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Rapid methods of landslide hazard mapping : Fiji case study

By D. Greenbaum, M.R. Bowker, I. Dau, H. Dropsy, K.B. Greally, A. McDonald, S.H. Marsh, K.J. Northmore, E.A. O'Connor, S. Prasad and D.G. Tragheim

Abstract

A landslide hazard probability map can help planners (1) prepare for, and/or mitigate against,\ud the effects of landsliding on communities and infrastructure, and (2) avoid or minimise the\ud risks associated with new developments. The aims of the project were to establish, by means\ud of studies in a few test areas, a generic method by which remote sensing and data analysis\ud using a geographic information system (GIS) could provide a provisional landslide hazard\ud zonation map. The provision of basic hazard information is an underpinning theme of the\ud UN’s International Decade for Natural Disaster Reduction (IDNDR). It is an essential\ud requirement for disaster preparedness and mitigation planning. This report forms part of BGS\ud project 92/7 (R5554) ‘Rapid assessment of landslip hazards’ Carried out under the ODA/BGS\ud Technology Development and Research Programme as part of the British Government’s\ud provision of aid to developing countries. It provides a detailed technical account of work\ud undertaken in a test area in Viti Levu in collaboration with Fiji Mineral Resources\ud Department. The study represents a demonstration of a methodology that is applicable to\ud many developing countries.\ud The underlying principle is that relationships between past landsliding events, interpreted\ud from remote sensing, and factors such as the geology, relief, soils etc provide the basis for\ud modelling where future landslides are most likely to occur. This is achieved using a GIS by\ud ‘weighting’ each class of each variable (e.g. each lithology ‘class’ of the variable ‘geology’)\ud according to the proportion of landslides occurring within it compared to the regional\ud average. Combinations of variables, produced by summing the weights in individual classes,\ud provide ‘models’ of landslide probability. The approach is empirical but has the advantage\ud of potentially being able to provide regional scale hazard maps over large areas quickly and\ud cheaply; this is unlikely to be achieved using conventional ground-based geotechnical\ud methods.\ud In Fiji, landslides are usually triggered by intense rain storms commonly associated with\ud tropical cyclones. However, the regional distribution of landslides has not been mapped nor\ud is it known how far geology and landscape influence the location and severity of landsliding\ud events. The report discusses the remote sensing and GIS methodology, and describes the\ud results of the pilot study over an area of 713 km2 in south east Viti Levu. The landslide\ud model uses geology, elevation, slope angle, slope aspect, soil type, and forest cover as\ud inputs. The resulting provisional landslide hazard zonation map, divided into high, medium\ud and low zones of landslide hazard probability, suggests that whilst rainfall is the immediate\ud cause, others controls do exert a significant influence. It is recommended that consideration\ud be given in Fiji to implementing the techniques as part of a national strategic plan for\ud landslide hazard zonation mapping

Publisher: British Geological Survey
Year: 1995
OAI identifier: oai:nora.nerc.ac.uk:9374

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