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<br />I
<br />
<br />,,. Objectives
<br />
<br />SliD-bas in to reclch the ",ost JownSlreJIIl1l I,,;rt of that S;JU-bdS i n. Tirr:~s
<br />of concentration w~r~ J~tenl1il\Cd oy olsses5ing udsin "Old chdnIl~l charac-
<br />ter; sties. Cor-cent rot i on to ;,,* to the ch~nnel (over1 Jtld flow tir',~) "us
<br />del-en"ined od<;ed 1m ul;~t!r I>~si" char"ct"r 4n,! cldd"rl to dldon~l flow
<br />t ill:e (jeter'I.li fled frOl,l le~~tli and average velocity. f'lQw veloci I;J ",1$
<br />est i Inated f rO~l tYlli Cd 1 eli,!'''I!.' 1 sllape, cond it; on and ,,1 Q~l.'. T j">e, of
<br />concentrdtion are tdbul dteJ for '-'JelL s'lb-OdS ill on T~blt: r'i-1.
<br />
<br />IV. HVDROLOGIC AN^lY$I~
<br />
<br />The purpose <Jf the hycrologic analysis h co udine the ~InQunt
<br />"rid till'!.' dhtribution of the rJrloff n.-'sultifJg frOin pr~cipitation which
<br />,'caches ~ si,ec if i c pc i nt of i nterust. Tile prec 1 ~ 1 tat H'" r~noff '"a..Y be
<br />de r 1 ve~1 f rOlll ra I n fall or <; nOW''ie It, 0 I" bot h, and 'dJY re5lJ 1 t f rOI" a 1 on~ ,
<br />period Of ~entl e rai nfall, Qt" a brief, intense tr.understorm. A sta-
<br />t 1st iCcll Jnalysfs uefl ,,~s the prohdu i 1 ity that d certiiin ""Iount of ;ire-
<br />cipitat ion runoff !;lay be expect~d "t a point of intere,t, on the
<br />Henl~e, of OIlcr every cerLain number of years.
<br />
<br />The result of the IlyJrol<.)~i~ a~ctlYSl'i I, d 11Jlloff Ilj~ro~rilpll f~,'
<br />~~cli sub-::'asin, for <'dc!r of the fow" dtsj~n ,turr., f"~'lIJ~,,,i~s. Th~
<br />hyd"o~raf!h, rel ate a1l10!l11~ of I"~noff to time. The pe"k lnO-year fre-
<br />quellCy r~noff rate ("Peak Q") for ('aci! sub-bas in is tallul at"d on TJb1e
<br />J V-2, a~ is t i one to peak ("tp") ,uld Cd,>e t i1l1e ("tb"). r IIHe to peilk is
<br />the tillle re\jui red after the sLorITl be~i~, for the peak runoff rate to
<br />occur. Base ti"re represents the ti"le reyuir~d after Ule stonn be~ills
<br />f()r the runoff rate to reduce to dp~roxi"iately 5% of its peak v"IIJ('"
<br />Th(' base tillle 'luant i ty Illay be used to '1uic~ly a;,;.,rox irr,ate the
<br />hydrogr~ph re1 atiollsliip with tile 1'f!,IK flo'll "nd L i",e to l1f!dk val ,,<,so
<br />
<br />The hydrologic ddtd estilblishes the basic fact5 upon which con-
<br />s ist~nt and orderly III anning IHay be bilSe<l witlj regard to SLar"l
<br />drainage. lnter<;isofoverall floodplain analysis, discharges are
<br />defi ned for tile variOus bas i ns (f or eacli f;f the fOLlr des i gn st;or~1
<br />freljuencfes)ofthethreestudystrealilS,fortlrepur;JOSCofdefinillj
<br />the flood water surface eleviltions.
<br />
<br />Tile 11usk i Ilgu~: 'Ilethod of st rea,_; fl ow ''<.ill t i ng lias el.l~ 1 ojed, to
<br />acco~nt for the alterat i011 in shape to tile <;trOOolll fluw hydrogra~h for
<br />fl LN tiF~e (and overbank stora~e), and 01 ';0 to cOldbi Ile h..l"h"ographs of
<br />the vJrio'js s~b-bas ins.
<br />
<br />Re~arding t.he urban drainage an<llysis, the a',jollnt of rUlloff '"Idch
<br />i s ex~ected at the various poi nts of interest thro~gh the ci ty alld
<br />ellvir~IlS is defined for Llie Initial and :,,~jQr (5 yea,' ond 100 year
<br />r€spect i ~€ 1y) des i ~~ storlllS. '
<br />
<br />B.
<br />
<br />~ethods
<br />
<br />For the urban {!1'"llId~" d"d1;sh, the ,"atiorlal f(),.,IIuld 'idS <It;liZt<(j
<br />to dtf.; ne rUllofr of a '"or€ loc"l il~,l IIOt'lre. based on th0 r~i"tJ1 I dot J
<br />deri ved froj,1 tile ilV~'UA and NWS records.
