Laboratory studies on soil scour downstream of chute and stepped spillways for varying conditions of flow energy
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Date
2013-01
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G.B. Pant University of Agriculture and Technology, Pantnagar - 263145 (Uttarakhand)
Abstract
The study of scour downstream of hydraulic structures such as large dams, stilling basins, diversion works, underflow gates, and culverts constitutes an important field of research due to its frequent occurrence in engineering applications. The performance of a drop structure depends largely upon its capacity to dissipate the hydraulic energy of flowing water. The amount of energy dissipation is the difference between the incoming and outgoing energies and the performance of a stepped spillway is dependent on the size of its individual step at a particular drop and discharge. In this study, laboratory experiments were conducted to study energy dissipation and its effect on maximum depth of scour and the amount of soil scoured considering different soil materials using a chute spillway and stepped spillway with three selected step sizes for varying discharge conditions. In all cases the total drop was kept constant. Observations were recorded for amount of energy dissipation, outflow energy, maximum scour depth and amount of soil scoured for various combinations of step size and flow rate using different soil materials. To conduct experiments the developed models were installed in the Hydrologic Simulation and Sedimentation Laboratory which is near to Soil and Water Conservation Engineering department. The amount of energy dissipated was minimum for chute spillway while in case of stepped spillway the amount of energy dissipation was found to be the maximum for step size of 2.54 cm and then decreased gradually as the step size increased for a given discharge. The maximum scour depths were found to be increasing with the increase in outflow energy of flow. On the basis of above, the maximum weight of the scoured soil was found to be increasing with the increase in outflow energy of flow. The above findings clearly indicate that scour depth and scour weight of soil downstream of a drop structure are directly related with the energy dissipation. The use of stepped spillway result in better energy dissipation and thereby resulting in lesser scour depth and scour weight.
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Keywords
agricultural engineering, flow energy, hydraulic energy, soil scour, spillway, flowing water