Nearshore Bar Development in Southern Gulf of St. Lawrence

Abstract

The evolution of nearshore bars at three sites is examined using a mathematical model to simulate wave-bed interactions induced by progressive wind-generated surface waves. The wave dynamics are described by nonlinear, dispersive, shallow-water theory; the wave-induced flux of sediment is calculated using an associated mass-transport velocity; and the bed topography is described using a continuity equation. The resulting coupled system of nonlinear partial differential equations is simplified using a modal decomposition of the surface wave and is approximated numerically. The model is used to simulate bar development from an initial plane shoreface slope (equivalent to the mean slope at each site) using peak wave periods for moderate and severe storms observed in the region. Predictions of bar number and spacing show good correlation with measured bathymetric profiles. The model provides a physical explanation for the observed correlation of bar number and spacing to basin dimensions and nearshore slope in fetch-limited seas and large lakes. Differences in bar morphology at nearby sites are attributed in part to sediment supply constraints.