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V <br /> 4.0 Off-Site Analysis <br /> This section evaluates the upstream and downstream drainage system. The intent of this section <br /> is to identify any existing or potential drainage impacts created or exacerbated by the proposed <br /> project and drainage facilities. <br /> Aerial imagery, Snohomish County topography and surveyed topography of the site form the <br /> basis of this analysis. <br /> 4.1 Upstream Analysis <br /> The upstream drainage basin for this project is relatively small as the project site is located close <br /> to a ridge line. The upstream drainage area encompasses approximately 1.5 acres. Storm drainage <br /> sheet flows in the southwest direction however most runoff flows into the existing combined sewer <br /> system before reaching the project site. The figure below shows the approximate upstream <br /> drainage area for the project site. <br /> , <br /> x+ 1 i r r <br /> 4 .' 4 11 <br /> • r ! i i ; <br /> a , �� 1 <br /> 1. <br /> 'r ; ,l { <br /> - a <br /> l 1 i% � F ' , <br /> i i <br /> I 1 ; <br /> � tI _ill <br /> 1 4 <br /> • <br /> Iiiiiikar _r <br /> . i!` e. 1 i <br /> f <br /> } <br /> I 1 t 1 <br /> l,IFSTRFAM R1,11.AGF ' <br /> AREA 1 A I 11 1 <br /> ) A i . <br /> } <br /> Figure 2: Upstream Analysis <br /> DAVID EVANS AND ASSOCIATES,INC. <br /> GRANDVIEW APARTMENTS CLUBHOUSE MARCH,2017 <br /> STORMWATER SITE PLAN PAGE 7 <br />