9331 18TH AVE W SITE DEVELOPMENT 2018-01-02 MF Import

.tr,ini ;in�t a ur�� Ir��ln��ni�•nt un `�.; , tit. SVV thal ul�� c�rotrihutc� u, thi� ,trc.im a(ter h�im_ �Ictain��l ancl tiralt�l. :Vum- Ihc ,��ulhcrn hurdcr ��( lhc _,c�l� coursc. �i �hruh 1 illc�l �litrh. running c;i�i ti� �c�.t. csi,t.. l)rain:�gc Irom thc �outhcrn partion ol tha cull a,unc cnt�n th� �li�rh an�l tra��l. «c,L ahcrc il cntcrs and cxi[> a I'_ inch cuncrctc culvcrt. f�nm� hrrc. �Ir;iin�rse cununuc, �vc,tcrh ��ntil it hils �i lu�� point ��hcrc it convcr ��s with driin.r�r �hai .ipp�an tu hr ci,m� (rum lh� �,ol( coursc's watcr fcatures. l�hc draina�,c travels �outh in a�cctland su'c.�m ihat i, .i u ibutar�' tu S�v�imp Crcck. Do�vnstrcam driina�_c was .m.ilyzcd lor I/-4 milc in accordancc with City �if Fvcrett standards. "1'he site has a 10 liiut drop an the castern purtiun �vhere draina� e�,nters a type � ,u'cam that is a trihutary tu S�ti.imp Crcck .ind h�ads soulh. City of Ev�retl Drainagc As- huilts indicatc this st�tam runs northcrly, ho�acvcr, licld investigation indicatcs othcnvisc. I he dnwnstrcam cunditions ,u'c over�_rown with wedand vegetation und brambles. Downed trccs tan�,lccl with vcgct�dion appc�ir to contributc to the restriction of stream �low �uid cuntribule to the weUand. South of thc pro�oscd sita thc dcvclopmcnt of Augusta Woads cxists. Hcrc, draina=c . u'a�'ds uadcr 95" SL SW throu��h what appcars to bc a 54" widc arch culvcrt. Drainu�� c�its this culvert and continucs southerly for approximately 300 feet before enterin�� a S'x 10' box culvert undcr 96"' SL SW. Thc sucam continucs on in a southcrly dircction and eventually crosses under l00°i St. SW through a culvert which hus two 18'bverllow risers with cone gratcs on top• It aPpears this dramaee eventu�illy enters Swamp Creek. 'I'hc downstream culvcrts within onc yuurlcr mile appcar to bc sired adequatcly for anticipated ilows• Howcver, obstructions in the form ot do�vncd trees and other vegetation contributc to Uackwatcr conditions. Purthcr downstrcam at 100i6 Strcct, an antiyuatcd intakc su•ucture (IR-inch overllow riscrs indicated above) connccted to approximately 300 feet of ripe (sir.c undetermined) appears to restrict ilows, based on vegetation, debris and other I icld obscrvations. Calculcitions wcre madc to cstimate thc 100-Year (low .md deterniinc an upproximeue 100-ycar ilood plain. The �low calculated just passes through thc ncarest do�vnstrcam culvett, ho�vever backwater effects further downstream may causc localir.ed Iloodine. As a result, the finishcd (loor clevations for the proposed wiits havc been s�t to ,ipproximatcly tcn fcet abovc thc ordinary high watcr mtuk in thc slrcam. IV, Analysis and Desi�n of Required I;rosion and Sediment Control I3A�IPs The soil fbr thc site consists of Alderwood L'rban Land Complex. Classilicd ati hydrological oroup "C" according to the SCS Snil Sm're�� for Snohrnni.sh Cnunr��. Alderwood soil is moderatdy deep over a hardpan and is moderately wcll drained. It liirmed in glacial till. Permcabiliry of the Aldenvood soil is moderately rapid above U�e luu�dpan und vcry slow through it. Runoff is slow and the har�u•d of watcr crosion is slight. The potential Ibr erosion for this ryp� �f soil is sli;ht, howcver special attention should bc ��iven to working the malerial in wet weaUier (October I through March 31). Soil compaction will be difficult, if not impossible to achicve during periods of sustained rainfall. pead stora��e in the type 11 catch basin will be the primary setding basin for the sit�. O!"cr than ruinfall, die source of erosion would come from dust and wheel traffic during construction. This risk would appcar to be minimal. Additional risk would bc tracking of nwd nnto thc roadw:q'. Thc rock construction entrance will help to minimize this risk. Pollo�ving final grading, all slopes will be stabilized with mulch. jule mesh. hydroseed or other mcans. � --� �� / �