Wave Setup

Wave setup is the rise in mean water level near the shore caused by the cross-shore gradient of wave momentum flux (the radiation stress) as waves break in the surf zone. As waves shoal and break, the loss of wave momentum is balanced by a slope in the still-water surface, raising it shoreward of the breakpoint by roughly 15 to 20 percent of the breaking wave height. Setup adds to tide and storm surge in total water level and coastal flooding forecasts. Alongshore variations in setup, combined with the offshore-directed return flow, organize the nearshore circulation and feed rip currents. Its counterpart seaward of breaking is the small set-down.