A Treatise On The Principles And Practice Of Dock Engineering

SLUICES AT OSTEND. 245 the tide, to reach the quay of the new outer harbour, and to remain there afloat; but, to this end, it is necessary to maintain a draught of 26 feet at low water. “ If it were considered essential to obtain this result by means of dredging, it is to be feared that the cost of the undertaking would be considérable, even excessive, and that the cumbersome appliances neces- sarily employed for its execution would be found only too often usurping, in front of the quay walls, berths destined for commercial vessels. “ Dredging, therefore, would constitute a drawback—a serious danger even—for navigation at the port; and the maintenance of great depths could with difficulty be assured by this means alone. “ In regard to ports on the Belgian littoral, the rapidity with which deposits of mud accumulate, in channels withdrawn from the action of natural or artificial currents, is well known. “Under these circumstances, the utility of a sluicing basin would appear to be incontestible. The sluices are designed to supplement the action of the upper waters and of tidal currents, with a view to maintaining uninter- ruptedly, along the tidal quay of the new outer harbour, the assigned depth of 26 feet, without having recourse to continuai dredging. “ The sill of the sluice is located 13 feet below datum, differing in this respect from existing sluices, the sills of which are level with, or not below, low water datum. “ The arrangement adopted is justified in respect of the efficacy of the current. Calculation, in accordance with observed results, enables it to be determined to what degree the useful work of the sluice is increased in this way. “In his inquiry into the improvement of ports on a sandy beach the late M. Mey demonstrates, in effect, that in ordinary conditions, relative to the dimensions of the sluice and the reservoir basin, the useful effect of the effluent varies in the ratio of about 1 to 6'5 when the sill of the sluice, assumed primarily at the level zero (low water), is lowered after- wards to 13 feet below this datum.” The following are particulars of the sluicing arrangements at Ostend:— Name of Basin. Area. Number of Sluices. Width of Opening. Level of Sill with reference to Local Zero. Acres. Feet. Feet. Écluse Militaire, 294 3 j Two each 191 1 ( One 39 J -^ Écluse Française, 64 2 194 +H Écluse Léopold, 421 6 13 + U New Basin, 1924 6 164 - 13 To prevent the sluicing basin itself from being silted up, it is in some ■cases allowed to be filled only on the top of high water, when the influent is comparatively clear. This is the case at Honfleur. Elsewhere, as at