Natural Terrain Risk Management in Hong Kong

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1 Natural Terrain Risk Management in Hong Kong Nick Koor Senior Lecturer in Engineering Geology School of Earth and Environmental Sciences

2 Slope failures in Hong Kong Man-made Slope Failure landslides per year on average kill 5 people per year Natural Terrain Failure Failure 300 per year mainly rural ~ 1 per 2km 2 5 potential loss of life per year

3 Expenditure of remediation of existing man-made slopes in Hong Kong to Annual LPM Expenditure 1977/1978 to 2009/2010 $ Million Actual Expenditure under LPM Programme Planned Expenditure under the LPM Programme including inflation adjustment / / / / / / / / / / / / / / / / /10 Financial Year Notes: (1) The figures given above also include provision for urgent repair works to Government land and expenditure for special studies and investigations. (2) All expenditure and estimate are given at MOD prices. 195

4 The topography of Hong Kong Land area of about 1100 sq km 60% of which are natural slopes with 30% > 30

5 Encroachment of the built environment into steep natural terrain

6 Risk Management Many landslides in a heavy rainstorm Small failure can be serious in HK Increasing risk due to developing closer to natural hillside Low-frequency large-magnitude event

7 1990 Tsing Shan Debris Flow (20,000m 3 ) Eastern side of Lung Mun Road developed in 1990

8 2000 Tsing Shan Debris Flow (1600m 3 ) economic loss light rail and construction site affected

9 1999 Sham Tseng San Tsuen Potential landslide source Check dam

10 1995 Shum Wan Road (26000m 3 ) 2 fatalities could have been much worse if area down slope was developed Man-made influence (road flooded with water during heavy rain)

11 1997 Shatin Heights residential damage Recent debris flows

12 Other near misses 1997 University Station KCRC affected (200 m 3 ) 1998 Bowen Road Building affected (20 m 3 )

13 Management of Landslide Risk Natural Terrain Landslide Inventory Mechanisms studies Digital & GIS technology Remote sensing technology Landslide modelling Policy

14 Natural Terrain Landslide Inventory (NTLI) interpretation of 8,000ft air photos

15 Enhanced NTLI identification of natural terrain landslides that have been missed in the NTLI interpretation of 4000ft air photos NTLI records NTLI records New ENTLI records High Flight AP (10000 ) Low Flight AP (4000 )

16 Mechanism Studies shallow landslide processes involving different geological settings and mechanisms Colluvium Weathered rock Rock topple Joint-controlled slide

17 Applying digital & GIS Technology Landslide susceptibility analysis Landslide rainfall correlations

18 Remote sensing technology Digital Photogrametry Terrestrial and airborne light detection and ranging (LiDAR) InSAR

19 Modelling debris runout & mobility consequence assessment for mobile debris flows Distresse d area

20 Current practice in natural terrain landslide risk management Existing development react-to-knownhazard principle New development contain overall risk increase (study and risk mitigation as part of new development subject to hazard)

21 Screening criteria for new developments planning and land disposal stage For sites subject to severe hazards For sites that may be affected by natural terrain hazards In-principle Objection to development proposal Study and mitigation of hazards required

22 Current practice for existing developments React-to-known-Hazard typically applied to sites affected by new landslides Sham Tseng San Tsuen: one landslide in 1999 resulted in 1 fatality and injury to 13 people Tung Wan: 2 landslides in 1999 resulted in temporary evacuation

23 Engineering solutions for risk mitigation Soil nailing Check dam (rigid barrier) Flexible barrier Check dam (rigid barrier)

24 Technical guidelines for risk assessment & mitigation