ABSTRACT
van Rijn, L.C.; Geleynse, N.; Perk, L., and Condon, D., 2025. Longshore sediment transport and sediment budgets, southeast Florida coast, U.S.A.
Longshore sand transport (LST) along the SE coast of Florida was studied based on measured and modeled data of waves and currents (tide and wave driven), including the effect of the Florida Current. Much of the white sands on Florida beaches comprises a mixture of quartz crystals, coral fossil fragments, and mollusk shell fragments. The median grain size varies from about 0.3 mm at Palm Beaches to about 0.4 mm at Miami-Dade Beaches. Coastal reef systems are especially typical phenomena in the SE Florida region. Beach erosion is a major problem along the SE Florida coast because of (1) presence of rather steep seabed slopes in the surf zone and nearshore zone, (2) absence of natural and protective dunes with sufficient sand, and (3) presence of many inlets with jetties and insufficient bypassing of sediment. Beach erosion is strongly related to the variation of LST. Three approaches have been used to determine the input data and boundary conditions for computation of LST using an empirical LST equation: (1) measured nearshore wave data, (2) modeled nearshore wave data by the SWAN model, and (3) modeled nearshore waves and currents by the Delft-SWAN model system. A reliable indication of the net LST values was also obtained from the annual inlet bypass volumes of sand at various inlets. The modeled results show that the LST along the coastal section between Lake Worth Inlet and Miami from north to south with net LST values decreasing from 150,000 m3/y (±30%) at Lake Worth Inlet to about 50,000 m3/y (±30%) at Miami. The decreasing trend is caused by a milder wave climate and slightly coarser sediments in the southern direction. The LST results, in combination with available data of beach nourishments, were used to determine the overall sand budget of the SE Florida coast.
