C154213 Contract - Laserfiche WebLink

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overflow of the left training walls has the potential to threaten the right abutment of the main dam. Based on the 2008 study,this appears at flows below the design flow of 6,600 cfs. The dam safety and operational issues described above combined with the value of the reservoir for optimizing water use for multiple stakeholders in the basin have driven the District to move forward with the rehabilitation of the Rio Grande Dam and Reservoir.The District is a proponent of the Rio Grande Cooperative Project where the District works with multiple stakeholders in the State, primarily the Colorado Water Conservation Board and the Colorado Division of Parks and Wildlife to restore the full use of the reservoir.The project is made up of final design and three primary components to address structural and/or operational deficiencies of the Reservoir, as described below Final Design—The rehabilitation of Rio Grande Reservoir requires that the proposed improvements be designed, managed, and inspected by a professional registered engineer in the State of Colorado. The engineering firm selected to conduct this work will provide overall project management, surveying, geotechnical exploration, geotechnical and hydraulic analysis, and the final design of the spillway, clay blanket liner, bypass tunnel and outlet works. The engineering firm will also provide cost estimating, QA/QC for the project, respond to State Engineer comments and assist will bidding and award for the project. This work is currently being conducted by SLVID under Contract C154210 at a cost of $1,256,134, under its sub-consultant—Deer and Ault Consultants. PRIMARY CONSTRUCTION COMPONENTS 1) Upstream Clay Blanket- In order to reduce seepage through the rock slide formation at the left dam abutment, a clay blanket slope liner will be installed on the upstream side of the dam at the left abutment.The clay blanket, will be a zoned fill placed over the rock slide and extending across the west abutment of the dam approximately 100 feet.The zones include a filter layer, low permeability clay core, and cover zone.This improvement is expected to substantially reduce seepage and allow full storage capability of the reservoir to be achieved. Clay liner materials will be obtained by borrowing and processing approximately 20,000 cubic yards of soil and rock material from reservoir property. Processing shall consist of screening various gradations from the existing landslide deposit. 2) Low Level Outlet-The existing low level outlet will be replaced with a hollow jet valve discharge structure at the downstream side of the dam.The existing low level outlet tunnel will continue to be used to provide conveyance between the upstream and downstream portals.The existing sluice gate control structure will either be demolished or abandoned in-place with a bypass tunnel providing conveyance around the structure. Schedule constraints for the work and the uncertainty of the demolition costs (for removal of existing sluice gate control structure) suggest that the construction bidding process may be the best way to determine the most economic solution.To that end, we recommend preparing the bidding documents with two options: Option 1—Demolish Existing Sluice Gate Structure and Option 2—Construct Bypass Tunnel and Abandon Sluice Gate Structure. The District can then select which option is most economic based on the results of the bidding. Another important element of the low level outlet works is the provision for the future addition of hydropower.To allow hydropower to be added in the future with minimal disturbance to the primary function of the project, a tap will be provided at the low level outlet (downstream of the tunnel portal)which can be used to route flows to future turbine generator units. 3)Spillway Improvements—In order to achieve the spillway capacity required by the State engineer's Office (SEO),the entrance training walls will require a substantial raise and the main channel training