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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 <br />Lot <br />Existing Peak <br />Flow Rate <br />Developed Peak <br />Flow Rate <br />Forested - Target <br />Peak Flow Rate <br />2-Year <br />0.41 <br />0.50 <br />0.015 <br />10-Year <br />0.60 <br />0.71 <br />0.09 <br />100-Year <br />0.89 <br />1.02 <br />0.24 <br />AREA B - Lot 7/South <br />Access <br />Existing Peak <br />Flow Rate <br />Developed Peak <br />Flow Rate <br />Forested - Target <br />Peak Flow Rate <br />2-Year <br />0.05 <br />0.08 <br />0.01 <br />10-Year <br />0.09 <br />0.11 <br />0.02 <br />100-Year <br />0.14 <br />0.17 <br />0.05 <br />AREA S - Swap/West <br />Parking Lot <br />Existing Peak <br />Flow Rate <br />Developed Peak <br />Flow Rate <br />Forested - Target <br />Peak Flow Rate <br />2-Year <br />0.07 <br />0.07 <br />0.003 <br />10-Year <br />0.10 <br />0.10 <br />0.01 <br />100-Year <br />0.14 <br />0.14 <br />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: Pertect Engineering Page 6 of 7 <br />