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after t�e design stara, grour.d slope and qroand .cover have <br /> been deterained !ar tiZe site, the allawable aut:lav rate in <br /> ets per acre ean be deter�ined by interpalatiori r=aa tables 2 <br /> thrauqh 5. Ir a site contains txo types a! ground cave:, far <br /> e�camnle, tY:er. a separate inter:alation is a�de !ar each ground <br /> cover type and the results added to dete�ine the total <br /> allowable outLlow rate in e:s per acre. <br /> After the allacrable out:low rate in c�s/acre is calczlated, <br /> the required deteztion in cubic feet pe:: acre is deterained by <br /> inte�olatian trom table 6 or 7. Again if t�o c:aund caver . <br /> tvpes are pronosed after develooment, a separate interolatior. <br /> ' is ma�e for eaeh y�ound cove= ty�e ar.d the result added to <br /> • dete Wiae the tetal detention recuireaeat in cu5ic leet per <br /> acre. The deteation requiremeat is then dete�ned by <br /> multielying by the site area in acres. <br /> For residential suhdivisians tae actual extent of ground cover <br /> types will nat be ]ciown duri,zg plan revieW. Based upon a <br /> s��vey uE existin3 hc�es in the E�reret� area, the average <br /> amount of iape=vieus sti:zfaee per single lamily lot is 2800 <br /> sauare feet. The �apnlicant shauld, therefore, multinly 2800 . <br /> by the number af lots and then add the result ta the area of <br /> imner�ious sur�ac�. contained orit4in any new road eans�—ucred <br /> for t'se subdivisioa ta estisate t4e area of i"�.ne:-vious surface <br /> that *.rill ultimately �e contained wit�in the plat.. � • . ' <br /> a ,o e• • <br /> Given: A ] .0 acre garce3 locate3 vrithin Nort� C�'ea�C <br /> Drainage Hasia. The slope,of ove�lznd llow is 3.5�. T1sa � <br /> existinq qround caver cons:sts of 2.0 ac:es ot fores:ed <br /> land and 1.0 zcre of ligh� grasss and sparsa trees. Tha <br /> proaosed land use is commeraia:_ wi� 5� lancscaninq and <br /> 95� imnervious graund cover canditions. <br /> Solution: Froa tt�le 1, t'�e desiqn s�or� c=iteria is a 5 year <br /> pre—devel�naent storm and 2S yea: pcst develooment s:ars. <br /> From tabl.e 2 the a1loWable release rate tor the fores:ed <br /> portion of the' sit= is by in'te�olation .085 cfs/ac. The <br /> a1loc:able release rate for t?�e grass area is .2]0 c:s per <br /> acre. The total allowzble relezsa rate is therefara <br /> (2) ( . 085) + (1) ( .230) or 0.40 c:s. This is .131 c�s pe: <br /> 'acre. Fro�a table •7 , the cetention raaui:e�ent for the <br /> lzndscanir.g area and imnervious area is 885 et/aCe and <br /> 4009 c£/acre, res�ectively. The -to:al det�ztion <br /> Tecuireaent is ( .95) (]) (4009) -� ( •�.5� �3) �68`� �= 11,558 <br /> c�. , <br />