Evaluation of hydrological design of dam spillway using copula based bivariate return periods (Case study: Golestan 2 dam, Golestan Province)

Document Type : Original Article


1 MSc Graduated of Watershed Management, Department of Watershed Engineering, Gorgan University of Agricultural Sciences and Natural Resources

2 Assistant Prof., Department of Water Engineering, Gorgan University of Agricultural Sciences and Natural Resources.

3 Associate Prof., Department of Watershed Management, Gorgan University of Agricultural Sciences and Natural Resources.


Multivariate analysis based on the flood discharge and volume variables can be useful, practical and really more accurate in designing some of the water structures such as dams. Due to the interdependency among the flood variables, it is necessary to consider this feature in the simultaneous analysis of the phenomenon. In this research, the Copula functions were used to simultaneously analyze the variables and to determine the joint return periods. Also, according to the reservoir routing, the maximum height of water above the dam and the risk of dam overflow were compared in the univariate and joint return periods. Therefore, the runoff data of a 40-year statistical period of the Tamer hydrometric station located in Gorganroud River at the upstream of Boostan Dam (Golestan 2) as well as the technical characteristics of this dam were used to meet the aim of the research. The results indicate that discharge and level of water over dam are different for different return periods based on two methods of univariate and bivariate frequency analysis. Water level above the weir corresponding to the output (routed) peak discharge based on the univariate analysis for the 50- year return period equals to 1.42 m. But when the output of the Copula functions (duscharge and volume) were used to storage routing, water level above the weir for the 50-year bivariate return period of "or" and "and" were estimated to be 1.70 and 1.55 m, respectively. in the bivariate analysis, the interdependence of flood variables is considered in determining the values of discharge and volume in a given return period. It can be so important to design a safe and affordable structure.  Also, with emphasize on the designing based on routed design flood, this research indicates that the routed flood in the joint return periods can be led to more accurate designing of the weir dimensions.


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