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<br />analysis. T~t su~.ary of roughness coefficient$ is inclu~ed in the T~chnical <br />AddendUIII to this report. Mannings "n" ~alues "Hied greatly throughout the <br />study reach. Ranges of "n"values used in this study were the follo'....ing: <br /> <br />The lOO-year floodplain train the Union Pacific Railroad to '~elcn Street is <br />confined mainly within the channel area. TIlere are rlO structures in the flood- <br />plain on this rNch. The bridge at the Union Pacific Rai1road is very larse <br />and, therefore, has only rdnor effects on the floodplain. <br /> <br />Channel Sections <br />Overbank Areas <br /> <br />.03 to .045 <br />.03to.10 <br /> <br />Cop i es 0 f t he ~~an n i ngs "n" V a 1 ue Repo rt a re on fi 1 eat The City of Fort Co 11 ins. <br /> <br />At Welch Street, there is some ponding upstream with sheet flow over the road. <br />The bridge at LeMay A~enue has been rebuilt and the topography in this area <br />is inconsistent with the mapping. The rebuilt bridge has the capacity to <br />Flooded Areas Description con~ey the lOa-year flood without o~ertopping. <br /> <br />The lOO-year floodplains for full development conditions and for existing develop- <br />rrentconditionsarepresentedonSheetsl-15. A ctescription of floodplain areas <br />in specific reaches follows: <br />Reach 1 ~ Confluence with Cache la Poudre Ri~er upstream to Timberline Road <br />(Sheets 1 to 3) <br />The lOa-year floodplain in the middle to lower portion of tl1is rea cl"., (down- <br />strealllfroml'rospectRoad) is very wide and floods an open field North of <br />ProspectStreetalongwithageneralminingoveratlonneartl1eCachela <br />PoudreRiver. Tl1is area is also flooded by a lOO-yearevent on the Cache La <br />PoudreRiver. Upstream of Prospect Road the flow splits and a portion (Sheet <br />flow) flows East along Prospect Road. A farm house downstream of Tir.t>erline <br />Road is inundated by a lOO-year flood. <br /> <br />Reach 3 - LeMay A~enue to Stover Street (Sheet 4 to 5) <br />The floodplain in this reach ranges from approximately 150' to 500' in width. <br />In an area just upstream from LeMay Avenue, a small culvert under a driveway, <br />together with flat topography, causes the lOa-year floodplain to expand to <br />widths of up to 350'. ASmdl1earthdamupstreamofthisareahaslittle <br />effect on the floodplain. In an area 800' downstream from Sto~er Street, the <br />creek has been di~erted and the "Shadow Brook" Condo",iniul!IS (Ire being con- <br />structednear the creek. Cross-sections in this area were surveyed to show <br />actual flood conditions and the floodplain was plotted accordingly. <br /> <br />BNCh2 _Timberline Poadto LeMay Avenue {Sheets 3to 4) <br />Upstream of Timberline Road and at the Colorado & Southern Railroad, the flood- <br />plain is ~ery wide due to ponding behind the embankments and the limited capa- <br />city of the box cul~erts at these loc~tions. ~~st of the pending occurs South <br />of tile creek,where thetopograpl1y is_eryflat. Thereisa farmhouse, a <br />tree nursery, and a power substation ir.undated by the lOO-year flo od. <br /> <br />Reach 4 _ Stover Street to College A~enue (Sheets 5 to 6) <br />The floodplain between Stover and Stuart Streets is very wide with so~ houses <br />inundatedbytheIUU-yea.revent. The wide floodplain in this area is caused <br />by limited capacity of the crossing structures and the channel itse1f. <br /> <br />Upstream of Stuart Street, the floodplain ranges up to 900' in width. The <br />flooded area is mainly a park; however, there are some single-fa~ily hOMes <br />North of Stuart Street within the floodplain boundaries. Flood wdters pd<;s <br />over the bridge at Remington Street and o~er the foot bridge at Mdthews <br /> <br />-20 <br /> <br />.19- <br />