Seasonal dynamics of runoff-contributing areas in a small mediterranean research catchment (Vallcebre, Eastern Pyrenees)

This paper analyzed the seasonal dynamics of runoff-contributing areas in a small Mediterranean catchment (Can Vila catchment, 0.56 km 2). The aim was to provide a more detailed spatially distributed picture of the behavior of the catchment, which would help explain the high spatio-temporal variability of its hydrological response. Contributing areas for runoff were mapped during eight field surveys performed under varied hydrological conditions. Low permeable bare areas were recognised as classic source areas for infiltration excess runoff, and two types of saturated areas prone to saturation excess runoff were identified: A-type areas, linked to groundwater rising to the surface, and B-type areas, associated with saturation restricted to the upper soil profile. The amplitude of the seasonal variation in these saturated areas was similar to the amplitude found in more humid catchments, even if their decrease was more marked under dry conditions. In the Can Vila catchment, terraced topography promoted, however, more scattered saturation patterns than those usually described. A linear relationship between the extent of saturated areas and baseflow discharge was found; the relationship with the position of the water table was also direct, when saturated areas linked to groundwater rising dominated the saturation pattern. Using very simple methodology, a tentative quantification of the contribution of precipitation on saturated areas to storm-flow was performed, improving the overall understanding of the Can Vila Mediterranean catchment.