Beach-head erosion of sandy beach plains in eastern Africa threatens tourism-related infrastructure and the livelihoods of beach users. The nature and drivers of physical shoreline change at Kunduchi, Dar es Salaam, and Bamburi, Mombasa, are described with analyses of beach sand transport through the annual monsoon cycle and the provenance and sustainability of the beach sand supply. Time-series records of wind-vectors at Dar es Salaam and Mombasa show similar averaged patterns. Because of the contrasting alignments of these coasts, the net wind-wave driven longshore transport at Kunduchi (trending NNW) is northnorth-westwards, while at Bamburi (trending NNE) there is little net transport. At Bamburi, the beaches are recharged with reef/platform-derived calcium carbonate sand and siliciclastic sand discharged from the hinterland via tidal channels. At Kunduchi, recharge comprises mostly river-borne siliciclastic sand, but riverine sand mining threatens natural replenishment, jeopardising beach maintenance. Eroding beach plain deposits contribute siliciclastic sand at both sites.