Beach Changes on Low Energy Lake Shorelines, Lakes Manapouri and Te Anau, New Zealand

Abstract

Sand and gravel beaches around the shores of Lakes Manapouri and Te Anau, New Zealand generally respond to fluctuations in wave energy and still water level in a similar manner to large lake and ocean beaches. However, there are some important differences. Short fetch lengths produce a narrow range of wave conditions and shore normal changes to the beach profile are minimal in order to maintain an equilibrium form. Largest beach changes are induced by fluctuations in lake level and alongshore transport of sediment in closed beach compartments. Low energy levels limit the size of sediment in transport and much of the shoreline is protected by lag pavement beaches, the size of the lag and winnowed sediment being controlled by maximum wave conditions. Frequent calms allow all types of beach morphology to be drowned or stranded by lake level fluctuations.