ESTIMATED INFILTRATION PARAMETERS AND MANNING ROUGHNESS IN BORDER IRRIGATION

Based on the volume balance (VB) equation, the surface water profile was shown to be a power function and Philip equation equal to the Kostiakov-Lewis equation when the infiltration parameter alpha = 0.5. With this assumption, an equation was proposed for estimating infiltration parameters together with Manning roughness. The method requires only multi-point water advance data of border irrigation. Solving the equation requires use of the nonlinear least-squares fitting technique by Matlab software. The proposed method was validated with field experimental data and some reported border tests. The solution procedure was analysed, the results showing that the values of infiltration parameters S and A are not changed, but Manning roughness n varies when sigma(h) were given different values (0.70, 0.75, 0.80, respectively). Alternative measures of subsurface water storage and water advance trajectory were used to validate the method. Errors between measured and estimated were 2.0-13% for subsurface water storage, in which the infiltration parameters S and A were estimated with the proposed method. The maximum average absolute error was 6.07% for water advance in all border tests when different Manning roughness n was used (for an n value was estimated when different the shape factor of surface profile sh values were adopt by the proposed method in this paper). Copyright (C) 2011 John Wiley & Sons, Ltd.