Surface storage in furrow irrigation evaluation

Assessment of the surface storage is of great importance in hydrological surface irrigation. For the Horton infiltration law used in the ALIVE model (Advanced LInear VElocity), an accurate measurement of surface storage is the key to successfully predicting infiltration. For the Kostiakov function, the conclusion is paradoxical due to the fact that this law systematically underpredicts infiltration for times greater than the time used for fitting. Measuring surface storage accurately is cumbersome, and, consequently, most of the models use empirical formulas, which are reasonable, if not always precise. The constant mean cross-section assumption that is implied in hydrological models is discussed from a practical point of view. A representation of nonuniform storage distribution is presented through the ALIVE approach, and the feasibility of an inverse solution is discussed. Finally field records and numerical tests indicate that if the variation of the cross-section remains low (less than half or double the mean) and is randomly distributed the constant mean cross-section assumption is acceptable. With large variations in the flow cross section, the error is lumped with variation in infiltration characteristics. Low variations that are not randomly distributed can affect the infiltration evaluation process. Models using the Kostiakov function are much more sensitive to this phenomenon than the ALIVE model, which uses the Horton law. The reason is likely that the ALIVE model is based on the analysis of the advance rate as a function of distance x'(x) rather than advance time at given location t(a)(x).