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Water storage dynamics in a till hillslope: the foundation for modeling flows and turnover times
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Hydrology and Climate Unit, Department of Geography, University of Zurich, Zurich, Switzerland.ORCID iD: 0000-0002-6314-2124
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.ORCID iD: 0000-0002-6537-0753
Swedish University of Agricultural Sciences, Uppsala, Sweden.
2017 (English)In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 31, no 1, p. 4-14Article in journal (Refereed) Published
Abstract [en]

Studies on hydrology, biogeochemistry, or mineral weathering often rely on assumptions about flow paths, water storage dynamics, and transit times. Testing these assumptions requires detailed hydrometric data that are usually unavailable at the catchment scale. Hillslope studies provide an alternative for obtaining a better understanding, but even on such well‐defined and delimited scales, it is rare to have a comprehensive set of hydrometric observations from the water divide down to the stream that can constrain efforts to quantify water storage, movement, and turnover time. Here, we quantified water storage with daily resolution in a hillslope during the course of almost an entire year using hydrological measurements at the study site and an extended version of the vertical equilibrium model. We used an exponential function to simulate the relationship between hillslope discharge and water table; this was used to derive transmissivity profiles along the hillslope and map mean pore water velocities in the saturated zone. Based on the transmissivity profiles, the soil layer transmitting 99% of lateral flow to the stream had a depth that ranged from 8.9 m at the water divide to under 1 m closer to the stream. During the study period, the total storage of this layer varied from 1189 to 1485 mm, resulting in a turnover time of 2172 days. From the pore water velocities, we mapped the time it would take a water particle situated at any point of the saturated zone anywhere along the hillslope to exit as runoff. Our calculations point to the strengths as well as limitations of simple hydrometric data for inferring hydrological properties and water travel times in the subsurface.

Place, publisher, year, edition, pages
2017. Vol. 31, no 1, p. 4-14
Keywords [en]
flow pathways, storage, storage dynamics, turnover time
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-331679DOI: 10.1002/hyp.11046ISI: 000441296100001OAI: oai:DiVA.org:uu-331679DiVA, id: diva2:1149734
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2018-10-12Bibliographically approved
In thesis
1. The value of experimental data and modelling for exploration of hydrological functioning: The case of a till hillslope
Open this publication in new window or tab >>The value of experimental data and modelling for exploration of hydrological functioning: The case of a till hillslope
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Successfully modeling one system response (e.g. hydrograph or solute transport) sometimes gives the false sense of well-characterizing the modeled system. This is partly because of the well-known equifinality issue; during the calibration process multiple parameter combinations can produce similarly good results. One step forward towards a better-defined system is using measured (at relevant scale) values for the model parameters, as well as using multiple conditions to constrain the model.

But when not enough, or relevant, field measurements are available, virtual experiments (VE’s) can be used as a supplementary method to model calibration. The advantage of VE’s over model calibration is that they can also be used to explore assumptions both on the system hydrological processes, and on the model structure.

One goal of this study was to utilize both field measurements and models for better characterization of the S-transect hillslope, located in Västrabäcken catchment, Northern Sweden. This included (a) characteristics in space: system vertical boundaries, hydraulic parameters, pore water velocity distribution, spatial correlation of flowpaths, soil water retention properties; (b) characteristic of system’s dynamic behavior: storage – discharge relationship, transit time distribution, turnover time; and (c) outputs’ sensitivity to external forcing, and to small scale structure assumptions. The second goal was to comment on the value of field measurements and virtual experiments for extracting information about the studied system.

An intensely monitored study hillslope was chosen for this work. Although the hillslope has already been the subject of multiple field and modelling studies, there are still open questions regarding the characteristics listed above. The models used were the Vertical Equilibrium Model (VEM), and the Multiple Interacting Pathways (MIPs) model.

It was found that the hillslope was well connected; from the near-stream areas up to the water divide the storage – discharge relationship could be described as an exponential function. Also, the dynamic storage (which controls the hydrograph dynamics) was much smaller comparing to the total hillslope storage. The unsaturated soil storage was found to be more sensitive to water table positions than vertical flux magnitude. The dynamic condition of external forcing (precipitation and evapotranspiration) affected the transit time distribution (TTD) shape. And, opposite to expectations, TTD was not sensitive to micro-scale structural assumptions tested here.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 80
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1579
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:uu:diva-331856 (URN)978-91-513-0115-0 (ISBN)
Public defence
2017-12-15, 13:00 (English)
Opponent
Supervisors
Available from: 2017-11-17 Created: 2017-10-18 Last updated: 2018-03-07

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Nino, AmvrosiadiSeibert, JanGrabs, Thomas J.

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