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D E ERE & AU LT <br />October 16,2013 <br />Ms. Minerva Lee <br />Consolidated Home Supply Ditch and Reservoir Company <br />c/o Northern Colorado Water Conservancy District <br />220 Water Avenue <br />Berthoud, Colorado 80513 <br />Re: Big Dam Diversion Structure, Examination and Proposed Repair; <br />D&A Job No. CG-0122.019.00 <br />Dear Ms. Lee: <br />This letter report presents our observations and recommendations for the proposed repair of Big <br />Dam on the Big Thompson River. The top five feet of the dam was washed out during the <br />flooding of September 11 through 15, 2013. Peak flows may have been of the order of 15,000 to <br />20,000 cfs with maximum overtopping of the structure of the order of 10 feet. <br />Our recommendations are based upon the examination of conditions during our site visit of <br />October 7, 2013. The examination was conducted by Don W. Deere, P.E. and Colby Hayden, <br />P.E. of our Longmont office. We were met on-site by Board Member, Gary Gerrard. <br />DIVERSION DAM CONDITIONS <br />The Big Dam is primarily a masonry thin arch dam constructed in 1895 by the Consolidated <br />Home Supply Ditch Company to provide diversion off the Big Thompson River. The main arch <br />dam is approximately 65 feet high, 70 feet long, and five feet wide at the crest. The arch dam <br />transitions into a short gravity dam on the left, or north, abutment. An aerial photograph of the <br />dam is shown on Figure 1. We understand that the dam is not considered a jurisdictional dam <br />because the reservoir area has been filled with alluvial deposits resulting in only a few acre-feet <br />of water storage. The dam serves as a diversion structure for the Consolidated Home Supply <br />Ditch and Reservoir Company and the City of Loveland. <br />The left 50 feet of the diversion dam is a straight gravity section only three to six feet high. The <br />gravity and arch sections are separated by a masonry and concrete buttress thrust block. The <br />intake and headgate to the Consolidated Home Supply Canal are located on the right, or south, <br />abutment, and the City of Loveland's intake is on the left abutment. <br />Visible damage caused by the flood includes: <br />1. Loss of the top five feet of the crest along 75 percent of the arch dam section <br />2. Severe damage to the left abutment concrete buttress <br />600 S Airport Road, Building A. Suite 205 <br />Longmont, CO 80503 <br />Phone 303-651-1468 • Fax 303-651-1469