width is assumed to remain constant in the streamwise direction, and the flow width-to-depth ratio is large (>=15, say). The bed material is cohesionless and homogeneous. The purpose of the thesis is to develop and test a numerical model for the computation of bed development, given the aforementioned idealized conditions. The model comprises: 1- an initial bed topography generator, to generate the bed at time t = 0 of the calculations; 2- the vertically-averaged hydrodynamic model of Zhang (2007) to calculate the flow fields; and 3- a sediment transport model to relate the bed deformation to the flow. Both the initial bed topography generator (expression of the deformed bed surface) and the numerical sediment transport model based on the sediment transport continuity equation are original and developed entirely by the author. The resulting model is computationally very efficient. In contrast to previous works on the theoretical determination of bed deformation, the beds at the beginning of the calculations may represent any stage of the development process, and not necessarily the initial flat bed. The bed deformation was tested for several test cases, devised on the basis of laboratory runs available in the literature. These include Run ME-2 by Hasegawa (1983) in a 30-degree-channel, Run 3 by Binns (2006) in a 70-degree-channel and the run by Termini (1996) in a 110-degree-channel. The erosion/deposition patterns of the computed equilibrium bed topographies were found to be in reasonable agreement with their measured counterparts. However, as evidenced by the difference plots included in this thesis, in detail there are substantial differences between the computed and measured equilibrium beds, especially in the regions near the banks. As a by-product of the present thesis, the functions representing the parameters required by the hydrodynamic model of Zhang (2007) were also evaluated. In particular, the present results suggest that the coefficient Alpha-q appearing in the expression of the local friction factor (used in the flow model of Zhang 2007) depends on the flow width-to-depth ratio and bed roughness to a much larger extent than previously thought. Considering this, a generalization of the expression of Alpha-q due to El-Tahawy (2004) (and adopted by Zhang 2007 in her model) is proposed. Future work should be carried out to address the application of the present model to real river conditions, including generalizations to irregular meandering plan shapes, unsteady-state flows and non-homogenous bed materials. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-12-19 21:32:06.645

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Soil material exported from river catchments by soil erosion is a key issue in environmental sustainability. Although soil erosion processes have been thoroughly investigated, their dynamics, specifically the continuity of erosion processes and sediment source locality, are less studied. The aim of this investigation was to evaluate the changes in the fluxes and characteristics of sediments during their downslope and downstream transport. The study was conducted in a 1000 ha catchment of the Drakensberg foothills, South Africa. Sediment fluxes were monitored at nested scales during the 2009-2011 rainy seasons using 1×1m and 2×5 m erosion plots and H-flumes coupled to automatic samplers from 23 ha, 100 ha catchments. In addition, soil texture, colour and total organic carbon and nitrogen contents in sediments exported from the nested scales and a 1000 ha catchment were compared to in-situ surface and sub-surface soil horizons in a 23 ha catchment river bank and hillslope soils and fluvial sediments. There was a sharp increase of sediment fluxes with increasing slope length (846±201 gm-1y-1 for 1 m2 vs 6820±1714 gm-1y-1 for 10 m2), revealing a limited contribution of splash erosion compared to rain-impacted flow erosion. Sediment fluxes decreased to 500±100 gm-1y-1 and 100±10 gm-1y-1 at the 23 ha and 100 ha catchments respectively, indicating the occurrence of sedimentation during sediment downslope and downstream transport. A principal component analysis (PCA) suggested that rain impacted flow erosion efficiency at the 10 m2 scale was significantly correlated with soil bulk density, clay content and antecedent rainfall (P<0.05). Moreover, strong correlations existed between runoff, sediment concentration and soil loss and selected soil surface and environmental variables at the plot scales. Correlations became weaker at the catchment scales due to increasing landscape heterogeneity and the complexity of soil erosion dynamics. An additional PCA suggested that stream bank erosion contributed to 63% of the soil loss from the 23 ha catchment. During their downstream transport, sediments were discriminated by the second PCA axis, which correlated with the clay and fine silt content, 100 ha sediments showed negative coordinates to this axis while 1000 ha catchment sediment had positive coordinates. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

