Coastal climate and beach dynamics at Ponta do Ouro, Mozambique

Abstract

Annual field surveys conducted at Ponta do Ouro in Southern Mozambique have determined that coastal variability is driven by high wave energy and consequent northward longshore drift. There is a log-spiral headland-bay system marked by 80 m tall forested dunes in the south that give way to a broad flat sandy beach. Marine climate processes that affect coastal erosion and accretion are studied using local and remote data sets. Since surveys began, the climate has undergone a prolonged dry spell (2002-2007) followed by increased run-off and easterly winds (2010-2013) that have re-built the beaches. Sand grain sizes vary from 240 - 410 m (coarser south – finer north) and are mobilized by frequent longshore wind events > 10 m/s. Ocean drifters reveal a northward current in the outer surf zone of 0.6 m/s and an onshore gyre of 0.1 m/s in the recessed bay. Wave-driven sand transport is estimated at 5 106 kg/yr/m. While the upper beach has flattened due to pedestrian traffic and urban development, the lower beach has recovered from erosion due to a greater frequency of easterly waves and rainy weather.