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SOUNDVIEW TECHNOLOGY CENTER <br />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 <br />Existing <br />Detained <br />2-yr <br />10-yr <br />100-yr <br />2-yr <br />10-yr <br />100-yr <br />A <br />0.12 <br />0.22 <br />0.34 <br />0.06 <br />0.14 <br />0.34 <br />B <br />0.24 <br />0.44 <br />0.68 <br />0.11 <br />0.23 <br />0.42 <br />C <br />0.10 <br />0.20 <br />0.30 <br />0.05 <br />0.12 <br />0.29 <br />D <br />0.03 <br />0.08 <br />0.10 <br />0.02 <br />0.08 <br />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 6.01 <br />Pervious Total 6.01, <br />Impervious Land Use acre <br />Impervious Total 0 <br />Basin Total 6.01 <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 6.01 <br />Impervious Total 6.01 <br />Basin Total 6.01 <br />MAY 23, 2017 STORMWATER DRAINAGE REPORT PAGE 20 <br />