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Source: https://erdc-library.erdc.dren.mil/jspui/ ; The model study reported herein was conducted to evaluate the gravity-flow and pump outlet discharge characteristics and the size and extent of stone protection required in the exit channel. The study indicated the need for minor modifications to improve flow characteristics in the approach to the gravity-flow section and in the stilling basin. The major problems encountered were generated by adverse entrance conditions to the gravity-flow section with both free and submerged flows. Satisfactory approach flows were obtained by excavating a portion of the approach channel immediately upstream from the structure and streamlining the gravity-flow abutments. The improved flow conditions eliminated the adverse drawdown at the abutments and provided a more uniform flow distribution in the stilling basin. The stilling basin was modified to permit more efficient energy dissipation by moving the original row of baffles downstream and adding a second row of baffles. Tests also indicated that the apron length could be reduced by 12 ft without significantly affecting stilling basin performance. The model tests indicated that an 84-ft length of riprap with a maximum stone weight of 292 lb located downstream from the stilling basin would remain stable under expected flow conditions with the recommended stilling basin design. The hydraulic performance of the pump discharge outlets was satisfactory for the range of anticipated flow conditions. Riprap protection (d?????? = 18 in., maximum stone weight = 292 lb) downstream from the pump outlets remained stable for various tailwaters and combinations of pumps operating.