Discussion. The Sea Approaches to the Port of Liverpool.

Abstract

The Paper brings up to date the very comprehensive paper by Cashinl in 1949.32. Much of the cost of maintaining the approaches depends on the effectiveness of the chosen dumping site, i.e. effectiveness in terms of the proportion of material that is not returned to the system. It is now established that if the site is moved a few miles further westward much that at present finds its way back into the Mersey will no longer do so. 33.It is easy to find such sites, but to find one which is economical in terms of ton miles hauled is more difficult.34. The Board, now The Mersey Docks and Harbour Company, has recently announced the closure of the south part of the Liverpool dock system. The possibilities of filling in these docks from dredgings are being examined.35. There has been no expenditure on training banks since 1965. Formerly these were maintained, but where limited settlement has occurred it is now thought cheaper to allow the material to spill over, and dredge rather than carry out the expensive remedial work necessary.36. Parts of the Seaville wreck have now been removed, enabling the channel to be widened to about 450 m at its narrowest point.37. The recent increase in depth to 8.5 m below Liverpool Bay Datum enables 200 000-t tankers, part-laden, to enter the Mersey, and the Port can cater for all the in-docks trade that offers, including bulk cargo ships of up to 75 000 t.M r D. Perfrement, British Transport Docks Board I should like to refer to Fig. 3 which shows the annual quantities of dredging from the Mersey. The variation year by year of the total quantities dredged is shown by the full black line and the dotted black line is an envelope of rounded-off figures.39. When one is looking at physical phenomena it is interesting to try to ascertain what particular patterns can be derived from them. Ignoring the peaks and troughs due to special dredging, there is a cyclical variation of quantities which appears at a roughly 12+ year frequency with peaks starting in 1897. One can also see a possible 50 year cycle.40. There has long been the contention of the Mersey that the physical states of the two ebb channels at Eastham and Garston are complementary, i.e. when the condition of one is good, the other is not so good. 41.The variation of dredging in, for example, the Garston Channel has been reviewed and this has tended to follow a roughly cyclical pattern similar to, but not in time phase with, the Mersey dredging shown in Fig. 3, but with the same average period of each cycle of about 12 years.42. Consideration could also be given to possible natural phenomena which influence the tidal or other physical factors, and since sun-spot activity is generally a cyclical activity of some 17 years, curves relating to this have been plotted. The Mersey dredging appears to be in an inverse ratio to the sun-spot activity prior to World War I1 and directly in line with it after the war.Paper published Proc. Instn Ciu. Engrs, 1971,49 (June) 145-156.