River Hydraulics and Sediment Transport

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I The 1.5-year flow is the annual peak flow that is equaled or exceeded, on average, every 2 out of 3 years. The Water Emphasis Alternative is fairly consistent at moving the most sand. The Water Leasing Alternative often ranks second in total sediment transported. The Present Condition and Governance Committee Alternative, Scenario 1, commonly move the least volume of sand. From the desired aspect of increasing deposition, the Water Leasing Alternative had the greatest volume and Governance Committee Alternative, Scenario 1, the least volume of deposition. Results from the grain size analysis show that Governance Committee Alternative, Scenario l, generally lead to the largest grain sizes in the Cooperative Agreement study area. The weighted average also indicated that in the short term (13 years), the alternatives with the same land plan-the Governance Committee, Scenario 2; Water Leasing; and Wet Meadow Alternatives- have the smallest average grain size. In the long term (61 years), the water plans for the Water Leasing and Wet Meadow Alternatives caused the finest grain sizes. ALTERNATIVES COMPARISON FOR SANDBARBUILDING POTENTIAL AND CHANNEL WIDTH Based on the summaries of the flow, sediment transport, and grain size values, it can be said that the alternatives that incorparate a land plan of island leveling and sand augmentation offer greater sandbar-building potential during the implementation of the land plan. In the long term (61 years), if the land plan is discontinued at the end of the short term (13 years), the water plan that appears most conducive to increased sandbar formation is Water Leasing with its larger 1.5 year peak floods, slightly greater deposition in the long term and finer grain sizes over the long term. In general, the alternatives with land plans that incorporate the clearing and leveling of river islands are predicted to have wider channel widths at the 13th year compared to widths under the Present Condition. Of the four alternatives that include the clearing and leveling of river islands, the Water Leasing and Water Emphasis Alternatives have the highest mean flows and 1.5-year flow. These two alternatives are predicted to have the greatest increases in channel width at the 13th year. The clearing and leveling of river islands at sites nearer the upstream end of the degrading river channel would be mare effective at controlling river channel degradation than at sites farther downstream. Therefore, the Governance Committee, Scenario 2; Water Leasing; and Wet Meadow Alternatives would be the most effective at controlling channel degradation, increasing and sustaining open view widths, and creating more sandbars at higher elevations. Of these three alternatives, the Water Leasing Alternative has the water plan with the highest annual mean flows and 1.5-year flow. The Water Emphasis Alternative also includes short-duration, high flows near bankfull capacity and the clearing and leveling of river islands, but with a much greater emphasis at downstream locations. The Governance Committee Alternative, Scenario 1, only includes the