Digging down to find how water flows through a hillslope

Flow pathways on forested hillslopes are highly heterogeneous and are influenced by many different features, such as roots, animal burrows, boulders, clay layers, decaying fallen trees, ash from forest fires and irregularities in the bedrock topography. On many hillslopes, lateral subsurface flow occurs when flow pathways over and through these features connect. Here, we present the results of blue dye tracer experiments to determine how stemflow and throughfall flow through the soil. Lateral flow was observed above a dense clay layer but where roots were able to penetrate the clay layer, the infiltrating water flowed deeper into the soil and (almost) reached the soil-bedrock interface. Stemflow flowed primarily through the 10 cm organic rich upper layer of the soil around the tree before flowing between or along live and dead roots, inside dead roots, and around rocks and boulders deeper into the soil and laterally above the clay layer. These results show not only how stemflow affects soil moisture recharge, despite it being a minor component of the water balance, but also the high variability in hillslope flow pathways. Forest clearing changes the abundance of dead and live roots and thus the abundance preferential flowpaths. This can lead to a change in the partitioning of the infiltrating water into lateral subsurface stormflow, deep (bedrock) recharge and surface runoff. We, therefore, end the presentation by showing how land use change affects how water flows through the soil and the hillslope runoff response.