Field observations of wave- and tidally-driven currents on a multibarred beach in a wind-sea dominated environment demonstrate that three different types of flow patterns occur: (1) a locally governed circulation cell, (2) an offshore current that is deflected shore parallel outside the surf zone and (3) a meandering longshore current. The transition from rip currents (flow patterns 1 and 2) to meandering longshore currents (flow pattern 3) occurs over a relatively small span of the tidal cycle and depends on the balance between cross-shore and alongshore forcing.
The cross-shore forcing is associated with the wave dissipation gradient between the bar and the rip channel, which is a function of the prevalent wave height, water level and rip channel depth. The alongshore forcing is a superposition of the tide and wave driven currents. The consequential longshore current suppresses the formation of a rip current when the flow is able to maintain its momentum across a rip channel (such as for a narrowrip channel). However, if the flow velocity reduces to zero within the rip channel (wide rip channel, low energy wave conditions or tidal current opposing the wave-driven current), a rip current is likely to be formed.The offshore extent and orientation of the rip current are determined by the tidal current, which deflects the rip current alongshore outside the surf zone. Rip currents extend furthest offshore in the absence of tidal currents or when tidal currents are weak and opposed to the wave-driven longshore current.