Morphology and movements of nearshore sediments in a non-tidal environment, K0ge Bugt, · Denmark

Abstract

On a non-tidal, medium- to fine-grained sandy coast, the morphology and material budget in the littoral zone - primarily on the nearshore terrace and the shoreface - have been analysed ori the basis of 65 detailed maps surveyed in a permanent grid for a period of two months. Simultaneously, records were made of wind, water, and waves. The map drawings and the calculations of variations in sediment volumes were made by EDP. The investigations showed that the nearshore bar might be built up during high as well as low waterle­vels, initiated either by a small breakpoint bar or a swash bar. The observed nearshore bar moved landward up to 30 cm per hour during periods with onshore winds and during constant water-levels and/or constant wind speeds. Analyses of the material budget showed that variations in volume ( down to minus 1 m) were mainly due to profile adjustments. Especially noteworthy was that, after a gale, the quantities of sediments supplied were larger than those removed from the area during the gale. Furthermore, it was demonstrated that the total quantity of material of the inshore and the beach by and large remained constant in spite of obvious occurrences of nearshore bars migrating towards the coastline during the investigation period. Only an extraordinary gale situation was able to add permanent material to the barrier.