The South Westland Continental Margin (SWCM) is incised by two major active canyon channels, the Hokitika and Cook canyons, which export large volumes of terrigenous sediment from the active New Zealand landmass to the deep ocean basins. This thesis examines modern sediment textures and compositions of shelf and canyon heads, to interpret depositional and transport processes in shelf-canyon interactions and the dispersal and provenance of SWCM surface sediments. This is the first detailed study of modern sediments south of the Whataroa River which focuses on both shelf and canyon head sediments. Submarine canyons that incise active continental shelves are major conduits for sediment transfer. The frequency and magnitude of this transfer has important implications for ocean nutrient cycling (i.e. organic carbon), the stratigraphy and morphology of continental shelves, and the development of economic mineral deposits. Grain size analysis, petrology, geochemistry, detrital magnetite analysis (microprobe), swath bathymetry, and wave hindcast data are used to interpret the spatial distribution, dispersal, and provenance of surface grab samples, canyon cores, and beach and river samples on the SWCM. Four main surficial facies are defined from textural and compositional results, primarily reflecting the supply and storm dominated nature of the SWCM. Facies 1 is comprised of inner shelf very fine to medium sand sized quartz, metamorphic lithics, and feldspar. This facies occurs above the mean Hsig wave base (48 m) where silts, clays, and sand sized micas are bypassed further offshore. Facies 2 is a transitional sand to mud facies between 40 -70 m depth where increasing clay, silt, and mica reflect a decrease in the frequency and magnitude of wave orbital remobilisation. Facies 3 is a mud dominated (80-90%), clay rich (7-9%) facies with the highest mica and Al₂O₃ content of all the SWCM facies. The shelves south of the Hokitika canyon are blanketed beyond the inner shelf in facies 3 towards the shelf break. Facies 4 is restricted to the canyon head north rims and is characterised by mixed relict and modern terrigenous sediments and glaucony. Net transport on the SWCM shelf is to the north, particularly during south-westerly storms where wind drift and storm swells may stir and transport the deeper Facies 2 and 3 sediments. The SWCM has an energetic wave climate and numerous high yield mountainous rivers. As a result the shelf has an extensive coverage of silts and clays with sediment transport most likely dominated by nepheloid layers and fluid mud flows during wet storms. North of the Hokitika canyon, shelf width increases as fluvial supply falls, resulting in a more storm dominated shelf as the prevailing hydraulic conditions prevent modern silts and clays from blanketing the outer shelf. Narrower shelf widths and higher fluvial supply between the Hokitika canyon and the Haast region results in more fluvial dominated shelves. Contrasting canyon rim textures and compositions reflect the major influence the Hokitika and Cook canyon heads impose on the SWCM by intercepting modern net northward shelf transport paths. This interception creates a leeward sediment deficit on the canyon north rims where low sedimentation rates prevail and relict sediments are partially exposed. The south and east rims of both canyons are characterised by modern fine grained terrigenous textures and compositions similar to the SWCM middle to outer shelf facies 3. The build-up and storage of these unconsolidated sediments at the south and east rims provides favourable environments for sediment gravity flows that feed into the canyon systems. Wave orbitals can resuspend fine sands up to 50 m below the canyon rims during large storms. This resuspension will be a main driver of canyon head sedimentation in the form of fluid mud flows. Gully networks along the south and east rims of the Hokitika and Cook canyons indicate active submarine erosion, unconfined fluid flow, and sediment gravity flows operate here. ii In contrast, the north canyon rims are characterised by gravels and coarse sands out of equilibrium with the prevailing modern hydraulic regime. Relict gravels