Investigation of flow profile and downstream scouring of V shape gabion weir (in plan)

Document Type : Complete scientific research article

Authors

1 water engineering department, soil and water faculty, gorgan university of agriculture and natural resources, gorgan, iran

2 water engineering department, soil and water fac. gua

3 Assistant Prof., Dept. of Water Engineering, Gorgan University of Agricultural Sciences and Natural Resources,

4 khuzestan water and power authority

Abstract

Abstract:
Background and Scope: Weirs are the most important portion of hydraulic structures utilized for flow measurement, flood control in reservoirs as well as water level control in open channels. Alternatives such as gabion weirs are recently preferred because of their adaptation to nature and ecological requirements. In latter weirs, physical and chemical materials such as sediments and organic suspensions could pass through the pores to the downstream and reduce sedimentation behind the structure. Turbulence in the pore can also increase flow aeration and lead to the treatment of river water. One of the major obstacles of structures such as weirs, valves, and stilling basins located upstream of erodible beds is scouring by the structure which not only directly affects the structure stability, it might alter the flow characteristics and consequently makes changes in their design. This purpose of study was to investigate the flow profiles of V-shaped gabion weir with different apex angles and their downstream scour. Materials and Methods: The experiments were carried out on a physical model of gabion weir with four vertex angles, three aggregates within the weir body, and two positions of the weir positioning upstream and downstream of the flow and four flow rates. Scour experiments were also conducted at three vertex angles, two grain sizes of weir body material, and two positions of locating vertices upstream and/or downstream of the flow and three discharges with erodible bed in a 12m long, 0.6m wide and 0.6m height channel. Results: The results indicated that thorough all vertex angles, upstream water level and maximum scour depth increased with increasing discharge and finer weir material grain size made both upstream water level and maximum scour depth arisen. Upstream water level also decreased by decreasing the vertex angle due to elongated weir length, the scouring was deeper at 120° vertex with respect to the scour depth at both 150° and 180° vertices. Scouring pattern is changed by weir apex location. Upstream weir apex induces one scouring hole at center of channel while downstream weir apex makes two holes in sides of channel.
Conclusions: Depending on the weir purpose, each of the mounting modes of gabion weir could be effective. Weir with finer grains is more useful if the objective is water supply with increasing in water levels. Weir with coarser material is helpful if the purpose is to control the flow energy. A V-shaped weir can be useful to control erosion on the sides. Due to its elongated weir length, V-shaped weir reduces the rate of fluctuation of water level versus discharge.

Keywords

References

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Journal of Water and Soil Conservation
Volume 27, Issue 4
November and December 2020
Pages 201-216

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