Abstract
Abstract. In this study, we explored the spatio-temporal variability of surface saturation within a forested headwater catchment using a combined simulation–observation approach. We simulated the occurrence of surface saturation in the Weierbach catchment (Luxembourg) with the physically based model HydroGeoSphere. We confronted the simulation with thermal infrared images that we acquired during a 2-year mapping campaign for seven distinct riparian areas with weekly to biweekly recurrence frequency. Observations and simulations showed similar saturation dynamics across the catchment. The observed and simulated relation of surface saturation to catchment discharge resembled a power law relationship for all investigated riparian areas but varied to a similar extent, as previously observed between catchments of different morphological and topographical characteristics. The observed spatial patterns and frequencies of surface saturation varied between and within the investigated areas and the model reproduced these spatial variations well. The good performance of the simulation suggested that surface saturation in the Weierbach catchment is largely controlled by exfiltration of groundwater into local topographic depressions. However, the simulated surface saturation contracted faster than observed, the simulated saturation dynamics were less variable between the investigated areas than observed, and the match of simulated and observed saturation patterns was not equally good in all investigated riparian areas. These mismatches between observations and simulation highlight that the intra-catchment variability of surface saturation must also result from factors that were not considered in the model set-up, such as differing subsurface structures or a differing persistence of surface saturation due to local morphological features like perennial springs.
Highlights
It is critical for flood risk assessment to understand where and when water is standing or flowing on the ground surface outside of perennial surface water bodies
Surface saturation and overland flow occur in forested, humid temperate catchments and other environments where runoff generation is dominated by subsurface flow processes, mainly – but not exclusively – due to saturation excess in the vicinity of the stream
We explored the intra-catchment variability of surface saturation in the 42 ha Weierbach catchment based on observations and physically based simulations
Summary
It is critical for flood risk assessment to understand where and when water is standing or flowing on the ground surface outside of perennial surface water bodies. Surface saturation and overland flow occur in forested, humid temperate catchments and other environments where runoff generation is dominated by subsurface flow processes, mainly – but not exclusively – due to saturation excess in the vicinity of the stream Dunne et al, 1975; Hewlett and Hibbert, 1967; Megahan and King, 1985) Such an occurrence of surface saturation and overland flow in the riparian zone can mediate a fast connection between the hillslopes and the stream, inducing quick responses of streamflow to rainfall events and influencing the mixing of different water sources and water quality in the stream Such an occurrence of surface saturation and overland flow in the riparian zone can mediate a fast connection between the hillslopes and the stream, inducing quick responses of streamflow to rainfall events and influencing the mixing of different water sources and water quality in the stream (cf. e.g. Ambroise, 2004; Birkel et al, 2010; Bracken and Croke, 2007; Tetzlaff et al, 2007; Weill et al, 2013)
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