A Treatise On The Principles And Practice Of Harbour Engineering

246 HARBOUR ENGINEERING. withdrawn from use, and have since been demolished, their sites being used for other purposes. A new sluicing basin of much larger area has been designed to take their place. At the same time, it was recognised that with the increased depth re- quired for modern shipping it would be impossible to realise an effective maintenance service by means of sluicing operations alone. Dredging, there- fore, was introduced as an auxiliary. The peculiar conditions appertaining to the port of Ostend are thus set forth by Mr Van der Schueren in his communication to the International Navigation Congress.1 “ We have pointed out that the method adopted at Ostend for preserving the navigable depth of its channel, consists of a combination of sluicing and dredging. “ It may be objected that what can be obtained by sluicing can be equally well obtained from dredging, and that it is not necessary to have recourse to the combined system. At most, it would be a question of cost. It would be necessary to ascertain whether the mixed system is more economical than that of dredging alone. Yet, it is not certain that from this particular point the advantage would lie with the combined system “But, in our opinion, the preceding considérations are of secondary importance, and ought not to furnish a basis for the solution of the problem. “ In point of fact, under the conditions in which the sluices were installed at Ostend, these latter not only serve to maintain the inner channel, but also, and specially, they maintain the deep berth in front of the new tidal quay, where navigation requires 26 feet of water at low tide. “Owing to the prevalence of mud in the port, a rapid diminution in depth may be expected to take place, unless very powerful counteracting agencies are brought into play, combatting the silting tendency without relaxation or discontinuance. “ lu default of sluices, dredging would be essential at the foot of the tidal quay; this would entail the occupation of the quay berth by eumbersome vessels, as inconvenient from the point of view of navigation as from that of trade. “ There is therefore every reason for limiting dredging operations at the tidal quay, and, from this point of view, sluicing has its advantages. It reduces the inconveniences to a minimum by considerably diminishing the quantity of material requiring to be dredged.” The new sluicing basin has an area of nearly 200 acres, and its contents are discharged through six openings each 16 feet 6 inches in width. Régulation Works on the Rhine.2—“The Rhine, between Mainz and the Dutch frontier, has been systematically regulated in wide, shallow reaches, chiefly by projecting spurs or dykes, generally extending into the river from one bank, but occasionally from both banks where the conditions are un- favourable, as, for example, in a wide reach between two bends ; and sometimes 1 Van der Schueren on Curage des Ports Maritimes, Proc. Int. Nav. Gong. Dusseldorf, 1902. 2 Vernon-Harcourt on Dusseldorf Congress, 1902, Min. Proc. Inst. C. E., vol. clii.