| This thesis analyzes the dynamics of rip current systems using both laboratory experiments and numerical modeling. The experiments primarily show the depth structure of rip currents. Offshore of the channel the rip current has strong depth variations, with strong seaward velocities near the surface and weak velocities near the bottom. The depth variations are shown to be sensitive to the total volume flux in the rip.; The nearshore circulation model SHORECIRC is applied for the rip currents case in a wave basin. The time-averaged flow properties show good agreement with the measurements. It is found that higher bottom stress leads to more stable flow where the rip current meanders less and fewer eddies are generated. Similar to the experiments, the flow in the two channels is found to behave differently because of the longshore variation in the topography. The wave current interaction creates forcing which prevents the rip currents from flowing too far offshore. The flow patterns are much more stable when the 3D dispersive mixing is included.; The vertical variations of the rip currents are modeled and show good agreement with the laboratory measurements. In the rip, the vertical variation of the current is governed by the convective accelerations in addition to the bottom stress and the short-wave forcing. The interaction of the currents and the waves, which was neglected in previous versions of SHORECIRC, turns out to play an important role in the vertical variation of the rip currents outside the breakers.; Finally, a study on the effects from varying topography and wave conditions is presented. When the channels are closer, a higher percentage of the total flux is returned by the rip currents rather than the undertow over the bar. When the shoreline is closer to the bar, less flow is returned by the rip currents. Waves with an incident angle create a longshore current which, if sufficiently large, has enough inertia to pass the channel without producing a rip current. When the waves break in the channel, the longshore variation in the setup which, drives the rip current is much weaker, thereby creating weaker rip currents. |
