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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. HIGHLIGHTS Investigated the flow behaviour in different stilling basins using FLOW-3D.; Assessment of energy dissipation in the stilling basins using numerical models.; Investigated the hydraulic jump and its effective parameters in the stilling basins.;