Revealing principles of hydrological response – The Schaefertal approach

Thursday, 25 September 2014
Ute Wollschlaeger1, Thomas Grau2, Edoardo Martini2, Markus Neubauer3, Andreas Schmidt2, Martin Schrön3, Ingmar Schroeter3, Peter Dietrich4, Jan H Fleckenstein1, Angela Lausch3, Andreas Musolff2, Hendrik Paasche2, Frido Reinstorf5, Hans-Joerg Vogel6, Ulrike Werban3 and Steffen Zacharias7, (1)UFZ, Leipzig, Germany, (2)Helmholtz Centre for Environmental Research - UFZ, Leipzig, Germany, (3)Helmholtz Centre for Environmental Research UFZ Leipzig, Leipzig, Germany, (4)Helmholtz Centre for Environmental Research UFZ Leipzig, Taucha, Germany, (5)University of Applied Sciences Magdeburg-Stendal, Magdeburg, Germany, (6)Helmholtz Centre for Environmental Research UFZ Halle, Halle, Germany, (7)Helmholtz Centre Env. Res., Leipzig, Germany
Abstract:
Abstract

The Schaefertal catchment is one of the intensive research sites in the TERENO Harz/Central German Lowland Observatory. During the last years it has been equipped with a multi-scale monitoring framework for measuring soil moisture content from the point to the small catchment scale. Research in the Schaefertal catchment predominantly aims at the physical description of hydrological processes at the small catchment scale with the aid of new measurement technologies and numerical models. Knowledge gained from these intensive measurements and related detailed process studies will in the future be used to transfer observation and monitoring concepts and process understanding to larger or less instrumented catchments.

Site description and instrumentation

The Schaefertal catchment (51°39'N, 11°03'E) is a low mountain headwater catchment in the Lower Harz Mountains covering an area of 1.44 km2 (e.g., Borchardt, 1982). Hydrological research in the catchment started in 1968, when a runoff gauging station with subsurface barrage that collects the total surface and subsurface outflow from the catchment as well as a meteorological station were installed (Reinstorf et al., 2010). Since these early investigations, a main focus of research in the Schaefertal has been on the characteristics of the long-term water balance at the landscape scale including feedbacks and interactions with climatological, pedological, geological, topographical, and ecological factors (Wenk, 2004, unpublished report). Currently, the catchment is operated by the University of Applied Sciences Magdeburg-Stendal which continuously extended and modernised the research infrastructure. Today, it comprises a modern climate station, a dense groundwater observation network, a multi-parameter water quality probe and automated sampler at the catchment outlet, and several plots to measure soil water content, soil water potential as well as snow water equivalent (Reinstorf et al., 2010). For numerous variables, records dating back to the 1960's are available. Due to more than 40 years of research in the Schaefertal the geological and pedological as well as the hydrological (e.g. Borchardt, 1982; Becker and McDonnell, 1998; Graeff et al., 2009; Reinstorf et al., 2010; Ollesch et al., 2010) characteristics of the catchment are very well known today and provide excellent conditions for testing novel measurement and modelling approaches for understanding the hydrological functioning of the catchment.

To reach this goal, the already existing research infrastructure of the Schaefertal catchment has recently been extended by a number of new state-of-the-art measurement technologies with a focus on the monitoring of soil moisture content at different scales (Fig. 1). At the point scale, modern high-precision lysimeters (e.g. TERENO SoilCan; Puetz et al., 2011) allow for a detailed monitoring of soil moisture dynamics and the separation of the different water balance components. In addition, a Vadose Zone Monitoring System (VAMOS) consisting of a lysimeter and a similarly instrumented measurement chamber at the position of lysimeter excavation allows for the identification of lateral flow processes in the undisturbed field soil, a process which cannot be determined using standard lysimeters. At the hillslope scale, a wireless monitoring network (Bogena et al., 2011; Qu et al., 2013) provides spatially distributed information about soil moisture and soil temperature dynamics from three different depths and helps to identify the dominant hillslope hydrological processes. In addition, at the same hillslope, a time-lapse digital snow camera allows for the quantification of snow accumulation and melt and, in combination with the wireless sensor network, the analysis of near surface freeze/thaw processes. At the even larger scale, four cosmic ray soil moisture probes (Zreda et al., 2012) are being employed to continuously and non-invasively monitor integral values of soil moisture content with a footprint area of approximately 600 m and up to 70 cm depth. This continuous monitoring is complemented by campaign-based measurements of soil moisture content or soil moisture proxies using traditional (e.g. TDR), geophysical (e.g., electromagnetic induction (EMI), gamma spectroscopy), mobile cosmic ray surveys as well as airborne and space borne remote sensing techniques (predominantly hyperspectral (e.g. Lausch et al., 2013; Pause et al., 2014) and active radar (SAR) measurements). With this, a unique research infrastructure is available which provides on the one hand static spatial information about soil properties and, on the other hand, temporally dynamic information about state variables. Both assist in the identification of hydrological processes within the catchment at different spatial and temporal scales.

Figure 1: Infrastructure for multi-scale measurement of soil moisture in the Schaefertal catchment

Exploring the functioning of the Schaefertal catchment

Research in the Schaefertal catchment primarily focuses on the understanding of hydrological processes from the point to the small catchment scale. The main difficulty in hydrological modelling at the catchment scale is the consideration of subsurface heterogeneity of hydraulic properties which follows the structure of the underlying geology and soil formation. In addition, rainfall, evapotranspiration and snowmelt lead to strong temporal dynamics of the system. The combination of heterogeneity and temporal forcing results in dynamic flow networks which determine transport velocities and residence times within the different parts of the catchment.

