Controls on monthly estuarine residuals: Eulerian circulation and elevation
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The Dee Estuary, at the NW English–Welsh border, is a major asset, supporting: one of the largest wildlife habitats in Europe, industrial importance along the Welsh coastline and residential and recreational usage along the English coast. Understanding of the residual elevation is important to determine the total water levels that inundate intertidal banks, especially during storms. Whereas, improved knowledge of the 3D residual circulation is important in determining particle transport pathways to manage water quality and morphological change. Using mooring data obtained in February–March 2008, a 3D modelling system has been previously validated against in situ salinity, velocity, elevation and wave observations, to investigate the barotropic–baroclinic wave interaction within this estuary under full realistic forcing. The system consists of a coupled circulation-wave-turbulence model (POLCOMS-WAM-GOTM). Using this modelling system the contribution of different processes and their interactions to the monthly residuals in both elevation and circulation is now assessed. By studying a tidally dominated estuary under wave influence, it is found that baroclinicity induced by a weak river flow has greater importance in generating a residual circulation than the waves, even at the estuary mouth. Although the monthly residual circulation is dominated by tidal and baroclinic processes, the residual estuarine surface elevation is primarily influenced by the seasonal external forcing to the region, with secondary influence from the local wind conditions. During storm conditions, 3D radiation stress becomes important for both elevation and circulation at the event scale but is found here to have little impact over monthly time scales.
KeywordsPOLCOMS-WAM-GOTM model Dee Estuary Hypertidal Baroclinicity Residual circulation Residual elevation Estuarine circulation Storm surge
The authors would like to thank the reviewers of this manuscript for their help in improving the content of this manuscript. This research has been funded by NERC through National Capability funding to NOC and the projects FORMOST (NERC grant NE/E015026/1), FIELD_AC (EU FP7 programme grant 242284) and iCOASST (NERC grant NE/J005444/1). Partial support was also provided by the MERMAID EU (FP7-OCEAN.2011-1) project. Jane Williams (NOC) is thanked for providing the operational surge model output and meteorological (wind and pressure) data, and Clare O’Neill (NOC, COBS) is thanked for providing the offshore temperature and salinity fields to the Irish Sea and supplementing the meteorological forcing with air temperature, humidity and cloud cover to enable full atmospheric forcing.
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