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<br />crrd 1n t!•,c \ational 1Ccathcr 5crricc IIt'dro•
<br />n:r,coroluyrlca( I:cporL; \o:;. ;:G and dv.
<br />(d) lhniun~e rlrra-An accuratz map ni
<br />the runoff cr.ntributin;; drail:a;:c ;u ca abotc a
<br />!root: of intrro;t a c.<SC nli:~.1 to any t',ood ti:ula~.
<br />f:uc c;;t;c•ct has brcn r.iscus-cd in sc:tiun •.^_.
<br />re) ~nr! n,:rl Corr.-The t.:pe of soil and
<br />rc~e;atit'c cnccr of a ,raters.hec! has a n'arF:^,'.
<br />it::i::~,nce t:por, it; r;:no;f potential, It is dil~;-
<br />cul: to espre~s roil and coyer :}'pcs i:: ::u•
<br />me:':c:,l value; t':hich represer.t th^_ di(ierrnce
<br />Lc; :•.cca precipitation ar.:ounts and rcnuT
<br />arnocn;;. If both precipitation and runc;t
<br />r:a;.: a:~~ aratlahi,: for sct'cral ccenis, practical
<br />raluc•s c: a be obtained by direct ana!y-sis (sec.
<br />51 1 : i( scch data : rc not arailabic, recourse
<br />r.-us'- },': made to comparisons v:ith ana'.•:scs for
<br />ot!rtr ~':aCCrs}:•^ds. -=, method dcrelopcd by the
<br />L•.S. Soil Conscrcatior. Scn'ice for csCima?inF
<br />rur.c:? on the basis of soil type and co`:er as
<br />me:i::icd ;for use i:: this test is discussc~ ir. sec-
<br />Lor. ;.1 and is presenCCd in detail in appc::dis -4.
<br />lf) i.r,rnrr U:.=!riu7,!ic,:.-The t:^.i!~raph
<br />h:.= ~rotrd to b^ a cer.: a;`cc::t'e tool for hpdro-
<br />1~- ~ ,':erk. --\:, eng ^ec- prep..n.rr good es-
<br />;ir..c;~s s^ccid i,c ia::iliar v:i:h its basic pr:n-
<br />cip:zs. .. Lriei outlir:e of unitgralfn.,:zrira-
<br />ll^^ and app.IC~r!Gn, inC!L'Cing a dlTea it O:]1CS5
<br />grac:^ approach for dericatior. of a spr.:hetic
<br />uc::~^ph for un;a~e(i areas, is ;irc•n ir, sec-
<br />t:or.s ;,'', ~.^., and ~;. .~ concept of represent-
<br />iny a unity;raph as a triangle and the re!a[ion-
<br />.v;:ip. th::r can be deri':ed therefrom is presenc-
<br />e(! m section 55. In:zrested en;;inecrs are
<br />mie:red to the tests listed in [he bibliography,
<br />section G0, for more detailed discussions of the
<br />ur.it~raph.
<br /><4, A Method of Comp~fing ~ta,<rnv.•n Proloble
<br />flood Cischorge.-The io1!oo:tr.~ discussion per-
<br />tsua in general to data cor.tafned it: the "13}~-
<br />dro!o~p %uide for L•sc ir. 1\-ater;ccd Plan-
<br />r.in~."' nub'.ished by thz Soil Cor.s^^ration Scrc•
<br />ice. The introduction states: "T~te Ii;:drol-
<br />o~y C,u;de is Intended for the u;z of Soa Con-
<br />sercar.en Ser: ice technicians and engineer;.
<br />I; presznts r:~te-ial needed for ic!riliing r.:~-
<br />tior.al szrc:cz rzspensibiLties in the field of soil
<br />"'f•,e-.:: cr Lmde (nr L're In k"r.r r•he[ P4nnme." A'a t.o+a: Ln-
<br />p+rm.p H=r_]~o:. SK a, HrG rub; r. S pple-,rn •. A, U.S. Daparo
<br />eect c: Aene'~l:u re, $q'. C=narr•'n.on Srn'¢e. 1:34.
<br />and tcatrr con=craation. Ot):.•r tc• F,nlr:;,t:•.
