Process identification through rejection of model structures in a mid-mountainous rural catchment: observations of rainfall-runoff response, geophysical conditions and model inter-comparison

• Published in: Hydrological processes Vol. 23; no. 5; pp. 702 - 718
• Main Authors: Graeff, Thomas, Zehe, Erwin, Reusser, Dominik, Lück, Erika, Schröder, Boris, Wenk, Gerald, John, Hermann, Bronstert, Axel
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 28.02.2009; Wiley
• Subjects: bimodal runoff response; Earth sciences; Earth, ocean, space; electrical resistivity tomography; Exact sciences and technology; generalized linear model; groundwater displacement; Hydrogeology; Hydrology; Hydrology. Hydrogeology; rejection; subsurface stormflow; threshold; Harz Mountains; Central Europe; Europe; Germany; ground water; rain water; threshold; drainage basins; hydraulic conductivity; aquifers; tomography; discharge; water content; rural areas; flow; electrical resistivity; electrical resistivity tomography; rainfall; atmospheric precipitation; runoff; bimodal runoff response; hydrodynamics; subsurface; linear models; rejection; subsurface stormflow; surface water; generalized linear model; depth; prediction; groundwater displacement; statistical analysis; errors; storms
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.7171

The intention of the presented study is to gain a better understanding of the mechanisms that caused the bimodal rainfall-runoff responses which occurred up to the mid-1970s regularly in the Schäfertal catchment and vanished after the onset of mining activities. Understanding this process is a first step to understanding the ongoing hydrological change in this area. It is hypothesized that either subsurface stormflow, or fast displacement of groundwater could cause the second delayed peak. A top-down analysis of rainfall-runoff data, field observations as well as process modelling are combined within a rejectionistic framework. A statistical analysis is used to test whether different predictors, which characterize the forcing, near surface water content and deeper subsurface store, allow the prediction of the type of rainfall-runoff response. Regression analysis is used with generalized linear models as they can deal with non-Gaussian error distributions as well as a non-stationary variance. The analysis reveals that the dominant predictors are the pre-event discharge (proxy of state of the groundwater store) and the precipitation amount. In the field campaign, the subsurface at a representative hillslope was investigated by means of electrical resistivity tomography in order to identify possible strata as flow paths for subsurface stormflow. A low resistivity in approximately 4 m depth--either due to a less permeable layer or the groundwater surface--was detected. The former could serve as a flow path for subsurface stormflow. Finally, the physical-based hydrological model CATFLOW and the groundwater model FEFLOW are compared with respect to their ability to reproduce the bimodal runoff responses. The groundwater model is able to reproduce the observations, although it uses only an abstract representation of the hillslopes. Process model analysis as well as statistical analysis strongly suggest that fast displacement of groundwater is the dominant process underlying the bimodal runoff reactions. Copyright © 2009 John Wiley & Sons, Ltd.