Wave Processes on Lake Mendota 

                               Madison, Wisconsin

Introduction

Wave Model

Wave Generation

Nearshore Processes

                                                           

Wave Model:

The wave model chosen for this project was MIKE 21 Nearshore Wave Module.  MIKE 21-NSW is a 2 - Dimensional model which can simulate wave processes such as wind-wave generation, refraction, shoaling and breaking analyses.  The model is used as a tool to assist in performing the numerous calculations involved in defining a wave climate. 

Wind wave generation can be handled by a number of methods in the model.  This model utilized the JONSWAP method for easy calculation comparison.  The model uses a conservation method approach to handle the shoaling processes.  Wave Breaking Criteria is defined by the method of Miche (1944), and wave breaking profile is defined by method of Battjes & Janssen ( 1978).

MIKE 21 NSW can also estimate effects of bed friction and currents.  However, these sub-routines were disabled to fully understand the results from the wave transformations.  Once the transformations results are confirmed, a follow up assignment could be performed to take into account lake circulation and currents. 

Limitations exist on MIKE 21 NSW as with any computer model.  One limitation is the fact that the module does not include diffraction effects.  This should be taken into serious consideration when selecting study areas.  An area with significant diffraction effects would not be correctly modeled with the NSW module.  Another limitation is the model cannot simulate mixed seas (wind wave and swell).  The last limitation is the model cannot simulate waves with periods beyond the range of 0.21 to 21 seconds.

Input to the model is a surface or grid of the bathymetry.  This is obtained by digital xyz bathymetry data.  The xyz data can be transformed to create the grid or bathymetry surface used by the model.  A grid with 20m by 20m resolution was created to obtain wave generation characteristics.  A tighter grid (1m by 5m) was then created to simulate nearshore processes.       

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.