Laserfiche WebLink
<br />a <br />il <br />~ <br />11 <br />9 <br />a <br />g <br />i <br />I <br />a <br />I <br />I <br />a <br />] <br />) <br />i <br />I <br />I <br />I <br /> <br />9 <br /> <br />10 <br /> <br />of the valley the s~rficial materials afe mostly eolian silt and residual <br />sol1s. The major supply of sand to the South Platte River has been from <br />1tsrfghtoreastbanktr1butaries. The left or west bank tr1butaries have <br />carrfed more clays, silts and gravels. <br />for the most part. the South Platte River is incised in or 1s <br />flowlng on the Wisconsin Stage gravel f1". The geological cross~sections <br />of the valley in Figure 1 show the different formations in the valley. <br /> <br />gravel mining operations. Between 1964 and 1978, the maximum lateral <br />movement of the meander loops has been approximately 900 feet. <br />There is one other bridge in the reach, a small one to service a <br />gravel mining operation along the west side of the river at River St~tion <br />2040+10. <br />The floodplain is mostly abandoned gravel pits filled with water. <br />The gravel operation is still actfve. Much of this area has been purchased <br />by the City of Littleton as a recreational area. <br />Columbine Valle~ to West Ha~pden Ave. In this 5.6 mile reach which <br />drops 11 feet, the Sout Platte is a Suburban river. The sinuosity is 1.25. <br />The outsfde banks on most of the bends have been blanketed with rubble to <br />stop the bank erosion. In places, the low bank has been built up with fill <br />and the river pinched to a narrower width. <br />There are three weirs of significant height (Table 3) and numerous <br />small drops over concrete casing or steel piles driven to protect pipe <br />crossings. Opposite Columbine Valley there is a new gabion weir approxi- <br />mately 8 feet high at River Station 1967.+ 00. I~diately downstr~am f~m <br />West Union Drive, there is a concrete wen, approxlmately 11 fe~t h19~ wh~ch <br />diverts water to Englewood. The weir sits on the Denver Format1on WhlCh 1S <br />exposed immediately downstream. The other weir protects the Denver Water <br />Board's twin aqueducts where they cross under the South Platte River . <br />approximately 700 feet upst~eam. fro'!l the ~est Oxford Avenue bridge. Th1S <br />weir causes an 8-foot crop 1n tne r1verbeo profile. <br />The width of the river bed varies 9reatly in this reach. The average <br />is 160 feet. Where encroachments have been made by dumping fill on ~he low <br />riverbank,theriverbedisonlyabout60feetwide. Thenarrowsect1onis <br />from West Belleview Avenue to West Hampden Avenue, except through the <br />Engiewood Municipal Golf Course. Due to the high weirs and the encroach- <br />n~nts and other works of man, the bank heights are also highly variable. <br />The alignment of the South Platte River has been changing in this <br />reach. Some movement is the result of natural streambank erosion, such as <br />had occurred at River Station 1817+00. Here, the left bank has eroded <br />approximately 6Q feet exposing a 36-inch diameter concrete ~ewer pi~e.. One <br />man-hole which was 20 feet away from the river on the bank 1n 1966 15 1n <br />the middle of the river now. <br />Other movement is the work of man. Between West Union ~rive ~nd <br />West Hampden Avenue, gravel miners have relocated the.r~ver var10US t1mes <br />in the last 25 years. That part of the Englewood Mun1clpa~ Golf Course on <br />the right (or east) side of the river was a large g~av71 p1t bef~re.. The. <br />large pond has been filled in with debris and the f1ll1ng operat1on 15 st11l <br />continuing out at a slow rate. The fill ~~teri:l forms the rig~t bank of <br />the river and is highly erodible. This bank is more than 10 feet high. <br />The river is ~ch wider than normal through the golf course. <br /> <br />Plan and Profile <br />The plan and profile of the South Platte River were obtained from <br />1 to 2400 scale, 2-foot contour maps prepared by Delta Aerial Survey Inc. <br />from 1 to 7000 scale aerial photographs taken on 16 April 1983, River <br />stationing was taken frOm previous studies listed in Table 1. As the river <br />has moved since those studies were completed, the river station does not <br />agree with what would be obtained from the latest alignment. The main <br />differences are in Adams County. <br />The water surface profile is that existing on 16 April 1983 when <br />the river was at low fTow. <br />General. From Chatfield Dam to Baseline Road flllrediately north <br />from Brighton, the low-flow channel of the South Platte River channel is <br />41.2 miles long. The valley length is 34.5 miles, making the sinuousity <br />1.19. <br /> <br /> <br />The generalized proflleof the river reach is shown in Figure 2 <br />(adapted from Hunt, 1954). The shape is generally concave downward a~ <br />expected with alluvial rivers. TheaverageriverbedslopefromChatfleld <br />Dam to the mouth of Clear Creek is approxfmately 13 feet per mile. There- <br />after the average slope decreases to approximately 9 feet per mile to <br />Brighton. Where there are no major tributaries, the general riverbed slope <br />of the South Platte River remains constant. Bed slopes of all major <br />tributaries are much greater than that of the main stem. <br />Chatfield to Columbine Valley, In this 3.7 mile reach, the South <br />Platte is a Rural river. The total drop in elevation is 40 feet and the <br />sinuosity is 1.02, The first 4700 feet of channel downstream from the out- <br />let works at the Chatfield Dam fs excavated in the former floodplain, This <br />gravelled ditch is approximately 100 feet wide. <br />Where the outlet channel empties into the South Platte River, there <br />is a check dam of rocks which drops approximately 6 feet. Thereafter, the <br />river flows in its natural channel for which the bottom is 160 feet wide on <br />the average. The high bank is approximately 7 feet high. <br />There is a low concrete weir across the riverbed immediately down. <br />stream from the State Highway 470 bridge. All bridges are li~ted in Table <br />3. Tnereafter, the South Platte River is eroding its bankS v1gorously 1n <br />places. The river has moved itself appreciably, probably aided by the <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />