Wave Processes on Lake Mendota

Madison, Wisconsin

Nearshore Processes:

A tighter grid (1m by 5m) was created to simulate nearshore wave processes in Lake Mendota. Such processes include refraction, shoaling and breaking. A case study is presented here along the northern edge of Lake Mendota, near the Yahara River Inlet. Using the coarse grid (20m by 20m), and a south wind, a peak wave height of 0.5m and Period of 3 seconds was obtained. These results were input into the tighter grid as offshore conditions. As seen above the offshore boundary is along the left (south) side of the grid. This wave height and period is assumed constant along this boundary. As the wave propagates to shore, refraction is noted by the change in direction of the vectors. The wave also begins to shoal and break as it gets close to the shore. A profile of water surface elevation was cut and is shown below. Here the effect of water level is also shown to see the differences it creates along the shoreline. As shown below, the wave height with a higher lake level is allowed to propagate further into shore because of the increased water depth. One can also look at the results above to make some qualitative observations on shoreline erosion potential. Breaking waves can induce sediment suspension and if they occur along angles with the shoreline, they can help induce erosion of shorelines. Preliminary results shown above can observe a northerly component of the wave vectors along the shoreline for this south wind run. This could indicate areas of erosion along the shoreline and deposition near the north end.

Author: Chris Petykowski

Date: Dec 20, 2001

****The computer model used in this project is the MIKE 21 Nearshore Wave Module, produced by Danish Hydraulik Institute. All results are preliminary in nature, have not been verified extensively and are NOT intended for any use by others.