Embankment dam probabilistic assessment for climate scenarios

For small earthfill dams exposed to climate scenarios such as those defined in UKCP09, deterministic assessments are insufficient, and more sophisticated models are required. This paper presents a hybrid probabilistic methodology that quantitatively measures the notional reliability index against upstream and downstream slope failure for such dams exposed to variable precipitation. Upstream and downstream slope stability are selected here as representative significant limit states governing the dam's long-term performance. The governing equations for the limit states are defined using the sliding-block method incorporating the effects of infiltration through the embankment. Using standard and sloping Green-Ampt and closed-form van Genuchten methods, the rainfall effects on soils with variable saturation are considered, and the standard first-order second moment method is applied. The probabilistic model encompasses uncertainties associated with soil properties, dam geometry and rainfall parameters. The paper demonstrates notional reliability indices for the dam for selected precipitation scenarios. A benchmark is developed that reflects the critical conditions conducive to slope failure. The paper reflects on the implication of inclusion of probabilistic climate models for associated risks. Therefore the analysis is an effective new management tool for risk assessment of embankment dams as categorised by the Flood and Water Management Act 2010.