The drag coefficient, bottom roughness, and wave-breaking in the nearshore

The bottom drag coefficient in the nearshore has been suggested to depend on bottom roughness (bedforms) or alternatively on wave breaking. The hypothesis that bottom drag coefficient depends on bottom roughness is tested with 2 months of field observations collected on a sandy ocean beach during the Duck94 field experiment. Both the drag coefficient (estimated from alongshore momentum balances) and bottom roughness (estimated from fixed altimeters) are larger within the surfzone than in the region farther seaward. Although the drag coefficient increases with roughness seaward of the surfzone, no relationship was found between the drag coefficient and roughness-related quantities within the surfzone. These results suggest that breaking-wave generated turbulence increases the surfzone drag coefficient. (C) 2003 Elsevier Science B.V. All rights reserved.