Physical hydraulic modeling of gabion stepped weirs with upstream blockage

Document Type : Research Article


1 phd student


3 Agriculture and Natural Resources Research and Education Center

4 Professor, Shahid Chamran University of Ahvaz, Ahvaz, Iran


Stepped spillways are one of the types of weirs used in waterway systems. This structure is used to discharge measurement, energy dissipation, and water aeration. Due to engineers' tendency towards environmental sustainability and not manipulating natural landscapes, porous spillways made of stone in the form of gabions are a suitable alternative to impermeable concrete spillways. These spillways have technical, economic, environmental, and hydraulic priorities compared to conventional concrete stepped spillways. Porous spillways are a suitable alternative to the usual concrete spillways in water transmission and distribution systems due to their high hydraulic and technical performance on the one hand and negligible negative environmental impact on the other hand.
In this research, the hydraulic performance of the porous stepped spillway under free flow conditions has been investigated in a laboratory manner. This research investigates the effect of different variables including flow rate, upstream blockage, and porosity, on the discharge coefficient of the porous spillway. The materials used in the porous spillway were selected from four gradations between 1.13 and 4 cm with a uniformity coefficient close to 1. Each porous spillway was tested for seven blockages between zero and 100%. Also, the results were compared with a solid stepped spillway model with and without blockage. In the following, it has been extracted to present the empirical relationship of the discharge coefficient in these spillways under blockage conditions, using the dimensional analysis of effective dimensionless parameters under free flow conditions.
Finally, in the final part, based on the dimensional analysis, two empirical relationships are presented using SPSS and GEP (gene-expression programming) for calculating the free flow discharge coefficient for porous stepped spillways.
The results showed that the free flow discharge coefficient increases with the size of the filling material. The percentage increase in discharge coefficient for porous stepped spillways is approximately 34 to 230% higher than that of solid spillways. Unlike solid spillways, whose free flow discharge coefficient increases with increasing the flow rate, in porous stepped spillways, the trend of free flow discharge coefficient changes in low flow rates is downward. With an increasing flow rate, it gradually becomes horizontal and then increases with a slight slope. As the blockage increases, the flow coefficient in the porous stepped spillway gradually decreases. In blockages above 80%, the flow coefficient of the porous stepped spillway is insignificantly different from the solid stepped spillway. In the solid stepped spillway, in the percentage of obstructions below 80%, the obstacle does not affect the free discharge coefficient. The presence of blockage upstream of the porous stepped spillways sometimes reduces the discharge coefficient by more than 70%. The extraction of empirical relationships based on the GEP meta-heuristic model has higher accuracy than those extracted from the nonlinear multivariate regression using SPSS. The average error of the relation of the GEP porous stepped spillway free discharge coefficient was 4%, and the nonlinear multivariate regression model was 7%.


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