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e EXECUTIVE SUMMARY The focus of the Dry Creek Flood Control Project is to protect structures located in the floodplain of the lower Dry Creek drainage basin, a region of Larimer County and Fort Collins that covers an estimated 16 square miles, see Figure ES-l. Presently, there are over 800 structures subject to flooding in the existing FEMA floodplain from the Dry Creek flood design event, which is based on the pre-l 999 hydrology. For purposes of this study the Dry Creek basin has been divided into 3 key areas defined as: Upper Basin - above Douglas Reservoir; Middle Basin - between Douglas Reservoir and the Larimer- Weld Canal; and Lower Basin - below the Larimer-Wcld Canal to the confluence with the Cache la Poudre River. e . The alternative projects developed in this report are the result of a cooperative effort to address regional and local flooding issues identified by the City, County, and affected irrigation companies through the construction of a structural flood control project. The vehicle for a cooperative solution was established with an Intergovernmental Agreement executed in 1997 between the City and the County. Additionally, the Final Recommended Plan that comprises the selected alternative and an irrigation water supply pipeline would provide flood control benefits to the middle drainage basin as well as water management enhancement and flood control bencfits to the Larirner and Weld Irrigation Company (Company). Plan elements include rnaximizing the use of detention capability existing in the private Douglas Reservoir owned by the Company, in lieu of building a new storage facility. Additionally, the new 48-inch irrigation water supply pipeline of about 22,000 feet with a capacity of 75 cubic feet per second (cfs) is planned between Douglas Reservoir and the Terry Lake Inlet Feeder Canal provides better water management and flood interception protection to the Company and the Dry Creek lower basin respectively, see Figurc ES-2. The pipeline improvement provides for access to the Company's storage facility at Douglas Reservoir and the Larimcr - Weld Irrigation Canal (L-W Canal) for flood protection. If the proposed detention in Douglas Reservoir was developed and a separate canal built as an independent flood control proj ect, the construction cost would be about double the cost of the proposed project. Estirnated project costs of the storage and diversion alternative range from approxirnately $12.6 million to $13.3 million including the cost of the improvements, the irrigation supply pipeline, the East Vine Diversion, the flood control structures, final design and construction engineering, permitting, construction right of way and contingency. The cost of rights-of-way for flood easements for detention structures was estimated to be about $2.1 to $3.99 million depending on the option and including the easement for the pipeline. Financial analyses developed in the repoI't assurne a project life of 50 years and an interest rate of 7 percent per year. The funding request from the Colorado Water Conservation Board (CWCB) Construction Loan Fund is approximately 75 percent of the total project cost or about $9.3 Million. The annual debt service on a 30-year, 4.5-percent CWCB loan is approximately $571,000 Larimer County and the City of Fort Collins plan to implement a Dry Creek Basin Stormwater Utility that will collect revenue from basin landholders that benefit from the project. The estimated average annual revenue during the repayment period is about 5