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A ERC CC&V Poverty Gulch Chicago Tunnel <br /> December 2016 <br /> ERC utilized the online calculator from South Dakota State University to check the hydraulics of each. For <br /> Structures#4 and#5,the open channel calculator was used.For Structure#6 we utilized the broad-crested <br /> weir calculator. Calculations for the spillway outlet conservatively assume that it is a 5-foot-wide <br /> rectangular weir and neglect the 2:1 side slopes. Results for each are presented as an appendix. Output <br /> from the hydraulic calculators follow the table. <br /> Overall ERC's results for the inlet and outlet channel are nearly identical to results from Steffens. We <br /> recommend that a minimum of 1.0 foot of freeboard be added to the design flow depth for the spillway. <br /> For the inlet and outlet channels ERC calculated required freeboard based on the maximum of either the <br /> velocity head or 0.5 feet. Steffens recommends small gravel (dso of 1.5" to 3")for these channels. ERC's <br /> results confirm that this armoring is adequate given the low calculated velocities. <br /> For the spillway,ERC calculates that the peak 100-year design flow will have a depth of about 0.6 feet.We <br /> recommend a foot of freeboard for a total spillway depth of 1.6 feet. Velocities through the spillway will <br /> be minimal. The Steffens' design which includes 6-inch riprap on the outlet channel is sufficient for <br /> armoring. <br /> Parameter Structure#5 Structure#6(Sediment Structure#4 <br /> (Inlet Channel) Pond Spillway) (Outlet Channel) <br /> Flow Depth 0.96 feet 0.60 feet 1.74 feet <br /> Flow Velocity 2.54 ft/s 2.34 ft/s 4.46 ft/s <br /> Froude Number 0.65 NA 0.78 <br /> Recommended 0.5 feet 1.0 feet 0.5 feet <br /> Freeboard <br /> Design Depth 1.5 feet 1.6 feet 2.25 feet <br /> Conclusions <br /> Inlet and Outlet Channels-Based on ERC's calculations,the constructed channels are sized appropriately, <br /> however they may not have the required freeboard. If it is determined that the slope of the ground <br /> adjacent to the channel does not provided the depth required for freeboard,then safety berms should be <br /> constructed along the channels to achieve the total design depths listed above. <br /> Spillway—The spillway as at exists has one foot of elevation difference between the spillway crest and <br /> the top of the pond. ERC found that when passing the 100-year flow, water would be approximately 0.6 <br /> feet deep leaving a residual freeboard depth of 0.4 feet. To provide the necessary 1.0 feet of freeboard <br /> Newmont could either raise the crest of the pond by 0.6 feet or excavate the bottom of the pond and the <br /> 3 <br />