EFFECT OF ALONGSHORE NONUNIFORMITIES ON LONGSHORE-CURRENT PREDICTIONS

Longshore currents have been primarily modeled by assuming alongshore uniformity. In this paper we revisit the problem of nonuniform longsho re currents to refocus attention on the importance of accounting for a longshore nonuniformity in longshore current predictions and to provid e an analytical estimate of the importance of this nonuniformity. We d erive a semianalytical solution for the longshore currents that allows for weak alongshore variations in the bottom topography. The solution shows that the alongshore pressure gradient induced by alongshore var iations in the bottom topography could contribute substantially to the forcing for the longshore currents. An example calculation shows that the longshore current could deviate by up to +/-30% from the mean for a +/-10% deviation of the bottom topography. Thus we suggest that in many practical cases it is important to include the alongshore pressur e gradient to accurately model longshore currents.