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I I I I I I I I I I I I I I I I I I I the ladder drops the water surface elevations by 0.03 feet. At 11 ,600-cfs, flows overtop the banks and inundate the ladders for both alternatives. 7.1.2 Alternative III Under Alternative III, water surface elevations at the intake to the Hartland Ditch are lower than existing conditions by 0.05 feet at low flows (350 cfs) to 0.52 feet during the 2-year event (6470 cfs) and 1.2 feet during the 100-year event (21,200 cfs). Hydraulic calculations indicate that the lower water elevation during the flood stages do not impact the ability to divert flows of 80 cfs or less into the ditch. Above the headgate water surface elevations are slightly above water elevations under existing conditions for most low flow and flood events. The 1 OO-year flood is 0.14 feet greater than existing conditions at cross section 1500, but by cross section 1600 is equal to or less than existing conditions. The chutes and plunge pools located between cross sections 1500 and 1000 create an extended high water elevation since the 5 foot vertical drop is now occurring over 320 horizontal feet versus the current vertical drop. As a result of the increased water surface elevations, the existing berm located on the east bank must be extended along the length of the improvements to contain flood flows. To provide additional hydraulic information, intermediate cross sections are included in the HEC-RAS model for Alternative III as shown in Drawing 4 in Appendix A. 7.1.3 Summary of Hydraulic Analysis The hydraulic evaluation for the headgate operations indicate that as long as flows are at, or above, elevation 4952.5, and as long as there is sufficient flow in the Gunnison River, HIC will be able to divert up to 80 cfs. The water surface elevations estimated for the three alternatives, for the lowest flow analyzed (350 cfs), are all above elevation 4953.2, which is 0.7 feet higher than the minimum required for diversion operations at the headgate. The net effect 34