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<br />I
<br />I
<br />
<br />sa"er~ I streams. For o"a"'ple, ttle max Imum ~ I scoarqe on Plum Creek
<br />prior to 16 JunB 1965 was 3,800c.f.s. Onthatdatf!adlsastrolJs
<br />II00d occurred with a maximum discharge 01 154,000 C.t.5. The
<br />Standard Project Flood dischar'jssfor the +wn.,tudy "tr""",s ar"
<br />also listed in table I.
<br />
<br />Table I
<br />FLOOD DISCHARGES AT MORRISON
<br />
<br />Location
<br />
<br />Intermediate
<br />Reginn,,'
<br />Flood,c.t.s.
<br />
<br />Standard
<br />Project
<br />Flood,c.t.s.
<br />
<br />.
<br />
<br />Bear Creek
<br />Mount Vernon Creek
<br />
<br />27,000
<br />4,600
<br />
<br />51,500
<br />11,600
<br />
<br />.
<br />
<br />Greater Floods
<br />Floods ovon larger than the Standard Project Flood are
<br />possible, but the combination of factors to produce such floods would
<br />be extremely rara. Such floods are not further discussed in this
<br />report although they Should not be overlooked where it 15 nocessary
<br />+08,,0Id,,11 riskoftloodinq.
<br />
<br />,
<br />,
<br />I
<br />,
<br />
<br />rklzardsofr.re<ltFloods
<br />Thu Intermediate Regional and STandard Project flood flows
<br />on Bear CreeK and Mount Vernon CroeK In the study reaCh wara analyzed
<br />i'odotermine thair flooding potential. Thoa""lyslswdsmadeusing
<br />34 br I dgo a nd va I I ey cross sect ions On Boar Creok a nd I 9 on ~~ou nt
<br />Vernon CreeK. Thecrosssactionsw.:>re0btaln&lbypllOto<)raomotric
<br />methOd"> trom aoriat pllOTOS maOe In Oecembor 19iO. The w,,-h,,- sur-fd""
<br />profiles wero determinad using backwater computations employinq the
<br />St,,"dardStepMethod. The head losses Ilt the bridge and larqecul-
<br />vBrtsworocO'Ilputeduslngdata in "Hydraulics of BridgeWilterways"
<br />published by the U. S. Dep(lrtm<lnt of Corn'Tlerce. Weir and submerged
<br />weir tlow waS used with the above whonover water overtopped any Dor-
<br />tiono/thero,'dw(lYs. SCI"1eo/thoSMallerbrldgoswereconsldered
<br />
<br />to ildv" ldil"tj '"OJ' i,~
<br />
<br />lio" ,,,,,,,,,1 id I i~I-Y"
<br />
<br />,,--"-
<br />. ,'-"'~~.
<br />
<br />"
<br />
<br />The axtent of flooding is Shown on the "Flooded Area"
<br />plates lor each strea", (see Index map on plate I l. Flood outlines
<br />were determined by m(ltchinq the aoproprlate water surface elevations
<br />from the profiles to tho contour maps to show the general areas ">ub.
<br />Joct to flooding. Foranyspeclt!csituatlonwheregreateraccuracy
<br />is nead..d It will be necessary to hKe th.. appropriate flood elElva-
<br />tion from the protiles(lnd locate by survey Its corraspondlng ground
<br />elevation on the flood plain.
<br />Water surfacoprotlles tor the Intermediate Regional and
<br />Standard ?rojoct Floods are shown on the"?roflle"plateswhlcb toll Ow
<br />the "Flooded Area" plates for each stream. The profiles show tho
<br />depths of flooding In the channel and the elevations of Thew"ter su r-
<br />faces over the adjacent flood plein.
<br />The "Cross Section" plates portray the channel and valley
<br />characteristics besides showing the depths of overbank flooding,
<br />Reference points have been provided to locate the flood
<br />elov"tlons at Intervals aloog the streams. The reference Dolnts coin-
<br />cide with the location of the cross sections Which werEl used for the
<br />~tLJdy, Th" loc"t Ions of the reference oolnts are shown on l>oth the
<br />"FloodedArea"platosandthe"Profile"platos. AtabulationOfreter-
<br />eoce point data is provided in tables tollowlng the text. ThAt"bula-
<br />tions show the eievatlons of the streambed, the Intermediate Regional
<br />FloodandStandard?roJectFlood.
<br />A tragic loss 01 II/e h(ls resulted from past floods on
<br />BellrCreekdnd Mount Vernon Creek (It Morrison. Flood conditions ThaT
<br />crrote.ddnngerdurlngthosefloods, rapid rise of water lovols,high
<br />water velocities, and extent of flooding would be more extrome In the
<br />event of the large potentl;'J1 floods studied In this r..port, ~uch of
<br />Morrison, iocludlng vlrtu"lly all of the business district, is subject
<br />to Inundation from large floods. M(lny homes and other structures
<br />would also be damaged or swept (Iway by the high velocity tlows. Only
<br />anlllert.."rnlngsyst(W11ilndetfectlv"oVdcuatlonwouldpr"ventloss
<br />of Ii Ie should ~ flood 11 k" tho I nte~m..d late Reg lona I F 1O()d occur.
<br />
<br />'"
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