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<br />(1) Lines 1 to 5 establi.h the index rainfall aDd the <br />magnitude and tillla arracgement ot 24-hour raintall lIIII01.IDt. that would be <br />obtained tor the entire basin Without reduction tor the tact that the <br />storr isohyets do not conform to the shape ot the basin. <br /> <br />(2) Lines 6 to l2 incorporate the adjustment r''luired <br />tor basin shape and the subdivision ot raintall 8lIlOIlg sub-basins. Theile <br />liDell can be e11llL1nated ..mere these retiDements are not required. Value. <br />giV'en iD liDes 6 to 8 were obtaiDed by plan!metering iIIohyetll on Platll 13. <br />Values ot liDe 9 are those ot liDe 5 divided by the total-storm rai.ntall <br />(15.7 iDches). Va.lues ot linell 10 to l2 are obtained by IDUltiply1llg <br />valuell ot 11lle 5 by those ot liDell 6 to,8 rellpectively. <br /> <br />e <br /> <br />(3) Linell 1.3 to 21 establillh the hyetograpbll tor each <br />area. Six-hour percentage ot 1IlIl.X1mum 24-hOllr raintall obta1lled trolII Platll <br />10, are applied to each succesaive 24-hour period ot raintall. Theee are <br />multiplied by respective values in 11lles 10-l2 to obtaiD 6-hour ra1ntall <br />lIIIIOuntS ill lines 14 to 16. The tabulation on Plate 13 iDdicil.tell that tR <br />is 3 hOl,Ir8 iD this calle (11l1li Plate 11). Appropriate percentage6 ot lII&XiIIua <br />6-hour rail11'all in 3-hour interval. shown on Plate II are entered in liDe <br />18, Plate 14. These are multiplied by the respective values ot tbe 66-hour <br />colUlllll, 11.l1es 14 to 16, to obtaiD 3-hour 8IlIOUlItS on 11.l1es 19 to 21. <br /> <br />(4) Lines 22 to 29 establillh rainfall excess BIIIO\lI1ts. <br />In1':I.ltration losses (lines 22 a:nd 23) are subtracted t1'Olll rai.nta.ll lIIIKlUJ11;. <br />tor the sub-areall A and :e to obtaiD ra1ntall excess lIIIICUlItS tor those sub- <br />areas (lines 24 and 25). These are converted to volUllles (lines 26 llI1d Z7, <br />a:nd are added to obtain raintall-excess volUlll8s tor the total area (11lle 28). <br />These volumes divided by the total area )'1eld average ra1ntall-excess depthll <br />tor the tota.l area (line 29). Values ot l1lIe 24 aDd 25 would be used in <br />conjunction with Ullit hydrogrephs tor the subareas 1.11 this case because ot <br />the existence ot a tlood-control reservoir at the lover end ot area A. In <br />cases vbere 8uuci1 vision 9t tbe area i8 made only to acc01.lDt tor area.l <br />d1tterenc~" in loss rates, values ot line 29 cm be used in conJUlIction With <br />a Ullit hyUl'ograph tor the entire area. <br /> <br />e <br /> <br />2-04. APPROXIMA1'ION OF SPF AS PEICENTAGE OF MAXDIUM PRO!lABLE FIDOD. <br />As stated in sub-paragraph 1-06 d (2), estimates completed to date iDdicate <br />that SPF discharges based on detailed studies usually equal 40 to 60 per- <br />cent ot the max1Jllum probable (or "maxi.lllUlll possible") nood tor the same <br />basin; a ratio ot 50 percent is considered representative ot averse;e cqndi- <br />Hons. Inasmuch as computation ot max1lllum probable nood estimates are <br />nonnally required as the basis ot des1gn ot spillways tor high dams, it is <br />convel11ent to estimate the SPF tor reservoir projects u equal to 50 percent <br />ot the 1IlIl.X1mlllD probable flood h)'llrosraph to avoid the 'prep&rStion ot a <br />s..parate SPF estimat.. (s..e paragraph 1-05 aDd 3-02 d resardiIlg SPF seriee). <br />Accordingly, this convention is acceptable tor reservoir projects in sener&!. <br />Th.. rul.. may also be applied ill estimating SPF h)'llrosraphs tor basillll out- <br />sid.. ot th.. region and range of areAS cOV'ered by gelWlral1sed charte presented <br />herein vh..re maximum probable flood estimates based on detailed h;ydrometeoro- <br />logica.l inveetigations have been cOlllpleted. Where SlIOW melt or extreme <br /> <br />l2 <br /> <br />e <br />