|
<br />'"',
<br />
<br />\
<br />r
<br />
<br />1!:I.II1!:KT COUNTY 1I0~KD O~' COlUlISSlONI!:KS
<br />COI.OK~DO "~Tj(K CONS~:K\'~T10N HO~KD
<br />
<br />r-
<br />
<br />"0
<br />
<br />',0 '.iMILU
<br />11 KILOMETERS
<br />
<br />ELBERT COUNTY
<br />
<br />"r"--"~--~-'~'---'l"----"--'1';--
<br />
<br />l
<br />
<br />w,'U.
<br />I
<br />\
<br />1
<br />.",." I
<br />39' ("..~ ~:,::~;,~:::- ~3~
<br />
<br />I JUAl."li... ~ I
<br />I -('ul,)rddt) I
<br />I Sprin." I
<br />
<br />~ P..hl" -t.,..... I
<br />
<br />
<br />
<br />
<br />."l--~-::::J_-~"-"~--"~103,__1
<br />107" 105-
<br />
<br />
<br />~,~,' 7,& l~OMllfS
<br />o 25 60 75 100 KILOMETERS
<br />
<br />LOCATION MAP
<br />
<br />I NTROOUCTI ON
<br />
<br />In 1978. o"lcl.1I of Elbert County. Colo., foresaw the need to
<br />pro....lde flood-pron.....'.. Inforlnltlon for un by both developer. and by
<br />citizens un.~r. of the poulblllty of flash floods along oorfMlly dry
<br />streams. Accordingly, the Elbert County Board of Commlnloner. and
<br />the Co lando W.t.r Con.ervat Ion Board Itstab II shed .. cooper.t I ve
<br />program with the U.S. Geological Survey to lTIIp flood-prone .'.,IS In
<br />Elbert County. Inexpenllve. office-compiled flood-prone-.r.a ""ps
<br />lack the accurlCy dellred. whereas detAiled flood studle. of rur..1
<br />are.., would be too costly. Thus.. compromise between the two 'method.
<br />w", choun. FI.ld lurvey. were nw.de .It Nny .electod stream croll
<br />,ectlon. and the relultlng computations provided a,cur.te 100"'yoar
<br />flood-level InforlNtlon- which wal pr...nted On enl..rged quadrangle
<br />b... IMPI. Aho prepared were this report, which give. background
<br />InformAtion regarding the Ule of these map., and a technical addendum,
<br />which contains all croll-.ectlon daU and.. detailed dlsculllon of tha
<br />methods used to IMk. the hydraulic computatlonl.
<br />
<br />The NIP" thll r.port, ..nd the technical addendum are available
<br />from:
<br />
<br />Elbert County land Use Adml n I strator
<br />County Courthouse
<br />Klowo, CO 80117
<br />
<br />The rqpS, report, and technical addendum may also be Inspected..t the
<br />offlcel of the Colorado Water Conservation Board In Denver, Colo'l and
<br />the U.S. G.ologlcal Survey, Water Resources Division, In Lakewood,
<br />Colo.
<br />
<br />The IYpS ..nd explanatory te)(ts were prepared by the U.S. Geolog-
<br />Ical Survey, W..ter "esources Division, Colorado District, under the
<br />dlr.ctlon of J. f. Blakey, District Chief. The field work was done by
<br />the U.S. Geological Survey; by the klow.. Soil Conserv..tlon Service
<br />District; by lt.Iff N:mbers of the Color.do Water Conservation Bo..rd
<br />und.r the direction of L. F. Lang, Chief, flood Control .nd Cons.rv....
<br />tlon Section, ..nd by Elbert County personnel under the direction of
<br />Ch..rl., KImsey, Land Use AdMlnlstr..tor. Access by survey p..rtles to
<br />the '3 stream cro51 sectlo". "'as a roost Imporhnt part of this pro-
<br />Ject. The cooperation of the IRIany Elbert County I..ndowners In provld'"
<br />1"51 accen to their properties II gratefully acknowledged.
