Revised Horton model for event and continuous simulations of infiltration

The Horton equation has been widely used to simulate infiltration under ponding conditions and many efforts have been made to expand the applicability of this method to non-ponding conditions. However, because of the absence of appropriate drainage controls, most existing modified Horton methods cannot be used for continuous rainfall-runoff simulations with long dry time periods. The objective of this study is to develop a modified Horton infiltration model (MHI) for both event and continuous simulations with soil moisture threshold controls. Unlike other modified Horton methods, nonlinear and linear equations are used in this new method to quantify the relationships between infiltration capacity and soil water storage respectively for wet and dry soil moisture conditions (wet: gravity-driven free drainage stage; dry: capillarity-dominated non-drainage stage). Two tests of the MHI model were conducted to evaluate its performance in both event and continuous simulations. Fourteen modeling scenarios were considered in the event modeling test of MHI, which involved three soil types of different initial water contents under various rainfall conditions. The simulation results of MHI were compared with those simulated by a modified Green-Ampt model and the reference data from Mein and Larson (1971). Furthermore, MHI was applied to a field site in Grand Forks, North Dakota for continuous modeling and compared against the observed data, which demonstrated its capability in the modeling of infiltration and soil moisture variations.