Document Type : Original Article
Authors
1 Gorgan University of Agricultural Sciences and Natural Resources,
2 Associated professor, Water Eng. Department of water and soil Eng., Gorgan university of agricultural science and natural resources, Gorgan, Iran
3 Associate Professor of Water Structures, Gorgan University of Agricultural -Sciences and Natural Resources
4 Water Eng. Department, Soil & Water faculty, gorgan Associate Professor of Civil Engineering, Gorgan University of Agricultural Sciences and Natural Resourcesuniversity of agricultural sciences and natural resources
Abstract
Abstr Abstract
Introduction
Masonry check dams are small structures that are built to reduce the slope of the canal, reduce the flow velocity as well as control bed erosion. The distinguishing feature of Masonary check dam and other similar structures is the presence of pipes in the body of check dams. This adds to the complexity of the hydraulic conditions of these structures. As the flow overflows through the Masonry check dams, only some of the kinetic energy of the flow is dissipated in the stilling basin and the excess kinetic energy is occurred downstream of the structure. This situation can cause erosion of the riverbed downstream of the structure. Various methods are designed and implemented to control this excess energy. These methods include changing the height of the bottom bed, roughening the bed and creating a protrusion at the end of the stilling basin in order to create a submerged hydraulic jump into the stilling basin. Due to the fact that the stilling basin used in the main structure is USBR type 1 and in this type of basins, no baffles or end sills are used to dissipate the flow kinetic energy, embedding a sill at the end of the stilling basin is one of the innovations of this research. Also, using a physical model of mortar stone dams has not been reported anywhere and hence, this is also one of the innovations of this research. Therefore, using the physical model of "Tol Beneh" mortar rock dam can help to better understand the impact of scour reduction methods in the main structure constructed on the Gorgan Ziarat River and similar structures
Materials and Methods
in order to identify scour in Masonary check dam and its control methods, a physical model with a scale of 1:20 was developed. The flow rate in all tests was 25 l/s At first First, experiments were performed to determine the amount of scouring at the stilling basin. The results of these experiments were used to compare with the remaining test conditions. In the second series of experiments, to create a rough bed, the 54 cm long distance (equal to the length of the stilling basin) was covered with materials with a median diameter of 2.5 cm. three heights of 3, 6 and 9cm were used to model the increase of bed elevation (third series experiments). In the fourth series of experiments, to create a sill at the end of the stilling basin, a plastic blade 3 cm high was used in four stages. In the first stage, only a 3 cm sill was installed at the end of the stilling basin. In the second stage, the height of the bed bottom increased by 3 cm along the length of 54 cm. It should be noted that the average diameter of bed particles in these two methods was 4.5 mm. In the third stage, the roughness thickness of the bed materials increased to an average diameter of 2.5 cm without increasing the bed height. In the fourth stage, in addition to increasing the roughness of the bed material, the height of the bed also increased by 3 cm along the length of 54 cm.
Results and Discussion
In the stilling basin model, the scour depth was 130 mm without any obstacles. In other words, this magnitude represents a scour of 2.60 meter in the prototype. The presence of the end edge at the end of the stilling basin as well as raising the end of the channel causes a submerged hydraulic jump and consequently reduces scouring. If it is used in combination with these two methods, the effect will be greater. The results show that the presence of the end edge at the end of the calm pool shows a greater scouring reduction than increasing the height of the bottom,
Keywords: scouring, stilling basin immersion, masonry check dam, stilling basin
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