<br />
<br />HAPS AND AERI~l PHOTOGIlAPHS
<br />
<br />Elbert County Base and Index Haps
<br />
<br />Three maps of Elbert County are presented In this report. The
<br />primary hlghw.ay system ..nd principal towns are shown In the bue map
<br />on the left. The U. S. Geo10glcal Survey topogr..phlc fNt,pS th.t cover
<br />the county are shown In the center map and ..re Indexed by row letter
<br />..nd colum" number. Aerial photographs also are .vallable for weltern
<br />Elb.rt County; the roll ..nd exposure number of each photograph are
<br />Indlcat.d In the Index InI.p on the right.
<br />
<br />Flood-Prone Area Bue Hcap,
<br />
<br />U.S. Geological Survey 7.5-mlnute topogr..phlc map' (..150 called
<br />quadr..ngle Milps) were uled to ,how the flood-pron. are.s In Elbert
<br />County. The IMpS were cut Into four parts. Each part wal then enl..rged
<br />to . scale of I Inch equ.Ils 1.000 feet. and 100-year flOOd-prone areas
<br />were Indlc..ted along the I.rger streams. The Indlvldu.l flood maps
<br />show .In ..rea of ne.rly 15 square miles. The maps are Inde)(ed by row
<br />letter, column number, and quadr.nt of the orlgln.1 quadrangle used.
<br />Thus, map C-3-NW de.crlbes flood boundaries In the northwest part of
<br />the Klow. 7.S-mlnute topogr.phlc IMp lhown as C-3 on the Index to
<br />topogr.phlc qu..dr.ngles.
<br />
<br />Topogr.phlc MapS, printed In color. can be '<..urch.sed. by mall from
<br />the Branch of Distribution, U.S. Geological Surv.y, Bo~25286, Denver
<br />Federal Center, Denv.r, CO. 80225. Topographic maps .ho NY be viewed
<br />at the office of the Elbert County land Use Administrator, Elbert
<br />County Courthoule. Kiowa, Colo.
<br />
<br />Aer lill PhotoQr.aphs
<br />
<br />Aerial photogr..phs of Kiowa County >owere t..ken In 1977 by the U.S.
<br />Agrlcu1turoitol Stablllzilt Ion and Conservation Service. The ground .r.a
<br />shown on e..ch photogr.ph I. .bout 30 square miles and p..rtly overl.ps.
<br />
<br />"I":
<br />
<br />r '
<br />
<br />"',e,arrlll I,. ('Oope,.lIo,. with Ihe
<br />\I. s. G~ulUMlul S..rn)'
<br />
<br />>Jrr'!>tl. ~'nr l. V,l.LIll:: 1.11. "'1~5'
<br />
<br />
<br />A
<br />
<br />1'0
<br />
<br />1,0 -..JUULE$
<br />i5 KilOMETERS
<br />
<br />
<br />
<br />\
<br />
<br />INDEX TO TOPOGRAPHIC QUADRANGLES
<br />
<br />the ..r.a. shown on adJ.c.nt photograph.. The photographs, whIch were
<br />enlarged to a sc.le of I Inch equall 1,320 f.et (it Inchel per mile),
<br />show r~ds and land development as of Mld-l'77. Other l..ndmark.,
<br />Including building., a..rthen d.ms, and .v.n Indlvldu.1 tr.el, Ny be
<br />Identified on the aelect.d a.rlal vl.wl. ThIs Id.ntlflcatlon helps the
<br />user comp.Ir. older IMpped Information with conditIons In 1'77. Aerial
<br />photographs of western Elbert County can be viewed at the office of
<br />the Elbert County Land U.e Admlnlurator, Elbert County Courthou..,
<br />Klow.., Colo.
<br />
<br />DISCUSSIOII
<br />
<br />Ar.. Descr I pt Ion
<br />
<br />Elbert County Is aouthe.Ist of Denv.r, Colo" within one of Colo-
<br />radoll cloudburat zone. about 50 ..lies ...U of the 'ront ".nge foot...
