Measurement of recent intertidal sediment transport in Morecambe Bay usingthe waterline method

An illustration of how sediment transport may be measured over a large dyna mic intertidal area at reasonable cost and spatiotemporal resolution using the waterline method employing remote sensing and hydrodynamic modelling is presented. Areas and volumes of accretion and erosion were measured in the study area of Morecambe Bay in north-west England over the period 1992-97. Tidal asymmetry is considered to be the dominant agent of sediment movemen t in the bay, with waves being of secondary importance. Waterlines (i.e. land-sea boundaries) were extracted from 31 synthetic aper ture radar images of the bay covering a substantial fraction of the tidal r ange. Heights were attached to the waterlines using water elevations from n ested hydrodynamic tide-surge models. Interpolation in space and time was c arried out to produce a continuous spatiotemporal height map of the interti dal zone. Height maps with a spatial resolution of about 50 m and height ac curacy of about 40 cm were constructed over an area of about 350 km(2). Str ong temporal decorrelation in the bay limited the height accuracy achievabl e. Differences between height maps for 1992-94 and 1995-97 allowed sediment vo lume changes to be extracted. The intertidal region showed a loss of 16.1 /- 4.5 x 10(6)m(3) over the period, almost all the change being due to a si gnificant decrease between mean sea level and the low water mark. Changes w ere also measured in three of the main river estuaries within the bay, the Leven, Kent and Lune. These included movement of the Leven north-east by ab out 2 km cutting into Cartmel Wharf, accretion seaward of Grange-over-Sands and changes in the low water channels at the mouth of the Lune. These chan ges could be used to validate sediment transport models of the bay. (C) 199 9 Academic Press.