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V II 1-4 There are 39 vehicular or railroad bridges in this reach. The foundations of the bridges are on, or in, the Denver Formation which is, for the most part, well below the riverbed. However, the rock outcrops periodically on the bed of the river. A subreach where the rock is prevalent is from Dart- mouth Avenue to Evans Avenue. Here, the soft weathered upper 1 ayer has been grooved by the river's currents. The riverbed width varies widely from Sand Creek to 104th Avenue. The average bottom width is 250 feet. Where the channel is straight and wide, there are numerous tightly spaced (overlapping) alternate bars, Point bars were noted on wide bends. Where the channel is narrow there appears to be no point or alternate bars. In the urban reach, the South P1atte River bed averages 120 feet in width varying from a minimum of 60 feet to a maximum of 180 feet. In general, both banks are bui It up to the same level. Bankfull depth ranges from 1D to 22 feet; the average is approximately 15 feet. There is no real distinction between the high bank and low bank. The average bank height is 9 feet with 1itt1e variation except where there are 1 evees. There are six bridges between Sand Creek and East 104th Avenue. The urban reach has been improved for the people's enjoyment. A bicycle and foot path follows the channel from opposite the Sewage Disposal Plant near Dartmouth Avenue in Englewood to East 78th Avenue in Adams County near Thornton, except for a gap north of Denver. Provision has been made for rafters and kayakers. East 104th Avenue to Baseline Road. The downstream reach of the South Platte River is rural in form. It falls 92 feet in a river distance of 11.4 miles. The sinuosity is 1.26. At the Brantner Ditch Dam there is aID-foot drop in the riverbed level. At the Brighton Ditch Dam the drop is 3 feet, There are only two bridges in the central portion of the reach and one at each end. Sand Creek to East 104th Avenue. From Sand Creek to East One Hundred-Fourth Avenue, the river channel falls 64 feet in 6.8 miles. There is a drop of 6 feet across the diversion weir for Fulton Ditch, and another 4-foot drop at the rock structure immediately downstream from the East 88th Avenue bridge. The sinuousity of the channel is 1.18. The river is termed suburban. The river here is actively eroding its banks and its bends are moving laterally. There are large gravel point bars where the bends are sharp. In these locations the river is wide. Where the channel is straight, there is a pattern of lateral bars with varying spacing. In this reach, there are low levees on one or both banks of the river over most of the distance. The floodplain is approximately 0.75 miles wide. Its principal uses are for agriculture and gravel mining. Former gravel pits are employed to store water. The density of buildings is low. The levees do not reduce appreciably the inundation of the floodplain caused by the 100-year flood. Only the ponds are protected. The average bankfull width of the South Pl atte River in the rural reach is 350 feet. The maximum width is approximately 800 feet at a location where there is a lateral bar and a middle bar. The minimum width is approximately 130 feet at one of the crossings. The mean bed width is 250 feet. The sharp bends in the river have been stabilized with rubble. However, the river has been moved laterally somewhat along its relatively straight stretches. Part of this movement is the result of gravel mining opera- tions. Because the river is free to move in most places, the bank height varies widely. Generally, the high bank is on the side where the current is erod- ing the bank. The low bank is opposite where deposits are occurring. The average bankfull depth at the high bank is 9 feet. The average low bank depth is 1 foot lower.