DREDGING
OF HARBOURS AND RIVERS Commander E. C. Shankland, F.RS.E., River Superintendent, Port of London Authority, has just published a descriptive and technical bcok, amply illustrated by maps, diagrams, and photographs, bearing the above title. It t cannot be doubted but that this is a most valuable addition to the scant total of works dealing with the subject of dredging, especially as it includes the relation to Conservancy, and Commander Shankland’s experience and observations over a long term of years give it additional weight. Sir John Biles, K.C.1.E., in his Foreword, says that “The Thames is a waterway which helps 'London to be the centre of the commerce of of world, and the keeping of tins 1 waterway up to and in advance of the requirements of the day is a seriqus and responsible duty in which Captain Shankland has had the honour of assisting for many years. In one section dealing with tides, Kipling’s rough generalisation regarding theu Thames of “five hours up and seven' down” is interestingly dealt with, and it is shown how the dredging of the low water channel of our river has the effect of ’etting the flood tide advance more easily and tending to keep the powers of ebb and flood more on equality. “The Thames” says Commander Shankland, “is probably the most instructive example of all. The artificial works executed upon this river in modenr times have been the deepening of the bed below the city, and the removal of old London Bridge. “The effect of the deepening has been that whereas in 1720 the flood tide commenced only 3 hours 50 minutes before high water, in 1840 the passage of the early flood had been so facilitated that the, water at London Bridge; began to rise 5 hours 15 min-/ utes before high water. The time of high water itself has also been accelerated. It ’ now talies place about 2 hours after the moon’s transit, but in 1913, according to an old time-table which is still in existence, the time of high water was given as 3 hours 48 minutes, when the moon was one day old, which would be rather more than 3 hours after the transit, so that in the 470 years pre-f vious to 1683 there appears to have been little alteration, while in the 170 years following the high wa+er aocelerated an hour and the low water at least 2-f hours. Within the last 20 years the change has been still more rapid. In 1833 high water at London Bridge was 1 hour 37 minutes after Sheerness; in 1851 it was only 1 llottr 20 minutes, being a gain of if minutes in 18 yfeai : S;
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Hokitika Guardian, 14 November 1931, Page 7
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448DREDGING Hokitika Guardian, 14 November 1931, Page 7
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