RANDOM WAVE KINEMATICS AND COASTAL STRUCTURES.

Abstract

A linear theory-based method for the prediction of wave kinematics in front of coastal structures for the general case of obliquely-incident waves is described. The method uses empirical equations to determine the reflection coefficient and wave phase shift spectra for given incident wave structure characteristics. Surface elevations, water particle velocities and bed shear stresses were obtained from a wide range of experiments conducted in the UK Coastal Research Facility involving steep and very non-linear incident waves. Wave behaviour at the structures varied from heavy breaking of steep incident waves onto sloping structures to high reflection of less steep waves from a vertical wall. Comparison of predicted and measured kinematics shows that the linear method yields good engineering estimates of the spectra and time series of surface elevation and water particle velocity. The results from no-structure experiments show that a 10% overprediction in velocity is inherent in the application of linear wave theory to the very non-linear wave conditions involved. Predicted near-bed horizontal velocities can be used to obtain estimates of bed shear stress which compare favourably with measured bed shear stresses.