longshore current

A two-dimensional, time-dependent numerical model for finite amplitude, shallow-water waves with arbitrary incident angles is developed to predict the detailed wave motions in the vicinity of the still waterline on a slope. The numerical method and the seaward and landward boundary algorithms are fairly general but the lateral boundary algorithm is limited to periodic boundary conditions. The computed results for surging waves on a rough 1:2.5 slope are presented for the incident wave angles in the range 0-80°. The time-averaged continuity, momentum and energy equations are used to check the accuracy of the numerical model as well as to examine the cross-shore variations of wave setup, return current, longshore current, momentum fluxes, energy fluxes and dissipation rates. The computed reflected waves and waterline oscillations are shown to have the same alongshore wavelength as the specified nonlinear incident waves. The computed variations of the reflected wave phase shift and wave runup are shown to be consistent with available empirical formulas. More quantitative comparisons will be required to evaluate the model accuracy.

In 1981, the Pacific oyster Crassostrea (Magallana) gigas was illegally introduced for aquaculture purposes in San Blas Bay located on the southern coast of Buenos Aires Province, Argentina. The presence and colonization of oysters north of Río Negro Province, 100 km to the southwest of San Blas Bay, was reported in 2005. There remains a controversy about whether or not the oyster was capable of migrating southwest to Río Negro Province from San Blas Bay, which motivates the present investigation. While one part of the local community supports that the Pacific oyster migrated naturally southwestwards reaching the northern coast of Río Negro in 2005, another faction denies this hypothesis. The aim of this work is to determine whether or not the planktonic larvae of this invasive species could have reached the mouth of Río Negro. We assume that the oyster can produce larvae after 2 years of being set on the bottom and the larvae can drift as zooplankton during 1 month. Longshore mean current was considered as the single forcing in natural transporting of oyster larvae along the coast. Shallow water wave parameters were computed from deep water wave parameters obtained from the Simulated WAves Nearshore (SWAN) model driven by NCEP/ NCAR I global reanalysis. The migration path was computed from longshore current intensities, which were estimated using the modified experimental expression given by Longuet-Higgins. Results obtained in this paper support the possibility that the Pacific oyster larvae could have arrived at Río Negro Province, between 2002 and 2005.