• Topographic Survey
• Bathymetric Survey
• Sediment Sampling and Analysis
• Water Level Analysis
• Offshore Waves
• Numerical Analysis-Waves, Circulation, Sediment Transport. SWAN, CMS-Wave and CMS-Flow
• Report and Presentation
Challenge
Immediately after the construction in 1988, significant sedimentation started to be documented at the harbor entrance and along the south side of the north armor stone breakwater. The Marina hosts 217 total boat slips and is a major focal point for boating and fishing access on Lake Erie. The sedimentation impacts the recreational use of the harbor. Every year, over 10,000 cubic yards of sediment needs to be dredged.
Solution
GZA was commissioned to conduct a numerical analysis to quantify the sediment transport processes and identify potential solutions that will reduce the need for frequent maintenance dredging operations. A number of alternatives were considered in order to reduce the need for annual, long-term maintenance dredging for the basin and the harbor entrance area. The alternatives considered were grouped in two categories: 1) revised dredging practices; and 2) harbor structural modifications. Our study found that revising the dredging practices would not result in significant construction savings. Five different harbor structural modifications were included in the model, with estimated benefits from modeling runs at selected storms, with sedimentation rates computed as a percent reduction (or increase) comparing to the existing conditions. Three of the main breakwater modifications would result in a sedimentation reduction rate of 63%, 48%, and 42%, respectively, compared to the existing conditions. One alternative increases the harbor footprint and provides space for additional slips, with economic benefits. The wave transformation was performed with SWAN (Simulating Waves Nearshore) 2-Dimensional model and the sediment transport with Coastal Modeling System (CMS)-Wave and CMS-Flow numerical model. GZA recommended three alternatives be considered by the Town of Evans (“Town”), with a marina economic analysis and Net Present Value analysis (accounting for all costs over a reference period of 20 years with a reduced dredging rate) to identify the Preferred Alternative. GZA also recommended changing the location of the sediment disposal area, or slight relocation upland, away from the wave run-up active area.
Benefit
GZA carefully analyzed and planned proposed harbor improvements that will reduce the sedimentation rates.