In our research approach, we seek to identify the hydrologically relevant structural patterns by continuous or campaign-based monitoring of soil moisture at various scales which is complemented by time lapse geophysical (EMI, gamma spectroscopy) and remote sensing measurements (hyperspectral, thermal, active radar (SAR)) and, perspectively, by estimating the spatial distribution of soil types and soil depths based on modelling of soil formation. The joint evaluation of the various datasets leads to an estimation of the explicit spatial pattern of regions having similar hydraulic properties. Based on these patterns, the local hydraulic properties can be estimated from the continuous or campaign-based monitoring of soil moisture at different scales. Finally, we will be in the position to evaluate to what detail the hydraulic structure needs to be known to arrive at a consistent description.

This structural information will be an essential part for modelling catchment-scale water and solute dynamics. The time water needs to travel through the catchment's subsurface is a fundamental parameter modulating catchment solute export. Our research aims at revealing the dominant controls of travel time distribution in catchments. Using physically-based catchment scale numerical models of surface water flow as well as water flow in the unsaturated zone and in groundwater we evaluate the spatial and temporal characteristics of travel time distribution within the catchment. We hypothesize that the probability distribution of travel times (i.e. the age distribution) of water leaving the catchment and of water residing in the catchment storage significantly deviate from each other as a result of climatic forcing. Based on the numerical models we want to assess the detail of information needed and the use of simplified modelling tools to sufficiently characterize dynamic travel time distributions. This allows to transfer the approach to less data-rich catchments and to larger scales.

References:

Becker, A., McDonnell, J.J. (1998): Topographical and ecological controls of runoff generation and lateral flows in mountain catchments. In: Hydrology, Water Resources and Ecology in Headwaters (Proceedings of the HeadWater'98 Conference held at Meran/Merano, Italy, April 1998). IAHS Publ. no. 248.

Bogena, H.R., Herbst, M., Huisman, J.A., Rosenbaum, U., Weuthen, A., Vereecken, H. (2010): Potential of wireless sensor networks for measuring soil water content variability. Vadose Zone J., 9, 1002-1013, doi:10.2136/vzj2009.0173.

Borchardt, D. (1982): Geooekologische Erkundung und hydrologische Analyse von Kleineinzugsgebieten des unteren Mittelgebirgsbereichs, dargestellt am Beispiel von Experimentalgebieten der oberen Selke/Harz. Petermanns Geographische Mitteilungen, 126(4), 251-262 (in German).

Desilets, D., Zreda, M., Ferre, T.P.A (2010): Nature's neutron probe: Land surface hydrology at an elusive scale with cosmic rays. Water Resour. Res., 46, W11505, doi:10.1029/2009WR008726.

Graeff, Th., Zehe, E., Reusser, D., Lueck, E., Schroeder, B., Wenk, G., John, H., Bronstert, A. (2009): Process identification through rejection of model structures in a mid-mountainous rural catchment: observations of rainfall-runoff response, geophysical conditions and model inter-comparison. Hydrol. Process., 23, 702-718, doi:10.1002/hyp.7171.

Lausch, A., Zacharias, S., Dierke, C., Pause, M., Kuehn, I., Doktor, D., Dietrich, P., Werban, U., 2013. Analysis of vegetation and soil pattern using hyperspectral remote sensing, EMI and Gamma ray measurements. Vadose Zone Journal, doi:10.2136/vzj2012.0217.

Ollesch, G., John, H., Meissner, R. Reinstorf, F. (2010): Anthropogenic alteration of water balance and runoff processes in a small low mountain catchment, Status and Perspectives of Hydrology in Small Basins, IAHS Publ. 336, 2010.

Pause, M., Lausch, A., Bernhardt, M., Hacker, J., Schulz, K., 2014. Improving soil moisture retrieval from airborne L-band radiometer data by considering spatially varying roughness. Canadian Journal of Remote Sensing, Doi: 10.1080/07038992.2014.907522.

Puetz, Th., Kiese, R., Zacharias, S., Bogena, H., Priesack, E. Wollschlaeger, U., Schwank, M., Papen, H., von Unold, G., Vereecken, H. (2011): TERENO-SOILCan - Ein Lysimeter Netzwerk in Deutschland. Proceedings 14. Gumpensteiner Lysimetertagung 2011, 5-10. (in German).

Qu, W., Bogena, H.R., Huisman, J.A., Bvereecken, H. (2013): Calibration of a novel low-cost soil water content sensor based on a ring oscillator. Vadose Zone J., doi:10.2136/vzj2012.0139.

Reinstorf, F., Tiedge, J., Bauspiess, J., John, H., Ollesch, G. (2010): Time series modelling in the Schaefertal catchment in the Lower Harz Mountains/Central Germany, Status and Perspectives of Hydrology in Small Basins, IAHS Publ. 336.

Wenk, G. (2004). Die hydrologischen Untersuchungsgebiete Schaefertal und Waldbach im Unterharz. unpublished report, University of Applied Sciences Magdeburg-Stendal (in German).

Zreda, M., Shuttleworth, W.J., Zeng, X., Zweck, C., Desilets, D., Franz, T., Rosolem, R., Ferre, T.P.A. (2012): The Cosmic-ray Soil Moisture Observing System, Hydrol. Earth Syst. Sci., 16, 4079-4099, doi:10.5194/hess-16-4079-2012.

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