Irrigation and hydraulic engineers are often faced with the difficulty of tedious trial solutions of the Manning equation to determine the various geometric elements of open channels. This paper addresses the development of a computer model for the design of the most commonly used channel-sections. The developed model is intended as an educational tool. It may he applied to the hydraulic design of trapezoidal, rectangular, triangular, parabolic, round- pormered rectangular, and circular cross sections. Two procedures were utilized for the solution of the encountered implicit equations: the Newton-Raphson and the Regula-Falsi methods. In order to initiate the solution process, these methods require one and two initial guesses, respectively. The results revealed that the Regula-Falsi method required more iterations to converge to the solution compared to the Newton-Raphson method, irrespective of the nearness of the initial guess to the actual solution. The average number of iterations for the Regula-Falsi method was approximately three times that of the Newton-Raphson method.