Mapping of bathymetry and tidal currents in the Dee Estuary using marine radar data

Bathymetric maps and tidal currents have been mapped in an estuarine environment through the analysis of marine radar image sequences to a range of 4 km and with 100 m grid spacing. the Dee estuary is located on the southern side of Liverpool Bay in the United Kingdom and contains a complex system of intertidal sand banks and channels with a peak spring tidal range exceeding 10 m. In order to understand how the estuary is evolving it would be helpful to regularly observe the positions of the sand banks and channels and the wave and current forcing driving the evolution of these features. To this end a marine radar has been deployed on an island in the estuary from which ten minute sequences of images of the sea surface are recorded once per hour. By fitting a wave dispersion equation to the observed wave behaviour it is possible to map the underlying water depth and mean current provided waves are visible on the radar images. Radar derived water depth and current maps recorded around a single high water were compared with survey data and show that in regions where the waves are feeling the sea bottom, the radar derived depths are generally witin +/-1 m of the survey data.