are particularly prevalent on the Hokitika canyon north rim between 90 – 150 m depth. A lack of active gully networks and the presence of relict terraces and cuspate channels provide further evidence for a relict origin of HCH north rim sediments and little influx of modern fine sediments. North rim sediments on the Hokitika canyon between 90 – 125 m have features characteristic of relict beach and littoral environments. These features include pebble and coarse sand sized siliciclastics, high heavy mineral percentages (i.e. garnet), high Zr and Y levels, elevated SiO₂/Al₂O₃ ratios, and relict shell fragments. Mature glaucony is common on the north rims of both canyons, especially between 180 -200 m depth providing further evidence for extended periods of little to no modern sediment deposition in the canyon lee. Glaucony grains have experienced limited transport and are probably parautochthonous. The bulk composition of SWCM shelf, canyon, river, and beach sediments is controlled mainly by the hydrodynamic sorting of Alpine Schist derived material. Regional changes in catchment geology are identified in modern SWCM shelf sediments. Ultramafic signals (i.e. enriched trace element patterns and Cr/V and Ni/Y ratios) from the Pounamu Ultramafics and Dun Mountain Ultramafics were identified on the North and Cascade shelves respectively. The contribution of other lithologies to the bulk composition of SWCM sediments is localised due to rapid dilution with Alpine Schist detritus. The low carbonate and skeletal content on the SWCM is due to the energetic wave climate and high fluvial supply on the shelves. A variety of Cr-rich spinels and magnetites are supplied to the SWCM shelves and vary with regional changes in catchment geology. The Cascade shelf is rich in chromites (containing up to 215,000 ppm Cr) and Cr – rich magnetites sourced from the Dun Mountain Ultramafics via the Cascade River. Shelf, beach, and river samples between the Haast River and Waitaha River are dominated by low-Cr magnetite grains which represent the ‘background’ magnetite composition sourced from rivers draining the Alpine Schist dominated catchments. The dispersal of Cr-rich spinels is limited due to the dilution with low Cr-magnetites from rivers and littoral sediments. Glacio-eustatic lowstands such as the Last Glacial Cold Period (LGCP), represented periods of robust connection of local rivers with the Hokitika and Cook canyon heads, increased interception of littoral transport paths, and compartmentalisation of inter-canyon shelves. Hokitika canyon cores reflect these changes with textural and compositional ‘spikes’ indicating higher terrigenous input during the LGCP. The geochemistry of the terrigenous fraction in the Hokitika canyon provides evidence for enrichment in ferromagnesian and Cr-rich minerals during the LGCP. This is due to the increased connectivity of the Cr-spinel bearing Hokitika River to the canyon head. The Cr/V ratio in particular demonstrates its effectiveness as a proxy for interglacial – glacial change in submarine canyon stratigraphy. Increases and decreases in the connectivity of Cr-bearing fluvial systems during lowstands and highstands respectively can be observed with this ratio.

Small lowland agricultural systems promote conditions where benthic biological communities can thrive. These biogeochemical processes have significant impacts on terrestrial ecosystem processes including POC flux and fate, nutrient balances, water quality budges, and aquatic biological functioning. Limited information is available on coupled biological and hydrologic processes in fluvial systems. This study investigates the mixture of biological and hydrologic processes in the benthic layer in order to understand POC cycling in the South Elkhorn system. Further, comprehensive modeling of POC flux in lowland systems has not been performed previously and the behavior of potentially controlling variables, such as hydrologic forcing and seasonal temperature regimes, is not well understood. Conceptual hydraulic and sediment transport models were simulated for the South Elkhorn. Based on data and model results it was concluded that during a hydrologic event, upland and bank sources produce high variability of POC sources. Likewise, over time, the density of hydrologic events influenced accrual of benthic algal biomass in the POC pool. Environmental variables such as temperature and light availability drove seasonal variations of POC in the streambed. Based on model estimates, around 0.29 metric tCkm-2yr-1 of POC is flushed from the system annually with 13 % coming from autochthonous algae.