1010 N BROADWAY EVCC 2018-01-01 MF Import

Table 2: Impervious Area Reduction Site Total Existing Impervious Developed Impervious(ac) Reduction Area(ac) (ac) Building 2.86 acres 2.08 acres 1.63 acres 16% 10th Street 0.42 acre 0.42 acre 0.25 acre 40% Parking Table 3: 2-Year,24-Hour Stormwater Volume Reduction due to BMPs Site Existing Volume Developed Volume Reduction Building 4385 cf 3088 cf 30% 10th Street 831 cf 553 cf 33% Parking 4.3 Conveyance System Analysis and Design 4.3.1 Onsite Conveyance System As described above,the City of Everett requires that all storm and sewer utility lines are separated onsite. Therefore, the Building site conveyance system consists of 6-inch and 8-inch diameter closed drainage pipe systems, which connect to an 8-inch storm pipe in the College Fitness Center parking lot. The 10th.Street Parking site conveyance system consists of surface swales (concrete and grass lined) and connects to an existing catch basin in the northeast corner of the site. See Appendix A, Exhibit A-7 for the Building site and Exhibit A-5 for the 10th Street Parking site. On the Building site,the unit hydrograph (Santa Barbara Urban Hydrograph (SBUH)) method was used in order to be consistent with the analysis of the Tower and Waverly Streets storm system provided by Reid Middleton. The 24-hr precipitation values were taken from the City of Everett Stormwater Management Manual,Table 5.4 (see Appendix B, Exhibit B-3). The individual pipe runs were calculated by Manning's Equation (basin calculations and printouts are included in Appendix B). See Appendix A, Exhibit A-6, for the Conveyance Basin Map and Exhibit A-7 for the Pipe Conveyance Map. The pipe system was checked for minimum velocity for the 25-year, 24-hour storm. All system components have a design velocity of at least 2 feet per second (fps)for the design storm. Pipe capacity was analyzed for capacity for both the 25-year and 100-year, 24-hour storm. The analysis indicates that no overtopping will occur during the 100-year, 24-hour storm event. Conveyance calculations can be found in Appendix B, Exhibit B-6. On the 10th Street Parking site,the SBUH method, and Manning's Equation were also used to size the two swales, the culvert, and the pipe that connects to the existing stormline in North Broadway. See Appendix B, Exhibit B-7, for conveyance calculations. Stormwater Site Plan Report 01200 Everett Community College Index Hall Replacement&Surface Parking Lot"M" 6 209459.10/209459.11