FLOOD11628 (2) - Laserfiche WebLink

Home Browse Search

the ~tream banl:s is 3 feet above the streambed. This indicat~e recent stream2low have not exceeded about 200 cubic feet per second. From the switchback in the road and downstream to where the channel is contained in a long culvert the road (age unkriown) has modi2ied and constricted the channel. The channel since the road was built average 5 feet in width. Recent orgariic flood debris and in channel small depositional features indicate the water may not have been much deeper than about 3 to 4 feet in the last 10 to :?0 years. This would indicate a recent peak discharge of 200 cubic feet per second. Had flows any larger than this occurred the Cave of the Winds road would have received substantial damage. A review of maintenance records (ig kept and available) for the road flows may provide additional flood information. Existing hydrology i.ndicates peak dis~harges frequently exceed 200 cubic feet per second; heancz, the road, particularly in the "narroWS" would be eroded o£ten. Has this b~`en the case:' ~ Ruxton Creek Ru::ton Creek drains 17.6 square miles and is steep, par~ticularly in the lower third of the basin. The channel is conta:ined in a concrete flume in Manitou Sprin~b upstream to the Pikes Peak railroad ~tation; hence paleohydrologic studles could not be done. Upstream trom the railroad atation the channel is filled.with m<sny large boulders (some as large as _houses) that have rolled off the steep canyon walls into thz channel. In many reaches the low s~treamflow flows under these rocks. The channel at an elevation of about 6,800 feet was moss and lichen covered except for about 2 feet above the ~ti-eambed. The channel here averages about 10 teet and the boulders in the center ~f the channel are well rounded and polished smooth. Small gravzl bars occur, there is some evidence of erosion of the channel banks, and some trees in the channel recent 5cars and contain flood debris. The channel evidence suggests that recent flows had a depth of 2 teet; hence, assuming a mean velocity of 10 feet p~r second the peak discharge is estimated to be about 200 cubic feet pe:r second. This discharge is one that is ce•nsidered to occur frequently, say once every year or two. At an elevation of 7,000 feet, the only significant flood deposits that fcould be identified in any part of Ruxton Creek, are flood deposits~ consisting of boulders 12 to 18 inches in diameter on the side of the channel and lodged against a 2-foot diameter spruce (eatimated to be about 120 yeaYa old) to a dEpth ot 4 zeet. Channel width is 25 feet; the mean dept.h is 3 feet. These deposits represent the l~rgest flood that has occurreQ in Ruxton Creek had a peak dischar~e of approximately 750 to 1000 cubic feet per second. (These deposits probably were from the 1882 flood (U.S. Army Corps of Engineers, Flood Plain Information report, Fountain Creek, 1974). Moss and extensive lichen covEr boulders in the channel to within 1- foot of the streambed. Boul.ders in the channel are not very well rounded indicating floods do not move the boulders very frequently, nor are they abraided by sedimer~t-laden water. 9