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The above gate repair is recommended for the existing dam or the enlargement. For the enlarged <br /> dam the outlet tunnel must be extended about 190 feet from the existing toe to the enlarged toe. <br /> The extended tunnel would be the same dimensions and slope as the existing tunnel. <br /> 12.3 Spillway: The sizing of the spillway involves several issues. The first issue is the <br /> classification of the dam which is presently an intermediate Class II which requires that the <br /> spillway pass 50% of the probable maximum precipitation (PMP); however, the existing <br /> reservoir is close to being a Class I dam which requires 100% of the PMP, because of the <br /> potential loss of life downstream. If the reservoir is enlarged, the dam will probably become <br /> Class I. The second issue is the State Engineers review of the PMP for high elevation drainage <br /> areas which will not be completed until about 1996 (has not occurred as of 2001). <br /> Based on current criteria and 50% of the PMP for the existing dam, the spillway needs to be 60 <br /> feet wider (total of 80 feet for the existing dam height) or 20 feet wider with a minor 3 foot <br /> increase in the embankment height. The 3 foot increase could be accomplished by adding <br /> material to the crest. Because of the reevaluation of the PMP, any work on the spillway, if the <br /> embankment is not enlarged, can be delayed until about the year 2005. <br /> The spillway for the enlarged dam is assumed to be required to pass 100% of the PMP; however, <br /> the amount of the PMP and resulting flood has not been determined. The spillway sizing and <br /> embankment height for adequate freeboard is based on current criteria. <br /> The inflow design flood would be about 8000 cfs requiring a spillway 60 feet wide and 7 feet <br /> deep, capable of passing 4000 cfs in combination with a surcharge capacity of 1100 acre-feet. <br /> The spillway could be located at the present location, on the east side of the embankment, or on <br /> the west side of the embankment. The present location was selected for the feasibility designs <br /> because of the existing channel to Hay Gulch. A spillway on either abutment would have <br /> problems with routing of the water to Hay Gulch. <br /> The spillway would include an ogee crest with a concrete chute on the downstream side of the <br /> embankment. The chute might be layered roller compacted concrete or formed concrete with <br /> energy dissipaters; the chute would be 60 feet wide at the crest and narrow to about 25 feet at the <br /> toe of the embankment. The existing channel would be used from the toe of the embankment <br /> with some modifications to widen the lower end of the channel and route water to Hay Gulch. <br /> 23 <br />