Longshore currents over a multi-barred beach: Field measurements and dissipation models

Abstract

Strong longshore currents were measured on a multi-barred beach at Stanhope Lane beach on the northern coast of Prince- Edward Island in Canada. The long time scale variability of the measured currents suggested considerable time dependence. In the scales of several days, the currents variability were correlated with the corresponding mean wind vector.There was lack of coherence between the longshore currents over different bars. However, flow on the same bar as measured by various current meters was coherent. This suggested that flow over different bars were forced independently. There

was no correlation between the estimated local radiation stress component and the longshore current response. This was interesting because longshore currents are clearly forced by radiation stress. The observed currents were compared to theoretical estimates based on a dissipation model. The results showed that longshore currents over a complex topography could be reasonably modeled using turbulent momentum exchange and non-linear bottom friction without surface wind stress. Both the observations and theory suggest that longshore currents are strongly tied to individual bar crests. However, the observations

were consistently displaced landward relative to the theoretical estimates.