Spatial and temporal variability of near-surface flow pathways in a Swiss pre-alpine headwater catchment

In catchments with poorly drained soils, a significant part of the lateral flow on hillslopes takes place at or near the soil surface. However, there is still little knowledge about these shallow flow pathways and the factors that affect their temporal and spatial variability. Therefore, a better understanding of overland flow and shallow subsurface flow is required to enhance our understanding of runoff generation and solute transport at the catchment scale.

We installed 14 plots on vegetated hillslopes in the Studibach catchment in the Swiss pre-Alpine area that is underlain by poorly drained gleysols. We measured the overland flow and shallow subsurface flow rates at small (3 m wide) trenches, as well as the groundwater level near each plot. We, furthermore, sampled precipitation, overland flow and subsurface flow, soil water, groundwater, and stream water over a two-month period to obtain information about the stable water isotope and geochemical composition. Isotope hydrograph separation and end-member mixing analysis were used to determine the event water fractions and to quantify the fractions of precipitation, soil water, and groundwater in overland flow and lateral subsurface flow. In this presentation, we will present the first results on the temporal and spatial variability in the occurrence, amount and chemical composition of overland flow and shallow subsurface flow and describe how these are related to rainfall event characteristics and topographic position.