نوع مقاله : پژوهشی
نویسندگان
1 گروه مهندسی آب، دانشکده کشاورزی، دانشگاه لرستان
2 خرم آباد خیابان جلال آل احمد بالاتر از بهزیستی کوی اساتید ۴
3 گروه مهندسی آب دانشگاه لرستان
4 گروه مهندسی عمران، دانشگاه مراغه
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction and Goal
The gabion vertical drop structure, as one of the modern hydraulic structures and also widely used in mechanical and structural operations of watershed management projects, is a combination of permeable rock mesh units that dissipates fluid kinetic energy by creating a hydraulic level difference between upstream and downstream. The passage of flow through the porous pores of the structure reduces the intensity of bed shear stresses and adjusts the peak instantaneous discharges, and as a result, the rate of channel erosion is reduced. The importance of these structures in unstable river beds and environments prone to supercritical flow is twofold in improving the hydraulic and environmental stability of the systems. The present study, using a laboratory approach, compared the flow behavior in the face of two types of gabion and solid structures and analyzed their functional differences in reducing flow energy, flood management, and local erosion control.
Materials and Methods
This research was conducted in the Hydraulic Laboratory of Lorestan University, in a flume with a length of 11 m, a width of 0.6 m, and a height of 0.5 m. In order to comprehensively analyze the hydraulic behavior, a total of 60 experiments were designed and conducted on two types of vertical slope-breaking structures: solid and gabion. In these experiments, three structural thicknesses (Xg) of 20, 30, and 40 cm were investigated in combination with five flow rates of 18, 21, 24, 27, and 30 liters per second for the control sample. Also, in the gabion samples, three effective porosity levels of 30, 35, and 40 percent were used, using three categories of gravel materials with fine, medium, and coarse dimensions, which had an average diameter (d50) of 21, 30.5, and 42 mm, respectively. It should be noted that in all models, the height of the structure was kept constant at 32 cm to provide comparability. Analysis of the obtained data showed that in all models, there is an inverse relationship between the flow energy dissipation parameter and the relative critical depth; such that with increasing energy dissipation efficiency, the relative critical depth decreases, and this trend was visible in all experimental scenarios.
Results and Discussion
The findings showed that the combination of the drop with the gabion bed significantly increased the energy dissipation of the flow; so that the use of gabions improved the energy dissipation efficiency by about 60% compared to the solid slope breaker. The flow passing through the gabion models was separated into two modes: overpass and throughpass. In the throughpass mode, the quasi-non-Darcy and nonlinear flow passed through the porous medium, and the main share of energy dissipation was allocated to this regime. Also, increasing the size of the gabion core particles and the effective width of the structure enhanced the energy dissipation process. Finally, the overpass and throughpass discharge values were calculated for all scenarios, which can be a valuable basis for hydraulic modeling and optimal design of similar structures.
Conclusion and Suggestions
This study investigated the hydraulic interaction of flow and energy dissipation in two types of vertical drop structures: simple and gabion. The results showed that gabion, by creating a porous and permeable environment, is able to independently dissipate flow energy and reduce the need for additional structures such as stilling basins and mesh plates. Also, parameters such as aggregate particle size, gabion porosity, and structure thickness have a significant effect on energy dissipation efficiency and the share of inflow and outflow flows. The findings indicate that the use of vertical gabion drop in water transfer projects in steep and mountainous areas is technically and economically more efficient and sustainable than the solid model. The results of this study can also be applied in optimizing the design of gabion drop in watershed management projects.
کلیدواژهها [English]
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