<br />and engineer, may iuld portion: ni t!:~. t;ulde
<br />useful in their oun e: uric, b::C thl' skr~l.l,! Irc-
<br />o;;nize that the Guil!c nitcmpts f:r,t to i:!I Srro-
<br />icc need: and rcquircmcna." :\ rcrl"~~I man•
<br />ual, "SCS ~:a iona! lir.glucr: u:;; 11:1:7.!i iUi,it,
<br />Scc:iml 1, Ilydrolo„~. Part I-'I'~':urr<Lrd 1'!::n-
<br />nin~," tt'ac i::cccd in rlugus[ 1`1„1. :1p;;;icaW,:
<br />data from this later m:unla! I::RC been Ic<h:did
<br />herein.
<br />The Soil ('OI:Re;'ra[ion Scrcirc 1~:-~:• ('.un•:
<br />a 1'C' lit: ~C'd OR C9 nC!nRl Ui:n 1'C;;:'.:'~~::: L' ::(~; .~::b1C
<br />at'cra;:c `.aloes ob:ainc(: iron :...::I•:>I'- o` -•::~nc
<br />r.:lun'a! Cool c•rc::Cs a::d ::rc u~c:l ts, c::al:ate
<br />runui' for >etaral psrpo.~;, n:r:::.`.i::;_ .nliou
<br />dC~I; n f100(1 CO^1pl:i:I:tOP.<. I hC ~cn'li^:i~' Ir•1'
<br />con:puti::;; an to:lu^: dcsl;rr. Conti a- rout!::.~ a 1,;
<br />the SCS Guide ha bcc^ a,iup0.•,i i:; (:u< test.
<br />along oath roan; of their ec-cl:a;on< rc:::n!il:~
<br />average ,appluablc t':.lucs for cni;~ra;•h (Ictcr-
<br />mirat:os : nd rclettunn rate estin'.c:c;. IIo•,r.
<br />c`:c:. t}:c• ch:::'s for ol~t:cric;; r,,`'.I;'::.. .... ::J.-
<br />ucs (sc•c. i,(I) r:rrc prrl:ar~.i r-p•.•r:.:'.'.:: :~n' thi<
<br />test to ire more c'Irrcily app::c::'~:!t .c::r~t•: d~'-
<br />si~n flood (le[crn:tnatien=, turd ... .i:r
<br />same a: presented in ;!te SCE C,uith:. -.:<o.:.
<br />m:n01'n10d:::Ca::Ori O[ the SCJ C.. .. i'rti-
<br />ma::n~ d:rcct runc:i fro.^.. dc;i_c: <:o:n: •.`:cclp-
<br />It:aion has been r:ade. as d:.cc~sed in :. ,: J3.
<br />The meit cd pre<enred i:orei:: is ap.,.:,..:plc to
<br />watershed; v:herc anti ot;;;i: r.:•:< ..: r.im•:: run•
<br />07 iron prcci p:;atio:: in ..._ for°, „i r.ti::
<br />(sec sec. :il (a) ). Tho.<c t`.:,:rl ,:~~ ,1, )::n'm;:
<br />runotC•dclaylno nudr.'. ,uch ;,: i:,:„,• .,::,nl;~~•
<br />hea•.- forest liter, a::d porrn;, ;:,~ ,~:. rdqu:rr
<br />special study. P; atcr;hc(!s inn:: t•. h:,•h max-
<br />imum runo:T tt'ill li4;e!o inc!udc s::c,•,ntc!: a!~o
<br />rcgtlit'c sp~•cial ;:udy. It i> bcyomi :'::c ;colic
<br />Oi IliiS IC.CL t0 duct:>5 t!:e$e :pnC:; ~ .,•,al;i'x IIl
<br />derail.
<br />This procedure for• corrpu;inc :. ^:asiu:un:
<br />prcbab!e good is b: s~`d on ,h~• !:.nit •: n:~•:ror,~-
<br />lc;::cal appro::ch anc' rr.;a:r,~> e:t.-:;<<; of
<br />storm potential and the amo::n: turd da:riinl-
<br />?ion of runoff. -as in a!I c~a.'ra:::~,: procr-
<br />dures, certain criteria haor bec^ ...:•_~,;c~l ar-
<br />bitrarily as ap,r.!icablc to t;~e ^ra:~-: r.t:mLcr
<br />OI C3SC5. -~ SICp-he-step Cspl:na:;G:. VI tl:d
<br />protect:rc and comsu:atior.s for a-, c~amplc
<br />are gi•:cn in scrio^ 53. -, brit," de-;:':~:ion of
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