The influence of coastal morphology on shoreface sediment transport under storm-combined flows, Canadian Beaufort Sea

Wind, wave and current measurements were carried in the nearshore zone of t he Canadian Beaufort Sea at two coastal sites having distinct morphologies. The first site is a sandy beach backed by a low bluff, while the second si te consists of low-lying barriers. Computation of potential sediment transp ort using a numerical model for combined flow conditions (Li and Amos, 1993 ) suggests that coastal morphology may play a significant role on circulati on and sediment transport on the shoreface during storm events. Downwelling near-bottom currents and offshore sediment transport were observed at all sites during storm surges, but with some variations in the shoreface curren t patterns and sediment transport. According to the numerical model used in this study, offshore sediment transport is more significant where the beac h is backed by a bluff acting as a natural barrier. Such condition appears to be favorable to the development of strong seaward-directed horizontal pr essure gradients that drive offshore bottom currents. Along low barriers th at are easily submerged and overwashed, sediment transport is mainly direct ed obliquely offshore due to more limited set-up of sea level at the coast during storm surges. These results suggest that coastal morphology may be r esponsible for variable offshore sediment dispersal on the shoreface during storms. Our results show that sediment may be transported offshore to dept hs from which fairweather waves may not be capable of returning the materia l onshore. Consequently, a loss of material to the offshore may be greater where overwashing is restricted due to the presence of a coastal feature th at acts as a boundary for onshore-driven surface waters.