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p,.ojectFol'm.lbtion 1 " I Project Formulation T. 10 N., R. 69 W., near the mouth of Rawhide Creek were clllttlared to Structure B-2. Structure B-2 was selected because it prmoides about equal benefits at a lower cost than any combination of the other three structures. The Larimer County Board of Ca:missioners is setting up enabling ord- inances that will pennit their wning the flood risk areas on Boxelder Creek to encourage continued agricultural use or for future parkway areas along the channel. B-S Alternatives Flood proofing measures will be required on any building in the area so that no damage will occur to the improvement for the 1000~year frequency stonn. Alternatives to Structure B-S studied were one upstream about 71}1} feet and the other downstream about Z,61}1} feet from the present site. All three sites for Structure B-S were evaluated and it was decided that the middle site would meet project objectives and sponsor requirements. B-2, B-3, B.4 Combination A three-floodwater retarding structure program consisting of structures B~2, B-3 and B-4 was evaluated and compared with the proposed five structure program. It did not provide adequate reduction of floodwater and sediment damages in the upper reaches of the watershed and did not meet the objectives of the sponsors. OIannel Improvement A channel iJrq>rovement proposal was ueveloped that ""Juld eliminate re. rnaining damages fron the 100-year frequency storm with the five flood- water retardir18 structures installed for the area between Interstate Highway ZS and the Cache la Poudre River on Boxelder Creek. The plan consisted of realigning, enlarging and stabilizing the channel for about 9,300 feet at a construction cost of about $ZOO,OOI} and a land rights cost of about $55,000. The proposal is economically feasible but the sponsors believe that a channel improvement is not desirable to provide a basis to promote the residential and c~rcial dev~lopment &f this type of land especially when consideration is given to: (1) overall costs for providing a lOO-year level of protection to this area; (2) other lands are available outside the flood plain area and (3) the operation and maintenance responsibilities for a cha.rulel of this type. The sponsors made a WTitten request that the channel improvement be deleted as a project measure and t:hat land use restrictions and zoning be imposed to reduce future damages on the flood plain lands of Boxelder Creek that are still subject to flooding from the 100-year frequency flood' wi!.~ !."'e works of iT.;lrovement ir,sullc<i. I , , Drainage and Irrigation No problems or project objectives for irrigation or drainage, that would require project structural measures, exist in the watershed. Fish and Wildlife and Recreation Fish and wildlife and recreation developments are desirable in the water- shed. Low water yields from the watershed and adjudicated rights to the existing water supply make pennanent storage for recreation or wildlife unfeasible. In addition, the B-Z site, where development is most desirable because of size and location, would be geologically difficult and eJCpensive to design to maintain a pennanent pool. A positive cutoff is not practical because it would interfere with the ground water flow and sealing the entire pool area would take extensive blanketin!{. For these reasons and by sponsor preference no multi-purpose conservation storage is included in the project proposal. The land treatment and structural measures proposed will enhance the environment of the water- shed and preserve and improve the existing fish and wildife resources. I I , I , I , Follawing a request by the Larimer County Board of Camlissioners the Colorado Water Conservation Board has approved tile designation of the flood plain area of Boxelder Creek that is subject to flooding from the 101}-year frequency storm runoff with the project works of improvement installed as a flood prone area. The Flood Plain Infomation Report ...aspreparedbytheSoilConservationServiceforthispurpose. -19- -20-