Investigation of hydrological response of three identical artificial hillslopes at the Landscape Evolution Observatory

Hydrological processes at the hillslope scale are complex due to subsurface heterogeneity, and monitoring hillslopes with a large number of sensors or replicate experimental designs is rarely feasible. The Landscape Evolution Observatory (LEO) at Biosphere 2 consists of three replicated, large (330 m²) artificial hillslopes (East, Center and West) packed with 1-m depth of initially homogeneous, basaltic soil. Each landscape contains a spatially dense network of sensors capable of resolving meter-scale lateral heterogeneity and sub-meter scale vertical heterogeneity in moisture content and water potential, as well as the hillslope-integrated water balance components. A 45-day experiment was conducted on the 3 hillslopes where a series of irrigation sequences brought the hillslopes to a periodic steady state. The storage, discharge and moisture states of the hillslopes were monitored throughout the experiment. The data shows that the initially identically built hillslopes showed significant differences in their hydrologic response. We used CAThment HYdrology (CATHY), a 3-dimensional hydrologic model; in order to understand how small-scale heterogeneities in soil water retention characteristics can lead to significant differences in the hydrologic response of the hillslopes. We also aimed to understand how a dense network of water content and matric potential can be used to acquire hillslope scale soil water retention characteristic curves that capture the storage-discharge behavior of the system.