Stream Restoration of Liberty Hills Pond: Where Geomorphology & Bioengineering Meets Urban Aesthetics & Hydraulics
Jeffrey B. Shaver, PE, CFM, CPESC
Jake Ward, EI
Civil & Environmental Consultants, Inc.
Nashville, TN
The Liberty Hills subdivision in Franklin, TN was developed with a retention pond that was constructed on the confluence of North Ewingville Creek and an unnamed tributary to Harpeth River. The outfall from the pond continues as the unnamed tributary and flows into the adjacent Royal Oaks subdivision. The retention pond has a history of ongoing maintenance issues including sedimentation within the pond and stream bank erosion downstream of its outlet.
The Liberty Hills Homeowners Association (HOA) and City of Franklin have evaluated various options to maintain the pond while alleviating erosion and mitigating flooding downstream of the pond in the Royal Oaks subdivision. Previous attempts to mitigate these issues such as regular sediment removal and streambank armoring with gabion baskets and concrete barrier walls have proved to be ineffective. Silt and sediment continued build up within the pond, requiring repeated dredging to maintain storage capacity within the feature. A study was conducted to evaluate options to alleviate the maintenance issues associated with the pond, including additional excavation of the pond to remove sediments or draining the pond and re-establishing the stream channels through the current footprint of the pond.
The study concluded that the most economical and preferred ecological approach would be to remove the retention pond and restore the stream channels within the footprint of the pond and beyond the pond limits. This approach will alleviate the ongoing maintenance issues associated with removing sediment from the pond as well as help alleviate the streambank erosion that was occurring downstream of the pond. The restoration work included removal of the pond and its associated outlet structure to remove the permanent pool, re-alignment of the culvert under Liberty Hills Drive to better align the culvert with the unnamed tributary, re-establishment of stream channels using natural channel design techniques, and restoration/stabilization of eroded stream banks of the unnamed tributary downstream of the pond. This approach eliminated ongoing maintenance issues associated with the retention pond, stabilized an eroding section of the unnamed tributary in the Royal Oaks subdivisions, and restore approximately 1,500 feet of perennial, intermittent, and ephemeral stream.
About Jeffrey B. Shaver, PE, CFM, CPESC
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About Jake Ward, EI
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