WATERTABLE FLUCTUATIONS IN A SANDY OCEAN BEACH

摘要

Fluctuations of the watertable level within a fine-grained beach were observed for 2 months in Fall 1996. The magnitude of fluctuations at diurnal and semi-diurnal frequencies decayed rapidly inland, but fluctuations at spring-neap frequencies remained significant nearly 100 m inland of the mean shoreline location. During two storms that coincided with spring tides, overtopping and ponding of water behind the berm resulted in increased watertable levels that persisted for several days. Beach erosion during the second storm resulted in landward displacement of the shoreline location, and subsequent watertable fluctuations also extended farther inland. Numerical solutions of the nonlinear Boussinesq equation, with the seaward boundary condition given by the observed shoreline location, agree well with the observations. The landward attenuation and phase shifting of tidal watertable fluctuations are predicted well, as is the location of the seepage face.