Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 13 11 2009 10.5194/hess-13-2105-2009 http://www.hydrol-earth-syst-sci.net/13/2105/2009/ http://www.hydrol-earth-syst-sci.net/13/2105/2009/hess-13-2105-2009.html http://www.hydrol-earth-syst-sci.net/13/2105/2009/hess-13-2105-2009.pdf 2105 2118 2009-11-06 Hillslope hydrology under glass: confronting fundamental questions of soil-water-biota co-evolution at Biosphere 2 L. Hopp luisa.hopp@oregonstate.edu C. Harman S. L. E. Desilets C. B. Graham J. J. McDonnell P. A. Troch Department of Forest Engineering, Resources and Management, Oregon State University, Corvallis, USA Department of Geography, University of Illinois at Urbana-Champaign, USA Department of Hydrology and Water Resources, The University of Arizona, Tucson, USA Department of Crop and Soil Sciences, The Pennsylvania State University, University Park, USA Recent studies have called for a new unifying hydrological theory at the hillslope and watershed scale, emphasizing the importance of coupled process understanding of the interactions between hydrology, ecology, pedology, geochemistry and geomorphology. The Biosphere 2 Hillslope Experiment is aimed at tackling this challenge and exploring how climate, soil and vegetation interact and drive the evolution of the hydrologic hillslope behavior. A set of three large-scale hillslopes (18 m by 33 m each) will be built in the climate-controlled experimental biome of the Biosphere 2 facility near Tucson, Arizona, USA. By minimizing the initial physical complexity of these hillslopes, the spontaneous formation of flow pathways, soil spatial heterogeneity, surface morphology and vegetation patterns can be observed over time. This paper documents the hydrologic design process for the Biosphere 2 Hillslope Experiment, which was based on design principles agreed upon among the Biosphere 2 science community. Main design principles were that the hillslopes should promote spatiotemporal variability of hydrological states and fluxes, facilitate transient lateral subsurface flow without inducing overland flow and be capable of supporting vegetation. Hydrologic modeling was used to identify a hillslope configuration (geometry, soil texture, soil depth) that meets the design objectives. The recommended design for the hillslopes consists of a zero-order basin shape with a 10 degree overall slope, a uniform soil depth of 1 m and a loamy sand soil texture. 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