<p>The relationship between discharge and water level in the river section is one of the most important input information for hydraulic models. The relationship proposed by Maghrebi et al. is one of the most accurate relationships to estimate the stage-discharge curve. This relationship is based on comparing the discharge of two different levels. In other words, it estimates the discharge in any level of water using the discharge taken from one level. In the ideal case, the difference between evaluated and reference discharges is zero. Since the perfect state can never be achieved, achieving the state of the relationship is desirable where the difference is the lowest possible amount. Thus, this paper proposes a new relationship between the evaluated and the reference discharges. It also deals with the stated difference by proposing a new error calculation and an auxiliary relation considering some allowable error. These relations are used as the Goal function and the auxiliary constraint in the optimization process. Then, using these two relationships, the values of the stage-discharge exponents are repeatedly evaluated, and the optimal values are presented. This evaluation is done using a genetic algorithm. In the end, using different problems, the new stage-discharge relation is tested, and the comparison results are presented. It is observed that the responses are improved compared to Maghrebi’s relationship, so there is a 7% reduction in error at some points (P08 of FCF-Series01). Also, the proposed relationship was compared with the SKM and the discharge evaluation error was calculated with the NRMSE and NSE relationships. The results showed that the proposed relation reduces the discharge evaluation error compared to the SKM. This improvement makes the proposed method a robust alternative for stage-discharge modeling in hydraulic applications.</p>