Laserfiche WebLink
MCOB, PHASE II <br /> Calculation: C-1 <br /> WATER QUALITY FLOWRATES Page 2 of 2 <br /> Design Basis: <br /> The existing storm drainage system at Community Transit's Merrill Creek Operations Base is designed to <br /> provide water quality treatment onsite in a wet vault and a stormfilter cartridge vault before discharging <br /> offsite to Merrill Creek. Onsite flowrates in excess of the water quality flowrate are considered clean enough <br /> to not require runoff treatment and can directly discharge to Merrill Creek.The flows are split with a flow <br /> splitter structure where incoming flows continue to the water quality system until the energy grade line <br /> (height of water)in the structure gets high enough to spill over a weir wall at which point it can go directly <br /> out to Merrill Creek. The height of the weir wall will be based on the calculated energy grade line in the <br /> flow splitter structure using the backwater analysis at the water quality flowrates. <br /> Methods and Assumptions: <br /> Continuous modeling software was used in this calculation to determine the off-line water quality flowrates. <br /> Since the flow splitters are upstream of the water quality treatment facilities they can be sized using the off- <br /> line treatment flowrate. The energy grade line will be calculated going up the mainline only this the water <br /> quality flowrates calculated are the cumulative water quality flowrates at each structure on the mainline <br /> which is the storm line system that runs north/south on the eastern edge of the property. <br /> The following software was used for this calculation: <br /> - AutoCAD C3D 2016—project site tributary area information <br /> - WWHM2012—continuous modeling software for stormwater runoff flowrates <br /> Findings and Conclusions: <br /> Off-line Water Quality Flowrates <br /> Structure Area Tributary to Water Quality Flowrate Cumulative Water Quality <br /> ID Structure tributary to structure(cfs) Flowrate(cfs) <br /> (acres) <br /> CB 6 5.177 0.3653 0.365 <br /> CB 14 0.255 0.0180 0.383 <br /> CB 70 1.701 0.1201 0.503 <br /> CB 13 0.492 0.0347 0.538 <br /> CB 5 2.138 0.1510 0.689 <br /> CB 12 0.379 0.0267 0.716 <br /> CB 11 0.167 0.0118 0.728 <br /> CB 10 0.637 0.0450 0.773 <br /> CB 4 1.865 0.1317 0.904 <br /> CB 3 3.030 0.2141 1.118 <br /> CB 2 2.020 0.1427 1.261 <br />