The purpose of the project is to reduce flood risk and damages in the upper portion of the Turkey Creek watershed. The proposed project consists of the construction of a system of new levees and floodwalls along Turkey Creek located in the City of Merriam, Kansas. The creek is subject to severe flash flooding through a fully developed, urbanized watershed. The non-Federal sponsor for project is the City of Merriam, Kansas.
The feasibility study focused on the Upper Turkey Creek watershed, located in a heavily urbanized area of approximately 20 square miles where Turkey Creek and tributaries are prone to damaging flash floods. The primary project sites considered for flood risk management plan formulation were: a) in the City of Merriam, Kansas; b) in the Unified Government of Wyandotte County and Kansas City, Kansas at the Roe Lane Industrial Park, and c) on a flood prone segment of Interstate 35 in Johnson County running between Merriam downstream to the Unified Government area. Only the City of Merriam site had an alternative plan carried forward for recommendation. The Unified Government declined to participate beyond initial study phase. There was no federal interest in structural measures to protect Interstate 35, and it already falls under the umbrella of an automated traffic management system along with a basin rain and stream gage system.
Structural alternatives for protection of downtown Merriam included channel widening, levees and floodwalls, and a combination of these. Nonstructural measures were reviewed in initial measures evaluation. A nonstructural buyout and relocation alternative was carried forward in detailed plan formulation in addition to the No Action plan. The buyout/relocation alternative was very high cost and did not compete economically with the cost effective structural plans. No nonstructural measures were retained in the recommended plan for federal participation. The local community will continue utilizing the existing stream gage network and alert mechanisms as part of their existing robust flood risk management and response system. Findings indicate that the most cost effective plan that addresses the flash flood threat and loss of life risk, and maximizes net annual benefits with least environmental effects, is Alternative 2d, the construction of a system of low height levees and floodwalls.
Under the Corps of Engineers concept of collaborative planning, after assessing the existing conditions in the watershed, environmental restoration measures were evaluated in a watershed system perspective along with flood risk management. This effort considered the possibility of multipurpose formulation including ecosystem restoration. Valuable baseline information and data were developed, and preliminary candidate sites for restoration identified. Due to there being no cost-sharing sponsor interested in ecosystem restoration in this heavily urbanized watershed, those measures were not carried forward into plan formulation.
The Recommended Plan is Alternative 2d, which is the National Economic Development (NED) Plan and consists of a levee and floodwall system along Turkey Creek in the City of Merriam. The features extend along portions of both banks from Shawnee Mission Parkway to Merriam Drive, for a reach of approximately 6,500 feet. Most of the protected area is on the right descending bank of Turkey Creek. The features were formulated and evaluated using updated NOAA Atlas 14 rainfall data. The plan includes 6,820 feet of floodwall up to 6.5 feet in height, 3,380 feet of levees up to 6 feet in height, a foundation system with approximately 12,400 auger grout piles, storm sewer modifications, and utility relocations. The plan includes a 2.14 acre-foot interior drainage area.
The total estimated first cost of the Recommended Plan is $37,579,000, with a fully funded cost of $43,697,000. The Federal share of the first cost is $ $24,426,000. The non-Federal share of the first cost is $13,153,000, with the LERRD requirement of $9,652,000 and estimated average annual OMRR&R costs of $40,800. Based on the current 3.375 percent discount rate and a 50-year period of analysis, the total equivalent average annual costs of the project are estimated to be $1,732,200. The equivalent average annual benefits are estimated to be $3,444,700 with net average annual benefits of $1,712,500. The benefit-cost ratio is approximately 2.0 to 1.
REPORT DOCUMENTATION: Pertinent documentation on the project, the results of the Civil Works Review Board, and subsequent Washington-Level Review Actions are listed below (items not linked will be provided when available):