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<br />~_.._::
<br /> F lccd $tvd,et
<br />• (b) Estimate base (lu«, Un L};ure 27(A)
<br /> and (P), by trial and error. $ub-
<br /> ;racl base Cot': fro:u recorded ht•dro-
<br /> y:rapit :u,,l I,!n; nc; h) du~ra;)'.t, •, on
<br /> f.{;urc °_~(h). if the base Ilotc has
<br /> Leer, e~tin:a;eci ccrrec;lr, the descend-
<br /> ir.r ;ir.lb of i:.:dro~ras,!: ~ on Gr;urc
<br /> 25(F,) t•: ill Le a su•ai);ht Lne (cx-
<br /> ponential rcccssiun). (~ _ ~ minus
<br />
<br /> (c) Compute volume of net hcdro;;taph
<br /> as fo!loc:s:
<br /> (1) Add aster.^.~e :sourly' disc}:arfres
<br /> (in sec.-f;.•huurs) to a point such
<br /> as ?I on t}:e exponent(a! recca;ion,
<br /> ,;. un fiyrw'e 3 ~ i G ).
<br /> (?) Coa:pu;f ^ourip rccessior, con-
<br /> s:an;, 1:,,, horn ;t•:o points on
<br /> e:cponentia: recession line b;: use
<br /> O: IGl!Ott'1,'.~ fQI:aCIOn:
<br /> r --
<br /> )
<br />_
<br /> -
<br />~•
<br />~~:
<br />• ~v)tcre
<br />n,„-[iischar;: ~• at firs: point,
<br /> q,-di~cn::r;:e a: second point,
<br /> and
<br /> t-time i^:c•r•:a!, in ?,ours, be-
<br /> tv:c^n points 1 and °_.
<br /> (3) S:orate, or cd.ntne Biter ~ in
<br /> (sec.-i:.-ho::r:) ec,ual>:
<br /> _ q•
<br /> I„_.I.
<br /> where:
<br /> q,-disci;arse in second-feet at
<br />t pair,: y, and
<br /> lop ': .,-''?.'C~n_u ('og„J:.,).
<br /> (4) Total volume i.:;.m. o` volume to
<br /> p!us col;;r.:c :after ~.
<br /> (d) f'or compari;en o:i;h ran:rall data,
<br />- convrr; eolumc o: ~ to inches of
<br />- t'ur.o1T:
<br /> Inches of rmo~-
<br />
<br />
<br />' tf) .yn::;cx r:un.`a'.I c~:~, ii ::callable;
<br /> ,1~;;.,^::nc penod Ti of ra:ri: a cxc~<;.
<br />• (fI Com pL'[C iit:"lC G: b;CltrrCr.CC GC OP.C-
<br /> h::l~ vulum~-,~i Ly~u:~c~:a,'h ,, t:;;ure _7
<br />6S
<br />(C). The lime to crntcr of e„lame,
<br />T,,, c ,gals time front bc; uunn;; of ri«'
<br />of nc: h^dro~r: ph to time onc•half
<br />tolur-l^ ha> pasc~d mracuric;; poi:, t.
<br />(g) I'Ind I::;r, l.,, time ir. hoc:~s from mi[f-
<br />point of excess rair.ia!I pcrin:! ;o time
<br />of occ:,rrcncc of on~•-itali tolunu.
<br />(h) Con',pu;c dimcnsionlca >;r.:ph as fol-
<br />]Ows an[I glut 011 5emilU„ p:,pcr, ~ un
<br />figure °_~ (B).
<br />(1) -abscissa-hours irom I,r;innin~
<br />of exces> rain expn'«rd ::.< per-
<br />cent of (L.,-Gl?). t`: hr•n railt-
<br />fall data are r.ot a•:ailai,le
<br />L.,=DI? ma>' Le ta'sen equal to
<br />T~, .
<br />(°) Orriinat.;s-dixch:u•~c in scron[1-
<br />fee; of (at respecticf a'o>ct,sa)
<br />multiplied by (L.,-D.'), all di-
<br />t•ided br net hcdro~ra~h co:,:-,',e
<br />expresse[I ..~ sec.-~;.-r.:n
<br />$S. Un,rgrpph Derivpl~on for Ungpged l,rcos.-
<br />All Bxan:piC 0; :nC r!r I't t';lUJll OI a'd 1111 L'!'a)1It 101'
<br />r,n ul:aged area 15 %nOl1'It or: fi:•un' '_'~. Si:lcr
<br />hpdrot:raphs recorded at a damsi;e arc seldom
<br />arai!abic, a mean; of :ran.;tcn'in~ ctutcr.:p!:>
<br />t0 Un~3(; C'd arC> :5 nc'CC'Sr:: 1-\'. Tr.c :::C'IO!' ••Ia'!
<br />time" is t:~ [! for this purposr. Lai time iF tut
<br />index to the time of concenu•ation u: rur.oll
<br />from ;: be;in. It rc::;}' be dctcrn'in~c irom re-
<br />corr.c:.' hp[!ro,raphs IICC Cmp:": C.n i!y' CN'1"Cla;rii
<br />with basin characteri.;ir<, .~<;)Im•:n nn lid::rr
<br />°_3, determinat;or. o` a'.a~ time (er an t:n~a;•r[i
<br />~~:[tc*>hc~' irom L•a;in me;u;nem^1:;~ prn~'l,ir<
<br />the key to ur.it~rapa compctatiur. for that
<br />wage:;h•;d if a mpresentaticc dim~•::<lo:ar«
<br />graph i< kcou'::. Th~~rc arr >cccr:,! r.•••'.•e:icn<
<br />of ):: time, each ;t~~rtainir.~ to a sp,c:;',c forr.',
<br />o; una~raph dcrica:ior.: two di:TCr~~:; d,:ini-
<br />tiors arc ascd i^ :hip ;ext. L,^;: umr i< d_fu:,,i
<br />a: (i) t'^c '.imc irum t'na cer.trr of cxcr=s r:,i:)-
<br />:all to the time of occurrence of or.e-he:( ;h.r
<br />~'Gi C.^.:C G: tnZ }l;.'C:'0;f.•L r^.^-C>Cf: \•: i!!: t:^.n d-
<br />men>:entc>s bra?h procedure et:;iined an :igure
<br />_°" .:nc' ^_S; and (^_) t~.e ti^•.. iron: ;hc rriu~'r
<br />o: c•:cess r.vr.:all to the tinx• o; pr:a` c,>ci:ary•:
<br />u% the hycrogs,ph-wig v: ith ;hc Cr:a C;'L'!ar
<br />hpdro~raph concept, tigt:re ^_9.
<br />
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