Physical processes that control the formation, evolution, and perturbation of the low-salinity front over the inner shelf of the South Atlantic Bight have been examined using a fully three-dimensional primitive equation and turbulent closure model. The model was forced by semidiurnal tides (M2, S2, and N2), climatological means of multiple river discharges, and upwelling-favorable wind. This model has provided a reasonable simulation of the fortnightly and monthly variations of semidiurnal tides. Computed amplitudes and phases of tides show good agreement with observational data available at tidal gauge stations along the coast. Spatial structures of buoyancy currents are significantly modified by stratified tidal rectification. As a result, the southward residual current intensifies significantly at the front and reduces or reverses close to the coast. A weak velocity area forms in the downstream region of each river, which blocks the low-salinity water to form multiple tongue-like domes in the inner shelf. For a given springtime climatological upwelling-favorable wind, isolated low-salinity lenses can form episodically in two steps. At first, a geometrically controlling wave-like frontal shape develops at the outer edge of the frontal zone as a result of the interaction between tides, multiple river discharges, and upwelling-favorable wind. Then, isolated low-salinity lenses form at the crest when water on the shoreward side of the crest is displaced by relatively high salinity water advected from the upstream trough south of the crest and diffused upward from the deeper region. Wind-induced upwelling is noticeable to compensate for the water loss due to the near-surface offshore Ekman transport, but it does not play a critical role in the formation of isolated lenses under the climatological conditions of river discharges and upwelling-favorable winds over the inner shelf of the South Atlantic Bight. ¿ 1999 American Geophysical Union