Laserfiche WebLink
1( <br />Bill Atutray-Drainagc Smdy <br />UPSTREAM - DOWNSTREAM ANALYSIS <br />DOWNSTREAM CONDITIONS <br />A site inspcction was conducted on Septertiber 8, 2001 to investigate the site <br />conditions and downstream conveyance system. The weather was clear and it had <br />not rained for scveral days previous ro the visit. Drainage for the parcel flows by <br />sheet flow to thc east over slopes ranging from 3 to 15"�0 on site. The east <br />property line of the site is the 1-5 right of way. There is a 3:1 slope from the right <br />of way down to a retaininb wall approximately 22 feet east of the site. The wall is <br />approximatcly 10-12 feet tall with the driving surface of 1-5 at the toc:. Runof'f <br />Ieaves the site as sheetflow and/or shallow channel flow and travels down the 3:1 <br />slope to the top of the retaining wall. At the top of the wall there is an eighteen- <br />inch wide concrete val'ey gutter, which intercepts flows. The guttcr conveys <br />runoff north to an inL:t located approximatcly cighty fcet north of the subject <br />property's north beundary. Thc inlet directs flows to a catch basin at the toe of <br />the wal! in the I-5 drainage system. From tliis catch basin flows travcl no-th in a <br />fiftcen-inch pipe to another catch basin on the west side of 1-5. Flows continue <br />north for about one hundred feet in an eighteen-inch pipe. From there the <br />drainage is convcycd east across I-5 throu�h a scries of catch b;�sins and eightcen- <br />inch pipes. Runoff is discharged cast of 1-5 into an open channel, which <br />contributes to Wood Creek. Wood Creek travels east and north and eventually <br />enters the Snohomisl; River. See Downstream and Basin Maps attached in this <br />report. <br />UPSTREAM CONDITIONS <br />There arc r�iinimal upstrcam tlows cntering the site. The rolled asphalt curb along <br />Broadway prevcnts strcet runoff from entcring the site. Somc runoff from the <br />unpaved right of way tlows by sneet-11ow onto the site. Upon developmcnt, thc <br />minimal upstrcam flows will continui: to flow onro thc site. These flows will bc <br />conveycd through thc site and discharged at the natural flow path. In conclusion, <br />thcre will bc no advcrsc impacts on thc upstrcam or thc downstrcam convcyancc <br />syst�ms as a result of this development. <br />'h'f.SIIiNN 1 �GI\IiIiRS.INC. <br />rRaecr.n i -n i -n <br />�� <br />