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~ "': ~ ~~ .":- /{ . acceptable technical solution to the existing problem. Its adop- tion, however, would have the effect of transferring the spillway flood threat from Sand and Toll Gate Creeks to Cherry Creek and downtown Denver, a more intensively developed area. The estimated construction costs of this solution would, therefore, represent only a portion of the actual cost because the magnitude of the existing problem would be increased. This increase should be considered as a negative project benefit or a project cost. (i) Plan 3. This plan would consist of raising the Cherry Creek Dam and emergency spillway crests to contain the probable maximum flood, and thus obviate the need to operate the spillway. To accomplish this plan, a 10-foot high concrete para- pet would be constructed along the crest of the dam. The emer- gency spillway crest would be raised to elevation 5650 feet, the maximum pool level, by means of an impervious dam across the existing spillway channel. All lands and improvements below the spillway crest would be acquired for project purposes. The total cost of this plan is estimated at $20.4 million, 75 percent of which is for real estate acquisition within the reservoir area. Although adoption of this plan would eliminate the threat of spillway discharges for all events up to the probable maximum flood, the intense development pressures on the lands involved would create serious acquisition problems. (j) Plan 4. This plan would utilize supplemental storage in the authorized Castlewood Reservoir in conjunction with raising the Cherry Creek spillway crest 31 feet to eleva- tion 5629 feet. Because of the supplemental storage in the Castlewood Reservoir, the existing Cherry Creek Reservoir lands would be sufficient to permit project operation. The Castlewood Dam and Reservoir project would be designed to store the volume of the standard project flood and about half of the volume of the probable maximum flood below the emergency spillway crest. The estimated cost of this proposal is about $23 million, includ- ing the cost of raising the Cherry Creek spillway. In addition to eliminating the threats from Cherry Creek spillway overflows and to the Cherry Creek Reservoir, the Castlewood Dam and Reservoir project would provide additional flood control and recreation benefits which would offset a portion of the project costs, perhaps as much as 45 percent. (2) Upstream areas. The solutions considered for reducing the flood hazards in the Cherry Creek basin upstream from the Cherry Creek Reservoir included zoning, evacuation, flood proofing, channel improvement, levees, and reservoir storage. . 27 04- ~ _ -----'-'------'--'---___-'-_....;.______~.z..ok.-~_"