C150375 Increase Approval Letter

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Consolidated Home Supply Ditch 8 Reservoir Company Agenda Item 7a September 11-12,2014 Board Meeting(Updated September 12,2014) Page 2 of 4 Background The Company serves approximately 15,000 irrigated acres in Larimer County near Loveland. Its diversion structure, known as the Big Dam, is located on the Big Thompson River just downstream of the canyon mouth west of Loveland. During the unprecedented flood of September 2013 in the tributaries to the South Platte River, a significant number of diversion structures and dams along the river corridor were damaged, including the Company's river diversion. The Big Dam on the Big Thompson River is a 65-feet high, 70-feet long, and 5-feet wide masonry arch dam built in 1895. It is a low hazard non-jurisdictional dam. The reservoir is filled with alluvium and only a few acre-feet of water are stored to create enough backwater to run the ditch. The Company's headgate is located on the south abutment and the City of Loveland's (City) headgate is on the north abutment. The Big Dam itself is owned by the Company. Prior to the 2013 flood, the diversion structure was fully functional and in place. During the 2013 flood, the top five feet of the masonry structure was washed out and the mortar between masonry blocks on the north abutment was partially lost. Field observations show that the river was overtopping the structure by approximately 10 feet. Project Update Phase 1 of the emergency repairs identified in the original damage assessment consisted of rebuilding the crest of the dam to pre-flood elevations. Approximately 75% of the Phase 1 improvements were completed prior to the 2014 irrigation season. These repairs withstood spring runoff flows well, and allowed the Company to divert its water rights. The remaining Phase 1 work was put on hold during the irrigation season. Work started up again this August and is scheduled to be completed this year. Phase 2 consists of repointing the masonry blocks on the downstream dam face and repair various holes with shotcrete and grout. Originally scheduled to commence and be completed in fall of 2014, this Phase is now scheduled for this winter. The cost associated with the Phase 1 Et 2 work have varied from the original loan approval estimate but are still within the total original loan request budget. As part of the design and evaluation process of the repairs, the Company worked with FEMA, the Company's Engineer (Deere Et Ault), and the Company's Construction Manager (Gerrard Construction) to identify any appropriate flood mitigation measures. As a result of these conversations, the following have been added to the Project's flood mitigation scope of work. Together, they will result in creating a spill capacity of approximately 1,200 cfs before flows will overtop the dam crest. Spillway- $737,000: To mitigate damages during routine high-flow events, a spillway will be installed at the location of the historic spillway. The original spillway was filled in to match the dam crest elevation when the City added its diversion on the north end of the dam. This allowed the City to divert more water but also meant that all flows not otherwise diverted by the Company, or the City, now overtopped and ran down the face of the dam. The new spillway will incorporate an Obermeyer gate to allow the City to divert during normal flows, and then will drop during high flows to activate the spillway. The new spillway will have a capacity of 800 cfs. Head Gate Modifications - $438,000: During the Phase 1 repairs, the south abutment of the dam had to be modified, resulting in the removal of one of the three existing headgates. In addition to increasing the size of the remaining two gates (to allow the Company to divert its full water right), the headgates will be oversized to be capable of diverting an additional 400 cfs. This additional flow can be spilled back to the river via the sand gates. Also included in the headgate modifications are funds to make the gates automation-ready in anticipation for a future flume replacement project that will see the gates integrated with new flume equipment. Additionally, an access road with retaining wall will be added from the county road to the head gate structure to allow equipment to access the front of the headgate for maintenance and debris cleaning. Finally, the ditch rider catwalk at the headgate, currently in an unsafe condition, will be replaced.