<br />hills. The-roiling hJgh pl..lnl of the ar.. cont.ln many cre.k ch..nnels
<br />which ..re dry much of the tlln8, yet ar. In wide stre.mbeds c..rved by
<br />floodwaters. This seems unulual, conllderll'lg that precipitation In the
<br />'rea .venges but 12 to 16 'Inchel per y..r. However, two-thirds of
<br />that ..mount ulually Q<<urs as Intenl. flood"produclng thunderstorms I
<br />dl:rlng the sunwner JftOnthl.
<br />
<br />Holt of the .tre.ml crolllng Elbert COUMy begin n...r III south'"
<br />western corner, wh.re a narrow pineau at an .Itltude of 7,500 teet
<br />forms the divide between the South 'hU. River and the Arkansas Rlv.r
<br />basins. As the str.....s traven. Elbert Countv In a northerly or eut..
<br />erly direction, t~lr slop.s decre... frOWl more th..n 100 feet per mile
<br />In the headw..ura to Ie.. th.n 50 f.et per mile at the Ar..pahoe-Elbart
<br />County Ilna downstr.am, where altltudel .v.nge about 5.500 teet.
<br />Draln.ge .reas of the creeks within the county r.nge from about ]0 to
<br />300 squ.re lit I I...
<br />
<br />Flood HIUory
<br />
<br />. HaJor flooding occurr.d In Elb.rt County during 1878. 1935. and
<br />1965. Although the most .xtre,.,.. peak-dl.ch.rg. v.lues wre r.corded
<br />during the wlde.pre.d flood. of 1935 .nd 1965, loc.llzed Intenle
<br />storml cov.rlng a fe", squ..re mll.s occur .randomly throughout Elbert
<br />County every year. Thul tributary atr.ams occ.llonally may produce
<br />flood dllch.rges approaching severll times thU lhown by a lOa-year
<br />curve. However, because the storm. are g.n.n.lly localized, the volume
<br />of runoff Is lmall and the Milln ch.nt'l": downstr..m usu.lly can pa..
<br />the addltlon..1 Wolter at heights below the 100"ve.r flood levels. In
<br />this cale, major daNg. I. confined to the Immediate ..r.. .ff.cted by
<br />the cloudburst.
<br />
<br />W.ter frOM the.. Intense stor",., ~Ich ulu.IIV occur during MaV
<br />through August, NY flow In sheetl down the ste.p hillside, until It
<br />re.ches .In .xlstlng w.lterw.y. Kat.rlal gouged from the flooded ar..
<br />Is clrrled downstre.m. As the flood Wilve slow., the .roded sedltnent
<br />Is deposited Onto the flood pl.ln of the r.celvlng Itre.",.
<br />
<br />Areal once modified by floods, "I eyldenced by the the wide
<br />str~am valley. In Elbert Courtty, prObably will be covered by flood"
<br />w..ters agaIn. The June 1965 flood occurred .fter the floodw..ter..
<br />retarding structures of the Kiowa Watershed IIroJect had been built by
<br />the U~S. Soil Conl.rvatlon Service (SCS). These SCS floodwder-
<br />retarding structures. which store .bout 1 'nch of runoff behind their
<br />emergency splllwaYI. delev trlbutery flows to klow. Creek. This stor-
<br />age decreases natural-flow peak dlsch..rges .nd helps to reduce down-
<br />stream property d..mage. Thus, even though retarding dams are placed
<br />across numerous trlbut.rles, unulually I.rge floods stili c..n r.sult
<br />from Intense thunderstorm..
<br />
<br />The largest probable flood Is dIfficult to define. but comp.rlson
<br />of the peak flow oblerved from. given drainage .rea puts past floods
<br />Into perspectlv.. Crippen ..nd Bue (1977, fig. 11t, p. 13) described
<br />maximum pe..k dllch..rge. observed for the region which .Includes ...stern
<br />Color..do. Crlppe" .nd Bu. drew .n envelope curve, p.rt of which h.1
<br />been r.produced In the graph below. flood data for site. In .nd ne.r
<br />Elbert County are Includ.d In the table. KeCaln and ..J.rr.tt (1976)
<br />det.rMlned that the IOO-ye.r flood v.1ues In e"Uer" Colorado are.
