Report No. : GEO Report No. 223

Report Title : Factual Report on Hong Kong Rainfall and Landslides in 2005 (2008), 135 p.

Author : H.S.W. Kong & A.F.H. Ng

Abstract

This report presents a summary of the factual information on rainfall and landslides in Hong Kong throughout 2005. Rainfall information was obtained from the Hong Kong Observatory (HKO) to supplement the information available in the Geotechnical Engineering Office (GEO). Details of the landslides were obtained from the records of incidents reported to the GEO. Supplementary information was provided by the Agriculture, Fisheries and Conservation Department, Architectural Services Department, Drainage Services Department, Fire Services Department, Highways Department, Housing Department, Lands Department, Water Supplies Department and the GEO's landslide investigation consultants, namely Fugro Scott Wilson Joint Venture and Maunsell Geotechnical Services Limited.

Rainfall at the HKO's Principal Raingauge at Tsim Sha Tsui in 2005 amounted to 3214.5 mm, which was about 45.2% above the mean rainfall of 2214 mm recorded between 1961 and 1990. It was the third wettest year in Hong Kong since records began in 1884, and June and August 2005 was the fourth and the second wettest months respectively. The rainfall in these two months (1865.2 mm) amounted to about 84% of the normal annual rainfall. One Red Rainstorm Warning was issued on 24 June 2005, and 16 Amber Rainstorm Warnings were issued between 8 May 2005 and 20 August 2005.

Two Landslip Warnings were issued on 24 June 2005 and 19 August 2005 respectively. A total of 487 incidents that occurred in 2005 were reported to the Government. Of these, 481 were classified as genuine landslides. Of the 481 genuine landslides, 82 were major failures (i.e. with a failure volume of 50 m³ or more, or where a fatality has occurred).

One fatality was reported as a result of a landslide incident. Other notable consequences of the landslides included the evacuation of 42 squatter dwellings and 12 buildings. Sixty-two landslides resulted in the temporary closure of sections of roads and another 46 landslides resulted in the temporary closure of sections of pedestrian pavements, footpaths or other forms of minor access. Thirty-nine landslides affected catchwaters, two of which had significant knock-on effects on existing developments, resulting in serious consequences.

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