Abstract Only a few observations are currently available from the tidal marine environment which can be used to evaluate sediment transport formulae. Research carried out on sandwave movement indicates that most of the sediment transport is restricted to the crestal area. Mean rates of sediment transport were calculated from volumetric changes, between successive slack waters, over a nine day period spanning Spring tides. The results were used, in conjunction with boundary-layer flow measurements, to calculate the threshold velocity for the movement of sediment and also to evaluate Bagnold's (1963) dimensionless coefficient of proportionality, K. Comparisons are made with the flume data of Guy et al. (1966) for the appropriate sediment grain size. The dependence of K, upon normalised excess shear stress was found to be weaker than that suggested by Sternberg (1972). Within the range of flow velocities considered there was no indication that K tended towards a constant at high flow velocities.