SLUICE, in hydraulics, a frame of timber, stone, earth, &c. serving to retain and raise the water of the sea, a river, &c. and on occasion to let it pass: such is the sluice of a mill, which stops and col lects the water of a rivulet, &c. in order to discharge it at length, in greater plen ty, upon the mill wheel: such also are those used in drains, to discharge water off lands ; and such are the sluices of Flanders, &c. which serve to prevent the waters of the sea overflowing the lower lands, except when there is occasion to drown them. Sometimes there is a canal between two gates or sluices, in artificial navigation, to save the water, and render the passage of boats equally easy and safe, upwards and downwards; as in the sluices of Briare, in France, which are a kind of massive walls, built parallel to each other, at the distance of twenty or twenty-four feet, closed with strong gates at each end, between which is a kind of canal or chamber, considerably longer than broad, wherein a vessel being in closed, the water is let out at the first gate, by which the vessel is raised fifteen or sixteen feet, and passed out of this canal into another much higher. By such means a boat is conveyed out of the Loire into the Seine, though the ground between them rise above one hundred and fifty feet higher than either of those rivers.
The construction of sluicesought to be conducted by an able engineer, who is well acquainted with the action of fluids in general : and particularly with the situation of the place, the nature of the 80;1, &c. where the sluice is to he erected ; if on the sea-shore, hey ought to be perfectly well acquainted with the effects of the sea on that coast, and the seasons when it is calm or stormy, that he may be able to prevent the fatal accidents thence arising: and if in a river, it is necessary to know whether it usually overflows its banks, and at what seasons of the year its waters are highest and lowest. The machines for driving the piles should be placed about forty yards from the side of the sluice, above and below it. As to the depth of sluices, it must be regulated by the uses for which they are designed ; thus, if a sluice is to be erected at the entrance of a basin for shipping, its depth must correspond with the draught of water of the largest ship that may, at any time, have occasion to enter thereby. The rule usually ob served is, to make the surface of the bottom of the canal on a level with the low-water-mark: but if the bottom of the harbour and canal be such, as to be capa ble of becoming deeper by the action of the water, Belidor very justly observes, that the bottom of the sluice-work should be made deeper than either.
When a sluice is to be placed at the bottom of an harbour, in order to wash away the filth that may gather in it, by means of the waters of a river or canal, in this case the bottom of the sluice-a ork should be two feet or eighteen inches higher than the bottom of the harbour, that the water may run with the greater violence.
An engineer ought always to have in his view, that the faults committed in the construction of sluices are almost always irreparable. We shall therefore lay down some rules, from Belidor, for avoiding any oversight of this kind: 1 In order to adjust the level of the sluice-work with the utmost exactness, the engineer ought to determine how much deeper it must be than kfixed point : and this he should mark down in his draught, in the must precise terms possible. 2. When the
proper depth is settled, the foundation is next to be examined : and here the en gineer cannot be too cautious, lest the apparent goodness of the soil deceive him : if the foundation be judged bad, or insufficient to bear the superstructure, it must be secured by driving piles. or a grate-woik of carpentry. 3. There should be engines enough provided for draining the water, and these should be entirely under the direction of the en gineer, who is to take care that they be so placed as not to be an obstacle to the *work and also cause proper trenches to be cut, to convey the water clear off from the foundation. 4. When the sluice is to be built in a place where the work men will be unavoidably incommoded by the waters of the sea, &c. all the stones for the mason-work, as well as the tim bers for that of carpentry, should be pre pared before-hand; so that when a pro per season offers for beginning the work, there remains nothing to be done, but to fix every thing in its place. 5. In order to show the state of the work, an exact journal should be kept of the materials employed, to be signed every week by the chief engineer and undertaker; ob. serving to distinguish the different pieces of materials, and the places where they were employed. 6. When an under taker is found, who is not only able to be at the expense of providing all the mate. rials, but likewise vigilant and active to execute whatever is judged necessary for the perfection of the work, it would be the worst of policy to give the pre ference to others, who, through igno. ranee, or dishonesty, bring in estimates lower than it is possible to execute the work as it ought. However, that the conditions of the contract may be pro perly executed, the chief engineer, or other persons of unquestionable under standing and honesty, commissioned for that purpose, should take care that able workmen be employed, and that they execute their several parts in a proper manner.
Sluices axe made different ways, ac cording to the uses they are intended for : when they serve for navigation, they are shut with two gates, presenting an angle towards the stream ; but when made near the sea, there are two pairs of gates, one to keep the water out, and the other to keep it in, as occasion re quires: the pair of gates next the sea present an angle that way, and the other pair the contrary way ; the space inclos ed by these gates is called a chamber. When sluices are designed to detain the water in some parts of the ditch of a for tress, they are made with shutters to slide up and down in grooves; and when they are made to cause an inundation, they are then shut by means of square tim bers let down into cullises, so as to lie close and firm. Particular care must be taken, in the building of a sluice, to lay the foundation in the securest manner possible ; to lay the timber-grates and floors in such a manner, that the water cannot penetrate through any part, other wise it will undermine the work ; and, lastly, to make the grates of a proper strensrth. in order to sunnort the ores sure of the water; and yet to use no more timber than is necessary.