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Hugh Kuyper <br /> From: Jane Zimmerman <JZimmerman@everettwa.gov> <br /> Sent: Tuesday,August 30,2016 1:45 PM <br /> To: Elise Gronewald <br /> Cc: Jim Miller;Souheil Nasr; Heather Griffin;Terrie Battuello; Hugh Kuyper <br /> Subject: overflow system analysis requirements <br /> Hi Elise— <br /> City staff held a meeting this morning and came to the following conclusions regarding the design of the Riverside <br /> Business Park roadway drainage system: <br /> 1)- An overflow system must be provided for the Riverside Road drainage system for flows that exceed the capacity of <br /> the pumps. The overflow pipes/system must be sized to meet City inundation allowances in the roadway for the <br /> 100-yr,24-hr flows from those lots draining to the overflow system, plus the 100-yr flows from the roadway subs <br /> basins calculated using the rational method. <br /> 2)- The tailwater elevation to be used for backwater analyses of the overflow system, using the above stated flows,is <br /> the 100-year flood elevation in the Snohomish River(12.75' NAVD88). <br /> 3)- If no changes will be made to the amount of area currently draining to Pump Station#4,and the remainder of <br /> Riverside Road will remain hydraulically isolated from that portion of the road that drains to Pump Station#4 during <br /> the above conditions,then an overflow system/pipe will not be required for Pump Station#4. <br /> If you have any questions, please let me know. <br /> Thank you, <br /> Jane <br /> Jane Zimmerman, Sr. Engineer <br /> City of Everett Public Works Department <br /> phone:425-257-8885 fax:425-257-8882 <br /> e-mail:izimmerman(a�everettwa.gov <br /> 1 <br />