Investigation of Surge and Wave Reduction by Vegetation
Watershed Physical Processes Research Unit
2009 Annual Report
1a.Objectives (from AD-416)
Conduct laboratory investigations to assess the dissipation of wave energy and water level changes induced by vegetation.
1b.Approach (from AD-416)
Use the wave tank facility housed at the NSL to investigate the effectiveness of vegetation for dissipating wave and storm surge energy. First, rigid elements in regular spacings will be subjected to monochromatic waves, and the results will be compared to currently established theory to ensure proper measurement and operation of the wave tank facility. Successful completion of this phase of work will lead to experiments with flexible elements and live vegetation being subjected to both monochromatic and random waves. Vegetation type and flexible model scales will be based on native vegetation in coastal areas.
Both inland and coastal shorelines are susceptible to erosion by waves and storm surges, but mechanical shore protection can be prohibitively expensive. Vegetative bank protection is self-sustaining and is a much more ecologically sound alternative. Adequate protection depends on both the type of vegetation and the amount available. It is essential for planning to be able to predict the performance of vegetation based on measureable quantities such as stem diameter and the number stems in a given area. The project is focused on measuring the performance of marsh grasses for attenuating waves in relatively shallow water. At this point, extensive improvements to the wave flume at the National Sedimentation Laboratory (NSL) are nearing completion. Among the improvements are: the new flume is significantly deeper and it is also wider and longer, it is now constructed of aluminum and polycarbonate which have much better longevity than the previous wooden flume, the viewing area has been expanded to 4 ft X 67 ft, an improved wave generator design is being implement, and provisions for current are being incorporated. Monitoring activities were performed through at least quarterly calls with the cooperators.