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SOUNDVIEW TECHNOLOGY CENTER EVERETT, WA <br /> HYDROLOGIC MODELING <br /> The hydrologic analysis for the project was performed using the computer-modeling program, Western <br /> Washington Hydrology Model (WWMH2O12), based on matching flow durations. The program effectively <br /> models predeveloped and post-developed runoff conditions using flow duration curves for a basin and a <br /> given area. See Table 4 for the existing and detained flowrate summary for all basins. <br /> Table 4 <br /> Basin Flowrates <br /> Basin Existing Detained <br /> 2-yr 10-yr 100-yr 2-yr 10-yr 100-yr <br /> A 0.12 0.22 0.35 0.06 0.15 0.37 <br /> B 0.24 0.44 0.69 0.12 0.25 0.57 <br /> C 0.12 0.23 0.35 0.05 0.12 0.31 <br /> D 0.03 0.06 0.09 0.02 0.05 0.29 <br /> FLOW CONTROL SYSTEM <br /> Stormwater discharges will match developed durations to pre-developed durations for the range of pre- <br /> developed discharge rates from 50% of the 2-year peak flow up to the full 50-year peak flow. Pre- <br /> developed conditions will be modeled as forested. See Appendix D for full WWHM reports. <br /> BASIN A <br /> Existing Basin <br /> Name ext A-1 <br /> Bypass: No <br /> GroundWater: No <br /> Pervious Land Use acre <br /> C, Forest, Steep 6.19 <br /> Pervious Total 6.19 <br /> Impervious Land Use acre <br /> Impervious Total 0 <br /> Basin Total 6.19 <br /> Developed Basin <br /> Vault#2 <br /> Name Bldg # A-D <br /> Bypass: No <br /> GroundWater: No <br /> Pervious Land Use acre <br /> Pervious Total 0 <br /> Impervious Land Use acre <br /> ROOF TOPS FLAT 6.19 <br /> Impervious Total 6.19 <br /> Basin Total 6.19 <br /> SEPTEMBER 23, 2022 STORMWATER DRAINAGE REPORT PAGE 23 <br />