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<br />~. Example: CClIlpUtaticm ot 8rn Ra.1D1'all and !la1DtaU Exc... <br />__ ('-.11llberllllld River Ballin ..bove Old Hickory Dell 8ite. <br /> <br />(1) The outline ot the CUIIlber1e.nd baain va. IuperUlpo..4 <br />over tbe total-storm isohyetal map ot the 23-27 March 1913 (OR 1-15 stOnll <br />in the s_ position !Ulsumed in cOlllplIting the "basin shape" factor referred <br />to in sub-pangre,ph 3-02 a (5). Portions of tbe isohyetal I118p within each <br />of .even sub-divisions Dr the basin ""re pl&nimetered to dete1"ll1ne the <br />ave~e depth ot total-storm ra1ntall betore adjustment tor tranpos1tlon. <br /> <br />e <br /> <br />(2) The transposition adjustment factor for each of the <br />~eV'en sub-areas of the buin ""re interpolated CD a straight li.ne baals <br />trolll values determined by the Iiy1irometeoro1ogical Section ot the Weather <br />'lreau, tor Clarksville, Tenn., end Burnside, Ky. The total !ltoN rain- <br />tall values com;ro.ted tor each ot Be~n aub-areaa were multiplied by the <br />appropriate tranaposition f&ctoI'8 to obtoin the total-BtoN SPS precipi- <br />tation for the area. <br /> <br />(3) Pr.ecipitation stations within the outline of the <br />Cumberland baein "" euperimposed on the iBOhyetaJ. up in step (1), and <br />stations irlIIIlediately adjacent thereto, were listed on Storm Study FoN 8-10, <br />grouping the stations as they appee.red in the sub-areas. The accUllllllatlT8 <br />precipitation at each ot these stations V&8 then copied from the Form 5-10 <br />tabulationa of the Part II Storn< Study data. <br /> <br />(4) Ave~e mass c~s ot unadjusted ra1:a.tall for the <br />23-27 March 1913 storm (OR 1-15) ""re computed by 6 hOUJ:' intervals for <br />..seb ot the seven sub-areas ot the basin, using data compiled in steps (1) <br />and (3), tolloviDg the a_ proc..dure used in comput1.llg averese lIll!.as cur- <br />ves tor "zon..s" in Part II Storm Studies (See Supplement C to Engineer <br />Bulletin R!.H No, 10, 1938 Form 3-12). These ave~e IIll!.BS curve values <br />vere then adjusted to correspond to the SPS rainfall values tor the <br />respecti ve sub-areas, e.od 6-hour increllll!nts of re,1:a.t&1l during the BPS <br />vere reduced from this cu"". <br /> <br />e <br /> <br />(5) PAinful-excess during succeedve 6-hour periods ot <br />the SPS \/ere computed by subtra<::ting losses correspond1:ng to an 1ntiltrati9l1 <br />index ot 0.02 inch per hour, vh1ch coD1'orms to values deduced trom aD &ll&lyds <br />Of a number of actual Vinter tloods in the area. <br /> <br />c. Variation in Procedure in Computing PAiD1'&1l-Exceas. In <br />computing ra1ntall-exce.s values for the l2O-hour SPS discussed in para- <br />graph 3-02 b, 6-hOUl" a","rage los.e. over each wb-area \/ere subtracted <br />from 6-hOUl" ..ve~e rainfall valuee tor the ....... cOlllPOa1te area. Treat- <br />ment ot eaeb lub-area al a unit was eat1etactory 1n th" particular stud3 <br />because of the ~ry lo~ infiltration index 1nvol~d. BDvever, in studieS <br />applicable to dr..l~age ballos of e1m11ar size in vhicb int11tration losses <br />llre ~lat1vely h1g;" raiofall-exceo. ~UADtitiee Ihould be computed tor <br />are.. lub-d1Vis100 correlponding to Th1elsen polygons surrounding each <br />prec1p1tat10n Itation, io order th..t appropriate &1love.nces may be made <br />tor area. net covered by ralntal1. eJlceeding loases during each period ot <br />the ItOT:ll. <br /> <br />16 <br /> <br />e <br />