Landslide hazard mapping and impact in the Holywell area of NE Wales

Abstract

Landslide hazard within urban environments in the UK is largely attributable to two distinct, but not mutually exclusive, types of landslide activity: i) relict landslides in the landscape that predate urban development, and whose presence may or may not have been known about at the time of development; and ii) new slope movements that postdate urban developments. Significant efforts have been made to delimit and categorise the hazard posed by relict slides through, for example, demarcation of known landslides on 1:50 000 maps produced by the British Geological Survey and the compilation of regional databases of landslide activity produced as part of the UK national landslides survey (e.g. Jones and Lee, 1994). This survey showed that much of the relict landsliding in the UK was originally the product of significant climate and environmental changes that followed on from the end of the last (Devensian) glaciation, and that many of these features are now stable in the British landscape, but with the potential to be reactivated either through human mismanagement and/or deteriorating environmental conditions; e.g. changing rainfall patterns linked to climate change (Jones, 1993; Arnell and Reynard 1996; Collison et al., 2000; Environment Agency, 2010). The mapping of landslide susceptibility beyond these relict features is far less complete within the UK, and varies in terms of the methodologies used. One common characteristic of many smaller scale studies is the assumption that the location and type of relict landsliding in an area can be extrapolated to identify new areas with similar geological and geomorphological characteristics that might be susceptible to failure in the future (Siddle, 2000). This assumption is explored in this paper with reference to the physical evidence for landslide damage within a moderately built up area of NE Wales. The research utilises the spatial analysis capabilities of Geographical Information Systems (GIS) to produce slope susceptibility maps using hazard controlling parameters identified from relict landslides, and then explores the relationship between the relict and anticipated landslide hazard with physical evidence for landslide impact upon aspects of the built environment.