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COMMENTARY SHEET 19 OF 45 STATlONSI292+00TOSTATlON1347+00 REACHES 4 ANO 5 from it or placed on a retaioing wall. From Station 1337 to 1344 the right bank should be replace<l by a vertlcal retaining wall. FrQ11 Stati(ln 1344t(l 1347 the right bank should be cut t(l form a bench approximately 100 feet wide. From Station 1292 to 1347 the channel bott()lll should be lowere<lby4 feet requiring the relocation of an lS_inchsanitaryseWf!r at Sta tionl298, a 48-inch water line at Station 1339, and the capping of a 54_inCh water line at Station 1337. Once the channel is lowered,thetoesofal1 slopes should be protected with riprap as shown in Detail S, Sheet 44. lowering the channel bottom will require the replacement of the Public Service Com- pany's collapsible diversion d,ynat Station 1326. The replacement struc- tureshould be 6 feet lower, and incorporate tWQ sections; one with abo at chute, and a larger one without. An a1ternative to lowering this dam at its present location W{)u1d be to relocate 1t upstream which would permit relocation of the maintenance trail under the 13th Avenue bridge. Theoverbanksin this reach includeresidentia1,commercial and industrial areas. A total area of 145 acres are in the lOO-year floodplain. The Interstate 25 embankment serves as a barrier against flooding to the east except for areas at 13th Avenue, the railroad underpass 200 feet north of 13th Avenue, and at Colfax Avenue where breaks in the embankment allow flood waters to flow east and north and return to the South Platte River in the area betW€en the Interstate 25 crossing of the River and the Speer Boulevard bridge. The first priority in this reach is lowering the channel bottom and improv_ ing the conditions at Interstate 25 and the adjacent pedestrian bridge. lOWf!ringthechannel bottom should proceed upstream to at least the Public Service Company dam, in order to reduce the arnount of water flowing east underneath Interstate 25. ThereCO"1l1endations from Station 1326 to Station 1347 should be aecompl ished after t~"se downstream improv"",(>nt~. The recoOOlended plan for this reach is limited structural impr(lvements. Between Station 1292 and the Interstate 25 bridge, the right bank should be benched 150 feet from the existing bank and include natural vegetation. The Interstate 25 bridge will be irnprovedbyremovingthedprapprote cting the abutments and replacing it with vertical retaining walls. The pedes- trian bridge irllllediately upstream of the Interstate 25 bridge should be lengthened, or relocated. At Station 1314 an abutment from the old Colfax viaduct should be removed and the bank moved back to provide additional flOw capacity. Underneath the 14th Avenue bridge the riprap protecting the right abutment should be removed and replaced with a vertical retaining wall, and the trail on the left bank relocated to be adjacent to the left abutment. The existing storm sewer, which has an outfall adjacent to the trail at the 14th Avenue bridge would be placed in a pipe underneath the trail. Between the Co1fax viaduct and Station 1326 the right bank should be cut to within 15 feet of the railroad tracks. In order to maintain a minimum bottom width of 100 feet, the left bank between 14th AvenLle and the Zuni powerPlantda'll at Station 1326 should be cut back within 15 feet of the railroad on the left bank. Between Station 1326 and 1339 the left bank should be replaced with avrrtica1 wall and the existing trail cantilevered The floodplain management strategy for this reach includes encouraging the purchase of flood insurance and enforcement of floodplain maoag!'11ll'nt regu- lations. COST ESTIMATE SflEET190F4S SOUTH PLATTE RIVER STATION 1292+00 TO STATION 1347+00 CONSTRUCTION Drainage improvement costs Street crossioo costs Utility relocation costs S3.003.754 1.078,802 555,167 4.fi37,723 ~otai construct ion costs Eno;necrlng and cont;ng~nc;c, (30'l:oftotal constructioncostsl 1.391,317 Prooertyacql.liSlt10l"l 225,000 $fi,254,040 TOTAL IMPROVEMENT COSTS operation and Maintenance $38.454