HYDRAULIC GRADIENTS AND BED LEVEL CHANGES IN THE SWASH ZONE ON SAND AND GRAVEL BEACHES

摘要

A series of field experiments were undertaken in 1998-2001 to investigate the interaction between surface and subsurface flows in the swash zone and bed level changes on the intertidal profile on a sand beach (Canford Cliffs, Dorset), a mixed sand and gravel beach (Seaford, East Sussex) and a gravel beach (Slapton Sands, Devon). Data collected included surface pressures under uprush and backwash, subsurface vertical and horizontal porewater pressures, uprush and backwash velocities, and bed level measurements at 10 minute intervals. This paper reports on the measurements from the gravel beach and presents comparisons of swash hydrodynamics on the mixed sand-gravel beach at Seaford and the gravel beach at Slapton. The bed level changes measured on the gravel beach were larger than those previously reported on sand beaches, with an increase of 0.15 m in three minutes and a maximum total elevation change of 0.38 m over the whole measurement period.