Modelling suggests that when swash infiltration is important, as on a gravel beach,rnbeach profile change is characterised by enhanced onshore sediment transport and bermrnformation. Studies of swash zone sediment transport have generally relied on discontinuousrnmeasurements from instruments such as optical backscatter sensors and sediment traps, orrnbeach profiles measured at the beginning and end of the measurement period. Relatively fewrnfield investigations have reported bed level measurements in the swash at intervals less thanrnhours, and even fewer studies have presented measurements of subsurface processes as wellrnas surface processes in the swash zone. This paper reports on field measurements collected onrna gravel beach, Slapton Sands, Devon, in April 2001. Data collected included surfacernpressures under uprush and backwash; subsurface pore water pressures; uprush and backwashrnvelocities; and measurements of bed elevations. The pressure transducer data were used torncalculate vertical, horizontal, slope-parallel and slope–normal hydraulic gradients within thernbeach so that the magnitudes of swash infiltration could be calculated. The field data werernanalysed further using the BeachWin model (Li et al. 2002), which simulates interacting wavernrun-up/run-down, beach groundwater flow, swash sediment transport and resulting beachrnprofile changes. Measured and simulated pore pressures and hydraulic gradients are comparedrnin this paper.
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