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Application of GIS-based distributed hydrological modelling for estimation of water residence times in the small Swiss pre-alpine catchment Rietholzbach

Abstract:

A concept of water residence time distributions in the pre-alpine catchment Rietholzbach in northeastern Switzerland has been developed. The catchment covers an area of 3.18 km2 and ranges from 680 to 960 m a.s.l. It is part of the Upper Freshwater Molasse overlaid by Quaternary deposits. The study combines runoff modelling with the use of the isotope 18O and consists of two parts. In the first part, runoff simulation over the period 1983-1997 was carried out using the model PREVAH-ETH. For the spatial data distribution, 100 m grid data were aggregated into hydrotopes by means of a GIS. An approach including the topographical index was integrated into the model, improving the simulation of runoff components. In the second part, the calculated groundwater recharge rates were used for the weighting of δ18O input functions. They served to estimate groundwater residence times at selected sites in the catchment over the period 1994-1997. The mean groundwater residence times range up to 2.5 years and depend on the mixing efficiency within the aquifers. The results form a contribution to the understanding of the water turnover processes in hilly pre-alpine basins with porous structures, as investigated using areal distributed hydrological modelling coupled with tracer techniques.