Variability in soil-water retention properties and implications for physics-based simulation of landslide early warning criteria
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Rainfall-induced shallow landsliding is a persistent hazard to human life and property. Despite the observed connection between infiltration through the unsaturated zone and shallow landslide initiation, there is considerable uncertainty in how estimates of unsaturated soil-water retention properties affect slope stability assessment. This source of uncertainty is critical to evaluating the utility of physics-based hydrologic modeling as a tool for landslide early warning. We employ a numerical model of variably saturated groundwater flow parameterized with an ensemble of texture-, laboratory-, and field-based estimates of soil-water retention properties for an extensively monitored landslide-prone site in the San Francisco Bay Area, CA, USA. Simulations of soil-water content, pore-water pressure, and the resultant factor of safety show considerable variability across and within these different parameter estimation techniques. In particular, we demonstrate that with the same permeability structure imposed across all simulations, the variability in soil-water retention properties strongly influences predictions of positive pore-water pressure coincident with widespread shallow landsliding. We also find that the ensemble of soil-water retention properties imposes an order-of-magnitude and nearly two-fold variability in seasonal and event-scale landslide susceptibility, respectively. Despite the reduced factor of safety uncertainty during wet conditions, parameters that control the dry end of the soil-water retention function markedly impact the ability of a hydrologic model to capture soil-water content dynamics observed in the field. These results suggest that variability in soil-water retention properties should be considered for objective physics-based simulation of landslide early warning criteria.
KeywordsHillslope hydrology Unsaturated zone Shallow landslides Numerical modeling Early warning
The East Bay Municipal Utility District facilitated access to the BALT1 site. Jonathan Stock, Kevin Schmidt, Mark Reid, and Skye Corbett provided invaluable field assistance. The authors appreciate the constructive comments provided by William Schulz, Anderson Ward, and two anonymous reviewers on earlier versions of this work.
This study was supported in part by a National Science Foundation grant (CMMI-1561764) awarded to Ning Lu.
Compliance with ethical standards
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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