throughflows

Throughflows are subsurface movements of water within the soil, transporting water from upslope areas toward streams or other receiving bodies. In hillslope hydrology, throughflow typically refers to lateral flow in the unsaturated or shallow saturated zone, occurring along soil matrices, root channels, cracks, and macropores. This lateral subsurface flow is distinct from vertical infiltration into deeper groundwater (percolation) and from surface runoff. Throughflow can be rapid in coarse-textured soils with preferential pathways and slower in finer soils where flow is diffuse.

The magnitude and timing of throughflow depend on climate, soil properties, and landscape features. Key controls include hydraulic conductivity, soil moisture, soil structure, topographic gradient, and antecedent rainfall. Vegetation and land cover influence throughflow by altering soil structure, interception, evapotranspiration, and root pathways. After rainfall, throughflow can contribute quickly to stream baseflow or groundwater recharge, depending on the depth and connectivity of flow paths. It also plays a role in transporting nutrients and contaminants from the soil to aquatic systems.

Measurement and modeling of throughflow employ field methods such as trenching, seepage meters, and piezometers, sometimes combined with tracer tests or isotope methods to identify water sources. Modeling approaches in ecohydrology and watershed hydrology often partition catchment flow into components for rainfall infiltration, throughflow (interflow), and baseflow to simulate stream responses and water quality.

See also: interflow, baseflow, infiltration, runoff, groundwater.