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and when fully laden has a draught of only 7'-6". It is considered that a depth of water of 12 feet at L.W.O.S.T. alongside any wharfage designed to accommodate this class of craft will be sufficient.
DATUM.
The tide tables have been compiled from the result of the analysis of the tidal observations taken at the Kowloon tidal observatory, under the direction of Dr. Doberek, during the years 1887, 1888 and 1889. Since then, systematic observations have not been recorded. The tables for 1924 predict only 7 occasions when the tides may be expected to ebb below the level adopted as Low Water of Ordinary Spring Tides (L.W.O.S.T.) and then only to a maximum of 0.33 foot. Whilst the wind force (apart from the greater effect of typhoons) may increase or diminish the rise or fall of the tide, the information necessary to determine the extent of such variation is not available. The level of Low Water of Extraordinary Spring Tides (L.W.E.S.T.) is about 1.03 feet below the level of L.W.O.S.T. and is the datum adopted by the Consulting Engineers. On the information available, I do not consider this datum a reasonable basis on which all shipping accommodation should be designed. Such a coincidence as a vessel arriving in the port at the hour of L.W.E.S.T., or when the wind has caused the tide to fall to an abnormally low level, and, at the same time loaded to its maximum draught, does not justify, in my opinion, the extra cost of constructing all solid quay walls providing the extra depth between these two data, viz. :-one foot.
The datum to which all works rocommended in this report is therefore L.W.O.S.T. or Ordnance Datum, or 17'-10" below "Rifleman's" copper bolt on the N.W. corner of one of the storehouses in His Majesty's Dockyard, Hongkong.
HEIGHT OF QUAY WALLS.
From the observations taken during the years 1887, 1888 and 1889, the level adopted as High Water of Extraordinary Spring Tides (H.W.E.S.T.) is 7.70 feet above L.W.O.S.T. During these three years the highest water level recorded was 8.55 feet above datum. The effect of a typhoon is to raise the level of the sea but to what extent the effect produced is felt within the harbour there is little information available.
As 8 a.m. (the hour of high water) on the 20th of September, 1922, a typhoon passed at a distance of about 270 miles and to the South of the Colony: It was then noticed that there was an abnormal rise in the level of the tide over that predicted, which was 7.19 feet above L.W.O.S.T., and observations were made. It was ascertained that the actual height of the tide was 10.05 feet above datum, being an increase of 2·86 feet.
In determining the height of the copes of quay walls, consideration must be given to the handling of cargo by vessels moored alongside. The construction of quay walls to such a level to prevent a certain amount of flooding of the wharves caused by the impact of waves against the face of the quay would increase the cost of handling cargo. I consider it would better to provide in the design of the transit sheds, precautions for the prevention of their flooding rather than increase the height of the quay walls beyond the level of 14.50 feet above L.W.O.S.T., which is an economic height for the handling of cargo.
TYPHOONS.
The
The records of the Royal Observatory, Hongkong, for the years 1884 to 1923 shew that, in that period of 40 years, 60 typhoon gales were experienced in the Colony. particulars of them may be summarised as follows:-