On the storm flow response of upland Alpine catchments

Detailed measurements of near-surface soil hydraulic conductivity, Ks, across the Bracciasco catchment(Central Italian Alps) are incorporated into a distributed, digital elevation model-based hydrological model toevaluate the effect of soil heterogeneity on catchment storm flow response. Surface and subsurface storm flowcomponents are simulated for different distributions of Ks, including that obtained directly from measurements,that obtained by averaging measured data and others obtained on the basis of a simple functional parametermodel. The reproduction of the catchment storm flow responses obtained using distributions of Ks based onmeasurements is satisfactory although an adjustment of such distributions is suggested to reproduce thehydrograph peaks owing to rapid surface runoff concentration and to improve the description of recessionlimbs at the same time. Numerical experiments indicate that the simulated storm flow response of the studycatchment is substantially insensitive to near-surface soil heterogeneity in as far as the predominant mechanismof channel storm flow generation is subsurface flow. However, Ks is found to play an important role in thegeneration of overland flow during intense rainfall and, under these circumstances, monitoring of near-surfaceheterogeneity may be important to provide accurate descriptions of both surface and subsurface storm flowcomponents.