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S'I OR\i\14�TGR SITr PLAN <br />AUGUS'fA \i'OODS CONilO�llMU\1S <br />b1AY 20, 2003 <br />PAGL- I? <br />V. ANALYSIS AAID DESIGN OI' RUNOi'F CONTROL I3VIP'S <br />nr.��lri��cc s��s�rr ���A�Ysis <br />The property contains six drainagc b;:sins and t�t�o ott�site basins. 'i6c first bas�n is located in thc <br />southwest comer of the site and cunsists of four units, the frontagc along I�''' .�.venuc and a <br />portion of thc access road. The second consists of the majotity of the sitc development and <br />contains 30 of thc eastem units znd the drivin�✓p�rking areas. Thc thi�d basin �•onsists of the <br />central portinn of die south access rondway. The tiiurth arca consists ��f the north access roadway. <br />Thc tifth basin includes five ot� the units on eidier side of die south acccss road and a portion of <br />the la�vn amas surrounding them. The sixth basin includes six units on eithcr side of the nortl: <br />acccss road and a portion of their yards. Thc [3ypass Offsitc Bnsin c�,nsists of a portion of du <br />offsite basin that b}'passcs dctcntion. Thc Detained Offsite Basin consists of an offsite arca that <br />will be detained to mitieate for Basins 3& d'hat are not proposcd to be ddained. The balance of <br />die site, the wcdand and 6uffer areas, �vill not be impactcd by tl�u propnsed de��elopment. All of <br />thcse basins dischargc to thc ccnd�ally locutcd cateoory II wed.�nd. Scc Pi;;urc 3: Dc��ciupcd Sitc. <br />111'DROLOGIC ANALYSIS <br />Thc drairagc dcsign for thc sitc wns pmpared using thc rcyuircmcnts oC thc City of I=��cr�tt <br />Stormwutcr �lana�cment Manuul, (CEM Manual). SCS cmvc numbcrs �vcrc takcn from thc <br />CL�4 Manual. SturniShed'", by Cngcnious, was uscd to calculatc runoff. <br />l�he rainfall cvcnts uscd in the calculations arc the SCS type IA distribution of the 24 hour <br />rainfall cvent for the Z, 10 and 100 year rcturn periods. Tot:il prccipit�tion, frum the'Cablc 1->.� <br />ul�thc CLM �ianual, is as Collo�vs: <br />Return Pcriod Rainfall <br />2 Ycar l.i� inchcs <br />10 Ycar 2.2� inchcs <br />100 Ycar 3.25 inchcs <br />SOIL D[?SCRIP'I�ION <br />Accurding to thc soil mapping prcparcd by Ihc SCS in thc Soi/ Sm�i c�v q%� Snohomish Cuunlr <br />:Irca, INnslrington dic site is underlain witl� Aldenvood-Urban Lan� Complcs, sce attnclicd SCS <br />Soils Map anJ Soils Dcscription in Appendix Ci. r\s ca.n bce seen on the soils map thc <br />surrounding propertics arc also undcrlain with this same so�' typc. <br />The etescriptiun of Aldcnvood Urban Land Complcx is as follo�vs: This soil is moderatcly dcep <br />ovcr a hard pan and is modcrntcly wcll draincd. Typica'.ly thc surfacc luycr is vcry dark grnyish <br />bro�vn gra� clly sandy loam about 7 inchcs thick. Thc upper part of the subsoil is dark ycllowish <br />brown and dark brown vcry gravclly sandy loam aUout 33 inchcs thick. Thc lower part is olivc <br />brown ��ery gravelly sandy lo�m about 5 inchcs Ihick. A weakly cemented hardpan is at a depth <br />of about 35 inchcs. Depth to hardpan rangcs from 20 to 40 inches. Penneability of thc soil is <br />n�,��lcratcly rapid :�b�,��e the hardp: n and very sfo�v t'irough it. rlccording to the DOE Manual, <br />this •�,il is in hydrologic eroup C. <br />i3 � <br />d�r.�G-���o�.c:a�q°n ,��m �vcoe, sn� ci,� m�or,�oocwn�r�i.�ssneaan uocD'NHlsrm <br />