Effects of preferential flow pathways on groundwater resources rainfall supply

Groundwater resources in unconfined coarse grained aquifers are generally supplied by rainfall infiltration. The presence of surficial fine textured soils prevents and delays infiltration of water flow toward deep groundwater. This is due to the lower permeability of fine textured soil but also to the capillary barrier effects and water retention at the bound between layers, until reaching critical conditions which trigger flow downward. These surface soils are commonly characterized by shrinking cracks which seriously affect rainfall infiltration, since they constitute preferential flow paths facilitating deep infiltration. A capillary barrier effect can happens also in fractures, which behave like capillary pipes. In order to show how these mechanisms affect deep groundwater supply and aquifer recharge, the present work applies a dual-permeability model simulating infiltration into fractured and stratified soils to a test soil. Results shows how intense rainfall may flow through fractures reaching groundwater resources, while weak rains may be entrapped in surficial strata without supplying deep groundwater resources, despite of their duration of several days.