Document Type : Research Article
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Abstract
Since measuring the flow discharge is difficult during a flood event in a hydrometry station, the estimated Stage–discharge relationship of non-flood conditions is extrapolated for flood conditions. Hence the results might show underestimated values. Indeed during the flood bed form is developed and flow resistance changes. In order to establish a more accurate stage–discharge relation, it is important to apply a method which considers (or takes into account) the bed form resistance. This research tries to determine the best method for developing such relationship in hydrometry stations located on the Qarasu river basin such as: Ghorbaghestan, Doabmereg, Khersabad, Hosseinabad and Sarasiab. To reach this aim, the required data (e.g. river cross section, bed material gradation) were measured for these hydrometry stations and methods of Einstein–Barbarossa, Shen, White, Engelund, Brownlie and VanRijn are used to obtain the stage–discharge relationship. A computer program was developed to estimate stage-discharge relation based on afore mentioned methods. Different statistical tests were accomplished to compare estimated and observed discharges. The results in Ghorbaghestan and Hosseinabad stations showed that the regression slope between the measures and calculated values by the Einstein–Barbarossa’s method respectively 1.029 and 1.182. by using Shen’s method in Doabmereg, Khersabad and Sarasiab stations respectively 1.08, 1.054 and 0.926 While regression slope in other methods is greater than 1, also AME and RMSE is much less than other methods on the appropriate methods. In hydrometry stations with coarse bed material Einstein–Barbarossa’s method is more convenient to estimate stage-discharge relation in comparison with other methods. Also for hydrometry stations with fine-grained bed material Shen’s method was found a reasonable method to estimate stage-discharge relation.
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