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LONG HOLLOW RESERVOIR <br />FEASIBILITY STUDY <br />1.0 EXECUTIVE SUMMARY <br />The Long Hollow Reservoir (LHR) is located in southwest La Plata County, approximately 22 <br />miles southwest of Durango, Colorado in Sections 29, 32, and 33, Township 33 North, Range 12 <br />West of the New Mexico Principal Meridian. The private parties shown on Exhibit 3.1-1 hold <br />ownership of the dam and reservoir site. <br />Feasibility level drawings for a 5,400-acre-foot (AF) reservoir are presented in Exhibits 3.1-1 <br />through 3.1-5 at the end of this volume in 11-x-17-inch format. The drawings, which will be <br />referred to throughout this report, were developed by combining the most advantageous <br />alternative for the dam and appurtenant structures based on available data.. The reservoir will fill <br />to the 5,400-AF capacity in 4 of 14 years, with an average fill of 3,540 AF per year. LHR will <br />release all or nearly all stored water in 10 of 14 years. A 300-AF La Plata River Compact <br />(Compact) reserve pool in LHR will be used to deliver water to New Mexico during the mid- <br />summer low-flow period when the La Plata River in Colorado must be administered as a split <br />river. <br />The Rules and Regulations for Dam Safety and Construction firom the Office of the Colorado <br />State Engineer (SEO) classifies dams according to their hazard and size (Department of Natural <br />Resources 1988). The regulations designate a dam for which loss of human life is expected in <br />the event of a failure as a Hazard Class I dam. Long Hollow dam will be a hazard Class I dam <br />and is in the large-size classification because it will have a height greater than 100 feet and a <br />reservoir capacity greater than 1,000 AF. <br />The SEO's proposed regulations require the inflow design flood (IDF) for determining the <br />spillway capacity of a Class I large-size dam to be 90 percent of the probable maximum <br />precipitation (PMP). The IDF flow predicted for LHR is based on a 6-hour local storm that <br />991-077.120 Wright Water Engineers, Inc. Page 1 <br />April 2005 4/14/2005 9:25 AM <br />