On the Generation of Stream Runoff in Till Soils

Isotope studies in Swedish till basins indicate that stream stormflow is normally dominated by pre-event water. The rapid response of the groundwater outflow to infiltration may be explained by a large increase in the hydraulic conductivity of the soil towards the ground surface. In homogeneous soils the effect of the capillary fringe may be important in building up large total head gradients towards the stream. In generating runoff peaks in the streams, the saturated discharge area contributes 100 %, by saturation overland flow. Various parts of the recharge area contribute less than 100 %, and less effectively the longer the distance to the recharge area is. The areal extent of the contributing recharge area is considerably larger than the discharge area.