<br />function of draln.ge ar... and basin .Iop.. A 100-ye..r flood"'dlscharge
<br />curv., computed ullng en average besln-stop. v.lue, h.s been .dded for
<br />vllual comparison with the envelope curve. Actual l00-y...r dllch.rge
<br />v.luel at a I'te may dlff.r from tho.e of the 100"ye..r curv. shown.
<br />
<br />The envelope curve does not repres.nt .. physical limit. but shows
<br />the m..gnltude of some extremely r.re events which h.ve occurred. East
<br />BIJou Creek, which draIns the centr.1 p.rt of Elbert County, produced
<br />a pe.k dlsch.rge In 1965 near the Ar..pahoe-E1bert County 'Ine which
<br />..pproached the envelope curve (site,). In 1935, . 50-year flood was
<br />me.sured ..t the lime al t..
<br />
<br />1000
<br />
<br />
<br />hOO
<br />
<br />~
<br />ijj
<br />~
<br />t;
<br />Ir 100
<br />u
<br />~
<br />l!i
<br />g
<br />~
<br />~
<br />II
<br />~ .
<br />~
<br />o
<br />
<br />1.119651 DATA I'OINT AND SlTfNlNBtA_
<br />N,ml.., In plll.not","l. I. y_.
<br />PMk lIow o..;c;~rlfd. s.. lable
<br />
<br />
<br />2119651. 1.119651
<br />
<br />. 4_119851
<br />
<br />1
<br />0'
<br />
<br />01
<br />
<br />5 10 50 100
<br />DMINAGE ARtA. IN SQJAAf UILES
<br />
<br />500 1000
<br />
<br />( .
<br />s_~ Of ..,tl'..... fl,ood duo/ouog.. fol' .t....".,. whloh flC1J Io1tthi"
<br />and Mal' Elb'l't COI'"t~. Colo.
<br />[Dot. for lit.. 1-12 'rOl!l IIott""l (1"', p. )7); .nd 'or alt. .)
<br />frOl!l Snip.. and otho" (l97~, p. 351
<br />
<br />Site
<br />No.
<br />
<br />Orlln.oe "'el,
<br />Counly In square
<br />Milu
<br />
<br />Olach.rge.ln
<br />cubic feel Ye.r
<br />per a.cand
<br />5.250 1957
<br />2.370 1965
<br />2.800 1965
<br />1,880 1965
<br />1,350 196&
<br />U.500 1935
<br />41.500 1965
<br />20.000 1965
<br />19.700 1986
<br />75.300 1935
<br />24,900 1915
<br />25,000 193&
<br />274.000 1965
<br />143,140 1935
<br />145,000 1965
<br />57,200 1965
<br />154.170 1935
<br />75,500 1965
<br />10.700 1965
<br />
<br />Stream and loc.lion
<br />
<br />Kiow. Creek It 1(-79 R81ervolr EI '''0 3.20
<br />near Elltonvillo
<br />
<br />Kiow. Crook Subwateuhed
<br />No. J-33 nur e.alonvilll
<br />
<br />Kiow. Creek Subwlltfnhud
<br />No. R-3 n'.f Elbert
<br />
<br />Kiowa Creek Subwlleuhed
<br />No. 0-61 n..f Elb6f1
<br />
<br />KjowI Creuk It Elbert
<br />
<br />EI '''0 1t: t,i"
<br />
<br />Elbert
<br />
<br />2.12
<br />
<br />Elbe,.
<br />
<br />.59
<br />
<br />Elbe,.
