7016 EVERGREEN WAY 2016-01-01 MF Import

� Sunrise Services-Drninage Study c 4. DCT�NTION D�SIGN CRIT�RIA Detention will be provided to satisfy the 2-yrir, 10-year and 100-year storm requirements per the City of Everett srorm drainage requirernents nnd the 1992 DOC Stormwater management Manr.aL The Storm Drainage calculations are � based upon the Santa Barbara Unit Hydrograph Method as described in thc Stormwater Management Ylanual for Puget Sound published by DO� in Junc 1991 (ReL 1). A 42�/o sofety factor is designed into the detention siruclure to protect the downstream conditions as described in the previoiis pages. � Rainfall intensity is detennined according to the referenced DOE Manual :vlethod using Isobaric Charts for Snohomish County. Flydrograph calculations are performed on the Watenvorks Program developed by Engenious Systems, Inc. The storm selected was the re�uired Type lA for Snohomish County. Concentration times assumed bascd upon Ilows from the most distant point on the site to the proposed discharge point. Developed concentration times were � assumed to be 7.3 minutes. Basin descriptions are provided on the computer reports for the design storms of interest, the 2-year, 10-year and 100-year storms for undeveloped and developed cases respectively. These detention criteria are the exact criteria imposed on the � s;;stem approved immediately east of this sile. Storm data is presented in tabul,v format on Ihe following paoes with brief summaries and explanations of thc results. The required Release Criteria for the dc��elopment �re as follows: i[ 5�°��-Q2-year Undev;loped = O.00d cfs Q 10-year Undeveloped = 0.028 cfs Q100-Year Undeveloped = 0.065 cfs (This assumes meadows or pasture as the irodeveloped condition) �� � :� �vesrea� enciurcus. iuc. � riaaecr:oi �o�, 1l