Report No. : GEO Report No. 138 (Second Edition)

Report Title : Guidelines for Natural Terrain Hazard Studies, Second Edition (2016), 173 p.

Author : H.Y. Ho & K.J. Roberts

Abstract

Natural terrain covers about 60% of the land area of the Hong Kong Special Administrative Region. Urban expansion in Hong Kong is gradually encroaching further upon the steeper natural hillsides that fringe the urban area. Landsliding on these hillsides during intense rainfall is common and can be widespread, and has led to extensive studies of natural terrain landslide processes, the implementation of control procedures to ensure safe development, and systematic mitigation of the landslide risk through the Landslip Prevention and Mitigation Programme (LPMitP).

For existing development, the current strategy for study and mitigation of natural terrain landslide risk is founded on the 'react-to-known-hazard' principle. Natural terrain is now systematically dealt with under the LPMitP, which commenced in 2010.

For new development, the preferred technical approach for dealing with natural terrain hazards is to mitigate the risk through implementation of hazard mitigation measures, adjustments to the facility layout or providing buffer zones, in preference to carrying out stabilization works to large areas of natural terrain, which may be both impractical and environmentally damaging.

This report documents current recommended practice and procedures for studying natural terrain hazards. A Natural Terrain Hazard Study (NTHS) normally includes desk study, detailed aerial photograph interpretation and field mapping. The study should provide sufficient information to determine the hazard types, their respective design events and runout distances. If the risk posed by an identified hazard needs to be lowered, formulation of a mitigation strategy is required as part of the study.

As our understanding about the complex interplay between the various attributes contributing to natural terrain instability is evolving, judgement by experienced and competent professionals remains a key aspect in assessing hazards and in formulating appropriate mitigation strategies.

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