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. Additional storage above this level at Kelly Road Dam would require extensive relocation of facilities on Lowry Air Force Base; costs of these relocations would be prohibitive. It is, therefore, the optimum plan of improvement for Kelly Road Dam because it would develop all the feasible storage available at this site. The total first cost of the plan that would store the SO-year flood would be $6,l73,000; $445,000 of this cost would be for lands, $3,6l4,OOO would be construction costs, and $2,ll4,OOO would be for purchase of lands and buildings immediately down- stream from the spillway. The average annual benefits would be $l,268,OOO, net benefits would be $826,000 per year, and the benefit-cost ratio would be 2.9. Although this plan provides for a substantial reduction in average annual damages, floods greater in magnitude than the 50-year event would pass through the 550-foot-wide spillway and floods of major proportions could result in catastrophic effects in the densely populated area downstream. The peak discharge for the standard project flood, as an example, would only be reduced from lO,380 to 9,010 cubic feet per second and this discharge would cause approximately $l2 million in damages. This plan would, therefore, require acquisi- tion of about 80 residential buildings downstream to reduce the potential for loss of life and severe property damage. The area considered for acquisition, however, includes only that area where the existing residential buildings would most likely be completely demolished by spillway discharges from floods which exceed the 50-year event. This acquisition would reduce but not remove the potential for loss of life and severe property damage could still reach catastrophic levels from major floods. A spillway operating frequency of once each 50 years in an area . 1-3