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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-125
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Mar 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Hydrology and Earth System Sciences (HESS) and is expected to appear here in due course.
A sprinkling experiment to quantify celerity-velocity differences at the hillslope scale
Willem J. van Verseveld1, Holly R. Barnard2, Chris B. Graham3, Jeffrey J. McDonnell4,5, J. Renée Brooks6, and Markus Weiler7 1Deltares – Catchment and Urban H ydrology Department, Delft, The Netherlands
2Institute of Arctic and Alpine Research, Department of Geography, University of Colorado, Boulder, CO, USA
3Hetchy Hetchy Water and Power, Moccasin, CA, USA
4Global Institute for Water Security and School of Environment and Sustainability, University of Saskatchewan, Saskatchewan, Canada
5School of Geoscience, University of Aberdeen, Aberdeen, Scotland
6Western Ecology Division, U.S. EPA/NHEERL., Corvallis, Oregon, USA
7Chair of Hydrology, Faculty of Environment and Natural Resources, University of Freiburg, Germany
Abstract. The difference between celerity and velocity of hillslope water flow is poorly understood. We assessed these differences by combining a 24-day hillslope sprinkling experiment with a spatially explicit hydrologic model analysis. We focused our work at Watershed 10 at the H. J. Andrews Experimental Forest in western Oregon. δ2H label was applied at the start of the sprinkler experiment. Maximum event water (δ2H labeled water) contribution was 26 % of lateral subsurface flow at 20 h. Celerities estimated from wetting front arrival times were generally much faster (on the order of 10–377 mm h−1) than average vertical velocities of δ2H (on the order of 6–17 mm h−1). In the model analysis, this was consistent with an identifiable effective porosity (fraction of total porosity available for mass transfer) parameter, indicating that subsurface mixing was controlled by an immobile soil fraction, resulting in an attenuated δ2H in lateral subsurface flow. Furthermore, exfiltrating bedrock groundwater that mixed with lateral subsurface flow captured at the experimental hillslope trench caused further reduction in the δ2H input signal. Our results suggest that soil depth variability played a significant role in the velocity-celerity responses. Deeper upslope soils damped the δ2H input signal and played an important role in the generation of the δ2H breakthrough curve. A shallow soil (~ 0.30 m depth) near the trench controlled the δ2H peak in lateral subsurface flow response. Simulated exit time and residence time distributions with the hillslope hydrologic model were consistent with our empirical analysis and provided additional insights into hydraulic behavior of the hillslope. In particular, it showed that water captured at the trench was not representative for the hydrological and mass transport behavior of the entire hillslope domain that generated total lateral subsurface flow, because of different exit time distributions for lateral subsurface flow captured at the trench and total lateral subsurface flow.

Citation: van Verseveld, W. J., Barnard, H. R., Graham, C. B., McDonnell, J. J., Brooks, J. R., and Weiler, M.: A sprinkling experiment to quantify celerity-velocity differences at the hillslope scale, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-125, in review, 2017.
Willem J. van Verseveld et al.
Willem J. van Verseveld et al.

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Short summary
How stream water responds immediately to a rainfall or snow event while the average time it takes water to travel through the hillslope can be years or decades, is poorly understood. We assessed this difference by combining a 24 day sprinkler experiment (a tracer was applied at the start) with a process based hydrologic model. Immobile soil water, deep groundwater contribution and soil depth variability explained this difference at our hillslope site.
How stream water responds immediately to a rainfall or snow event while the average time it...
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