MAUSAM. 48. 4 (Oclober 1997), 515·5 18

551.465.755: 551.515.2(512.317)

Statistics of storm surges in Hong Kong

YING WA CHAN and WEN LAM CHANG

The Hong Kong Observatory , Honglwng

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ABSTRACT. Storm surge statistics are essential for the design of coas tal structures in Hong

Kong. This research note describes some of the characteristics and statistics o f storm surges in Hong

Kong.

Key words - S torm surge. Storm tide. Extreme storm tide analysis . Return period and chart

datum.

I. Introduction

A major response of the ocean to tropical cyclonesis the rise of sea water level due to the fall ofatmospheric pressure and more importantly thestrengthening of winds as tropical cyclones approachthe coastal areas (Pugh 1987). This phenomenon isdescribed as storm surge, generally defined as thedifference between recorded and predicted sea levels.The tot al sea level, consisting of bo th normalastronomical tide and storm surge is called storm tide(WMO 1993). A detailed description of storm surgescan be found in Bretschneider (1967) and Murty (1984)and storm surge modelling in Jclenianski et ol. (1992)and Guo and Wang (1994) amongst others.

The Hong Kon g observato ry has long beenconcerned with the study of storm surge for operatingstorm. surge warnings and for providing inputs forinfrastructure projects. The purpose of this paper is todescribe some of the storm surge statistics obtained inHong Kong.

2. Tide data for storm surge estimation in IIongKong

Early observations of tide levels in Hong Kongwere made by reading tide poles. A recording tidegauge was installed at Nonh Point in 1950 and relocatedto Quarry Bay. about half a kilometre to the east ofNonh Point in 1985. Hong Kong's tide gauge networkhas expanded gradually throughout the years and thereis now a network of 9 tide gauges (Fig. I). Thisallows storm surges in different parts of Hong Kongto be characterized,

J. Storm surges in IIong Kon g

On an average. Hong Kong is affected by aboutsix tropical cyclones a year. Statistics show thai stormsurges arc the highest for tropical cyclones makinglandfall to the west of Hong Kong. Historically. themaximum storm surge recorded in Hong Kong wasabout 4 metres. This occurred in Tolo Harbour (referto Fig. 1 for geographical locations) during the passageof a typhoon on 2 September 1937. The narrow inletsat the head of Tolo Harbour provided conditionsfavourable for the amplification of surges and during

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