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Intermec/Kenilworth Hills Stormwater Analysis Everett, WA Introduction The purpose of this stormwater analysis is to discuss the new Intermec stormwater design and how it relates to the existing Intermec and Kenilworth Hills #1 stormwater facilities. Lot 1 of the Intermec development was designed and constructed in the 1980's to the City's standards of that time. The development of Intermec Lot 2 is now proposed and the stormwater requirements must be satisfied. The stormwater management requirements for the development of Intermec Lot 2 are dependant on the following items: Downstream Capacity ' As is required prior to any proposed site development activity, the capacity of natural drainage path downstream of the existing drainage facilities must be field verified to ensure stability. The downstream analysis was performed from the outfall of the Intermec Lot 1 pond, through the Kenilworth Hills pond, down Edgewater Creek to the point where the previously approved downstream analysis for the Interair Commerce Center by PACLAND, dated June 10, 2005, converges with Edgewater Creek. As noted in the downstream analysis (See page 3) Edgewater Creek shows no signs of stream bank instability. Peak Flow Analysis 111 The affect of the Lot 2 development on the peak flow from the Kenilworth Hills #1 pond had to be analyzed to verify that existing requirements of the Kenilworth Hills pond would continue to be met. The drainage basin includes the Kenilworth Hills development, Intermec lots 1 & 2, and run-on from upstream properties. Per the rezoning ordinance for the site, the drainage requirements are as follows: "For development in Edgewater Creek drainage basin, detention must be sized for a 25-year developed storm and a maximum release rate to prevent the existing detention pond of Kenilworth Hills No. 1 from overflowing during a 25-year storm (the maximum release rate from the existing pond is 0.5 cfs)." This drainage requirement does not specify the duration for the 25-year storm. However, it was determined that the intended duration for the requirement is the 1-hour storm. Per an email from Jane Zimmerman at the City of Everett on March 24, 2009: 1 "...the method used to determine the release rates and detention volumes for the Kenilworth Phase I pond was the Yrjanainen and Warren (Y&W) method. This method used the rainfall intensity-duration curves to base detention volumes on a storm duration equal to the site's time of concentration (which was figured at 51.57 PACLAND Job# 50175001 Page 1