<br />
<br />28,8
<br />
<br />W.'I Kiow.. Creok .1 Elbeft
<br />Klow~ Creek .It KiowI
<br />Klowl Creek II Bunnell
<br />
<br />Elborl
<br />Elbert
<br />
<br />35.9
<br />'11
<br />231
<br />
<br />Adama
<br />
<br /> EIII 100u Cr8Cllk .II Deer Trill Arapahoe
<br />10 Middle lIiiou Creok nur Ar.pahoe
<br /> Deer Trail
<br />11 West 8ijou C,.utk nUr Kiowa Elbert
<br />12 W"I SIJou Cr..k ..I Byera Arlp.ho.
<br />13 Big Sandy Creek n'.r Calha" EI Puo
<br />
<br />302
<br />
<br />190
<br />
<br />85.7
<br />277
<br />
<br />49.0
<br />
<br />~
<br />
<br />He,vYI Intenl. rainfall ..nywh.r. In Elbert Countyl, 10ng, narrow
<br />.nd rather st.ep draln..ge b.slnl will caule flooding. The ....tlon..1
<br />We.ther Service (1973) determined that the l00"year, 6"hour ralntall
<br />for Elbert County II ]..1, 'nch... However, a. IlnUch .. 12 Inch., fell In
<br />about 3 houri southelst of the town of l'bert, on Jun. 17. 1'65. The
<br />probabl. Nxlmum 6-hour precipitation for. "Iv.n 10-.quera.mll. .rea
<br />In Elb.rt County I. .bout 22 Inch.. (Hatth.I, 1969). Flooding .ho
<br />ea" r.lult from I...er MtOunU of r.lnf.ll on .uece..lva daYI or when
<br />s.to".. celli move .lonG .Ir.ady swollen cr.aks.
<br />
<br />Th. 100-y...r flood discharge It mOlt of the lurvey.d croll lac-
<br />tlons wa. c.lcul.ted lolling methodl lhown In the IlM..nual for Estl....tlng
<br />flood CharacteristIcs of Natural"flow Str...ms In eolondo,ll bV McCal"
<br />and J.rrett (1976) .nd Is shown on the flood..pron....re.. IMPI. S.lmple
<br />dlsch.rge v.luel were then comp.Ir.d with tho I. obt.lned by using the
<br />U.S. Soli Conservation Service (1975) method. Thla procedure verified
<br />that the r.lulu were re.,on..ble. Also, con.ultlng enolneerlng fl"",
<br />have prepared detailed flood reporu for the towns of klc::.w., Elbert,
<br />.nd Ellzabethj .r.aS covered by thele r.ports are outlined on the .n-
<br />larged maps.
<br />
<br />Hydr.ullCl
<br />
<br />Information from several lourcel Will lolled to dete""ln. the 100-
<br />yelr flood limits on the flood-prone-are. NPS. Channa I crOll sec"
<br />t Ions were fleld-survey.d at polntl 2 to ] .11.. .Plrt on the stre.ml.
<br />Thl, provided det.ned Infor....tlon on the Actual shape of the It,.......
<br />b.d In 1979-80 and It I .blllty to conv.y floodwo,.". 5""", chann."
<br />h.d b.en Ilgnlflcantly .It.red Ilnce tha topographic maps were
<br />prepared, either by floods or by man'l construction actlvltl.s, .nd
<br />occa.lonal1y by both.
<br />
<br />for this Itudy, U.S. Geologlc..1 Survey computer progra,. ("]1,
<br />glv<<n In HUs.r'l ".nuII, Computer Applications for Stap-Backw.ur and
<br />rloodw.lY An.IYI.slI (Sh.arman, 1976), was ul.d to calcul..ta hydraulic
<br />propertlel of the Itr.alft at e.c.h surveyed croll lectlon. By ule ot
<br />the m..pped Itre..m Ilope ..nd 100"ye.r flood discharge, flood height was
<br />computed .nd transf.rred to the enl.rged b..sA maps. Flood width,
<br />depth. and ve'oclty ..ho were plotted adjacent to the numberad crOll
<br />sections shown On the map..
