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Chapter III
<br />
<br />Flood Stua'ies
<br />D. L. MILLER.` P.. A. CLARK= and S. SCH:.M;.CH ~
<br />A. GENERAL
<br />36. Scope.-This chapter considers methods
<br />of dctermin:ns ;food flows to be expected from
<br />tr;c drainage area tributar}• to th_ resen•oir
<br />site, for vrhich provision must be made in the
<br />desi;rn o` a dam. ?he flood used for design
<br />,. ^.;ns; faa::re is termed the "in;3o•.r design
<br />Coo;i." L. most ir.;tances, particularl;: for
<br />>trucwres .r.:po::nd:n;; considerable stora;;e,
<br />the ,ntlu~~ d~si~n `god is Lire maximum prob-
<br />'' ;lone', t•.:~.ich i~ de:ir,ed as the largest food
<br />• ca:. r~'asona:~i}' bz expected to occur on a
<br />,,.•e:: stoat:-. at a selected point. :adoption of
<br />an inPo«' desgn "god less than the mzxir.',um
<br />probauie f,om_ a a polic>' decision to be made b>•
<br />the o:•:ner, a~cnr:, or orsaniration responsible
<br />for cony:ruct;on o` ;::^e pro)ect. Factors to be
<br />cou~ilicrcd in an'icrns at such a decision are
<br />l4~tcrm:n:Iuun of the maximum probable
<br />IIrnI•; i; La~cl! on rational considcraUOn of the
<br />ch:utces of ~imul::.neous occurrence of the
<br />m:uimam o,` the sc•.~crnl clc•mcna or conditions
<br />e:hich conU'ibute to t}:e flood. A major con-
<br />xil!~n'ation I: the dct^_rmination o:` the rur.alT
<br />that •,vould result from an occurrence of a
<br />prnLab!c n;a>.imcm storm based on meteorolos-
<br />ical isctors. This hpdrometcorolo;ical ap-
<br />pr~arl: i~ ncccxsar~' bceause streamflo•.c rec-
<br />In~l'..:Ire of such rc!:ulccl•: short duration in ihc
<br />l lut~,l Statr: ;h:;t ~:aUs:real ana'•:scs thcrccf
<br />I'I~ n~~'. llrn•;11!1• r~li::blr l~a~es for cs•Imatcs of
<br />n:;I•~.Irnl;^ pn,hablc Il~od fig::;.
<br />• 1 ,n. 1:.-..I IL~I~~ i•rr ~^'~^•^. 14v.~.u of Rrcl. m.uon.
<br />.1~.,..r ,•,., 1..,..,..r ~.I u„•..~ nr.~~o"„m.I~...,
<br />. i.. u,,,..~ ,.1 lo-. ,~ ~ I.,~u...u.
<br />In additior. to de,erminatio.^. of in9or: design
<br />P.o~ids, this c::napter u'il; ir.dica;e methods cf de-
<br />terminins the mac-nitude and freG;,enc~: of
<br />floods as indicated b~• statistical ar.:,ly'ses of
<br />s.reamf',otc record;. These zta pri:naril)' for
<br />use in cor,ncction Frith c..=.timatirs di•ter=ion re-
<br />quirements during cons:n,c_ioa, es:ab!i>';in~
<br />freGucnc:' of u_e o: emer~enc:: ~, i!1•.cay~ used in
<br />con~un^_:ion kith outict, or small sriil•;:a_,,
<br />detcrmin:n~ peak disc•rarge es:ana'-cs fer di-
<br />~etsicn dams, or prot'idin~ other inior^:.^.tion
<br />useful to tr.e designers. Discussions ir, : - .~
<br />of this chapter zre general; details of su;;es;-
<br />ed procedt:res are given in part B.
<br />39. Srreamflow Dpro.-ihc hpdre!osic data
<br />most directlc useful ir. determining f;ood9ott's
<br />zre actual sa'eamflor: records of considerable
<br />length at the location of the d:Ir.:. Such rec-
<br />ords arc rarc!}• available. The atittccr shoc!d
<br />obtain the strcamflor: records available fu: the
<br />general rcrien itt t•:!ticlt the dam is to be sit-
<br />uated. Locations of streatn casing st~[lons
<br />and prccipitatior, stations in the United St:ae<
<br />arc sho«'r. on a series of maps entitled, "lacer
<br />Basin :laps S'r,c~cir.o H>'drolosic Stations,"
<br />edition 19u1', prepared u:;dcr t?:e super:aior:
<br />of the Rational t`,•cather Scrvlce. Such d:a:a
<br />collectins stations arc subject to ch :n^z in lo-
<br />cation, discont:nuatior., or initiation cf net•:
<br />s;atior.s. Thcsc maps cannot be kept curter.:,
<br />and inforr.:a;ion theroon m;at be sapplcmer.t-
<br />ed by arldl;inn:Il invcstisatrons in order to be
<br />sure of the location and opcraLOn o; station, in
<br />a sivcn arcs. Titc cnr;inccr should cor.s:rl: the
<br />~ra1t•r sutll,lp papcr~ and indcxc> of the L'.ti.
<br />]~
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