Hydrological modelling with an improved flexible hybrid runoff generation strategy

Abstract

The saturation-excess mechanism, infiltration-excess mechanism and subsurface stormflow mechanism are the fundamental of the hybrid runoff generation models. Existing hybrid runoff generation methods pay much attention to the surface runoff and subsurface runoff, but less to the characterization of subsurface stormflow. Additionally, the subsurface stormflow was mostly separated from the saturated-excess. This kind of separation ignores subsurface stormflow in unsaturated areas, and therefore may result in significant errors sometimes. Therefore, a novel conceptual method for subsurface stormflow in unsaturated areas over the interface was proposed through a combination of the Green-Ampt equation with the parabolic infiltration capacity distribution curve. Then, the subsurface stormflow was considered as the sum of the infiltration excess over the unsaturated areas and the saturation excess over the saturated areas. On this basis, an improved flexible runoff generation strategy was developed to incorporate the spatial heterogeneity of underlying surface conditions and rainfall conditions based on the three single runoff generation mechanisms. Finally, the Xun River basin was selected as a case study. Performances of different runoff generation strategies were compared and discussed based on flood events and continues flow. And the sensitivity analysis of the parameters was carried out. Results show that the proposed strategy performed the best among the five strategies, and the accuracy of the simulation results was affected significantly by the infiltration-excess subsurface stormflow over the unsaturated areas. The proposed method can be used for the watersheds where there may be abundant subsurface stormflow.