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2717 RoekNNl�r Av�nu� <br /> p OMEGA f�...et,w�asso� <br /> � ENGINEERING, INC. azs.se�.sazo <br /> fax 425.259.1958 <br /> of 3%. The total peak runoff rate for the parking lot of 0.09 ds was calculated using WWHM3 <br /> for the 100-year storm event. Manning's Equation was then used to anaiyze the pipe for <br /> capacity. It was determined that a 6" PVC pipe with a siope oi 3.4°h flowing full has a peak <br /> capacity of 1.11 cfs. Therefore, this design has more than ten times the capacity necessary to <br /> convey the expected flows. Copies of the output from both the WWHM3 software and the <br /> Manring's Equation calculations have been included with this letter. <br /> Due to the City's definition and interpretation of "New Impervious Surfaces" within the 2010 <br /> Stortnwater Manual all of the new pavement is considered new impervious. However, since this <br /> project does not propose to construct more than 5,000 sf of effective impervious surfaces for <br /> this project only minimum requirements #1-5 apply. The use of dispersion and amended soils <br /> where practical meets the on-site stortnwater management requirements and since this project <br /> is located in the combined stortn-sewer basin for the City treatment will be provided in the <br /> landscaping strip on-site or at the wastewater treatment plant. The existing system will provide <br /> the required treatment downstream and no flow control is required as noted above due to the <br /> proposed amount of new impervious surfaces. <br /> Thenk you for taking the time to review this project. Please feel free to contact me with any <br /> questions you may have. <br /> Sincerely, � '� <br /> o QM'�f/���� ''�'•l�' <br /> '� • <br /> � <br /> Joseph M. Smeby '••!;U� � <br /> : <br /> Project Engineer � �•� <br /> �/,�jrr <br /> . <br /> , <br /> ; �'� % <br /> --, , <br /> � <br /> � ; <br /> __� <br />