Effect of canal bed slope on the working efficiency of water energy dissipaters downstream control structures

Abstract

Abstract The design of open irrigation channels typically includes a bed slope to achieve the desired hydraulic performance, governing key parameters such as velocity, water depth, and discharge. Diversion head structures, often constructed across these channels, raise upstream water levels, generating potential energy that converts into high-velocity kinetic energy downstream Previous research has studied the type and configuration of water energy dissipaters, considering most hydraulic parameters affecting their performance, except for canal bed slope. The current work aims to explore the extent to which canal bed slope affects the performance efficiency of water energy dissipaters behind head structures, ensuring their safety. The experiments utilized a tilting flume under controlled conditions at six different bed slopes (0.05% to 0.30%) in addition to a zero bed slope, with five discharge values ranging from 9.76 to 17.14 L/s. Through 150 experimental runs, all hydraulic parameters affecting the performance efficiency of the water energy dissipater (relative energy loss, hydraulic jump, sequent depth ratio, and jump length) are measured and recorded. The results clearly show that increasing the canal bed slope to 0.20% enhances the water energy dissipater’s performance efficiency by 31.9%, reduces the jump length by 20% and lowers the sequent depth ratio ( $$\frac{{y}_{2}}{{y}_{1}})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mfrac> <mml:msub> <mml:mi>y</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi>y</mml:mi> <mml:mn>1</mml:mn> </mml:msub> </mml:mfrac> <mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> by 20%. The recommended relative dissipater location $$(\frac{{L}_{b}}{\text{b}})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>(</mml:mo> <mml:mfrac> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>b</mml:mi> </mml:msub> <mml:mtext>b</mml:mtext> </mml:mfrac> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> of 5.83 is accurate for canals with slopes up to 0.20% but for steeper slopes, this ratio must be checked.