<br />
<br />ECONOI4IC CONSIOERATIONS
<br />
<br />A flood h.vlng a recurrence Interval of 100 y..rs hla Men
<br />,elected .1 the design flood by the Colorado Weter Cons.rvatlon Board
<br />for the admlnlstr.tlon of flOOd-plain man.geNnt program.. Many p..rts
<br />of Elbert County h.d floodl In 1'35 and 1,65 that equeled or exc..ded
<br />the lOa-year flood. Knowl.dge of aree' which wi' I be under wolter frOll
<br />.. 100-ye..r flood II helpful for thou persons who must consider rllkl
<br />of hnd us. wIthIn the flood pl. In. Generally, livestock and farming
<br />operations .r. .mong the ..cceptabl. usel of low"'lylng .r.al. Permanent
<br />bul'dlngs should be pl..ced In loc..tlons not likely to be flooded-"
<br />usually..t lites away from the streambed and .bove the expected 100-
<br />ye.r flood level s.
<br />
<br />Building II tes higher than and It 10M dllt.nce from w.ter
<br />courlel are not ..lwaYI ufe from flOOding, . It hough .Iev.tlng the
<br />structures to .llow for proper draInage In all dlrectlonl can mlnlmlz.
<br />the poulblllty of d..m.ge. Intenle thunderstorMI Can send .heets of
<br />water down Iloplng hillsides. Such an overllnd flow. termed by one
<br />.resldent .II a fll.ke tipped sldeways,lI .110 cln deatroy buildIngs In
<br />Its p..th. To leuen thll natunl h..zard, contoured furrows (ditches)
<br />hive been cut I nto numerous hili, I des In the county. They Intercept
<br />overland runoff .nd divert It to existing waterways at either end of
<br />the dltchel. Thele furrows are visible In some of the .erlal phott"l..
<br />gr.phs mentioned e.rller.
<br />
<br />Stilte .nd county offici." have be.n given the r.lpanslblll ty for
<br />regulating development along Itreeml. The foregoing dllcunlo". a10ng
<br />wi th ..ppropr I ate f100d"'prone-.rea IMPI, will h.lp them to lTIIIet th Is
<br />r..ponllblllty.
<br />
<br />FLOOD-PRONE AREAS IN ELBERT COUNTY, COLORADO
<br />Bv
<br />Theron R. Dosch, U.S. Geological Survey
<br />1981
<br />
<br />'.,
<br />
<br />"I
<br />
<br />r-~ 3674
<br />
<br />-,.... - .----..r.-__
<br />
<br />.X......ANATION
<br />B AI:I.J,,!. 1.01.1. NO. In
<br />
<br />[;':]1 A~.IAL I.OLL NO. U'J
<br />
<br />I
<br />I
<br />,
<br />,.-.
<br />)9~J'
<br />I
<br />I
<br />,-
<br />L~
<br />
<br />.
<br />I
<br />I
<br />!OJ
<br />'" ..I
<br />.;'J
<br />
<br />--~'-. j
<br />~"l;;"1
<br />"' ~ , -
<br />1-....... ~ 1
<br />. ....r~ .~ ~.~\~!
<br />, f.\", -.:.. ~'\ ",J
<br />
<br />10
<br />
<br />',0 ',6WUI
<br />,', IULOMfTlAS
<br />
<br />INDEX TO 1977 AERIAL PHOTOGRAPHS
<br />
<br />HETR I C CONYERS IONS
<br />
<br />Inch-pound unitt used In thla rarrt May be converted
<br />to !Ntrlc $I (Intern.tlonal Syltem units by the fOllowing
<br />factors:
<br />
<br />,^,IHpl~
<br />
<br />BJI
<br />
<br />O. ~0~7
<br />0.0012))
<br />0.02832
<br />D.02832
<br />O. )0~8
<br />0.189~
<br />).785
<br />0.06)08
<br />H.~O
<br />1.609
<br />1.590
<br />
<br />7b pbtol"
<br />
<br />.cre
<br />.cre-foot
<br />cubic foot
<br />cubic foot per second
<br />foot
<br />foot per IItlle
<br />g.llon
<br />gallon per mlnuta
<br />Inch
<br />mil.
