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Hydrologic Calculations <br /> Hydrographs for the 2-, 10-, and 100-year storm event for existing and proposed drainage <br /> basins were developed using the Santa Barbara Urban Hydrograph (SBUH) method. The <br /> data used to determine the storm results are area in acres, time of concentration, SCS <br /> soils curve numbers, and acres of impervious surfaces. The WaterWorks computer <br /> program was used for hydrograph computations. All the input data for WaterWorks can <br /> be found in Appendix A. <br /> The existing and proposed stormwater peak runoff flows for the PDA are summarized in <br /> Table 2 below: <br /> Table 2 - Summary of Peak Flow Rates (CFS) <br /> AREA A—NW Parking Existing Peak Developed Peak Forested-Target <br /> Lot Flow Rate Flow Rate Peak Flow Rate <br /> 2-Year 0.41 _ 0.50 0.015 <br /> 10-Year 0.60 0.71 0.09 <br /> 100-Year 0.89 1.02 0.24 <br /> AREA B-Lot 7/South Existing Peak Developed Peak Forested-Target <br /> Access Flow Rate Flow Rate Peak Flow Rate <br /> 2-Year 0.05 0.08 0.01 <br /> 10-Year 0.09 0.11 0.02 <br /> 100-Year 0.14 0.17 0.05 <br /> AREA S-Swap/West Existing Peak Developed Peak Forested-Target <br /> Parking Lot Flow Rate Flow Rate Peak Flow Rate <br /> 2-Year 0.07 0.07 0.003 <br /> 10-Year 0.10 0.10 0.01 <br /> 100-Year 0.14 0.14 0.03 <br /> Targeted Drainage Report for Everett Public Schools Section 2—Risk&Erosion Control <br /> Silver Lake Elementary Parking Lot Expansion January 6,2003 <br /> By: Pertcct Engineering Page 6 of 7 <br /> II <br />