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<br />a<;t ivity in the high pl ain~ and foothills portions of the basin. Snowfall
<br />in themountdins and higher foothills results in rvnoffpedks in the late
<br />sprinq, however, these peaks are reduced by Chatfield Oam. Snolll1leltinthe
<br />lower foothills and high plains is not normally associated with large flood
<br />peaks. Most major floods on theSolJth Platte River have been associated
<br />'~ith thunderstorm a<;tivity. Recurrent major storm tracks have been identi_
<br />fied which cross the South Platte River watershed and generate!T'lOst flood
<br />flows.
<br />
<br />111-2
<br />
<br />COMMUNITY AMENITIES. MJst
<br />floods occurrlng downstred'l
<br />of Chdtfield Reseno;r are
<br />the result of thunder.
<br />storms. Some structures
<br />such as Shoemaker Plan
<br />have been designed to with-
<br />stand the ravages of the
<br />river when thunderstor>1S
<br />occur.
<br />
<br />TABlElll_3
<br />TRIBUTARY BASIN PEAK INFLOW
<br />
<br />Tributary
<br />
<br />Pea~ lOO-year Inflow
<br />(cfs)
<br />
<br />
<br />Dutch Creek
<br />Big Dry Creek
<br />Bear Creek
<br />Little Dry Creek
<br />Sanderson GulCh
<br />Weir GulCh
<br />LakewoodGulch
<br />Cherry Creek
<br />First Creek
<br />S~nd Creek
<br />C)e~r Creek
<br />Grange Hall Cree(
<br />
<br />7,400
<br />l2,6f)0
<br />8,200
<br />7,100
<br />3,300
<br />l,goo
<br />7,400
<br />9,71)0
<br />7,400
<br />30,500
<br />23,000
<br />2,200
<br />
<br />TA3LEIlI-4
<br />SOUTH PLATTE ~IVER
<br />PEAK FLOOD FLOWS
<br />
<br /> Oi schargc (c~s)
<br />Location Recurrence Interval
<br /> 2-Year 10-Year 50-Year 10O-Year
<br />OIS Outch Creek . . 5,060 6,400
<br />s. Platte ~ Littleton . 3,100 6,FO 7,940
<br />O/SBig Dry Creek . 4,350 9,600 12,600
<br />OIS Little Dry Creek . 5,750 12,200 16,000
<br />OIS Cherry Creek 3.5BO 9,700 18,000 22,500
<br />s. Platte at 19th Ave. 3,580 9,700 18,000 22,400
<br />U/SSand Creek 3,5'<\0 9,700 17,400 21,700
<br />O/SClearCreek 3,550 13,000 28,&00 38,000
<br />O/SFirstCreek 3.550 12,700 27,500 36,000
<br />s. Pl~tte at Henderson 3,400 12,300 27,000 35,500
<br />Baseline Road 3,130 11,400 25,500 33,600
<br />*Snowmeltand dam releases predolTIi~ate
<br />
<br />Peak flows from ~uth Platte tributaries in the study reach are shown in
<br />TablellI-3. TMesetributaries are shown on Figure Ill.l. Th" flood peak
<br />flows presented in Table 1:1-4 are based on future development conditions
<br />an~ existing channel and floo~plain co~ditions ~s is typic~l of Urb~n
<br />Draioage&FloodControl O;strictpractices. The flood flows were cOlllputed
<br />without ~aking an allowance for on-site detention of storm water by Merrick
<br />& Company under d separate contract with the Oistrict. The discharge pro_
<br />file developed for the South I'latte from Chatfield to Brighton is snoWJl on
<br />Figure 1l1-2. Hydrographs for two locat ions, ne~r Sdnderson Gulch and near
<br />Sand Creek, are shown in Fi9ures 1l1_3clnd 111-4.
<br />
<br />AverageRiverOlscharge
<br />The regime of the South Platte River can be characterized in terms nf
<br />,wer,lge monthly flOw> at spl..cted points ~long thp forty mile long corri_
<br />dor. An an a 1 ys is Of the av"r age month I y floW'; over the: p'~riod of ~ecord
<br />indicdtes thdt the th"ee flood control reser"oir, hd"elnini"'dl effect on
<br />~verage monthly flows.
<br />
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