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C. Rea~h 2 - Perry Street to Bri~~s Street For a new bfidge at Perry Street to be effective, the ~hannel must be improved downstream to the Union Pacific railroad. A crOBs section similar to that which is already constructed downstream from the railroad is adequate (gO feet botto..width and 4:1 bank slopes). With the new bridge and the channel improvement the entire flood is conveyed to the UPEE without flowing into town. As described in the hydraulic analysis chapter, the 100-year flood will overtop the Union Pacific railroad WPRR) arld Perry Street at the ao uthedge of Erie (Plate_IS). Major flooding two to three feet daep will occur through the town. Approximately 180 residences, mobile homes, businesses and other buildings are within the 100-year floodplain in this reach. All plans for this reach arC ai..ed at preventing flooding in the developed portion of town. The first atage of flood protection for the town concerns preventing water from entering the town at the south end. This ~an be a~hieved by either diverting the water to the east into thc main Coal Creek channel or by lowering the elevation of flooding su~h that water will not overtop the Union Pa~ific railroad. The UPRR bridge will ~onvey approximately 10,600 cfs of the 12,260 ~fs peak flow. The re~aining 1660 cfs will overtop the railroad onder present conditions. The water which overtops the railroad on the west side of the channel can be intercepted by a dit~h on the downstream side and returned to the main channel. With the cooperation of the UPRR the existing bridge Con- veyance ~ould be improved to prevent overtopping. Minor cleaning under the bridge and ~oncrete slope paving at the abutments would provide adequate ~onveyan~e. Diverting water to the east will require a dike along the upstream side of the UPRR. The dike would begin at the Perry Street - UPRE interse~tion and extend approximately 1000 feet west. The elevation of the top of the dike would be two [0 three feet sbove the estimated 100-year flood elevation. The U.S. Army Corps of Engineers proposed a similar solution in their flood protection plan fot the Town of Erie prepared in 1944: a dike along the downstream side of the DPRR. Assuming [hat the dike is conatru~ted, the entire flood would be tor~ed to cross Peny Sneet cast of the railroad intersection. H ia anti~ip4[ed that the road and bridge would be washed out if nO improvements are made to Perry Street. However, the dike should still prevent flooding Downstream from tbe UPRR bridge an improved ~hannel has been constructed which extends to Cheesman Street (Plate-14). The ~hannel, as originally constru~ted, was capable of conveying the entire IOO-year flood without bank overtopping. Ho"ever, brush and other vegetation whiCh hilS gro"n in the channel in re~ent years limits its present flood COrlveyan~e capability. Without Channel maintenance the channel ~apacity will be exceeded and water will flow over the west bank into tovo. A program of initial ~hannel ~leaning and annual maintenan~e is propoaed for all improved protions of the ~hannel. This program vould include r~mo~al of undesirable trees, bushes dnd d~bris as well as mowing to ~ontrol growth. this plan. Downstre8Iilfrom its natucal shape. north part of town. Cheesman Street the Coal Creek channel narrOwS down to This consttiction will ~ause water fo inundate the lower A combination of channel improvement and a dike is in the southern portion of the town. A shallow ditch conne~ting the upstream from the railroad to Coal Creek would also be included w.~h low area Lowering the flooding elevations near Perr, Street will require a new bfidge at Perry Street. A bridge approximately 100 feet long with a minimum cl~arance of 12 feet i~ required to convey th~ entire flood under the road and thu_< prcHrv" acr.esS to the town. It appears that the dike along the railroad will sti.ll be "e~essary, but the top elevation "ill be 10I<e,. proposed to prevent this flooding potential. Under this alternative the improved ~hannel section would be extended downstream to approximately reference line station 151+00. A dike would he constructed on the west bank from Cheeaman Street to the Boulder and Weld CQunty Dit~h bridge at Brig8S -76- . , I , I -77-