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Feasibility Study <br />WRCC, Inc. <br />Cobb Lake Inlet Structure Replacement <br />1.0 INTRODUCTION <br />A. Background <br />Cobb Lake is an approximately 22,300 acre-feet water storage reservoir located northeast of Fort <br />Collins in Larimer County that is owned and operated by WRCC, Inc., (formerly Windsor Reservoir <br />and Canal Company). The reservoir is supplied by the Poudre Valley Canal that diverts water <br />directly from the Cache la Poudre River. The existing ditch inlet to the reservoir consists of <br />engineered cast-in-place concrete structures that were constructed in the early 1900's. <br />The inlet structures and ditch are located approximately 60 vertical feet above the normal reservoir <br />water surface and have been badly eroded over the years. Vertical degradation of the inlet ditch <br />channel has resulted in approximately 10-30 feet of vertical degradation and lateral bank erosion. <br />The vertical degradation has resulted in overly steepened ditch slopes that are a significant safety <br />concern. Unless addressed, this degradation will continue and the overall integrity of the inlet will <br />continue to deteriorate. Appendix A includes several photographs of the existing structures and inlet <br />ditch. <br />The original ditch continued past the inlet to Cobb Lake and, as such, there were several gates/stop <br />log slots incorporated into the existing structures. The ditch down gradient of the Cobb Lake inlet <br />has been abandoned and therefore no flow control structures are required as part of any new <br />improvements. <br />This memorandum summarizes several alternatives and associated implementation costs to <br />rehabilitate the existing inlet ditch to Cobb Lake. <br />B. Project background and need <br />The inlet structure has deteriorated over many years and with periodic patching to the point that it is <br />dangerous and subject to sudden complete failure. Note Appendix A, which shows water flowing <br />completely under the remains of the structure supported only by a shale shelf. <br />If the inlet failed, substantial flooding and wash out would occur and the reservoir could not be <br />filled. <br />The outfall ditch is about 50' deep and has very steep sides caused by historic washout and <br />sloughing of the embankment walls. With the development of adjacent residential properties, we <br />have received continuing concerns for child safety from neighbors. Sloping the sides of the <br />canal and chain link fencing will greatly mitigate the danger. <br />1 <br />