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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 5
Hydrol. Earth Syst. Sci., 18, 1873–1883, 2014
https://doi.org/10.5194/hess-18-1873-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Hydrol. Earth Syst. Sci., 18, 1873–1883, 2014
https://doi.org/10.5194/hess-18-1873-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 May 2014

Research article | 22 May 2014

Incipient subsurface heterogeneity and its effect on overland flow generation – insight from a modeling study of the first experiment at the Biosphere 2 Landscape Evolution Observatory

G.-Y. Niu1,2, D. Pasetto3,4, C. Scudeler3, C. Paniconi3, M. Putti4, P. A. Troch1,2,**, S. B. DeLong1,*, K. Dontsova1, L. Pangle1, D. D. Breshears5,**, J. Chorover6,**, T. E. Huxman7,**, J. Pelletier8,**, S. R. Saleska9,**, and X. Zeng10,** G.-Y. Niu et al.
  • 1Biosphere 2, University of Arizona, Tucson, AZ, USA
  • 2Department of Hydrology and Water Resources, the University of Arizona, Tucson, AZ, USA
  • 3Institut National de la Recherche Scientifique, Centre Eau Terre Environnement (INRS-ETE), Université du Québec, Quebec City, Canada
  • 4Department of Mathematics, University of Padova, Padova, Italy
  • 5School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA
  • 6Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ, USA
  • 7Ecology and Evolutionary Biology, University of California, Irvine, CA, USA
  • 8Department of Geosciences University of Arizona, Tucson, AZ, USA
  • 9Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA
  • 10Department of Atmospheric Sciences, University of Arizona, Tucson, AZ, USA
  • *now at: United State Geological Survey, Menlo Park, CA, USA
  • **LEO Research and Design Team, Tucson, AZ, USA

Abstract. Evolution of landscape heterogeneity is controlled by coupled Earth system dynamics, and the resulting process complexity is a major hurdle to cross towards a unified theory of catchment hydrology. The Biosphere 2 Landscape Evolution Observatory (LEO), a 334.5 m2 artificial hillslope built with homogeneous soil, may have evolved into heterogeneous soil during the first experiment driven by an intense rainfall event. The experiment produced predominantly seepage face water outflow, but also generated overland flow, causing superficial erosion and the formation of a small channel. In this paper, we explore the hypothesis of incipient heterogeneity development in LEO and its effect on overland flow generation by comparing the modeling results from a three-dimensional physically based hydrological model with measurements of total mass change and seepage face flow. Our null hypothesis is that the soil is hydraulically homogeneous, while the alternative hypothesis is that LEO developed downstream heterogeneity from transport of fine sediments driven by saturated subsurface flow. The heterogeneous case is modeled by assigning saturated hydraulic conductivity at the LEO seepage face (Ksat,sf) different from that of the rest (Ksat). A range of values for Ksat, Ksat,sf, soil porosity, and pore size distribution is used to account for uncertainties in estimating these parameters, resulting in more than 20 000 simulations. It is found that the best runs under the heterogeneous soil hypothesis produce smaller errors than those under the null hypothesis, and that the heterogeneous runs yield a higher probability of best model performance than the homogeneous runs. These results support the alternative hypothesis of localized incipient heterogeneity of the LEO soil, which facilitated generation of overland flow. This modeling study of the first LEO experiment suggests an important role of coupled water and sediment transport processes in the evolution of subsurface heterogeneity and on overland flow generation, highlighting the need of a coupled modeling system that integrates across disciplinary processes.

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