A fractional-order infiltration model to improve the simulation of rainfall/runoff in combination with a 2D shallow water model

In this work, a distributed 2D shallow water (SW) flow model is combined with a fractional-order version of the Green-Ampt (FOGA) infiltration law to improve rainfall/runoff simulation in real catchments. The surface water model is based on a robust finite volume method on triangular grids that can handle flow over dry bed and multiple wet/dry fronts. When supplied with adequate infiltration laws, this model can provide useful information in surface hydrology. The classical Green-Ampt law is generalized by using a Caputo fractional derivative of order less than or equal to 1 in Darcy9s law. The novelty of this combination is that, on the one hand, the distributed SW simulation provides a detailed surface water distribution and, on the other hand, the FOGA model offers the possibility to model infiltration rates not monotonically decreasing. In order to obtain the best results, a non-uniform order of the fractional derivative depending on the cumulative infiltration and the existence of available surface water is proposed for realistic cases. This allows significant improvement of previous published numerical results in the literature for several storm events in catchments where the infiltration process occurs.