Development of a Cohesive Sediment Transport Model of the Thames Estuary

The UK government funded Environment Agency (EA) has commenced its Thames Flood Risk Management Strategy investigation and has initiated a series of studies to provide a sound basis to furnish its decision making process. Within the Thames Estuary, cohesive sediments play an important role and understanding their present behaviour and the effects of any flood risk management strategy on them is an important issue to be addressed. The studies have been undertaken in three phases. Firstly an Estuary-wide data collection exercise was done covering the whole 100 km length of the Estuary for a range of tides. The through-tide flow and suspended solids data obtained were processed using the SEDIVIEW technique to calibrate the attenuation of the acoustic backscatter signal from ADCP results to determine suspended solids concentrations and hence sediment fluxes along a measurement transect. These fluxes provided the key calibration data for the establishment of the model. The second phase of the study was a pilot modelling exercise designed to provide a foundation to the third phase of the study, the detailed calibration. The pilot study explored the choice of modelling methodology, key processes and parameters. In particular it was found that even a well mixed Estuary like the Thames which features a prominent turbidity maximum requires resolution in the vertical to establish the correct sediment balance in the model. This conclusion resulted in the choice of the fully coupled mud transport and flow model SEDI-3D, developed by EDF-LNHE as the modelling tool. The third phase of the study was the detailed model calibration including the use of objective statistical methods for assessment of model performance.