Experimental Evaluation of Negative and Positive Stepped Stilling Basins with Various Baffle Block Shapes under Submerged Hydraulic Jump Conditions

Local scour downstream of sluice gates poses significant risks to the safety and performance of hydraulic control structures. This study investigates the hydraulic behavior of a stepped stilling basin incorporating various combinations of negative and positive steps, with and without baffle blocks, to control scour under submerged hydraulic-jump conditions.

A total of 16 basin configurations were tested across 96 experimental runs to examine the effects of step arrangement, block shape, and block height on scour depth, scour geometry, and energy dissipation downstream of the sluice gate. Multiple linear regression analysis was applied to develop empirical equations for predicting scour characteristics under limited flow conditions.

Positive steps were more effective than negative steps in reducing maximum scour depth. The configuration C₁ (two negative steps followed by four positive steps) achieved a 48% reduction in scour depth compared to the flat basin. Adding a single row of baffle blocks further improved performance. Maximum scour depth reductions at a Froude number of 1.91 and relative block height h/K = 1.5 were: square blocks 54%, cylindrical 47%, and rectangular 44%. Energy dissipation increased modestly (3–24%), while scour reduction was more pronounced (20–54%), highlighting the sensitivity of scour behavior to geometric modifications rather than total energy loss.

These findings demonstrate that geometric modifications, especially positive steps and appropriately sized baffle blocks, effectively stabilize hydraulic jumps and weaken near-bed velocities. The study provides practical guidance for designing stilling basins to mitigate scour in sluice gate applications.

Properly designed negative–positive step combinations with square baffle blocks (h/K = 1.5) can significantly reduce scour depth while maintaining efficient energy dissipation. The empirical equations developed offer a predictive tool for engineering design under similar flow conditions.