1808 MERRILL CREEK PKY 2016-01-01 MF Import

• Preliminary drainage basin information (existing and developed conditions) for the large detention pond and wetland pond was submitted to the City of Everett in May 1994. The City of Everett used this infonnation to run a SWMM model which provided design volumes and allowable release rates for each of the two facilities. The SWMM drainage basin cl�z;acteristics, design volumes, and allowable release rates have been outlined in two letters addressed to Gordon Witcher, Everett Public Works; dated May 15, 1994, and May 18, 1994; respectively. Copies of these letters have been provided in the Appendix. The detention pipe was considered small enough to run a standard SBUH model for the sizing of the facility. The volumes and release rates received from the City of Everett have been adjusted slightly to re8ect minor, recent changes in the areas tributary ro the two larger facilities. SBUH models for all three facilities have been prepared with the adjusted SWMM criteria using the Water Works computer hydrograph modeling program. The drainage basin cliaracteristics and summary of the results have been provided in the Storm Water Calculations section of this report: S]'ORM WATER CALCULATIONS WET POND / DETENTION POND Release Rates The wet pond has been sized to detain the developed 25-year, 24-hour storm event. During this srorm event, the wet pond will release 031 CFS. This allowable release rate was determined by adjusting the release rate received from the City of Everett's SWMM model. The SWMM model was based on a r�t:,; area of 14.02 acres. Using the tributary areas, an adjusted release rate was determined fbr the revised area of I 1.90 acres: 0.36 cfs x cfs � = 0.3 I cfs [Adjusted allowable release rate] �14.02 Ac� �l 1.90 Ac� Four orifices in a 12-inch standpipe were sized to discharge from the �vet pond/detention pond during tlie 2-year, 5-year, 10-year, and 25-year storm events. Eacli orifice has been S7'ORnI URAINAGE REPOR7'FOR INTILI�VEST-SEAIVAY - PAGE 3