Experimental investigation of temporal variation and of scour depth at triangular labyrinth weir without apron

Document Type : Original Research

Authors
M. Morsali 1
A. BABAKHANI 2
1 M.S. in Water and Hydraulic Structures, Faculty of Civil Engineering, University of Zanjan
2 Assistant professor, Faculty of Civil Engineering, University of Zanjan,
Abstract
Weirs are widely used in many different shapes to control a water level, facilitate flow diversion, and to regulate the flow of water. Given that the overflow zone is often laterally restricted, the overflow depths can become excessive. As a result, non-linear weirs e.g., Labyrinth with different forms have been developed to increase weir length and discharge capacity within a fixed overflow width. Accurate estimation of the maximum possible depth of scour at weirs is important in decision-making for the safe depth of burial of footings. The design of labyrinth weirs foundations based on equilibrium clear water scour depths may yield considerably greater values than if the flow is of short duration. For a known time-to-peak value of the design flood hydrograph, smaller scour depths may be obtained, which reduces the total cost of construction. Therefore, investigation of temporal variation of clear water scour at labyrinth weirs is important to estimate the possible extension of the scour hole. This would provide useful information for the safe design of footing and the selection of scouring counter-measure to be implemented. In the present study, temporal variation of scour and at labyrinth weirs was studied. In experiments, labyrinth weirs were used and seven head to weir height ratios ( H/p =0.1-0.7) for cycles with 6 different sidewall angles (150, 300,450, 67.50, Linear). In this study, the effect of Alfa and sidewall angles on temporal variation of scour depth and scour depth location were investigated. The results indicated that the mechanism and the value of scouring at weir varied for the different value head and sidewall angles. When head to height weir increased, the value of instantaneous scour depth significantly increased.

The results also showed that in all experiments, the scour rate is more severe in the early stages and 80% of the development of scour depth occurs in the early 10% of equilibrium time. Furthermore, When H/P increased 5 times, the equilibrium time of scour depth increased to 6, while whit increasing the sidewall angles to 6 times, equilibrium time decreased 45%.

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Modares Civil Engineering journal
Volume 21, Issue 3
May and June 2021
Pages 35-44