Observations on runoff generation mechanisms in small Alpine catchments

An observational network was set up in an Alpine research basin for catchme nt areas between 1200 m(2) and 16 km(2). It has a nested structure, and the refore allows to trace an observed process from one scale to the other. Run off coefficients for a saturation area showed significant dynamics and rang ed between 0.3 and 0.9. The effect of diurnal variations in evaporation due to solar radiation appears in the runoff hydrographs at all scales. Howeve r, this effect is nearly "averaged out" at the largest scale. Similarly, th e contrasting responses of overland and subsurface flow, on saturation area s clearly to be distinguished as two peaks, are averaged out at the larger scale. The hypothesis that direct runoff is mainly generated on saturation areas was substantiated by an attempt at upscaling the runoff from a satura tion area to the 16 km(2) catchment. Upscaled runoff volumes showed reasona ble agreement with measured data.