Parsimonious modeling of mountainous catchment hydrology at various spatial scales – initial results and evaluation

Friday, 26 September 2014
Jana von Freyberg1,2, P. Suresh Rao3, Dirk Radny4 and Mario Schirmer1,2, (1)EAWAG Swiss Federal Institute of Aquatic Science and Technology, Duebendorf, Switzerland, (2)University of Neuchâtel, Centre for Hydrogeology and Geothermics, Neuchâtel, Switzerland, (3)Purdue University, Civil engineering, West Lafayette, IN, United States, (4)EAWAG Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland
Abstract:
Mountainous catchments serve as important freshwater resources that sustain surface water bodies and groundwater aquifers in the lowlands. However, the understanding and description of the hydrologic behavior of mountainous catchments remains a challenging task due to complex landscape properties and flashy rainfall-runoff responses. Further, these regions are often used intensively as agricultural landscapes, which poses a potential risk of pollution of the local aquatic systems. Therefore, the identification of hydrologically active landscape units and the improvement of the existing understanding about dominant physical processes controlling streamflow generation and solute export is required in order to preserve the vitality of mountainous catchments.

By analyzing rainfall-response dynamics of shallow groundwater and river discharge, as well as identifying the relevant geomorphological properties in an extensively equipped pre-Alpine catchment in north-east Switzerland (Rietholzbach, ~1km2), a conceptual model could be developed, which reflects the spatial organization and hydrological functioning of the landscape. It was found that only a small fraction of the entire catchment area (~25%) generates event flow, from which approximately 30% and 70% were riparian zones and hillslopes, respectively. Both landscape units differ in terms of their major hydrological and hydrogeological processes. The conceptualization was verified by a parsimonious modeling approach that accounts for spatial variability and represents catchment outflow as linear depletion of several linear storage reservoirs. The simulation results successfully reflected the hydrological behavior of the chosen case-study site.

Previous studies at the Rietholzbach catchment have demonstrated that it can be considered representative for the hydroclimatic conditions of north-east Switzerland. Thus, in a next step the minimalistic modeling framework will be applied at a larger scale in order to test its up-scaling capability, to analyze the effects of spatial organization of land use and geomorphology, as well as to identify the main limitations accompanied by the representation of distributed hydrological processes with a parsimonious approach. For this, the discharge signals of various individual pre-Alpine catchments with areas up to two magnitudes larger than the case-study site in northeast Switzerland will be simulated. A dense network of federal streamflow gauges and meteorological monitoring stations in that region provides an excellent opportunity to evaluate the modeling results with observed data. Further, effective parameters that reflect the distinct catchment-inherent streamflow generating mechanisms can be obtained by optimizing the model against the observations. This facilitates the assessment of the essential diversity of hydrologic functionality associated with landscapes and scales. The presentation will give an overview about the deployed minimalistic modeling framework and will present preliminary results at different spatial scales from several individual pre-Alpine catchments.

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