No abstract

Abstract. Stepped spillways are employed to reduce excess energy encountered with exiting ow from high hydraulic structures. Study of local scour evolution downstream of stepped spillways wilt, therefore, provide the required information to reap the bene ts made from these structures to minimize the scour hole dimensions. This paper provides the results of 67 experiments downstream of some stepped spillways subjected to di erent Froude numbers, basin lengths, tail-water depths, sediment sizes, and two di erent sloped spillways. The experiments were continued for 6, 8, 12, and 24 hours from which 824 pro les and 85000 data points were recorded and analyzed. The results show that, in certain circumstances, the dimensions of scour hole increase in accordance with particle Froude number. It was also observed that an increase in the slope of spillway would result in reduction in the geometries of scour hole. Under certain conditions, as the tail-water increases, the depth of scour hole increases and elongates the hole. The relations of duration of scour evolution downstream of stepped spillway are presented in this paper. Finally, it was observed that the stepped spillway would considerably decrease the dimensions of scour hole compared with ogee spillways, re ecting the excess energy downstream loss of stepped spillway.

No abstract

The discharge coefficient of sluice gates in free and submerged conditions plays an important role in determining the flow rate past such structures. The effects of relative gate opening and submergence ratio have been widely considered by several investigators, mainly based on experimental work. Most of this work, however, lacks an analytical approach to include the variation of discharge coefficient as influenced by gate opening and submergence ratio. This paper, using energy and momentum conservation theory, presents an analytical method to determine the contraction ratio and discharge coefficient of sluice gates under free and submerged flow conditions. Based on suggested relationships for the contraction ratio, variations in energy loss under free and submerged flow and the submergence limit are determined and some graphical demonstrations are adapted. The results are compared with experimental data reported by several investigators and show good agreement.

© ASCE 07015005-1 J. Irrig. Drain Eng. J. Irrig. Drain Eng., 2015, 141(9): 07015005 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 07015005-4 J. Irrig. Drain Eng. J. Irrig. Drain Eng., 2015, 141(9): 07015005 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20. Copyright ASCE. For personal use only; all rights reserved. © ASCE 07015005-5 J. Irrig. Drain Eng. J. Irrig. Drain Eng., 2015, 141(9): 07015005 Downloaded from ascelibrary.org by 44.224.250.200 on 07/05/20.