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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.

The use of cosmogenic beryllium-7 (7Be) as a soil and sediment tracer relies upon a number of important assumptions which to date have not been fully underpinned by supporting data. As a catchment management tool 7Be offers unique potential to assess the effects of recent land use or climate change but further research is required to provide confidence in key data and elucidate sources of uncertainty. Through a range of laboratory and field studies, this thesis aims to explore knowledge gaps relating to i) the temporal and spatial dynamics of 7Be activity in rainfall which has importance in the context of estimating fallout input during erosion studies ii) adsorption behaviour in soils which is of critical importance when considering tracer stability at the field and catchment-scale and iii) the reliability of erosion estimates using 7Be inventories at the slope-scale to address the current lack of model validation. Findings showed temporal and spatial variability of 7Be fallout emphasising the need for regular site-specific sampling to determine fallout flux during erosion studies. Data supported the assumption of rapid tracer adsorption upon fallout although highlighted the potential for 7Be mobility under changing environmental parameters, thus, raising questions with regard to tracer stability at the catchment-scale. Field investigations demonstrated the potential for current models to overestimate erosion rates by failing to accurately represent key model components, namely, 7Be depth distributions, particle size enrichment and fallout input dynamics. Where these factors cannot be determined directly, a range of erosion estimates should be given based upon realistic sensitivity analysis of model components. In this manner, reported uncertainties will reflect field processes rather than propagated analytical uncertainty alone.

This study aims to determine the late-Quaternary evolution of an ephemeral, transverse river system developed in southeast Spain, with particular reference to sediment provenance variation. The Rio Alias drains two inter-montane east-west orientated Neogene sedimentary basins; the Sorbas and Almeria basins. Pliocene to present transpressional tectonics has led to inversion of the sedimentary basins and incision of the developing fluvial system. Fluvial incision has led to the preservation of a suite of alluvial terraces recording the late-Quaternary development of the Rio Alias. Fluvial system inauguration began in the Plio-Pleistocene epoch. The primary fluvial system developed as a consequent river later becoming superimposed and transverse to structure. The drainage basin of the Rio Alias has been sub-divided into 4 sub-basins; The Lucainena, Polopos, Argamason and El Saltador sub-basins. Each basin is structurally controlled. The impact of climate, tectonics, river-capture and eustatic sea-level variation on the fluvial system evolution varies both spatially and temporally across the sub-basins of the Rio Alias. Across the region alluvial aggradation is thought to relate to global glacial periods and incision to interglacial periods. The Lucainena sub-basin is largely controlled by climatic variation related to glacial interglacial cycles with slight modification due to local small scale river-capture and regional epeirogenic uplift. The Polopos sub-basin is also largely controlled by climatic variation, however a major river-capture event c.70ka beheaded the Rio Alias of c.70% of its drainage area. Following the loss of drainage the beheaded Rio Alias system lost stream power, this is reflected in the decrease in size of bedform geometry and the reduced incisional capacity of the fluvial system of the post-capture terrace sequence. In the Argamason sub-basin the Rio Alias crosses the Carboneras Fault Zone, a left-lateral strike slip fault. Late-Quaternary tectonic activity has significantly modified the climatically generated signal. Large tortuous meanders developed in response to normal tectonic activity and continued tectonically driven base-level lowering led to abandonment of terraces and local incision. The El Saltador sub-basin is located at the seaward end of the system and the climate generated phases of aggradation and incision have been greatly complicated by eustatic sea-level variation related to glacial/interglacial cycles. The lowering of base-level due to sea-level regression initially led to pronounced incision along steep gradients and to the development of meander loops in the seaward end of the Rio Alias, during what regionally was a climate driven phase of aggradation. Analysis of the alluvial sediment using a combination of field based clast analysis and laboratory analysis (petrology, SEM, magnetic analysis) allows a detailed picture of sediment provenance variation to be established throughout the evolution of the Rio Alias. Provenance analysis provides information on the timing and extent of river-capture related loss of drainage area, the relative timing of local tectonic activity and also provides new information regarding sediment source area variation throughout the development of the fluvial system. Detailed analysis of the terrace sediments and the modern channel indicates that as the fluvial system incises, local input of sediment from the steepening valley sides grows increasingly dominant. The coupling between the hillslopes and the channel thus changes through time. Sediment provenance analysis has increased our understanding of the long-term fluvial evolution of the Rio Alias, identifying not only sediment provenance variation due to river-capture and changing geology but to fluvial system development.

No description available.

No description available.

No description available.

Particle Image Velocimetry, Laser Induced Fluorescence, pressure transducers and wetting front digital image measurements were made for two steep immobile beaches with different roughness and permeability (1.5mm and 10mm sediment).  The experimental results proved valuable in revealing the interaction mechanisms between the swash and the subsurface flow, in particular, showing the significant role of entrapped air.  The comprehensive dataset was used for the development and validation of a numerical model of swash consisting of a surface and subsurface flow model. The surface flow model, capable of simulating the movement of a steep bore over a permeable coarse-grained beach, is based on the non-linear shallow water equations solved using the Godunov-type finite volume ADER scheme.  The subsurface flow model simulates the vertical movements of the wetting front and the horizontal movement of air and groundwater within a beach.  Vertical movement is simulated as downwards or upwards piston-like flow, with the drag term parameterised by the Forchheimer equation.  Air and groundwater flow are simulated using simple Darcian modules. The experimental and numerical results reveal the distinctly different behaviour of filtration and pressure within the beach for the two types of sediment.  The considerable build-up of air pressure, induced by entrapped air below the wetting front in the unsaturated region of the 1.5mm sediment, minimise the loss of surface water to the beach by reducing infiltration rates.  Moreover it causes the flow within the bed to reverse and induce exfiltration.  Conversely, the build-up of air pressure in the 10mm beach is considerably lower, resulting in higher infiltration rates and a greater exchange of water from surface flow to the subsurface.

This thesis describes research carried out to study steep streams. Step-pool sequences, a typical feature of such streams, were found to occur on every steep stream studied in the field. The most important control on the spacing of the steps was width. Flume experiments produced steps (at an average Froude number of 0.88), and showed that the presence of steps increased resistance to flow at lower than step-forming flow and decreased resistance at above step-forming flows. In the field, flow resistance was found to be controlled by sediment characteristics and the amount of step protrusion. The hydraulic geometry of the steep streams was also studied, and was found to differ considerably from hydraulic geometry characteristics of lowland streams. The formation of steps and pools was not found to be related to antidune processes; rather they were built up individually as large particles captured other large particles that had been entrained by the near critical flow. It was concluded that it is not the absolute values of slope and discharge that determines whether steps form. Near critical flow and high relative roughness appear to be the only requirements necessary. Previous equations were generally found to perform poorly when used with the experimental data, and an attempt to model the velocity profile using sediment characteristics and considering stresses on the flow also produced poor correlation with the actual field data. Modifications to these were made with some success, especially in the ability to predict friction factor based on relative roughness using D84 . Flume velocity profiles identified characteristic velocity profiles at different locations within the step-pool sequence and the presence 'S-shaped' profiles downstream of the step.