Wave attenuation in federal navigation channels has become a pressing issue throughout the Great Lakes. Waves on the Great Lakes can reach heights of well over 20 feet in deep water and cause dangerous commercial navigation and recreational boating conditions. Additionally, erosion can be impacted putting private and public property in jeopardy. To remedy this situation, the Detroit District has begun installing wave absorber cells in some of their harbors.
Introduction to Great Lakes Wave Absorbers
Many Great Lakes harbor structures were originally built in the mid to late 1800's using stone filled timber cribs, but over the years weathering deteriorated them to point where repairs were necessary. The normal course of action has been to drive steel sheet pile on both sides of the deteriorating structure and pour a concrete cap over the top. Because steel sheet piling is a very reflective material, wave absorber cells were installed to dissipate wave energy traveling up the entrance channel.
How Do Wave Absorbers Work?
Channel geometry and coastal structure material contribute a large portion to wave attenuation. Water waves act similarly to sound waves. When they hit a highly reflective structure, they bounce off with relatively no energy absorbed. Steel sheet pile is a good example of this because it is vertical and non-porous so little if any wave energy is absorbed. By contrast, approximately 40% of a rubblemound structure consists of voids. These voids between the rocks can absorb a significant amount of energy, in turn reducing wave heights. A wave absorber is basically a modified rubblemound structure integrated into an existing steel sheet pile harbor structure. Figure 1 shows a wave before it enters the wave absorber.
Figure 1 - Waves before entering wave absorber
Figure 2 shows the same wave moments later. This wave has now traveled past the wave absorber. It is easy to see just how much energy can be absorbed. Both of these photos were taken at Pentwater, Michigan.
Figure 2 - Wave after leaving wave absorber
The following animation (Figure 3) shows a computer model of Pentwater Harbor. As it can be seen in the computer model, wave absorbers have been effective in reducing wave energy.
Figure 3 - Pentwater Harbor wave absorber animation
Wave Absorber Locations
Wave Absorber Location Map
This map shows harbors and locations that have additional wave absorber information available. Light blue dots are shallow draft harbors. Dark blue dots are deep draft harbors. Click on the name of a location to get additional wave absorber information for that location. Alternatively, click the harbor names located below the map.
Available links to information on the various wave absorbers on the Great Lakes.