Experimental Study of Downstream Scour of Piano Keys Weirs

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Ahmadi Dehrashid F.; GOHARI S.

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Journal: Journal of Water and Soil Conservation Year:2019 | Volume:26 | Issue:1 Page(s): 91-109

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Title

Experimental Study of Downstream Scour of Piano Keys Weirs

Author(s)

Ahmadi Dehrashid F. | GOHARI S. | Issue Writer Certificate

Keywords

Experimental StudyQ1

Froude NumberQ1

Piano Key WeirQ2

Scour HoleQ1

Water DepthQ1

Abstract

Background and Objectives: Spillways are a simple and practical hydraulic structure in water conveyance systems and irrigation drainage channels which used to measure the flow, transfer excess water and control the water surface of the reservoir. The Piano Key Weir (PKW) is a rectangular-labyrinth-type weir that used to maximize the allowable weir length that can fit in a given weir channel width, while reducing the required structural footprint. Piano Key Weirs is a new form of long crest weirs that have a relatively simple structure and high economic efficiency structures. Due to the advantages of this weirs, we need to study and investigate the downstream scouring of this structures. In this research, the downstream scour of Piano Key Weir has been studied. Materials and Methods: To study the downstream scouring, two different physical models of Piano Key Weirs in different hydraulic conditions have been used. The experiments were carried out in a flume with a 10 meters length and 50 cm width and height. Two type of Piano Key Weir with 5 and 9 keys were used in this experiments. In order to compare the Scour Hole area a linear weir with a height of 20cm and a width of 50 cm were used in comparison with linear weirs, the corresponding hydraulic conditions was also studied. The Scour Hole dimensions were measured with a point gauge with ± 1 millimeter reading accuracy which has located on top of the channel that can moving along to the channel. The effect of the particle number on the maximum scour depth and location of maximum Scour Hole was investigated. Results: The results show that in Piano Key Weirs, with increasing effective crest length, Water Depth decreases over weir crest and so on decreases the amount of scour depth by decreasing the flow velocity at downstream of weir. Bed profile shape at eroded area is completely three dimensional. Increasing rate of Scour Hole depth is related to number the of piano keys. By increasing the number of keys the maximum depth, length and location of the Scour Hole as well increased. The results show that even at the low level downstream Water Depth, scouring of this weir is less than the sharp crested linear weirs. The profile of the Scour Hole in the Piano Key Weir is almost similar to the linear weir but the only difference is in the height of the dune at the downstream of Scour Hole. The height of the dune generated at higher downstream Water Depth of Piano Key Weir is even lower than sharp crested linear weir and also, with increasing the particle Froude Number, the maximum scour depth parameter and length of occurrence was increased. The maximum scour depth at the 9 key spillway and in 10, 15 and 25 l/s were 30. 7% more than the 5-key spillway and 7% less than the sharp linear spillway. Conclusion: In Piano Key Weirs reducing downstream Water Depth increases scour depth and far it away from downstream apron. Also, by increasing the particle Froude Number, the maximum scour depth, the location of the maximum scour depth and the maximum length of the Scour Hole was increased. The rate of increase in the scour depth is also dependent on the number of overflow keys, and in a fixed Froude Number and downstream Water Depth, increasing the number of keys, the maximum depth and location of maximum scour depth also increase.

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APA: Copy

Ahmadi Dehrashid, F., & GOHARI, S.. (2019). Experimental Study of Downstream Scour of Piano Keys Weirs. JOURNAL OF WATER AND SOIL CONSERVATION (JOURNAL OF AGRICULTURAL SCIENCES AND NATURAL RESOURCES), 26(1 ), 91-109. SID. https://sid.ir/paper/156506/en

Vancouver: Copy

Ahmadi Dehrashid F., GOHARI S.. Experimental Study of Downstream Scour of Piano Keys Weirs. JOURNAL OF WATER AND SOIL CONSERVATION (JOURNAL OF AGRICULTURAL SCIENCES AND NATURAL RESOURCES)[Internet]. 2019;26(1 ):91-109. Available from: https://sid.ir/paper/156506/en

IEEE: Copy

F. Ahmadi Dehrashid, and S. GOHARI, “Experimental Study of Downstream Scour of Piano Keys Weirs,” JOURNAL OF WATER AND SOIL CONSERVATION (JOURNAL OF AGRICULTURAL SCIENCES AND NATURAL RESOURCES), vol. 26, no. 1 , pp. 91–109, 2019, [Online]. Available: https://sid.ir/paper/156506/en

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