An analytical relationship was developed for determining Manning's roughness coefficient (n) for border irrigation. Manning's n is considered as a function of border length and its value at each point of the border is regarded as a function of the variation in water depth. The proposed relation was evaluated for 12 irrigation events at three farms and using WinSRFR software. Results showed that Manning's n computed using the proposed relation had an error of less than 2% compared to the coefficient obtained by the WS software. The proposed relation was sensitive to the exponent in Kostiakov– Lewis’s infiltration equation and to inflow into the border
