U.S. Engineering Research and Development Center (ERDC) decided the best way to evaluate current harbors conditions in Chicago was to make a physical model and simulate various wave conditions. They created a 1:120 model to prototype of the harbor. Below is a picture of their model.
Figure 1: Picture of ERDC 1:120 Scale Model
Simulations are based on waves produced from three directions (25, 78 and 131 degrees relative to North) at two different levels (+1.68 meters and +1.78 meters). Wave periods range from 6.6 to 13 seconds and heights range from 1.71 to 6.16 meters. It should be noted that the current breakwater structure has crest elevations of only about +1.52 to +1.83 meters. These selections are based on Lake Michigan storm conditions with return intervals (how long until another storm of this magnitude returns) ranging from 2 to 100 years. The input parameters are summed in a table generated by the ERDC. This table displays model input values based on return year. Note, the longer the return interval, the larger the period and wave height.
The general simulation objective was to generate offshore waves using the criterion listed above and to measure the wave height using 29 wave gauges. The locations of the wave gauges were chosen in an effort to model the entire harbor, but it should be noted the more gauges were placed near places of concern (Navy Pier, water treatment plant, etc.). Once a proper model is created, the ERDC can simulate failure and do an impact analysis under all sorts of conditions.
However, the first simulation did not go as smoothly as the ERDC had hoped. When I talked with Drew Benziger from the U.S. Army Corps Hydrology and Coastal Department, he explained that software technicians suspected two problems during the first simulation. First, they believe bugs exist the software. Second, the model wave generator temporarily malfunctioned during part of the experiment. The ERDC did produce a table of results, but it was clear that model debugging and more simulation runs were needed to increase model accuracy.
Recently, the ERDC ran more simulations, but the data will not be released publicly until 2004. In the meantime, I decided to use a program called STWAVE to model the harbor. I then used some basic hand calculations in an effort to check the accuracy of my STWAVE model and ultimately the results from the ERDC simulation.