Scour of sand beaches in front of seawalls.




Herbich, J.B.
Ko, S.C.

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Many previous studies were confined to the problem of beach erosion due to waves breaking on the structure. The investigation reported here involved regular non-breaking, shallow water waves progressing toward a seawall. An analytical solution was developed and compared with laboratory-scale experiments. The shallow-water wave theory and boundary layer equations were used in theoretical development, which resulted in a mathematical model for the ultimate scour depth in front of a seawall. The theoretical equation for scour is as follows: S=(D-1/2A) [(1-Cr) u* (3/4 Cd Rho(cot Theta - d(Gamma s - Gamma)))to the 1/2 power - 1] where D = still water depth, A = Hi+Hr, Hi = incident wave height, Hr = reflected wave height, and Cr = Hr/Hi = coefficient of reflection, also u* = horizontal velocity within boundary layer, Cd = coefficient of drag, Rho = fluid density, Theta = seawall slope angle, d = effective sand diameter, 50% finer, Gamma s = specific weight of sand, and Gamma = specific weight of water. The comparison between theoretically calculated values and experimental results indicates fairly good agreement. The model experiments also indicate that depth of scour depends to a large extent on wave characteristics and that scour length (distance between scour trough or crests) is independent of time, but is a function of wave length.


p. 622-643.


sea walls, scouring, wave action, beach erosion, mathematical models, modeling, wave effects, wave dynamics, beaches, erosion, coastal erosion, coastal processes