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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:509137 |
| Date | January 2010 |
| Creators | Steenhauer, Kate |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=59381 |
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