Prediction of cross-shore sediment transport at different spatial and temporal scales

Coastal sediment transport and associated morphological change can be examined at many spatial and temporal scales. These scales range from instantaneous movement of single grains on a time scale of the local turbulence to seasonal and long-term movement of large sand bodies such as longshore bars and tidal deltas. Researchers have begun to recognize that a first-principles (microscale) approach to calculating long-term and large-scale (megascale) coastal change may not be possible or even adequate. Therefore, new approaches are being sought to advance quantitative understanding and prediction of large-scale coastal behavior. The present paper opens with a discussion of compatible spatial and temporal scales for calculating sediment transport and morphology change. Motivation is given for the need to calculate morphologic change at scales greater than the typical one of microscale. Example calculations are made at different scales, showing the assumptions and approximations of each. The main conclusion is that calculations at different scales can be related and reconciled if limitations in prediction of initial and boundary conditions and in the fluid forcing are recognized.