The Influence of Coastal Morphology on Shoreface Sediment Transport under Storm Combined Flows, Canadian Beaufort Sea

Arnaud Hequette, Marc Desrosiers, Philip R. Hill, Donald L. Forbes

Abstract


Wind, wave and current measurements were carried in the nearshore zone of the 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 site consists of low-lying barriers. Computation of potential sediment transport using a numerical model for combined flow conditions (LI and AMOS, 1993) suggests that coastal morphology may play a significant role on circulation 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 current patterns and sediment transport. According to the numerical model used in this study, offshore sediment transport is more significant where the beach is backed by a bluff acting as a natural barrier. Such condition appears to be favorable to the development of strong seaward-directed horizontal pressure gradients that drive offshore bottom currents. Along low barriers that are easily submerged and overwashed, sediment transport is mainly directed 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 responsible for variable offshore sediment dispersal on the shoreface during storms. Our results show that sediment may be transported offshore to depths from which fairweather waves may not be capable of returning the material onshore. Consequently, a loss of material to the offshore may be greater where overwashing is restricted due to the presence of a coastal feature that acts as a boundary for onshore-driven surface waters.


Keywords


Shoreface sediment transport; combined flows; storm surges; Beaufort Sea; Canada.

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