The above forms are self-acting, and swing back to their places as the water subsides. For larger streams, it is necessary to construct fences that give way before the flood, and can be brought into position again when it is over. One of these, for a stream which is liable to bring down much driftwood, is shown in [figure 135]. The logs are the trunks of straight trees, about eighteen inches in diameter, which are hewed on two sides; posts are mortised in each of these logs, and on them planks are firmly nailed. The logs are then linked together with inch iron rods, and the first one connected by means of a long link to a tree or post firmly set in the ground upon the banks of the stream. The links must all work freely. When high water occurs, the fence is washed around and left on the bank; after the water has subsided sufficiently, the logs may be dragged back to their places, as shown in the engraving, by means of a horse, hitched to a staple in the end of the log. [Figure 136] shows a lighter fence made of poles or rails, held by interlinking staples to the posts on the side of the stream. As the floods come down, the rails are washed from the center, and float freely at either side of the stream. They can be laid up in place again when the water subsides.
Fig. 136.—Fence Of Movable Rails.
Fig. 137.—An Extemporised Flood-fence.
The fence shown in [figure 137], though rather rude and primitive, has the advantage of being cheaply constructed and permanent. Two strong posts are driven into the banks on the margin of the stream, to which a log, a foot or more in diameter, is fastened by pins, spikes or withes, about twenty inches above low water mark. Then fence rails are sharpened at one end, driven into the stream above the log, upon which the other ends rest, projecting about a foot. They are then securely spiked or pinned to the log, and the work is done. The pointed ends of the rails are up the stream, and in case of flood, the water pours over the obstruction, carrying with it brush, driftwood, etc.
Fig. 138.—Automatic Flood-gate.
The flood-gate, [figure 138], is designed to prevent small stock from passing from one field to another through a water-course under a fence where there is low water, while in time of high water the gate will rise sufficiently to allow the floating trash to pass through, but not higher, as it is self-fastening. The invention consists of a gate constructed of perpendicular slats hinged above, and moving. This hangs across a stream or ditch. On the down-stream side of the gate a swing paddle is fixed, which hangs in the water. This, marked a in the illustration, is attached to an angular bar, b, which is moved when the flow of water presses with force against the paddle. Two notched pieces, c c, attached to the gate, rest upon the angular bar, b, at low water; when both the paddle and the gate hang at rest, perpendicularly, these notched pieces, c c, hold the gate firmly shut; when, however, the water rises and the paddle is moved sufficiently to disengage the notches, the gate will be moved by the force of the water, and if sticks or rubbish of any kind float down against it they will be swept under it by the water. When the water subsides, the paddle swings back, the pieces, c c, catch and keep the gate closed at any height it may fall to. Let the cross-piece, d, that is halved into the posts, be about one foot above the banks of the ditch. The pieces, f f f f, represent the fence above the ditch, the small posts, g g, with the pieces nailed to them, are to prevent the stock from passing when the gate is partly closed, at the same time bracing the posts, e e; the holes at h are to raise and lower the paddle a; if small, a cleat on one of the arms upon which the piece B is hung, prevents the paddle from swinging towards the gate.
