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Reservoir Site Characterization I is unknown as that portion of the reservoir has remained submerged since the original reservoir filling. Limited field observations of sediment flow and corresponding streamflow rate by Muller , Engineering, together with average monthly influent flows estimated by Hydrosphere, enabled the development of an approximation of annual average sediment movement by month. That relationship shows that 91 % of the annual total water volume and 98% of the annual total sediment inflow occurs during the runoff months of April, May and June. Utilizing above- reservoir and below-dam sediment sampling data obtained during the course of the present study, it can be concluded that 99% of the total sediment load is suspended material comprising 70% sand and 30% silt/clay. It is further concluded that 100% of bed load and 92% of all suspended sediment is captured by the reservoir. During the 53-year study period the gross sediment inflow was estimated, using the flow/sediment rating curve, to be an annual average of 81 acre-feet/year. Using the information for the 19 years the reservoir has been in place, and assuming 93 % sediment capture, a total of 1,531 acre feet of sediment has entered the reservoir and 1,416 acre-feet of that sediment has been retained. This corresponds well with the aforementioned 1,170 acre- feet of measured sediment accumulation from the stage-area-volume curve information. The current estimate of 81 acre-feet/year gross sediment yield developed from actual measurements and reservoir mapping is 59% larger and more accurate than the regionally-based 51 acre- feet/year gross sediment yield estimated during the Phase I Study (Hydrosphere, March 1993). For the purposes of reservoir storage allocation, it is therefore estimated that the annual average sediment inflow to the reservoir is 81 acre-feet per year. Assuming 95 % capture of sediment at the higher reservoir size and 254 acre-feet of space created by construction-related excavation within the reservoir yields a net 7,403 acre feet of sediment accumulation over a 100-year reservoir life. Therefore an allocation of 7,500 acre-feet of sediment storage volume in the reservoir is suggested. Based upon the apparent historical pattern of sediment deposition, this sediment is allocated 70% to the inflow delta, 10% to the reservoir ring in the elevation range between five feet above and fifteen feet below the service spillway, and 20% evenly distributed over the remaining deep areas of the reservoir. Downstream Channel Stability As with reservoir sedimentation, much can be ascertained about downstream channel stability impacts by examining pre-reservoir and existing conditions. Unfortunately, in this instance information about preconstruction conditions and interim physical changes is not sufficient to allow precise conclusions to be reached. Some indirect information, qualitative observations and examination of current conditions can also be used to confirm general theoretical channel impacts and provide an approximation of future fluviomorphologic characteristics. Examination of maps and aerial photographs provides an overview of downstream Ml channel changes since the dam was built in 1973. The most obvious and direct channel impact downstream of the dam was the abandonment of the natural stream channel between the dam and the confluence with the new spillway tailrace/channel. While the general location of the channel has remained relatively unchanged, available mapping also indicates a general channel widening and local bank retreat of up to 50-feet at several bends has occurred in the first 3/4 1 3-16 1