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• ' ?.f�er t�:e desiqn stora, grour.d slope and q:ound .caver have <br /> . beea dete�ined for t'�e site, t`:e al�.o:rable out:law rate in <br /> c�s per ac�e can �e dete�ined by :ate�olation f_oa tsbles 2 <br /> t..4rough' S. T_P a site cantains :;:c t�es of g�oun� cover, for <br /> examnle, then a separate interolat_on is made for each grcund <br /> cover t�*pe and the results adde3 to dete�ine the total � <br /> allowable outflow rate in c:s per ac:e. ' <br /> After the allowable aut:low rate _n c=s/acre is calcslated, <br /> the reeuired deteation in c.ibic feat per ac:e is dete�ined by <br /> inte�olation from table 6 or 7. Aqain if t:+o a:ound caver <br /> types are pr000sed after developae.^.t, a separata i.nte rolation <br /> ' is mafle for each g:ound eoves tre and t`se resu'_t added ta <br /> • deta�-aiae the tetal detention :ecsiremeat in c•.ibic teet ner <br /> acre. The deteation reauire�e.^.� is then dete±-�ine3 by <br /> multiplying by the site area in acres. <br /> eor residential subdivisions t�e ac'_ual e.�ctent �f craund cover ' <br /> types will not be ?ciown duri.-tq �lan revie�M. Sased upor_ a <br /> s�+—�ey of existing hoaes ia t`�e �re:ett area, the avarage <br /> amount of iape^�ious sur'ace per single fami�ly lot is 2s00 <br /> sauare feet. The tpglicant should, t�ereiora, multiply 2800 . <br /> bv �`:e numcer oi lots and t'�en zcc t�e result to t�e dr23 or <br /> imnerrious surracb. cantaine3 �°�-.'s any new raad cons��-uc`e3 <br /> •Par tYe stlbdivisioa to es��ata "e area of iaper�_ous stL�`ace <br /> that aill ulti.mately be conta�Zed ::it`�ia t'�e plat.. • . • <br /> ��,d�'�� �, , , � ! ' ' <br /> � <br />>�'"#,�" i=, ' �cz v e: . <br /> tE r r� y1 : . ., • <br /> � ` ' " i Given: A 3 .0 acre earcel lecate3 wit`�in Nor`'..h G'e�k <br /> `<' � ' � ` ! Drainaqe Basi*�. The slope,o= overland flow is. 3.5�. The . <br /> ' existing cround cover car.sis�s of 2.Q acres of forested <br /> land and 1. 0 acre of lig�t c:ass and s�arse tzees. The <br /> pronosed land use is conaerc:al With 5� landscapinq and <br /> 95k i.mnervious ground cover canditions. • <br /> Solution: From table l, t'se cesic: s�or� c=iteria is a 5 year <br /> pre-develocmea= stox� and 2S .�eaz post develonmeat stors. <br /> From table 2 �e allowable ==-lease rate for t�e foresta3 <br /> portion of t'�e site is by ir.=e^olation . 085 c�s/ac. The <br /> alloaable release rzte for t:e grass area is .230 c�s per <br /> ac:e. The total alloa�le release rats is t.herefare <br /> (2) ( . 085) + (1) ( .270) or 0.40 c�s. This is .173 c�s per <br /> 'ae=e. From table •7, the cetention reauire�ent for t`�e <br /> landscaninq area and imper�:ous area is 8s5 ct/ac:-e and <br /> 4009 cE/ac:e, res�P�ivel.�. T�e total deteatiotl <br /> recuirement i.s ( .95) (3� (4009) -+- ( .os) (3� {sas-) 'or ii,ssa <br /> cf. <br /> � <br />