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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />NEED FOR THE PROJECT <br /> <br />Dam Safety Status <br /> <br />The State Engineer's staff has periodically inspected the Keeton Dam and <br />Reservoir. In a 1990 inspection, the reservoir was classified as a "Class 3" dam, a <br />structure for which failure would not be expected to result in significant property <br />damage or loss of life. Under this classification, the spillways are required to safely <br />pass the 100-year flood. The dam was inspected again by the State Engineer's <br />staff in 1997, when it was to be reclassified with a Class 1 or Class 2 hazard <br />rating, based on the proximity of the trailer houses below the dam. According to <br />the State Engineer's current rules and regulations, a Class 1 or Class 2 hazard rating <br />means that the spillway must be capable of passing, as a minimum, the flood <br />generated by 75 percent (Class 1) or 50 percent (Class 2) of the Probable Maximum <br />Precipitation (PMP). The 50 percent of the PMP is equal to approximately 17 inches <br />of precipitation for a 24-hour period, compared with approximately 4.7 inches for a <br />100-year precipitation event. Therefore, even the one-half PMP event would result <br />in a flood that is vastly more severe than the 100-year event. The peak flow at the <br />reservoir for the 100-year flood was estimated to be about 6,400 cfs. The existing <br />service and emergency spillways have a combined capacity of about 2,OOO-cfs. <br />Maintenance and operations requirements described in the 1997 dam safety <br />inspection report include the following: <br /> <br />1 . StoraQe Restriction - The inspector has required a ten-foot storage <br />restriction below the spillway crest elevation due to inadequate <br />spillway capacity. We understand that the water level has been <br />lowered below this level. It is noted that the outlet works pipe is not <br />large enough to allow the water level to be maintained at this level <br />during the spring runoff. In a verbal clarification, the inspector <br />acknowledged that it is unrealistic to expect the water level to comply <br />with the storage restriction at all times. <br /> <br />The proposed modifications to Keeton Dam will reduce the spillway <br />design flood requirement and increase spillway discharge capacity, <br />thereby addressing the spillway inadequacy. <br /> <br />22 <br />