Stilling basin of the Tuansa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which includes impact baffle and friction blocks. Soon after the barrage's operation, baffle blocks were found to be uprooted. Additionally, previous studies also highlighted the issues of rectangular baffle blocks, i.e., less drag, smaller wake zone, and flow reattachment. On the contrary, the use of wedge-shaped splitter blocks is found limited downstream of diversion barrages. Therefore, this study focuses on the hydraulic effects of wedge-shaped splitter blocks on hydraulic jump (HJ) and energy dissipation using FLOW-3D and confirms its suitability downstream of the diversion barrage. The study mainly investigated the free surface profiles, roller lengths, relative energy losses, velocity profiles, and turbulent kinetic energies for three different stilling basins. The results of free surface profiles indicated that new basins stabilised the HJ and produced smaller lengths of HJ. The results also showed that as the flow increased, the roller lengths decreased in the new basins. Similarly, with an increase in the flow, the relative energy loss increased in new basins. Furthermore, within HJ, and at the basins' end, the results showed higher decay of velocity and turbulent kinetic energy in the new basins.

The hydraulic performance of stilling basins is affected by their size and geometry. Taunsa Barrage, Pakistan, was constructed in 1958 and remodelled in 2008. In remodelling, baffle and friction blocks were replaced by chute blocks and dentated sill. After remodelling, sounding, and probing data during 2010–2014 revealed that flexible apron in front of some bays was washed away. This study quantified hydraulic parameters such as free surface, flow depth, Froude number, roller length, velocity, hydraulic jump efficiency, and turbulent kinetic energy for stilling basins before and after remodelling using FLOW-3D. Comparing results with the literature showed that results in the old stilling basin were closer to the literature results. The results of old stilling basin showed linear trends of tailwater depths with Froude number and roller lengths. Results of the new stilling basin deviated from the literature results because relatively weak trends of tailwater depths with the Froude number and roller lengths were revealed; velocities were higher on the basin's floor; energy dissipation was less, and there was more turbulent kinetic energy on downstream. In conclusion, hydraulic studies for other discharges, tailwater levels, and turbulence models have to be conducted to analyze hydraulic issues in the new stilling basin.

The hydraulic performance of stilling basins is affected by their size and geometry, which can be predicted by local scour. In 2008, based on a rigid bed study, the stilling basin of Taunsa barrage was remodeled, in which the old friction and baffle blocks were replaced with chute blocks and end sills. However, the study did not consider the effects of the remodeled basin on the erodible bed and only investigated hydraulic jumps. Therefore, this study developed FLOW-3D scour models for a designed flow of 24.28 m³/s/m to investigate the flow field and local scouring downstream of old and remodeled basins. The results showed that as compared to Large Eddy Simulation (LES) and Standard K-ε models, the Renormalization Group (RNG-K-ε) model predicted the scour profiles with better accuracy, for which the coefficient of determination (R²) reached 0.736, 0.823, and 0.747 for bays 33, 34, and 55, respectively. Downstream of the remodeled basin, the net change in sediment bed was 88%, 91%, and 95% in the LES, Standard, and RNG-K-ε models, respectively. However, downstream of the old basin, the net change in sediment bed reached 51%. Conclusively, based on the results, the study suggests investigating scour downstream of Taunsa Barrage using other discharges and sediment transport rate equations.

The present study investigated the performance of three different stilling basins, i.e., modified United State Bureau of Reclamation (USBR) Type III, USBR Type II, and wedge-shaped baffle blocks (WSBB), using FLOW-3D scour models. Field data of the riverbed profile are employed to validate the present models. After comparison, the results of statistical indices, i.e., coefficient of determination (R²) and Nash–Sutcliffe model efficiency coefficient (NSE), indicated that the Renormalization Group (RNG-K-ϵ) showed good agreement with the field data, with R2 and NSE values of 0.9094 and 0.896, respectively. Validated models are used to simulate velocity field and local bed shear stress (BSS) and scour for design and flood discharges of 28.30 m³/s/m and 17.5 m³/s/m, respectively. At 28.30 m³/s/m, the results indicated that the riverbed downstream of the remodeled basin was completely exposed, while, at 17.5 m³/s/m, the net change in bed reached 85%. At 28.30 m³/s/m, the net change at the centerline of models reached 51% and 67% in USBR Type III and WSBB basins, respectively. At 17.5 m³/s/m, compared to Type II and III basins, the WSBB basin indicated less BSS, which significantly reduced the scour. Conclusively, the Type II basin showed less energy dissipation for the studied flows, while the WSBB basin improved flow fields downstream of the barrage.

The stilling basin of the Taunsa barrage is a modified form of the United States Bureau of Reclamation (USBR) Type-III basin, which consists of baffle and friction blocks. Studies revealed uprooting of baffle blocks due to their vertical face. Additionally, the literature highlighted issues of rectangular face baffle blocks: less drag, smaller wake area, and flow reattachment. In contrast, the use of wedge-shaped baffle blocks (WSBBs) is limited downstream of open-channel flows. Therefore, this study developed numerical models to investigate the effects of USBR and WSBB basins on the hydraulic jump (HJ) downstream of the Taunsa barrage under lower tailwater conditions. Surface profiles in WSBB and modified USBR basins showed agreement with previous studies, for which the coefficient of determination (R2) reached 0.980 and 0.970, respectively. The HJ efficiencies reached 57.9 and 58.6% in WSBB and modified USBR basins, respectively. The results of sequent depths, roller length, and velocity profiles in the WSBB basin were found more promising than the modified USBR basin, which further confirmed the suitability of the WSBB basin for barrages. Furthermore, WSBB improved flow behaviors in the basin, which showed no fluid reattachment on the sides of WSBB, increased wake regions, and decreased turbulent kinetic energies.

Hydraulic structures, such as barrages, play an important role in the sustainable development of several regions worldwide. The aim of this novel study is to identify the critical hydraulic parameters (CHPs) of Taunsa Barrage, built on the Indus River. These CHPs, including free surface profiles, flow depths, Froude number, velocity profiles, energy dissipation and turbulence kinetic energy, were investigated using simulation via FLOW-3D numerical models. Incompressible Reynolds-averaged Navier–Stokes (RANS) equations on each computational cell were solved using the numerical methods available in FLOW-3D. The simulation results indicated that the locations of hydraulic jumps (HJs) were lower than that were reported in the previous one-dimensional study. Similarly, the distances of the HJs from the downstream toe of the glacis were reached at 2.97 m and 6 m at 129.10 m and 130.30 m tailwater levels, respectively, which deviated from the previous studies. In higher tailwater, the sequent depth ratio also deviated from the previous data. The maximum turbulent kinetic energies were observed in the developing regions of HJs, which were found to be decreased as the distance from the HJ was increased. The results of this research will be highly useful for engineers working in the field of design of hydraulic structures.