Report No. : GEO Report No. 362

Report Title : Study of Geological and Morphological Controls on the Occurrence of Natural Terrain Landslide Clusters in Selected Catchments in Hong Kong (2022), 169 p.

Author : D.L.K. Tang, C.C.J. Wong, Y.M. Sin, A.H.Y. Wong, S.H.S. Leung & K.L.H. Lo

Abstract

Understanding the distribution of natural terrain landslides, in particular when and where they occurred in clusters, is vital for managing the landslide risk. Previous rainfall and landslide susceptibility analyses revealed the connections between intense rainstorms and general slope gradient with landslide frequency. Yet, the observed spatial distribution of landslide clusters requires more specific physical, geological and/or geomorphological explanation. This study investigated seven catchments, located in west Lantau Island (4 nos.), central New Territories (2 nos.) and east Kowloon (1 no.), all with notable landslide clusters but of various morphological settings and underlying geology. Detailed review of catchment characteristics, geomorphological mapping, spatial analysis of relict and recent failures were conducted. The clustered landslides were generally small, shallow failures in thin colluvium or saprolite, which suggest that they were primarily caused by continuing weathering on over-steepened slopes. Based on our findings, mature bowl-shaped drainage depressions, break-in-slopes associated with geological contacts and over-steepened incised slopes have been recognised as prime locations of multiple, repeated landslides. Potential influence of human disturbance and catchment characteristics on landslide clustering has been reviewed, although no conclusive correlation could be identified from the seven studied catchments.

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