7000 HARDESON RD 2020-06-05 - Laserfiche WebLink

MCOB, PHASE II Calculation: C-2 Page 2 WEIR WALL HEIGHT Design Basis: The project will replace the existing flow splitters. The new flow splitters will use a weir wall to restrict the flows from exiting the Merrill Creek outfall pipe until the flows are greater than the water quality flowrate at which point they will start to spill over a weir wall and exit out the outfall pipe. The weir wall elevation correlates to a water surface elevation expected in the system at the water quality storm event. This elevation was calculated to be equal to the Energy Grade Line elevation in each flow splitter structure when the water quality flowrate is entering the system and taking into account backwater effects. Methods and Assumptions: The Energy Grade Line was calculated using the Hydraulic Engineering Circular No. 22,Third Edition (HEC-22)methodology which allows for more accurate evaluations when pipes are not expected to be flowing full. The energy grade line was calculated up the mainline including the flow splitters only. All flow coming into the system from upstream branches was included. The water quality flow rate was used for the Q as calculated in calculation C-1 Water Quality Flowrates. The following software was used for this calculation: - Flowmaster was used to calculate some of the values used in the table. Assumptions: Manning's n=0.012 Findings and Conclusions: The Energy Grade Line elevation within each flow splitter corresponds to the calculated water elevation when the water quality flowrate is entering the system. Top of Weir Wall Elevations Structure EGLa(Energy Grade Line)=top of weir wall, from Column(16),Table A CB 6 427.99 CB 5 423.60 CB 4 422.93 CB 3 422.07 CB 2 421.80