<br />squ..re mil.
<br />
<br />,qu.r. hectometer
<br />cubic hectometer
<br />cubic meter
<br />cubic Meter per second
<br />Nter
<br />Nter p.r kilometer
<br />Ilt.r
<br />II ter per lecond
<br />..1111_ter
<br />kll"""'tor
<br />tqu.r. kilometer
<br />
<br />National c;"oa.tio V.l'tiDal llatUlll of 1981 (NOVD of 1929);
<br />A geodet Ie d.tum derived froe a gen.ral edJustment of the
<br />flrlt-ord.r I.vel naU of both the United Stat.. .nd Canad..,
<br />formerly c.ll.d ffN4lan S~ L1v.t. to tlGVD of 1'2' Is referred
<br />to IS ,ea I.vel In th'a report.
<br />
<br />GlO&SARY
<br />
<br />QO,..-foot. --A volume of wet.r covering 1 .cr. to. depth of 1 foot;
<br />~3.560 cubic f..t.
<br />01"0" ..otion......A r.prel.ntltlon of the .r.. batween a ,tre.mb.d .nd
<br />an INg'nary l.v.1 string .tretchad .cro'l . Itream ..t right ..n-
<br />gle, to the .tr..lIlflow. The aile .nd sha~ of the crall section
<br />Is determln.d by using lurveylng InltrUI'Nnu to lM.sure distances
<br />down to the str..mbed ill varlou. loc.rlon. .Iong the lmagln..ry
<br />.trlng. rloods usually.wlll ch.nge the crols-s.ctlon conffgura-
<br />tlon unl... the stre.mkd II compos.d of Itabl. Nterl..l.
<br />ol.lblo foot p.'" ..oond.--A unl t 0' discharge ~lIln9 a croll sect Ion of
<br />. Itrea... lbe unit of dl,c""rge r.pres.nu 1 cubic foot of water
<br />p.nlng . given point In I second and I. equivalent to .pproxl-
<br />Ntely 7i g..IIonl per ..cond or itso g..1 tons per ",Inute.
<br />diaoharg..--Th. water flOWing p.tt . particular point. such AI . point
<br />at a crall .ectlon. The rilt. of flow genenlly II measured In
<br />cubic feet p.r lecondj the VOlUMe of flow, In acre.feet.
<br />droinag. a,.~.--A I.nd .re., ulu.lly Ma.ur.d In .qu.r. ",II.. In a
<br />Korl.zontal pl.ne, which collecta precipitation and ellowI the
<br />r.,ul hnt runof' to flow towardl the IOOIl downltr..m point In the
<br />ar.a.
<br />.,.v.lop.ourv..-"A line' dr.wn above plott.d polnu on.. gr.ph to
<br />.nclo.e the I.rgest floods .ver mea.ur.d In . regloni the points
<br />lhow atr...m dllch.rges for given drlln..se are.s. larger f100dl
<br />are poulblei If they occur, the envelope curve II roved up~..rd
<br />to enctos. the new, higher values.
<br />{tood plain,-"'An .Ire.. thu Is adJ.cent to the Itre..mbed and Is covered
<br />with w.ter when the Itr.a,. overflows Its b..nks during floodl.
<br />flood-proM QrotkJ map.......A "'Ip lhowlng are.1 ..long the stre.mbank. which
<br />.re subject to flooding. Ar.as expected to be cov.red by Wolter at
<br />leut onc. In any 100-y..r period .ra lhown on the Elb.rt County
<br />flood-prOf'll .r.. Nips.
<br />flood v.Zootty.--Spe.d with which WIItar IItOV.s downure.m. ^ velocity
<br />of 10 feet per .econd (n..rly 7 ..II.. per hour) ~uld move .n ob-
<br />Ject flo.tlng In the center of the Itre.I" one township (6 II\lles)
<br />hrth.r downstr.am In hll than 1 hour.
