3.11
The average tide levels predicted for 1969 in Victoria Harbour are:-
Higher high water
+7.1 ft.
Lower high water
+5.1 ft.
Higher low water
+3.7 ft.
Lower low water
+2.0 ft.
Mean level
+4.5 ft.
3.12
3.13
On the approach of a tropical cyclone the normal high tide is augmented by a surge caused by wind setup and the low barometric pressure. This surge has been measured and found to be as much as 6 ft. in Victoria Harbour and should this coincide with a predicted high tide of say 8 ft. above Chart Datum, flooding is likely to occur. Fortunately the chance of this coincidence happening is small as the return period for a 6-ft. surge alone is 10-20 years and a 7-ft. surge 20-50 years.
From an analysis of the predicted tides for the months of May to October 1959, 1963 and 1964 the water level exceeded 8 ft. above Chart Datum for only 0.1% of the time and 7 ft. for 4.6% of the time. The highest sea level recorded in Victoria Harbour since the establishment of the North Point tide gauge in 1955 was 10.3 ft. above Chart Datum but there have been reports of 13 ft. or more prior to this.
Currents
3.14 The main flood tide through Victoria Harbour flows from east to west and splits on reaching Tsing Yi Island, part going through Rambler Channel and part through the channels between Tsing Yi and Lantau Islands. Near Tsing Chau the maximum current recorded in Rambler Channel is about one knot on the flood and two knots on the ebb. The directions of these are approximately north and south-east respectively.
3.15
To the south-east of Tsing Chau in the vicinity of the area reserved for the container terminal recent current observations taken during spring tides indicated that velocities exceeding half a knot would rarely occur here. The present current regime in this area will however be modified when the reclamation of Gin Drinker's Bay is completed and the present flow between Tsing Chau and the breakwater ceases.
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