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. for the Missouri River main channel with existing overbank conditions and with the 10-, 25-, and 50-foot wide proposed pilot channels are also included in this appendix, c, Flow - Through Chute (Non-Constructed) Engineering analyses for this alternative included hydraulic calculations to determine floodplain velocities for three potential chute channel widths for various discharges, The three widths represent an assumed initial condition, an intermediate condition, and the ultimate condition (assumed to be 200'), Chute discharges through the non- constructed chute for various Missouri River stages were not specifically computed, However, for the purpose of qualitative assessment of possible chute formulation through natural dredging, normal depths and velocities for various chute discharges were calculated for the three assumed conditions, A summary of depths, discharges, and velocities for the three channels are included in this appendix. The results generally indicate that velocities for these configurations are on the order of 1 to 3 fps for depths ranging from 2 to 10 feet. Although the calculated velocities appear to be low, a qualitative assessment indicates that there is potential for natural chute channel formulation through scouring action, Scour in the chute channel is probable due to the fact that its slope is steeper than the main channel slope, The natural dredging would take place only if the existing grade control structures were lowered and inlet and outlet structures were constructed to help "form" the chute, Additional analyses for this alternative include the investigation of overbank floodplain delineation for the natural chute channel with the proposed inlet, outlet, and dike lowering, The purpose of this evaluation was to determine the approximate flow paths and inundation limits for a discharge which WOuld represent normal summertime flow conditions, The results indicate that a non-constructed flow-through chute would yield a very wide inundation area consisting of several flow paths with varying depths and velocities, Although this condition most closely represents the 1923 pre-project Missouri River configuration at Hamburg Bend, substantial construction features may be required to protect the Federal Levee from lateral chute migration, to prevent early capture of the chutes by the main channel, and to ensure at least one complete and unobstructed flow path from the inlet to the outlet. In addition, natural chute channel development (with proper construction features) may not fully take place until significant overbank flows occur as a result of flood events on the Missouri River, It is estimated that two or more events with main channel discharges exceeding approximately 120,000 cfs for a substantial duration would help form the natural chute, A flow of 120,000 cfs is approximately a 5-year flood event. Flow in the overbank chute area is estimated to occur at a river discharge of about 15,500 cfs with the inlet structure in place, The flow in the main channel and overbank area would become hydraulically connected at an approximate discharge of 65,000 cfs, It is difficult to estimate the future morphology of the point bar area for this alternative given that there would be no pilot channel to "guide" the flow in the desired direction, It is true that substantial control structures would help to channelize the overbank flow, however there is a potential for the formulation of undesirable flow paths and/or early capture by the main stream with this alternative, d, BackwaterlWetland Complex Hydraulic modeling for analysis of the backwaterlwetland complex was performed using HEC-2 backwater models, The 100 acres of wetted area and 10 acres of islands were modeled by modifying the existing conditions HEC-2 run provided by the Corps, . c " ~ .