Abstract: The Mill Creek Flood Risk Management Project will reduce equivalent annual flood damages to residential and commercial structures in the watershed by nearly 50%. The National Economic Development (NED) plan consists of two structural measures (channel modification & detention basin) and the buyout and removal or elevation of 89 repetitive loss residences. The project has a total first cost of $28.5M. The non-Federal sponsor for implementation of the project is the Metropolitan Government of Nashville and Davidson County.
Located in one of the most rapidly urbanizing areas of Middle Tennessee, the 108-square mile Mill Creek Watershed drains about 13% of Metropolitan Nashville and Davidson County, Tennessee and 6% of Williamson County, Tennessee. The watershed has a teardrop shape, is approximately 18 miles long and averages 6 miles wide. The project study map is included. The City of Nashville is represented by a purple dot located in the upper left-hand corner.
The City of Nashville experiences damages from flash floods due to historic encroachment into the floodplain. This encroachment causes a loss of flood storage capacity and insufficient flow capacity or flow restrictions along Mill Creek and its tributaries. The area along Mill Creek is heavily urbanized and includes extensive infrastructure associated with commercial, industrial, and residential developments. The objective of the project is to reduce flood risk and improve the overall quality of life for the residents of Nashville, Tennessee and surrounding communities. The planning objectives are: reduce residual risk to life and property in the Mill Creek watershed, increase flood attenuation opportunities, and restore riparian and floodplain connectivity in the Mill Creek watershed.
The plan recommended for congressional authorization is the NED Plan. The NED Plan includes a detention basin at Sevenmile Creek, with a 377-acre-foot capacity given the 0.2-percent flood, targeting moderate to major flooding; and bridge and channel modifications of 200 linear feet at Briley Parkway, targeting major flooding. The plan also combines these structural components with the buyout and removal or elevation of 89 residential buildings. The United States Fish and Wildlife Service issued a take statement for potential impacts to the federally listed Nashville Crayfish. No mitigation is required for stream and wetland impacts at this time.
The NED Plan has a first cost of $28,504,000, (October 2014 Price Levels); an annual cost of $1,251,000 including Operations, Maintenance, Repair, Rehabilitation and Replacement costs (OMRR&R); annual benefits of $2,390,000; net benefits of $1,139,000; and a benefit-to-cost ratio (BCR) of 1.91 at a discount rate of 3.375 percent, a 50-year period of analysis, and a three year construction period. The total project first cost is estimated to be $28,504,000 with a sponsor contribution of $10,745,000 and a Federal contribution of $17,759,000. The sponsor is responsible for 100 percent of the OMRR&R costs, estimated to be $51,728 annually.
Report Documentation: Pertinent documentation on the project, the results of the Civil Works Review Board (CWRB), and subsequent Washington-level review actions, are listed below (items not linked will be provided when available):
- CWRB Agenda
- Project Map/Placemat
- Project Summary
- CWRB Briefing Slides
- CWRB Lessons Learned
- CWRB Meeting Record
- State & Agency Review Comment Letters
- Documentation of Review Findings
- Signed Chief of Engineers Report
- Advance Copy to Congressional Committees
- ASA(CW) Memo to OMB
- OMB Response
- ASA(CW) Transmittal to Congress
- Signed Finding of No Significant Impact (FONSI)