California Sea Grant College Program

Nearshore circulation is the mean flow in the region from the shoreline to about a kilometer offshore. An understanding of nearshore circulation is important to understanding sediment transport, pollution dispersion, and the distribution of various marine invertebrates. This thesis addresses the following question. Are the dynamics of the alongshore current described by a 1-D balance (neglecting along­ shore variations) between wave and wind forcing against bottom stress and lateral mixing? Observations are used to close integrated momentum balance, suggesting that a 1-D balance is appropriate. The alongshore bottom stress must be parame­ terized in models. Various parameterizations are examined in detail and it is found that most nonlinear parameterizations are adequate for modeling purposes. The alongshore current may also be unstable. For marginally unstable Reynolds num­ bers, the instability of the alongshore current is investigated analytically, and an amplitude equation for a weakly nonlinear shear wave is derived. The characteris­tics of a equilibrated shear wave (obtained from a 2-D numerical model) are well described by the theory. FUture work will involve numerical modeling of nearshore circulation, and a nearshore circulation model I have implemented is described.