Coupled two-dimensional surface flow and three-dimensional subsurface flow modeling for drainage of permeable road pavement

Permeable road pavement has been used widely as a sustainable alternative to the traditional impervious pavement and has become an increasingly important component of the hydrological cycle. The benefits of permeable pavement depend on its hydraulic performance and drainage efficiency, for which there have been very few rigorously tested numerical models. In this paper, a new computational model is presented to simulate fluid motion above and within the porous road pavement. This model solves the coupled equation system for surface and subsurface flows using a finite-volume method. The surface flow and the subsurface flow are modeled by the two-dimensional diffusive wave equation and the three-dimensional Richards equation, respectively. A modified Dirichlet-Neumann partitioning method is used as the coupling algorithm to ensure the continuity of pressure head and the conservation of mass. The diffusive wave model for the surface flow is solved with a flux correction transport (FCT) scheme that considers the dry/wet interface and guarantees the positiveness of the water depth. The three-dimensional Richards equation for the subsurface makes it possible to model complex drainage configurations. With the present model, the infiltration process from the road surface into the permeable pavement can be captured more accurately in comparison with many previous models that assumed direct rainfall recharge into the free surface without the leaching process. This capability is important for predicting the timing of road surface ponding, which is critical for safety. The proposed model is extensively validated and an example application for porous pavement design is provided. Results show that the porous pavement with limited thickness considered in this research delays the timing of surface ponding but has less impact on the steady-state water depth and spread.