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Long Hollow Reservoir <br />Feasibility Study <br />• storage in the Red Mesa Aquifer is estimated preliminarily to be 165,000 AF, with approximately <br />one-half (or 82,500 AF) available for withdrawal. <br />WWE found that the amount of water stored in the Red Mesa Aquifer could be increased through <br />artificial recharge practices. Artificial recharge of the aquifer could be reasonably expected to <br />increase the stored water available for withdrawal to 125,000 AF, with a maximum of 200,000 <br />AF. Groundwater discharges to surface streams could be increased from increased irrigation <br />recharge and infiltration of water at recharge basins. Recharge to the Red Mesa Aquifer could <br />provide needed temporary storage to better manage Compact deliveries and the water resources <br />in the La Plata River basin by providing an increase in base flow in the La Plata River and Long <br />Hollow. <br />3.3 Dam Hazard and Size Classification <br />The location of the reservoir and the confluence of Long Hollow with the La Plata Rivers are <br />• shown on Exhibit 2.1-1. A field reconnaissance was conducted to evaluate the consequences of <br />the failure of Long Hollow dam, absent flooding conditions, assuming that the reservoir was full. <br />The confluence of Long Hollow and the La Plata Rivers is approximately 0.5 mile downstream <br />of the enlarged embankrnent. The enlarged dam will impound more than 100 feet of water at the <br />m~imum water surface. In our opinion, if this water was released as the result of the dam's <br />failure, the flow depths and velocities on the La Plata River could result in loss of life. <br />The Rules and Regulations for Dam Safety and Construction from the SEO classifies dams <br />according to their hazard ar~d size (Department of Natural Resources 1988). The regulations <br />designate a dam for which loss of human life is expected in the event of a failure as a Hazard <br />Class I dam. The enlarged dam will fall in the large-size classification because it will have a <br />height greater than 100 feet and a reservoir capacity greater than 1,000 AF. <br />The SEO's regulations require that the IDF for determining the spillway capacity of a Class I <br />large-size dam shall be the PMP. <br />~ <br />991-077.120 Wright Water Engineers, Inc. Page 15 <br />April 2005 <br />