Flood routing is a procedure to determine the time and magnitude of flow at a point of watercourse from known or assumed hydrographs at one or more points upstream. If the flow is a flood, the procedure is specifically known as flood routing. There are two different systems for flood routing called hydrologic and hydraulic methods. The nonlinear Muskingum method is a commonly used hydrologic routing for handling a variable discharge-storage relationship. An alternative method for Muskingum routing can be developed by solving the equation using a numerical method such as Runge-Kutta method. In this research we calculated outflow using the above mentioned methods and compared it with observed one, then using genetic algorithm the coefficients of nonlinear Muskingum method were optimized using geometric characteristics of the river. To test new equations, data from Doab Samsami River are used. With geometric characteristics of this river, the nonlinear Muskingum’s method coefficients were calculated. Then the outflow of the river during 5 floods was calculated using new coefficients. Also this amount was calculated using Muskingum-Cunge method. To compare the accuracy of new equations with other methods of flood routing, a parameter calling RMSE was calculated. Comparing this parameter for observed outflow with calculated ones shows that new equations are more accurate than Muskingum-Cunge method. Results indicate that using these equations will make nonlinear Muskingum method an independent method for flood routing in different rivers and there would be no need to calibrate the method for new rivers anymore. Keywords: Flood routing, Genetic algorithm, Muskingum method, Muskingum-Cunge method, Optimization