Field comparison of selected methods for vertical soil water content profiling T. Vienken a,⇑ , E. Reboulet b,1 , C. Leven c,2 , M. Kreck a,3 , L. Zschornack a,4 , P. Dietrich a,c,5 a UFZ – Helmholtz Centre for Environmental Research, Department Monitoring and Exploration Technologies, Permoserstraße 15, 04318 Leipzig, Germany b Kansas Geological Survey, University of Kansas, 1930 Constant Ave., Lawrence, KS 66047-3726, USA c University of Tübingen, Center for Applied Geoscience, Hölderlinstr. 12, 72076 Tübingen, Germany article info Article history: Received 2 March 2013 Received in revised form 29 July 2013 Accepted 5 August 2013 Available online 12 August 2013 This manuscript was handled by Peter K. Kitanidis, Editor-in-Chief, with the assistance of Niklas Linde, Associate Editor Keywords: Vertical soil water content profiling Direct push Gravimetric analysis Neutron probe Water Content Profiler summary High-resolution information about vertical variations in soil water content is important for applications ranging from agricultural water management to flow and transport modeling. Commonly applied tools for the investigation of vertical soil water content distribution in hydrogeological field investigations are: gravimetric laboratory analyses of soil samples, logging a cased borehole using a tool with a radio- active source (neutron probe), or yet less well established, direct push-based moisture sensor probes. Due to differences in their underlying measurement principles as well as different operation modes, each of the aforementioned methods is associated with certain advantages and limitations. A common field eval- uation of these methods has not been performed until now – raising the question of how well these indi- vidual methods perform when applied under different depositional and hydrogeological conditions. For field evaluation direct push-profiling was performed at three different test sites under different hydro- geological settings and varying degree of sediment heterogeneity and compared with results obtained from gravimetric analysis of soil cores and neutron probe measurements. In direct comparison the applied direct push-based Water Content Profiler proved to be a suitable alternative to neutron probe technology for measuring the vertical water content distribution. Moreover, the Water Content Profiler proved to be advantageous over gravimetric analysis in terms vertical resolution and time efficiency. Results of this study identify application-specific limitations of the methods and thereby highlight the need for careful data evaluation, even though some of the methods described in this paper are well established. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The importance of determining volumetric soil water content (h) has been long recognized in hydrology (see amongst others Robinson et al., 2008; Vereecken et al., 2008). Application exam- ples include agricultural water management (Michot et al., 2003; Iqbal et al., 2005; Cassiani et al., 2012), water resources manage- ment (Sciuto and Diekkruger, 2010; Bales et al., 2011; Swarowsky et al., 2011), and ecology (Kieft et al., 1993; Sandvig and Phillips, 2006). Thereby, knowledge of the spatial distribution of soil water content is a prerequisite for the parameterization and calibration of flow related models. In addition, soil moisture content determi- nation is an efficient way to estimate total porosity of sedimentary aquifers in the phreatic zone. A variety of experimental techniques to determine volumetric soil water content is available; see Dobri- yal et al. (2012) for a review. For vertical (semi)-continuous profil- ing of soil water content distributions (in depths of up to tenths of meters), approaches such as gravimetric analyses of soil samples, borehole logging methods, and direct push (DP)-based sensor probes are applicable. Borehole logging methods include neutron probe (NP), gamma, and nuclear magnetic resonance (NMR) log- ging technology; see amongst others for a detailed overview and further references: Keys (1990), Serra and Serra (2004), and Kobr et al. (2005). A recent development is the application of NMR in small diameter wells (Walsh et al., (2013). Another commonly- used technique is Time Domain Reflectometry (TDR), however, it is often limited to shallow depths or excavations. A rather novel exploration strategy is the application of non-invasive surface geo- physics to map the vertical distribution of soil water content, such as ground penetrating radar (GPR) and surface NMR data, see 0022-1694/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhydrol.2013.08.004 ⇑ Corresponding author. Tel.: +49 (0) 341 235 1382; fax: +49 (0) 341 235 451382. E-mail addresses: thomas.vienken@ufz.de (T. Vienken), reboulet@kgs.ku.edu (E. Reboulet), carsten.leven-pfister@uni-tuebingen.de (C. Leven), manuel.kreck@ ufz.de (M. Kreck), ludwig.zschornack@ufz.de (L. Zschornack), peter.dietrich@ufz.de (P. Dietrich). 1 Tel.: +1 785 864 2173; fax: +1 785 864 5317. 2 Tel.: +49 (0) 7071 29 73168; fax: +49 (0) 7071 29 50 59. 3 Tel.: +49 (0) 341 235 1006; fax: +49 (0) 341 235 1939. 4 Tel.: +49 (0) 341 235 1382; fax: +49 (0) 341 235 1939. 5 Tel.: +49 (0) 341 235 1281; fax: +49 (0) 341 235 1939. Journal of Hydrology 501 (2013) 205–212 Contents lists available at ScienceDirect Journal of Hydrology journal homepage: www.elsevier.com/locate/jhydrol