Modelling solute transport in the Tweed Estuary, UK using ECoS

Predictions of the tidal variation in water elevation and the advection-dispersion of solutes have been made for the Tweed River Estuary (UK) by application of a modelling package called ECoS. The estuarine model consisted of a one-dimensional hydrodynamic scheme with tidally variable channel cross-sectional area. The model was driven by predicted tidal elevation at the mouth of the estuary, and combined fluvial inputs observed for the River Tweed at the head of the estuary and the River Whiteadder, a tributary within the tidal reaches. Model results were compared to field data collected during routine surveys of the river estuary, conducted as part of Natural Environment Research Council Land-Ocean Interaction Study (LOIS). Validation protocols showed that the model reproduced tidal- and river flow-driven changes in surface elevation, and explained over 90% of the variation in salinity when field data were averaged through the water column. The study demonstrates that ECoS can be used to model tidal hydrodynamic processes, and that in a stratified estuary a depth-averaged model is able to replicate depth-averaged data. However, in rapidly rising and partially stratified estuaries with highly variable river flows, sufficient and appropriate data must be available for model set-up and validation. This has implications for how field studies should be planned and conducted.