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PROJ00269
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Last modified
11/19/2009 11:43:15 AM
Creation date
10/5/2006 11:46:49 PM
Metadata
Fields
Template:
Loan Projects
Contract/PO #
FS0016X
Contractor Name
Lyons, Town of
Contract Type
Loan
Water District
0
County
Boulder
Loan Projects - Doc Type
Feasibility Study
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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />overburden and bedrock foundation materials will have to be protected from deterioration <br />due to seepage. <br /> <br />Hvdrololric Evaluation. The Inflow Design Flood was determined following the requirements of the <br />Office of the State Engineer of Colorado, DAM SAFETY REGULATIONS AND RULES. This requires <br />the design of an emergency spillway which will pass 100 % of the Probable Maximum Precipitation (PMP). <br />Based on this criteria, the emergency spillway will have to pass a peak flow of 16,500 cfs. <br /> <br />To pass this flow, we have considered several alternatives and believe the most cost effective to be a broad <br />crested weir which is protected from erosion by riprap and grouted riprap. The spillway required will have <br />an overflow crest length of approximately 300 feet. The spillway will terminate in a plunge pool to <br />dissipate the energy which will discharge into an open channel to direct the flow into the natural drainage. <br /> <br />Structure Plans <br /> <br />1. Embankment. The dam embankment considered will be constructed with 3 horizontal to <br />1 vertical slopes on both faces as shown on Figure 4. The dam crest will be 20 feet in width and <br />will be gravel surfaced for erosion protection. The upstream face will be protected with riprap and <br />bedding from the dam crest to an elevation approximately 20 feet below the dam crest. This is <br />expected to be the active drawdown zone for the reservoir and providing rip rap to a lower <br />elevation will not be necessary. <br /> <br />The embankment will be constructed in two zones with an interior clay core utilizing the clay soils <br />found on site, and an upstream and downstream shell constructed of random materials excavated <br />from the upstream borrow. <br /> <br />2. Drains. Drains to control the seepage from the dam and foundation are of high importance <br />for this dam site due to the nature of the soils. The soils are low to nonplastic and contain <br />significant quantities of silt which are susceptible to erosion and piping. Due to this, the dam will <br />contain an interior chimney drain and a blanket drain to control piping through the dam core. <br />These drains will discharge into a toe drain located near the downstream toe of the dam. <br /> <br />3. Slope Protection. The upstream slope will be protected with an twenty-one inch (21 ") <br />layer of riprap with a six (6") layer of riprap bedding. The riprap sizing will range from eighteen <br />inches (18") to three inches (3"), and the bedding from three inches (3") to sand size. <br /> <br />The downstream slope and any other fill or excavation areas, such as in the spillway, will be <br />protected by applying topsoil and grass seeding. Areas of high erosion potential, such as in the <br />outlet channel and around the spillway control section, will be protected with riprap and bedding <br />of the same size described for the dam slopes. <br /> <br />4. Outlet Works. The outlet works considered for the reservoir consists of a 36-inch <br />diameter steel conduit encased in concrete. The outlet discharges will be controlled by a heavy <br />duty slice gate placed at the upstream end of the conduit. The gate will be protected by a trash <br />rack and the outlet end will be controlled by an energy dissipater to minimize downstream erosion. <br /> <br />This outlet will easily meet the State Engineer's requirement to be able to release the water from <br />the top five (5) feet of the reservoir at a rate of one (1) foot per day. This will require an outlet <br />that will release approximately 10 cfs and the proposed outlet will release in excess of 75 cfs at <br />full pool. <br /> <br /> <br />A smaller outlet could be utilized, however, the 36-inch size is the minimum we recommend due <br />to limited access in smaller outlets for maintenance and repair, A 36-inch outlet could be lined <br />and still ,meet any discharge requirements required by the State Engineer. <br /> <br />The main control gate operator will be manual, hand crank type, enclosed gear pedestal. The gate <br /> <br />Stone Canyon Dam Feasibility <br /> <br />Page 10 <br />
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