Modeling rainfall-infiltration-runoff processes on sloping surfaces subject to rapidly changing soil properties during seal formation

Abstract

The effect of rapidly changing soil properties during surface sealing is usually neglected in hillslope infiltration-runoff modeling practices despite its substantial impact. Based on the modified seal formation model and a two-layer infiltration-runoff model, a physics-based, computationally efficient modeling framework is developed to simulate the rainfall-infiltration-runoff process on slopes during seal formation. The framework considers the rapid variations of soil properties of the surface layer over time to reflect the soil sealing process, while accounting for the steepness of the slope. On sloping surfaces, the raindrop impact can both facilitate soil sealing via the normal component to the slope (dominant role) and reverse the process because of the tangential component (secondary role). The proposed solution approach needs no numerical grid adjustment to address the progressive sealing layer compaction. The model simulations accord well with the runoff experiments of different rainfall intensities and slope gradients. During seal formation, rainfall intensity and slope gradient can significantly affect the variation of soil hydraulic properties. The new approach is compared to the case where the seal layer formation is not accounted for and to the case where a completely formed seal is assumed at the rainfall onset. It is found that accounting for the sealing process affects the hydrological processes. Neglecting seal formation or assuming a completely formed seal layer would lead to large errors in both infiltration and runoff predictions. The proposed model can improve rainfall-infiltration-runoff models applicable for hillslopes subject to fast changing soil properties during surface sealing or rapid soil compaction.