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<br /> 'T��c •'ulh��„in�t ��•:ci�-�I. t•,rc-.cr,� itir •r�vc�.cn1�����• ��,lum: �,t ruun�t hy� Uic Rational
<br /> calcwa[ivn mc:hod (ur .� typ.c:u lwv-�uc plclhod, �t iocs attrnipt to pradir.[ morc
<br /> basin. icalistic lrydrogra��h v� ume� charactcii,tic of
<br /> tl�c l�i�;)icr frcyucncv ;torms.
<br /> Cramplc No. I
<br /> Givcn �—
<br /> Arcac A - 2.0 acres .�
<br /> 'Cype of dcv�lopmcnt: commcrcial �i �1
<br /> parking lot, fully r.�vcd. C = U.9 ' ;;\
<br /> Dc .�i�n raintall frcyucncy: fivcrycar '{ \:�,
<br /> 1{ain;all timc--intcnsity—frcqucncy . �\ �� ;
<br /> curvcs: !s indicatcd in Figurc !0, R:�inf•rlI � , ,� ``;�
<br /> Timc—hi.cnsity—Crcqucncy Chart `.
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<br /> Timc of Conccntntion: T� = 3 minutes ; ' � � �\�
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<br /> Rcquirc;l: ; ' � �\ '�<�._.',,
<br /> pcv�lop family of cun�cs rrtprescnling ; . ` �. - •:;-=:_- --
<br /> ;.lodificd Kational �9c11iod hydrographs �=��---_.__-
<br /> for the 8, 10,15,20.30 and 40 minute �'••-------
<br /> �ainfall durations. „ � ,�'—;� ---.�:a--w;,
<br /> Rainfsll Rainfall Pcak •�� .,, .•�..,�.�.
<br /> Duration InlensiiV R;uiu[( _�
<br /> (minWcs) (in./hr.! Ratc (cfs) FIt;URE: !0 RAINF/�LLTIML•-lhTENSITY-
<br /> 8 4•3 '•7`' J'ItL�1UENCY C[lAftT
<br /> 10 3.9 7.(��
<br /> 15 3.2 5.7G ��>>c ncxt ;Icp in detcmiining thc
<br /> ,,0 z,� ,S H�� neccisary slorage oolumc tor thc dctcntior,
<br /> 30 2.0 j.(.p ��`����Y u �o (I) set a release ratc and
<br /> GU � ^ a �� determinc thc volume o(storage nccessary to
<br /> Ans�vcr. The resulting stonn hydrographs are �ccomplish this rcicase rate or (2) detemiine
<br /> dc,ictcd in Pi�irc 9. thc �mounl o( stortnwatcr storagc volumc
<br /> it i; rccommcndcd th31 ,S��rr�icrit b� �v:�ilable on the sitc and lhcn delcrminc the
<br /> nddcd to thc R��tional Mcthod (o account for minimum relr.asc tatc rcquircd so as to not
<br /> cxcecd the storaEc volumc. The first
<br /> an ecedent proci. ilation condilions for m�,nr possibility, that o� determu:ing nece�sary
<br /> ^rorms w•ith rccurrcnro in!crvals are�t�r than. storagc volumc whcr� .� prc-dctcnnined rel^_ue
<br /> . 5 yc �rs. TaUlc 1 3, Rccummo,uded rate is xciccted, will be Gzalt with first:
<br /> A�tsedent Frecipitanon Faclors, prescnts a To de:tcrmir,c [;.� st .iay,: volume
<br /> sri of rocommended cecfficicn�s. Under thcsc
<br /> , rcquircd, a r.scrvcit rou ing . ioccdaro ;hould
<br /> conc.iti<�ns, thc R^tional Gormula b�comcs Q bc accom��lishrd on cach .d iiic hydro�raphc,
<br /> = G:'.iA. Althaugh this appn��ch docs nol ��ilh tl�e �'�lic]i Slo�m du�.�u�n and mauired
<br /> t •�tr�l� re�oncile the difficulties in volume hcing determined. Tlre irnportance of
<br /> thc par�icular projcct should govcm thc typc
<br /> 1�,\I3LE 13 of ruuting uti(izcd. For small arca� tequuing
<br /> l+crc�rumcn�;�d An�ccrdent Prccipitation rr.pclitivr r;..;;���ations, such zs in bay5 of a
<br /> ; ,�tcrs for thc Ralioual I�ormula p�rking f��t, an :�ssumed relcase c�arvc is
<br /> ;+.rcurccmm �ortnally saiisfactory. For largcr arws, such as
<br /> lntcrvnl ❑ pond in :, sntall �:ark area with 20 aacs of
<br /> _LYcars �:�_ tributary arca, a simplc rescrvoir routing
<br /> ptoccdurc would be in urdcr.
<br /> 2 to 10 1.0 Fi�,�ne 11, Typical Iixample of On-Site
<br /> 'S 1.1 llctention -- Rational hiethod Analysis,
<br /> 50 1� rcp�esc�ds thc method actually utilized by
<br /> 1 GO 1.25 Frasicr & Gingery, Inc., for .small area
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<br /> . 'R�RRjwv�n.�aiYrsew.ow..►aev.n.....�.r-a..+.��---+..�+-�,.--..�— �—.���-- �
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