Modelling and numerical simulation of turbulence, waves and suspended sediments for pre-operational use in coastal seas

Abstract

The role of small-scale processes in models of coastal seas is reviewed, and the respective uses of vertically integrated and vertically resolving models are described. Although applied with heavily tuned empirical parameters to the Holderness coast a vertically integrated model shows the importance of surface waves for predicting suspended particulate matter (SPM) and their distributions. In formulating a generic vertically resolving module, as kernel, the k– ε turbulence closure has been selected. On a uniform vertical grid this model gave reasonably accurate results for a neutrally stratified channel flow forced by an M 2 tidal wave (Elbe estuary) as well as on a nonuniform grid highly refined in the high-dissipation near-bed region for short-period (8 s) surface waves in a laboratory flume. The model was completed with modules accounting for the effect of waves on the turbulent kinetic energy (TKE) influx at the surface and on the apparent roughness at the bottom. It was finally coupled with different versions of vertically high resolving SPM models. In test applications to the English Channel and to the Sylt–Rømø Bight (Germany/Denmark) the generic model versions performed with sufficient accuracy. However, in both cases: (i) fine tuning of erosion and deposition terms was necessary thus underlining the need for further experimental research towards an improved data base on erodible sediments and SPM; (ii) the parameters of the submodel for the TKE injection by surface waves could not be determined consistently and indicate the existence of a further still hidden parameter; (iii) the technical basis for in situ observations of small-scale processes in the coastal zone needs further improvements and consolidation.