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Roaring Fork River Floodplain Infonnation Report Town of Basalt, Eagle & Pitkin Counties. Colorado Roaring Fork River Floodplain Information Report Town of Basalt. Eagle & Pitkin Counties, Colorado 3,2 Flood Protection Measures The total April through September inflow was 154,235 acre.feet, which was 130% of average and greater than the reasonable maximum forecast inflow. The high inflows were due, in part, to waters left in the Fryingpan River Basin which nonnally would have been diverted to the East Slope but were not because the reservoirs on the East Slope had filled during the spring runoff. The only substantial structure that affects the flow in the Roaring Fork River is the Ruedi Dam, located on the Fryingpan River approximately 17 miles east of Basalt. The Ruedi Dam is part of the Fryingpan- Arkansas Project to divert water from the Colorado River basin to the Arkansas River basin, Ruedi Reservoir was conslructed by the V,S, Bureau of Reclamation and made operational May 1968, No call was placed on the Colorado River at the Cameo gage by senior water right holders due to highflows in the Colorado River throughout the irrigation season. Because of that, there were no releases made for either Project depletions or for depletions caused by Ruedi Reservoir water contract holders during the 1995 water year, High flows in the Colorado River also eliminated the need to release any water to augment the habitat of endangered aquatic species in the Colorado River downstream of the Grand Valley Diversion Dam and above the confluence with the Gunnison River, The dam was designed for an inflow design flood of 17,500 cfs at a 15.day volume of 100,000 acre-feet. The probable maximum discharge is 5,540 cfs from the spillway and 1,810 cfs from the outlet struclure, The total probable maximum discharge from the outlet structure and spillway is 7,350 cfs, approximating the 500-year flood in the Town of Basalt, Ruedi Reservoir has a total capacity of 102,373 acre-feet at the spillway and provides replacement water for out-of-priority depletions to the Colorado River by the Fryingpan Arkansas Project, as well as water for West Slope agricultural, municipal, and industrial uses on a contractual basis, The reservoir is also operated for recreation, wildlife habitat, and indirectly for flood control. The Corps of Engineers estimated that the operation of Ruedi Reservoir to fill the operating storage, the Boustead Tunnel diversion and Turquoise Lake prevented $1,770,000 of flood damage in the Colorado River Basin during 1995, Permanently assigned flood control storage in Ruedi Reservoir could not be economically justified at the time of construction, However, annual storage of snowmelt runoff indirectly provides the objective of flood control and can appreciably reduce the downstream flood menace in the Fryingpan, Roaring Fork and Colorado Rivers, If the reservoir is operated carefully for flood control by evacuation of storage prior to forecasted heavy inflow, complete control of most snowmelt floods in the reservoir can be attained. There is still a possibility of rare extreme floods that exceed the capacity of Ruedi Reservoir to control them. With the exception of these extreme events, the operation of Ruedi Reservoir reduces and stabilizes flows downstream from the dam, By providing more uniform flows, fish habitat can be established to provide better fishing conditions in early months of the fishing season. 3.4 Summary of Historical Floods Information pertaining to the older flood history of the study area came form two main sources; interviews with long time local residents and a V,S, Army Corps of Engineers letter report entitled "investigation of Flood Problems on Roaring Fork River, Colorado, "March 7, 1958, The V,S, Army Corps of Engineers hydrology for the Roaring Fork River is based upon the assumption that Ruedi Reservoir will act as a flood control reservoir for major runoff events, including the one in 500,year event. Ruedi Reservoir was not constructed as a flood control reservoir, but provides residual storage that can capture flood events based upon normal operation, It is conceivable that the storage volume reserved in the spring for filling would not be adequate to contain a prolonged flood event, and the emergency spillway would release water uncontrolled, This situation began to occur during the spring runoff in 1995, although the discharge on the Fryingpan River was maintained below the maximum safe channel capacity, Mr, Richard Lucksinger of Basalt, was an Eagle County Commissioner during the July of 1957 flood and was interviewed by the Corps of Engineers, Mr, Lucksinger said that around July 4, 1957, a heavy rain melted large volumes of snow, which still remained due to an unusually cold spring and late summer, He remembered that the river rose rapidly to flood height in about 15 minutes and stayed up for three days, According to Mr, Lucksinger the Roaring Fork River rose high enough to wash against the bottom of the Emma Bridge, which washed out and had to be replaced. Pilings for the new bridge were about 60 feet deep, During the flood, the river changed course several times; sometimes going under the bridge, sometime to one side or the other, The areas now occupied by trailer parks in the floodplain in Basalt were several feet deep in -water. 3.3 Ruedi Reservoir Ouerations durin!! the Surin!! 1995 He stated that a couple of agricultural fields along the Roaring Fork were washed out and also that the entire valley where the KOA Campground is now located had been completely flooded several times in his memory, Mr, Lucksinger also said the Fryingpan River does not flood very often but during the] 957 flood, it washed out a road 60 feet from the river, According to the Annual Operation Plans of the Fryingpan Arkansas Project for the Water Year 1995- 1996, the following describes the operation of Ruedi Reservoir during the 1995 flooding event: The following excerpts from the Corps of Engineers letter report also described the July 1957 flood, Releases were increased throughout June to delay the filling of the Reservoir beyond the customary date of July 1 to avoid a spill of the reservoir caused by continuing precipitation on an unusually late occurring snowpack. The peak average daily inflow of 1,796 cfs occurred on June ]7, 1995. The Reservoir filled to the crest of the spillway on July 1], 1995, Outlet works releases were reduced, forcing [the water/evel to rise above the overflow spillway J. and the flow below the Reservoir was maintained below the maximum safe channel capacity, The maximum average daily release of933 cfs was made July 13, 1995, and the maximum storage of 103,927 acrejeet occurred on July 14, 1995. Releases were then reduced until they were below the recommended maximum fishery flow [250 cfsJ by the middle of August, ]n compliance with the requests, an inspection of the problem areas on the Roaring Fork River was made by Corps representatives on 12 and 13 December 1957. The inspection covered a 14- mile reach beginning 2 miles above Basalt, Colorado, and ending at Carbondale, Colorado, 12 miles below Basalt.., Floods on the Roaring Fork result from snowmelt and occur principally during the month of June, The flood of July 1, ]957 had an instantaneous peak discharge of ]8,700 cfs at the Glenwood Springs gage, This flood was the maximum of 49 years of record, and its magnitude has an estimated frequency of occurrence of once in approximately 60 years, ,..... '"",,,,,,,,<ro.,>,. t..---- s.::: Page 10 November 14,2001 't~~~~~ Page 11 November 14,2001