PROPERTY MANAGEMENT PROJECTS
Lake Bank Erosion Assessment, Retrofit Design and Implementation
Danforth Creek Subdivision, Palm City, FL
The Danforth Creek subdivision storm water management system consisting of four (4) interconnected lakes was built in the early 1990’s. Three (3) smaller lakes are interconnected to a major central lake.
Problem: The Danforth Creek subdivision lakes have been experiencing steady shoreline bank erosion. Lake bank erosion is caused by a variety of natural factors including:
- Continuous change in water elevation due to the change of seasons (groundwater table) and from lake withdrawals for irrigation needs,
- Strong winds can cause waves that damage the shoreline of rather large and long lakes,
- Stormwater runoff causes damage without proper drainage, especially when lake levels are low and the shoreline is exposed,
- Fish, such as the armored catfish, can burrow into the bank.
Typical problems experienced by homeowners at lake shorelines included: backyards "shrinking" as the lake bank erodes and the shoreline moves closer to their property line; unstable lake banks get steeper; visible gullies and exposed drainage and/or irrigation pipes.
Solution: WRMA established the severity of problem and performed a topographic site visual survey to measure and document existing lake bank slope, lake easement right-of way encroachments, tree trunk and canopy extent along shoreline, utilities, culverts, and site accessibility for alternative design analysis. The visual inspection identified locations of lake bank erosion and assigned a level of severity, a type of erosion and a potential erosion cause. Each location was photographed for documenting and further review. A Geotechnical Survey (soil borings) was also performed to establish native soil stability factors of safety. Geotechnical services included 26-foot deep Standard Penetration Test Soil Borings and Failure Evaluation (probable cause of shear failure and surface sloughing in the very loose sub-soils along lake banks). The final phase of this project is currently in pre-construction and will include the implementation of the recommended retrofit design alternatives.
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