<br />fZoodJ.Jat.I"-NtaMtng .tM40tur......A d... pl..eed .crolS . small upstr...m
<br />w..ter cours. to provide floodwater Itorage. Earthen d.ml con-
<br />.structed In Elb.rt County by the U.S. Soli Conservulon Service
<br />In the l'501s ~re de.lgned to hold about 1 Inch of runoff from
<br />the. b.sln aba,,'e .nd to r.I..n It gr.du..lly through pipes over a
<br />period of 2 to ) daYI. Exc... runoff palle. over the emergency
<br />splllw..ys et one lid. of the d."". Th. structures delay storm-
<br />wat.r trav.llng towardl the Ilrger creek .ch.nnels .nd help reduce
<br />conl.quent flooding.
<br />/n",d,.od-~OQ1' (100-~oal') flood.--P..k dlacharg.. 10 large ,hat they may
<br />be expected to be .qual.d or exceed.d on the 10ng...term .ver.ge
<br />of .bout onCe ev.ry 100 ye.rs .nd have . I-~".nt chance of oc-
<br />curring In ..ny given y...r. The recurrence Interval Is an .ver.ge,
<br />no Ichedul. of regularity h Implied.
<br />l"Ut1Off,-"'Th..t part of the precipitation that appe..rs In surf.ce
<br />Ur.."'I. One Inch of runoff I. .qual to lbout 27 cubic feet per
<br />.econd of wat.r flowing for one day frOff! each square mile of
<br />draln..ge ar.a ..bove the location conlldered.
<br />.t,.QQm .Zop"."Th. vertical distance. Itr..", drop' In tr..vellng.
<br />given horlzont.1 dlst.ne.. When the str.am fal Is more than about
<br />SO f.et per 1'111 la, floodflows Ira shallow Ind very fast and milY
<br />caul. conlld.rable chennel .rollon. AI the slope flattens to
<br />Ie.. than about 50 te.t p.r 1111 Ie (. l..foot drop .bout every
<br />100 f..t). floodflow. become relatively d..p .nd spread out .s
<br />the wat.r velocity slows.
<br />topographic' map.--A rrI.Ip that lhows .urhr.e :'e.tur.s of .. given .r....
<br />
<br />REFERENCES CITED
<br />
<br />Crippen, J. Ill., and Bue, C. 0" 1977, HaxllftUfll floodflows In the
<br />contel"1lllnous UnIted Stat.SI U.S. Geological Survey W.ter-Supply
<br />P.per 1887, 52 p.
<br />"atthal, H. f., 1,69, Floods of June 1,65 In South 'I..tte River basin,
<br />Colorado: U.S. Geologica' Surv.y Water-Supply Paper 1850-8,
<br />6~ p.
<br />HeC.ln, J. f" andJ.rr.tt, R. D., 1'76, "'nual for estimating flood
<br />charact.rlatlcl of natural...flow stre..ml In Colorado: Colorado
<br />Water Conlervatlon ao.Ird Technical Manual 1,68 p.
<br />Nation..' We.ther Servlce, 1913, Precipitation-frequency atl..s of the
<br />Western United Stat.1I NOAA Atlas 1. Volume III-COlorado, 67 p.
<br />She.rman, J. 0., 1976, U,.r's manual, computer applications for step-
<br />b..ckweter and floodway an..1 Yleu U. S. Geo log I ca I Survey Open-
<br />FII. R.port 76-~99, 103 p.
<br />Snipes, R. J., and others, 1'7", floods of Jun. 1965 In Arkan... River
<br />b.,ln, Colorado, Kanns, .nd New f4exlco: U.S. Geologic.. I Survey
<br />Wat.r-Supply P.p.r 1850-D, 97 p.
<br />u. S. 50.1 Conserv.t Ion Service. 1975, Urban hydrology for small water..
<br />sheds: Engineering Division. Technlc.1 Relea.. 55. 97 p.
<br />
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