The development of a national Geographic Information System (GIS) for British karst geohazards and risk assessment

Britain has four main types of karstic rocks, limestone, chalk, gypsum and salt, each with a different character and associated problems. Subsidence problems, difficult engineering and foundation conditions are widespread on these rocks. The triggering of subsidence by water abstraction and the enhancement of dissolution processes are relevant to some areas. Aquifer vulnerability and pollution tracing are concerns in most areas, especially the chalk, which is the major aquifer in southern Britain. The British Geological Survey has embarked on a comprehensive digitisation scheme of the base 1:50,000 scale geological map information. In conjunction with this, the recording and assessment of geological hazards, including karst problems, are being undertaken to provide complementary digital information that enhances the basic map data. Digital map capture has been established at 1: 10,000 scale using a customised interface with the ArcView GIS application. For the karst geohazards, this application is being extended to allow the digitisation of the karst features and the population of the associated Oracle database tables. For each type of karst feature, polygon or point attributes will be defined with suitable dictionaries for the appropriate morphological, stratigraphical or lithological entities. Linked features and databases for springs, stream sinks, dye tracing are being developed, tied to the existing hydrochemistry tables where appropriate. Cave survey and plan data derived from published sources may also be incorporated. From the factual data, hazard areas will be derived. When the GIS is fully established and populated, the system will highlight the presence of karst features to non-specialists and allow the rapid interpretation of potentially hazardous karst areas by geological, hydrogeological and engineering geologists. With suitable links to polygon feature descriptions, basic geological reports derived semiautomatically are also feasible. The GIS will act as a desktop data capture facility with the intention that it can, ultimately, be extended to the capture in the field of information when suitable portable, robust computers become available.