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DETERMINATION OF THE EXISTING THRESHOLD FLOOD The Office of the Chief of Engineers' "Gu:ldelines for Evaluating Modifica- tions of Existing Dams Related to Hydrologic Deficiencies" describes the existing threshold flood as follows: "Based on the lexisting clam design, there is an inflow event that will exceed the design crite:ria of the dam and thr,eatens dam failure. This event. called the existing threshold flood, is determined by routing flood events, expressed as percentages of the PMF, through the reservoir and identifying the event for which the still water level encroaches on the freeboard necessary to accommodate potential wind and wave condi cions and threatens the safety of the structure." The threshold flood for Cherry Greek Dam was determined by routing percentages of the "existing conditions" PMF through the re.servoir on a half full flood control pool. The inflow hydro graphs were a percentage of the PMF hydrograph ordinates, As shown on plate 20, the existing threshold flood for Cherry Creek Dam is 63 percent of the PMF. The threshold flood and lesser floods reservoir routing summary, which includes the peak inflow, total vo].ume, peak pool elevation, and peak outflow, is shown in table 5, It should be noted that the existinl; threshold flood is increased to 66 percent when flows through the outlet works are considered in the routings. Also, if the starting conditions were based on a full flood pool, the existing threshold flood would be 58 percent of the Inflow Design Flood with 3 feet of freeboard, ROUTING OF THE EXISTING THRESHOLD FLOOD The existing threshold flood was routed through Cherry Greek Reservoir using DAMBRK to determine the outflow hydrograph for the "with" and "without dam 23