Due to great velocity gradients among the outgoing flow, it is much common to form large‐scale reverse flow with oblique movements outside the conventional separated stilling basin. Aimed at above problems, this paper proposes to remove the longitudinal splitter wall and then physically and numerically investigate the corresponding influence upon the compound stilling basin. The standard k‐ε, renormalization group k‐ε, realizable k‐ε, and large eddy simulation turbulence models are all employed to reveal downstream three‐dimensional flow field. Experimental validation of numerical results shows that the renormalization group k‐ε turbulence model is the most successful in predicting the flow field among the four models. Both methods prove that the removed splitter wall exerts great impact upon downstream stilling basin. In view of the removed splitter wall, discharging inflow would greatly diffuse to form a typical three‐dimensional (3D) hydraulic jump with large‐scale reverse flow. High energy dissipation region and high turbulent kinetic energy region are both moved upstream. Thus, the velocity decay among the discharging flow in the compound stilling basin is significantly enhanced. Compared to the separated stilling basin, the maximum velocity and average velocity of the outgoing flow, respectively, decrease more than 30%, and 20% in the compound stilling basin. Additionally, the velocity gradients between the left and the right outgoing flow reduce by over 65% with turbulent kinetic energy gradients almost down to zero. The outgoing flow from the compound stilling basin becomes much uniform with the phenomenon of obliquely moving flow totally eliminated.

Flaring gate piers (FGPs) have been used to increase energy dissipation in stilling basins downstream of spillways. For projects with a low water head and large unit discharge together with a deep tailwater level, energy dissipation inside a conventional stilling basin is usually insufficient. This paper proposes a new partial flaring gate pier (partial FGP) scheme to intensify the energy dissipation inside the stilling basin. The results for the no FGP scheme, the conventional FGP scheme, and the partial FGP scheme were compared using a physical model study and numerical simulations. It was found that the partial FGP scheme (the alternation of flaring and no flaring gate piers in chambers) can contain the submerged hydraulic jump and high-speed water jet in the upstream region of the stilling basin. Thus, the water jet from the FGP chamber was forced to laterally diffuse, thereby intensifying the shear friction and turbulent kinetic energy and forming a vertical vortex from the bottom to the surface. Compared with the other two schemes, the flow pattern in the partial FGP scheme was improved significantly with much deeper air entrainment depth inside the stilling basin and much lower turbulent kinetic energy in the outgoing flow. The mean velocity of the outgoing flow also decreased by more than 20%. The common problems of secondary hydraulic jump outside the stilling basin were eliminated.

Aimed at the engineering problems of uncontrollable outburst flood process and large outburst flood peak in a high risk barrier lake, this paper successively adjusts the lateral and longitudinal spillway structure through an indoor physical model and then investigates the consequent outburst flood process differences between the trapezoidal spillway, the compound spillway and the vertical scarp spillway. The results show that the outburst flood process for all kinds of spillway can be successively divided into four typical stages, the initial stage, the retrospective stage, the swift failure development stage and the recovery stage. Compared to the relatively hysteretic initial stage in the trapezoidal spillway, the compound spillway can effectively accelerate the development of initial stage by decreasing down the overtopping elevation, thereby shortening the outburst flood process and cutting down the outburst flood peak by 17.0%. Moreover, the vertical scarp spillway can artificially make a vertical scarp to increase the local velocity at the retrospective stage and further accelerate the initial outburst process, thus significantly shortening the water storage time with upstream maximum water level greatly down. Correspondingly, the barrier body in the vertical scarp spillway would collapse slightly faster due to the excessively accelerated initial outburst process, but the maximum outburst flood peak can still be 11.4% lower than that of the trapezoidal spillway. These investigations can provide reasonable and abundant choices for the emergency disposal in the high risk barrier lake.