CLIFFS - climate impact forecasting for slopes
Slope instability of both natural and constructed slopes presently has a significant impact on the built environment and infrastructure in the UK. The topography, geology, present and past climatic conditions and human modification of the landscape result in slope processes being active over a significant area of the UK.
Many tens of thousands of people live with continuing slope instability or the threat of instability. This includes many population centres on actively eroding coasts (e.g. Ventnor, Lyme Regis, Holderness) and on inland slopes (e.g. London, Edinburgh, South Wales Coalfield).
Thousands of kilometres of transport links and utilities are located in areas susceptible to failure of natural slopes. In addition, construction often involves the formation of cut and fill slopes that can also become unstable.
Slope instability can have a major detrimental affect on the UK’s infrastructure as demonstrated by the disruption of the road and rail networks resulting from the many slope failures that occurred during the period of high precipitation in winter 2000/2001.
Climate change will have important consequences for the activity of mass movement processes on slopes. Groundwater pressures are a controlling factor for the stability of soil and rock slopes and their magnitude and distribution, which vary both spatially and temporally, are dependent upon climate.
Climate change models predict an increasing rate of change of seasonal and inter-annual variations in precipitation and temperature during the next 100 years. As a consequence, the evapotranspiration-precipitation balance will change. This will affect the hydrological environment governing the majority of mass movements in the UK through, for example, changes in antecedent pore pressures and alteration of trigger event magnitudes. This in turn will lead to a change in the frequency, distribution and mode of landsliding in the UK.
Landscape sensitivity, in terms of the degree to which it can cope with these rates of change, should therefore be considered as a consequence of combined changes in the triggers (e.g. precipitation events) and preparatory factors (e.g. the antecedent groundwater conditions). It is clear that climate change will significantly modify these and other controlling variables (such as land-use, vegetation cover and soil water chemistry).
To date, studies have assessed the consequences for triggering first-time landslides at individual sites (both natural and constructed). More focused generic research has recently started. For example the CRANIUM project - analysing uncertainty and making robust risk-based decisions for infrastructure design and management in the face of climate change - and the BIONICS embankment project.
However, the general process-response issues are still not well understood. This problem is exacerbated by poor communication between groups involved in research, consultancy and the stakeholders (although project specific groupings do exist).
Current limited understanding and the dearth of data has major implications for both land use and construction. At present, planners use geological maps produced by the British Geological Survey that show areas of past slope instability to help inform decisions on future land use. At the detailed design stage of a project, slope stability assessment is carried out using past records of groundwater levels and/or measurements made during a site investigation (often over a limited time period). These assessments of stability are valid only as long as the groundwater conditions are relevant (i.e. a steady state is assumed).
With the projected climate change scenarios this is not a valid assumption because the time period over which designs and land use decisions are being used can readily exceed 50 years. It is thus questionable whether the information is relevant at best, or misleading at worst.
Forecast scenarios of slope instability and distribution must therefore be developed. These must be communicated as widely as possible to make stakeholders and the general public aware of the scientifically feasible refinements in confidence level and potential societal impact. This approach will cover both constructed (cuttings and embankments) and natural slopes (inland and coastal).
Improved understanding of slope dynamics under changing climate conditions will assist the development of appropriate engineering solutions for the economic design and the optimum management of constructed and natural slopes.
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