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'-2 On the right bank between 8th Avenue and Colfa(and west of Interstate 25 the lOO-year floodplain includes about 30 acre>, and is approximately 500 feet wide. Flood depths are about 2 feet. A floodplain area east of Interstate 25 inc' udes about 40 acres and flood depths up to 4 feet. '~ater enters this area by flowing underneath the Interstate 25 embankment at 13th Avenue and at the railroad underpass dOWTlstream of 13th Avenue. reach is overtopped in the laO-year flood. This bridge along >lith an adjacent ,.ailroad bridqecauses a Ita 2footr;,,,, inth", 100-year flood watersurf<lceelevation. This r1se, coupled with the low banks insevera.l places along this reach, cilusesflooding along the left bank. The flood- plain covers ahout 300 acres with shallow flooding abO\lt 2,400 feet wide. The sewage treatment plant located in this r~dch Is not incl \lded in th~ flooded area. REACH 5: COLFAX AVENUE TO CHERRY CREEK Flooding ill this reach is caused by the 10wbanks, a se."er crossing, low elevation of the grO\lnd next to the river. inadequate channel capacity, and the Farmers and Gardners diversion dam. REACH 7: FRANKLIN STREET TO SAND CREEK The Burlington Oamcauses a4to 5 foot rise in the loo_year floodwater surface elevation which is carried upstream of the Franklin Street bridge. Inaddition, the York Street drop structure causes a 3 foot rise in water s\lrfaceeleVltion. Oepthsofflooding are from 2to 3 feet. The flood. plain is 2.400 feet wide in this reach and includes several major streets and railroads. 8th Aven\le A low spot 10 the river bank at the Frog Hollow parking lot allows water to leave the South Platte channel, flo"down 8th Avenue and flood an area on the east side of Interstate 25. Flood depths in tf'tis area would generally be shallow. A.pprox imately 30 ilcres on the left bank of the South rl at~e River from Co1fil~ to I -25 are flooded duri nq the lOO_y!'ar flood. Flood water 1 eaves the 50uth Platte Channel on the right hank b~tween Colfax and Interstatp 25 creating a floodplain \lp to 1,000 feet wide. REACH 8: SANO CREEK TO BASELINE ROAD The reach of the South Platte River between Baseline Road and Sand Creek e~periences flooding due primari ly to insufficient channel capacity. Cros~ings of less than 100-year capacHy ~l so contribute to SO'l1!' minor degree to the flooding situation in this reach. Levees exist in"uchof this reach to protect agricultural land and on_going and past gravel mining operations from flOOd flows, but they are largely ineffective in containing flood events within the channel for flows in excess of about6,000cfs. In thi s same reach, flood w~ter w~ i ch has I eft the channe 1 in the 13th A.venue area and at tile 1-25/Col fa~ Avenue interchange flows east of the intero;tate embankment in a llydraulic~lly separate channel. This w~ter joins overflow from the South Platte below Interstate 25 and flows to Speer Boulevard. Thi s flood ar~a includes about 180 acres. R~ACH 5: CHERRY CREEK TO fRANKLIN ~rRoET The lOO-year flood is contained within thl' channel from Cherry Creek to lnter~t"te 70. The Frankl in Strpet bridge at the downstream ~nd (}f thh The f100dpl di n width i,; generally between 4,000 and ~,O()() feet and lTIdny agricultural Jndgrave1 mining lands are flooded. The limit, of overbank flooding are generally determined by the natural topography of the flOOd- plain rather than mall-made levees of constraint~. From Sand Creek to SteeleStreetthereisqenerallylittlefloodingintl'teoverbank. Overbank fluu,l ;119 due~ (}c~ur between East 74ti1 Avenue dnd Steele Street and i '; caused primari I y by bdckwater frr)[)) thl' Union Pacific Rai lrnall brill'll" dow~_ stream of Steele Street and the severe meander .ss0ciated wHh the br"idge.