Beach Ground-Water Oscillations

Oscillations of ground-water table were measured in perforated piezometers distributed across the Baltic beach at the coastal research station of Lubiatowo, Prom spectral and correlation analysis it appears that the most pronounced wind-wave oscillations having a period of about 6 seconds have not been detected in the beach, while longwave oscillations, dominant in the beach spectrum, correlate well with nearshore long waves. Among the longwave oscillations, it is only those having periods about or slightly longer than 100 seconds that obey the Boussinesq law. However, some longer waves may also be generated by the interaction of shorter waves. Oscillations with periods from 50 to 100 s are very coherent throughout the beach. In the absence of stochastic noise and variety of inputs, low values of coherence for other periods indicate presence of nonlinear effects. More light should be shed on the origin of this nonlinearity and theoretical tools should be tried to complement the Boussinesq model.