Conceptual examination of climate-soil controls upon rainfall partitioning in an open-fractured soil: I. Single storm response

A simple two-domain model was used to gain an improved conceptual understanding of climate-soil controls upon volumetric rainfall partitioning, between matrix domain infiltration, fracture domain infiltration and surface runoff, for a soil with surface-exposed fractures. Dimensionless similarity parameters, relating the storm duration to the characteristic drainage response time of each domain, and relating the storm intensity to the potential drainage rate of each domain, were developed to characterise the response of the soil to a single storm event. Criteria for the triggering of fracture flow and the triggering of surface runoff were developed based upon these similarity parameters, and the influence of fractures upon altering surface runoff generation behaviour quantified. The relative importance of matrix infiltration excess, saturation excess, within-storm variability in rainfall intensity and the antecedent moisture condition upon response behaviour was also investigated. A diagrammatic device, termed a partitioning triangle, was used to illustrate partitioning for a given set of similarity parameters. This analytical approach provides a suitable framework for stochastic examination of the long-term hydrological response behaviour of fractured soils.