Prediction of Stage - Discharge Relationship in Ghorbaghestan Hydrometry Station According to Bed Form Resistance Equations

Stage – discharge relationship is mainly developed from measured data in any hydrometry station. Measured data usually obtain in low to medium flow discharge، because in most cases it is very difficult to measure the flow discharge during flood. Therefore، the stage–discharge is extrapolated beyond the measured data to compute the flood which may estimate low or higher value. This is because during the high flow، the bed form is developed which causes the flow resistance to change. In order to establish a better stage – discharge relation، it is important to apply methods which consider the bed form resistance. In this study an attempt has been made to determine the best method for developing such relationship. To reach the goal، the required data such as river cross section، discharge and related stage and bed material gradation from Ghorbaghestan hydrometry station were measured for two years. Then a computer program was developed. Using this program and applying the measured data، the stage – discharge relationships were computed by five different methods. From the statistical comparison of the results of these methods with measured data، it was found that Shen، Brownlie، Engelund and White’s method overestimate the flow discharge. The best method was found to be the Einstein – Barbarossa’s method that provided the minimum absolute mean errors 0. 31 and 1. 468 m3/s and minimum root mean square error 0. 112 and 0. 466 m3/s for the two study years، respectively