<br />
<br />The quanti ty of r~ inf"ll whic!: eventu"lly reache,; a major
<br />drainage channel is de~endel1t upon tire durat ion Jnd intensity of the
<br />roinfal 1, UPOll the qUilnt i ties of "Jl n eVJl-'orat€d or illtcr~oopted by
<br />., ~get. t i <)n, L~pon the su i 1 i nf i ] t ,. d t I on dld r ac t € r i S l j c, (wh i c II ~ re
<br />Jflecti'd by the slope of the lJn~) ~nd by th~ yolurI,e M local ,-urloff
<br />reta; ned in de~ress fons.
<br />
<br />The rJt; olla I f ornlu I a is 'J W C,,! XI\ "h'~"e;
<br />
<br />The Soi 1 Conser vat. iOIl ~ervice (SCS) lidS marte extensive ,tudies
<br />JndobservJUonsonstornLrullofffrOUldifferent<lgricul<;urdl1andu,;e<;
<br />ano <.liff~rent so11 groups. The SCS rUlloff complJtation procedure J~
<br />l'1odHied by the Iluredu of Recl~",dtion "JS used for each subbil,ln (see
<br />References 3, 24).
<br />
<br />Q ~ flm.. (cis)
<br />C ~ COt! I ICI~"t .,t ""'lI'I"'. lJ! ,'.:nuJ I eXI'~LLe,i tr:l;:: .In ,1!,10;11l!.
<br />01' ralllta.11
<br />I ~ ra 1 nfa 11 i nlen, i Ly (i II/I,,') (~,,~ i i ')UIOO : V -3)
<br />" " drc i nau~ ~r€~ (,I(;"'''S)
<br />
<br />A ;;rnr" Jetcliled Jiscussion Iday b~ fO!,,,,1 11\ ,L,nL!ct,.J ~"~i",,,,,'i'l~
<br />tex,booh (j.e., Rcf,~,-"ncc 43).
<br />
<br />The '"UIlO ff COllLp~Jt<lt i on ~ro~edu'-e i nVlll veIl def i ni ng the bas i n
<br />"cul've IM,b~,'" (eN). HilS eN value corre~~oncs to a tabulation of
<br />r<li nfall-runoff r~lJtionships of the SCS. Curve 'hl'dlJt'r st'lection is
<br />l'dS~d <,)'1 sOIl type, soj I perr.reabi 1 i tj (lTIoi stlJre illli I trat ion rate),
<br />soil cover type Jnd cond it ion Jnd 1a~d use. The SCS \I<lS consu 1 teti in
<br />definin~ tile eN values. T~e eN d~ter",inood lor edch 01 the st;b-basins
<br />is ,>hown onT<lb1c IV-I. as is the infiltration rJteutilized.
<br />
<br />c. i'recivitdtion:,nal,.sis
<br />R J i n fa) I data f rOlll tlH! II '1W~J A and L I,i' N ~S (J I> r Llle C i tj of
<br />!\UlltrOSe), as well ~s the rWM ,~tlas (Rl1f~'-~llc~ 1) "dS Scali$licdlly
<br />,irld1yz~u tu dcfille "~(lJrr~n~e illL~rvJl I'rohdtJilities and t.he r~s"IL'rl'
<br />rail\fall-fr~~LJr.ncy relJliorrship for IXlt.h th~ up~er tJa,i'l ar~ds, ~'i I,rll
<br />a<; th~ ri ty of Montros~. Th i '; rd inf"l! rel ,1t i 011 ,idS t"ler. gradllJte<l
<br />l!ct\iCen the Cit.y cf :~ontro,>" dnd tile '+I:,lr basin arCd, dcc(lrdin'l to I.I\"
<br />pr~<ln.dlll~nt n,~i<ln,1l 1"'~(il,it"li"" l<<t.h-"'I :;llml'1 I" Llle ~J()M MiaS.
<br />T~e r2,>~lt \s J r,ybnd "Iill: i;l~llr,'U,.~.~irr~ Il\'iJlIA, I,',;~ JIl~ I:U;\A ,'i'II.,LII
<br />
<br />.'Ilso dff~cLillg u,.; ~l~IJ-b~,;i" rolilll~ll-n,J1()ff r~l.ltion is tile >IIr.-
<br />h.3s i ~',; t i ,," . of concerlt rat i on ~ rh i s Vo 1 ue r~pre,;"nt s tht' t i "'" roo'1<11 re<J
<br />flJr th~ I-'reClv'Lltlo~ ~'l1ic'l fnst f.~lls at tile u;!p~r ~xtr~I,'e or t~e
<br />
<br />~J7-
<br />
<br />-18-
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