STATISTICAL MODELING OF NEAR-BED PRESSURE GRADIENTS MEASURED ON A NATURAL BEACH

摘要

The wave-induced pressure gradient, partial deriv p/partial deriv x, at the bottom is related to fluid acceleration and sediment movement in the surf zone. Following similar large-scale laboratory work by Suzuki et al. [2008a], this paper deals with the observations and analysis of bottom pressure gradients on a natural sandy beach. The cross-correlation coefficients between partial deriv p/partial deriv x and the water surface elevation are high even in the surf zone, and the coefficients are higher than the coefficients between partial deriv p/partial deriv x and the vertical velocity component or partial deriv p/partial deriv x and du/dt. The observed nonlinear characteristics of partial deriv p/partial deriv x are weaker than the laboratory experimental data but extreme values of partial deriv p/partial deriv x are larger than the experiments. The distributions of exceedance probability of partial deriv p/partial deriv x are evaluated using the two-parameter Weibull distribution. The modulus of the Weibull distribution is evaluated as a function of local significant wave height normalized by the offshore significant wave height. The exceedance probability distributions of partial deriv p/partial deriv x show a broader distribution for the field data compared to the laboratory, but are, nevertheless, predicted reasonably well with the Weibull distribution.