Estimation of Discharge Coefficient of Combined Weir- Gate Structure by Genetic Programming

Background and objectives: Weirs and gates are the common and important structures which are used for controlling and adjusting the flow in irrigation channel and rivers. In order to increase the efficiency of the weir and gate structure, the combined weir and gate structure can be used. In this case Weirs and gates can be combined together in order to pass the floating materials above weir and to move the sediments depositions in upstream of the gate simultaneously. This compound device create a new hydraulically condition in compression with weir or gate, each other alone. Before the year 1985, very little information about the use of these combined devices for flow measurements were available when Ahmed published his study on a combination of rectangular weir above a rectangular sluice without contraction. He tried to obtain a common discharge coefficient for the combined system, but his data were not enough to make generalization (15). After him Many researchers have tried to investigating of hydraulic characteristics of the combined structure such as El-saiad (1995), Alhamid et al (1996), Negm et al (1994) and Negm (1997) (6, 2, 14,16). They studied combined flow over V-notch weir and below contracted rectangular gate. The objective of this research was to determine the discharge coefficient of the combined weir-gate and provide the relation for estimation of discharge coefficient based on the hydraulic and geometry parameters.
Materials and Methods: In this study, the effects of hydraulic flow and chanal geometry on the discharge coefficient of weir-gate system was studied by variation of parameters such as discharge, opening the gate and height combined structure in laboratory channels. Finally several relations was obtained with high accuracy for discharge coefficient by the genetic programming. For selecting the best relation, determination coefficient (R2), root mean square error (RMSE), average error (AE) and the average absolute deviation of the data (δ) were used.
Results: The results of the experiments were analyzed after checking and refining data and discharge coefficient was calculated by the above-mentioned relations. Then, by dimensional analysis and genetic programming, A relation was obtained for discharge coefficient of weir-gate system that determination coefficient is for teaching data 84.2 percent and for test data 88.1 percent.
Conclusion: Geometric parameters of combined model have a fundamental role on discharge coefficient. Also the genetic programming can be used for presenting a relation for estimation of discharge coefficient with high accuracy.
Keywords: weir, gate, discharge coefficient, combined flow, genetic programming.