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Floodw~ter elevations determined at any particular lacatic" ~nl- not ah.'~yB bdicative of t~e height~ actually attained. Often, ~lo~lwaters become isolated and entrapped in overbank areas resulting ir. flood elev..tions higher thdn those shown On the high ",at"rpt"otiles. AS can be seen from the cross seetio~ of Platn 21 thn the Highway 50 bt"idge at mile 1.06 can ~ expected to remain clear during peak flow periods. It should he noted that in the case of high simultaneous flOOd flows on the ;Ikansas Rivnr much more severe flooJing will occur at the mouth of Salt Ct"~~k than under flood situations limited to only the SaltCre"k Basin. The severity of thesituaticn in the caseofsJ.:oultaneous flooding W<luld depend on 8uch factors as the frequency of flood occurring on both str~ams and thp tim~ rpl~tion~h;F of the peak flow periodS On both strea~s. For ~~c purpo~os of this r~port the most severo conditions were assumod; thus for the Standard Project Flood on Salt Creek the samE frequency with simultaneous peak flows was assumed on the Arkansag River. The ~me also applied for the IntermMiate Regional FlooJ. stream is well c~a~n~lized abOve St. Charles Reservoir ~o. 3. ~s a result the flood water~ remain in the stream r~qime for almost the entire reaeh abova Ra~et"voir No. 3. ~~ exceptio~ is the Burnt Mill Road ll>"idgewhere. rlueto the channel constriction caused by the abutment~, the roadw3Y is inundated during both the Standard Project Flood and th~ Inte..-rnediate Regio~al Flood. ~fter discharge over Reservoir No.3 spillway flood waters move as sheet flow over flat gra.sland toward the ~ighway 85-87 embankment. Cross section No. 82 on ~late 20 is a typical section descriptive of this reach. At cross ~~tion 82 tho Standnrd Project Flood waters cannot be contained in th~ shallow wide ~ection and the e~cess ~pills into the Lake Minnaqu~ Basin of So~thwest Pu~blo and moves northw~rd ev~ntually in~ l",ke ~inne'1UA. As thQ $hQet flow ~eache~ the highWayS at mile 6.50 it pond. up due to the limited capacity of the HigrMay 85-87 bridge. This callses th.. r"adway t" be inunl1ated. A s\\h"tanthl flo'" is aiso lost to the north in the channels between the three parallel highways. The Interstate 25 Highway will not be vulnerable to flooding, however. Downstream of the Interstate Highway pending will occur behind several of the C"F & I haul road ernbanlrnents which were constructed with inadequat~ capacity to pass high flows. It was ~ssumed for this stUdy th~t these roads would remain intact throughout the fl~l i",riod, however, stress damage Ls lik~ly and may cause complet~ failure in sOll\ecases. The railroad bridges at mile 4.58 ~nd 1.09 and the highway ht"idge at mile 0.81 will be inund~ted by both the Sta~dard Project Plood and the Inte~ediate gegional Flood. 7he higher bridges such as the railro~d bridges at miles 1.32 and 2.09 and Velocities, Rates of Rise. <lnd ~uration The occurrence of the Intermediate Regional or Standard Project Flood would result in the flood characteristics shown in Table 3. This data r"flects the av~ragod "",,,io\\m ~.<lnditi."ns with heights of rise, rates of rise, and durations of flooding measured above bankfull stage. Floodflow velocities depend upon the general waterway configuration, and the 6i~e, shape and slope of th.. streambed and overbank flow areas. Average velocities may range from the rna~imwms appearing in Table J to less than fifty percent of these values. Obstructions Brush and debris washing downstream during floods often collect a~ainst bridges or other restricted flow areas, redUCing the waterway openings and otherwise impeding flood flow. The brush and debris create a damming effect and, depending on the degree of clogging, c~use greater backwater depths with resultant increased overbank flooding. Watet" pressure building up against embankment~ a~d bridges can result in Stress ddmage, or total destruction of the " "