SWASH ZONE BED LEVEL CHANGES AND SEDIMENT ENTRAINMENT AT THE SURF-SWASH BOUNDARY

Abstract

In the process of estimating the effect of sediment advection into the swash zone from bore collapse, a method in which buried self-logging pressure transducers are used to measure bed level changes in the swash zone, over a timeframe of several hours to inter-swash level, has been tested against bed level changes obtained from rod measurements. The test shows perfect agreement in the upper and mid swash while minor disagreement (1 cm) in the lower swash occurred. The deployment of self-logging pressure transducers has proven to be an accurate, easy and flexible method to obtain highly detailed data on water levels and bed elevations in the swash zone. Water levels derived from the pressure transducers show that swash zone characteristics vary from the upper to lower swash. Using pressure transducers in the swash zone coupled with measurements of the hydrodynamics and sediment concentrations at the outer boundary of the swash zone will improve the ability to explain the role of sediment advection from bore collapse. In relation to this, a method which consistently identify bores at the surf-swash boundary and quantifies the suspended sediment load carried by such bores prior to their collapse and run-up in the swash zone, is also presented.