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December 2007 Georgetown – Final Alternatives Analysis Report <br />page 1 <br />1.0 Introduction <br />The Town of Georgetown applied for a Junior Water Storage Right decree in 1999 to store and use 315 ac- <br />ft of water in Georgetown Lake. The estimated total capacity of the lake and lagoon is 385-387 ac-ft. <br />Downstream users opposed the decree due to problems with the existing outlet capacity. Issues with the <br />outlet capacity include existing gate operation and maximum release capacity. This report examines <br />several alternatives addressing the maximum release capacity issue. <br />2.0 Site Specific Information <br />The Georgetown Lake and Dam are located off of Interstate 70, north of the Town of Georgetown on Clear <br />Creek. The dam release capacity is about 275 cfs, which includes 235 cfs from the existing 48” square <br />slide gate on the spillway, and 40 cfs through the hydro plant downstream. The hydro plant currently <br />acquires water from the lake through a siphon, which goes over the embankment. The purpose of this <br />project is to investigate options for releasing additional incremental flows of 75 cfs, 150 cfs, and 225 cfs. <br />The current release of 275 cfs and the highest additional incremental release of 225 cfs give a maximum <br />release of 500 cfs. <br />The Town is required by State statute to release all inflow that is stored out of priority. It has been <br />estimated that most inflows can be released through the dam in approximately 24 hours with a 500 cfs <br />discharge rate. <br />3.0 Existing Features <br />The Georgetown Lake Dam is a composite dam consisting of embankment sections on either side of a <br />concrete ogee spillway section. A 48-inch by 48-inch slide gate is located in the spillway section on the left <br />side (looking downstream) and serves as the low level outlet for the dam. <br />The ogee spillway section of the dam is 100-ft long and 13-feet high. The crest of the spillway is at <br />elevation 8447.85-ft per the NAVD 88 Datum 1 . The spillway apron is at elevation 8434.85-ft. The <br />maximum spillway base width at the apron elevation is about 19.5-feet. The top of the dam is at elevation <br />8457.85-ft. See Figure 1 below. <br />The existing outlet works consist of a 48-inch square ARMCO slide gate on the face of the spillway. A 48- <br />inch square concrete conduit passes through the spillway at elevation 8434.85-ft. The conduit outlet is <br />contoured to compliment the ogee shape on the downstream side of the spillway. The gate is operated <br />either manually or with a recently installed solar powered electric actuator. <br />An approximately 30-inch diameter siphon penstock constructed over the dam embankment serves a <br />privately-owned hydro plant downstream. Operation of this siphon is considered unreliable by State <br />officials and downstream users. <br />x 1 The elevations included in this report are based on the NAVD 88 datum. The referenced maps are <br />based on the NGVD 29 datum, which is 4.89-ft lower than NAVD 88.