Effect of channel deepening on tidal flow and sediment transport: part I—sandy channels

Natural tidal channels often need deepening for navigation purposes (to facilitate larger vessels). Deepening often leads to tidal amplification, salinity intrusion, and increasing sand and mud import. These effects can be modelled and studied by using detailed 3D models. Reliable simplified models for a first quick evaluation are however lacking. This paper presents a simplified model for sand transport in prismatic and converging tidal channels. The simplified model is a local model neglecting horizontal sand transport gradients. The latter can be included by coupling (as post-processing) the simplified model to a 2DH or 3D flow model. Basic sand transport processes in stratified tidal flow are studied based on the typical example of the tidal Rotterdam Waterway in The Netherlands. The objective is to gain quantitative understanding of the effects of channel deepening on tidal penetration, salinity intrusion, tidal asymmetry, residual density-driven flow, and the net tide-integrated sand transport. We firstly study the most relevant tidal parameters at the mouth and along the channel with simple linear tidal models and numerical 2DH and 3D tidal models. We then present a simplified model describing the transport of sand (TSAND) in tidal channels. The TSAND model can be used to compute the variation of the depth-integrated suspended sand transport and total sand transport (incl. bed-load transport) over the tidal cycle. The model can either be used in stand-alone mode or with computed near-bed velocities from a 3D hydrodynamic model as input data.