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| Titel |
Using a physically-based water flow model to explore the dynamics of transit times and mixing in a small agricultural catchment |
| VerfasserIn |
Jie Yang, Ingo Heidbüchel, Andreas Musolff, Jan H. Fleckenstein |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143697
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| Publikation (Nr.) |
 EGU/EGU2017-7445.pdf |
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| Zusammenfassung |
| Catchment-scale transit time distributions (TTDs) for discharge and residence time
distributions of the water in storage (RTDs) are promising tools to characterize the discharge
and mixing behavior of a catchment and can help to interpret the associated solute loads to
the stream in a spatially implicit way. TTDs and RTDs are dynamic in time, influenced
by dynamic rainfall and evapotranspiration forcing, and changing groundwater
storage in the catchment. In order to understand the links between the dynamics of
TTDs and groundwater mixing in the small agricultural catchment Schäfertal, in
central Germany, a 3D hydrological model was set up for the catchment using the
fully coupled surface-subsurface numerical model HydroGeoSphere (HGS). The
model is calibrated using discharge and groundwater level measurements, and runs
transiently for a period of 10 years from 1997 to 2007. A particle tracking tool was
implemented in HGS to track the movement of water parcels in the subsurface,
outputting TTDs of channel discharge and RTDs of groundwater storage at daily
intervals.
Results show that the mean age of the discharge water is significantly younger than that of
the water in storage, indicating a poorly mixed subsurface. Discharge preferentially
samples faster flowing younger water originating from the more conductive top
parts of the aquifer. Spatial variations of the age of water in storage are observed,
highly influenced by aquifer heterogeneity. Computed StorAge Selection (SAS)
functions [Rinaldo et al. 2015] show clear shifts in the discharge sampling preferences
between wet and dry states: during wet states in winter and spring, discharge has a
preference for younger water because the shallow flow paths are active due to high
groundwater levels and low evapotranspiration. Conversely, during dry states in summer
and autumn, discharge has a preference for older water because the shallow flow
paths are inactive due to low groundwater levels and stronger evapotranspiration.
Measured nitrate (NO3) loads in discharge, mainly originating from fertilizer in
shallow soils, decrease significantly with decreasing wetness of the catchment. This
trend confirms the shifts of discharge sampling preferences between wet and dry
states.
Reference:
Rinaldo, A., P. Benettin, C. J. Harman, M. Hrachowitz, K. J. McGuire, Y. van der Velde,
E. Bertuzzo, and G. Botter (2015), Storage selection functions: A coherent framework for
quantifying how catchments store and release water and solutes, Water Resour. Res., 51,
4840–4847, doi:10.1002/2015WR017273. |
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