JWSS - Journal of Water and Soil Science

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Direct measurement of discharge in rivers is time-consuming and costly, and sometimes, impossible under flood conditions because of the high speed of water, its transitory nature, and the existence of different floaters along the water. Therefore, the discharge-stage relation, known as Discharge Rating Curve is used. Moreover, to design hydraulic constructions, the maximum flood discharge and its maximum height are required. Therefore, to calculate the flood discharges, one should extend the discharge rating curve by using appropriate methods. In this study, in order to determine the best method for the extension of discharge-stage curve, and to estimate the corresponding discharge with high stages, the logarithmic method, the Manning method, the Chezy method, and the Area-Velocity method in 13 hydrometric stations at the Karkheh watershed in Lorestan province were compared. Data measured at each station were gathered for a ten-year statistical period. Results of calculating the Root Mean Square Error (RMSE) and the Mean Bias Error (MBE) for each method showed that the logarithmic method was more accurate than other methods, and it was more appropriate for the extension of the curve at the low average discharge stations. The Area-Velocity method, after the logarithmic method, especially at the stations with higher average discharge showed good results. The Manning and Chezy methods showed the least accuracy.

Keywords: Stage-Discharge relation, Discharge rating curve, Kharkheh watershed

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