Scour reduction downstream of a sluice gate using stepped basins under submerged hydraulic jump condition

Abstract This study experimentally examined the performance of pooled stilling basins with positive and negative steps, with and without baffle blocks, for mitigating local scour and enhancing energy dissipation downstream of sluice gates. The study combined 1, 2, and 3 negative steps with 1, 2, 3, and 4 positive steps. Additionally, the experimental setup included the investigation of adding 1, 2, or 3 rows of baffle blocks, with each row configuration being tested at three different vertical height specifications. Experiments were conducted in a 15.6 m long, 0.30 m wide, and 0.468 m deep recirculating flume at Froude numbers 1.0 to 2.0 under a fixed submergence ratio ( $${s}_{r}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:math> = 3.3). A 2.0 m long and 0.1 m deep mobile sand bed was installed downstream of the basin. A total of 12 models with 81 test runs, were examined in the laboratory under various flow conditions. Results showed that steeped basin, model $${C}_{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>C</mml:mi> <mml:mn>1</mml:mn> </mml:msub> </mml:math> (two negative steps followed by four positive steps), reduced scour by up to 48%. Adding baffle blocks; with the tallest blocks ( $${E}_{2}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>E</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> , $$\frac{{h}_{b}}{K}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>h</mml:mi> <mml:mi>b</mml:mi> </mml:msub> <mml:mi>K</mml:mi> </mml:mfrac> </mml:math> =1.5) and blockage ratio of 5%, further increased the reduction to 54%. Energy dissipation improved by up to 59% for model $${B}_{4}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>B</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:math> (one negative step followed by four positive steps). Adding single row configurations of baffles with blockage area 5% and relative height ( $$\frac{{h}_{b}}{K}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mfrac> <mml:msub> <mml:mi>h</mml:mi> <mml:mi>b</mml:mi> </mml:msub> <mml:mi>K</mml:mi> </mml:mfrac> </mml:math> =1) provided the most efficient balance between scour reduction and energy loss. Finally, experimental data are used to derive empirical formulas through multiple linear regression analysis.