Bed shear stress in the southern North Sea as an important driver for suspended sediment dynamics

Abstract

This paper addresses the spatial and temporal patterns of drivers for sediment dynamics in coastal areas. The basic assumption is that local processes are dominating. The focus is put on the bed shear stress in the southern part of North Sea giving the basic control for depositionsedimentation and resuspension-erosion. The wave-induced bed shear stress is formulated using a model based on the concept that the turbulent kinetic energy associated with surface waves is a function of orbital velocity, the latter depending on the wave height and period, as well as on the water depth. Parameters of surface waves are taken from simulations with the wave spectrum model WAM (wave model). Bed shear stress associated with currents is simulated with a 3D primitive equation model, Hamburg Shelf Ocean Model. Significant wave height, bed shear stress due to waves and currents, is subjected to empirical orthogonal functions (EOF) analysis. It has been found that the EOF-1 of significant wave height represents the decrease of significant wave height over the shallows and, due to fetch limitation, along the coastlines. Higher order modes are seesaw-like and, in combination, display a basin-scale rotational pattern centred approximately in the middle of the basin. Similar types of variability is also observed in the second and third EOF of bed shear stress. Surface concentrations of suspended matter derived from MERIS satellite data are analysed and compared against statistical characteristics of bed shear stress. The results show convincingly that the horizontal distribution of sediment can, to a larger extent, be explained by the local shear stress. However, availability of resuspendable sediments on the bottom is quite important in some areas like the Dogger Bank.

Turbulent Mixing due to Surface Waves Indicated by Remote Sensing of Suspended Particulate Matter and Its Implementation into Coupled Modeling of Waves, Turbulence, and Circulation

“…details, see appendix D and Gayer et al (2006), Stanev et al (2009), andDobrynin et al (2010). Dynamics of the process is shown on Fig.…”

Introduction to the Assessment—Characteristics of the Region

“…Evolution with increasing distance from shore (numbers refer to stations off the island of Sylt) Fig. 1.14 Characteristic wave heights (m) in the North Sea (Stanev et al 2009) tidal amplitude around which the tidal wave rotates (see solid co-phase lines in Fig. 1.15 depicting the same phase of the tide).…”

Observations of a narrow zone of high suspended particulate matter (SPM) concentrations along the Dutch coast

“…A tidal wave moves in an anti-clockwise direction through the sea with strong tidal currents near the coast, similar to a Kelvin wave. Surface turbulence by wind and waves has a marked effect on the stability of the water column and local resuspension of SPM (Stanev et al, 2009). Besides the limited depth, the research area is characterized by the large buoyancy flux from the Rhine-Meuse estuary.…”