If it is desired to raise the shutters after the subsidence of the flood, the lock-tender places the "needles" in position, and thus constructs a protection, behind which he can raise all the shutters, with ease, by hand.

After the shutters are all raised the "needles" are again removed, and the planks of the foot-bridge replaced, in case they were removed during the high stage of the water. Should the water-wheel remain in motion longer than is necessary for the complete movement of the iron rod, there is an arrangement attached to the mechanism by which the pinion that moves the rod is thrown out of gear. (Annales des Ponts et Chaussées, 1851-52.)

METHODS IN USE IN INDIA.

The arrangement of double shutters, shown in Figs. 8, 9, 10, 11, and 12, has been successfully used in Orissa, in India, on the anicut or dam across the Mahanuddy River at Cuttack. The following description is taken from the Roorkee Treatise on Civil Engineering, volume ii, paragraph 703:

Instead of the small sluices provided as in the Kistna, and other anicuts, a larger kind of sluice, on the French pattern, has lately been successfully employed on the Mahanuddy anicut in Orissa.

The center sluices are divided into 10 bays of 50 feet each, by piers of masonry. Each bay is closed by a double row of timber-shutters, which are fastened by wroughtiron bolts and hinges to a heavy beam of timber imbedded in the masonry floor of the sluices. There are seven upper shutters, and seven lower or rear shutters; the latter are 9 feet in height above the floor, and the former 74 feet.

During floods, therefore, the upper row of shutters, which fall forward, is fastened down by clutch-gearing in an almost horizontal position, while the rear set of shutters, which fall backward, is kept during flood in a horizontal position by the water rushing over.

During the summer season these rear shutters have to do the duty of damming up the water, and for this purpose they are provided with strong wrought-iron stays or struts attached to them behind or on their lower side. As it would be almost impossible, however, to lift these back shutters with a depth of 54 feet of water tearing over them, the upper shutters are so constructed as to render this a matter of comparative ease. As the upper shutters point up stream, the natural tendency of the powerful current passing over is to lift them up. By simply unclutching them, therefore, they immediately rise and dam up the water, being retained in position by two sets of chains, which take the strain off the hinges. The water being thus dammed up, the back shatters are easily lifted, and permit in their turn of the upper shutters being lowered forward into their horizontal position.

The superintending engineer, Mr. Walker, in reporting on them, considers it is established

1st. That, with the shutters constructed on the French pattern, and with a head or pressure of between five and six feet, 500 linear feet of shutters can be easily lowered in one hour.

2d. That, under the same condition, an equal length of opening can be closed in 25 minutes. In closing, the shutters may be said to be self-acting.

3d. That when the back-stays are released, the falling shutters are received upon a cushion of water in time to prevent any undue concussion.

4th. That the action of the water in lifting the upper shutters brings no excessive jerk on the chains, but that it is advisable that chains have an adjusting-screw fitted on, so as to make the strain perfectly uniform. The shutters were brought home in a current of 10 feet per second.

5th. That three men can knock away the back-stays with a pressure of between five and six feet with ease and security.

6th. That twelve men are necessary to lift each of the back shutters into position.

An immense dam, two and one-third miles in length, is now in process of construction across the Soane River at Dehree, where it emerges from the Kymore hills and enters the plains of Behar, through which it flows sixty-five miles to its junction with the Ganges. At each end of the dam, and at its middle, under-sluices are provided in order to prevent an accumulation of alluvial deposit above the dam. Those at the ends are especially designed to keep clear the heads of the irrigation-canals which start at each bank, and take their water from the pool formed by the dam.

The sluice gates are to be made on the double-wicket plan, with some modification, and the following description is taken from the London Engineering, vol. xvi, p. 219:

We proceed to give a short description of the self-acting shutters invented by Mr. Fouracres, which are used to open or close the under-sluices in the wear. We have already stated that there are three sets of sluices, of 25 openings, of 20 feet in each set, and that only in times of flood, and in order to scour out any deposit which may be formed opposite the lock-entrance on either bank, are they required to be opened. The usual practice in works of this kind is to have small openings of six feet in width, with a roadway overhead, the openings being closed or opened by gear from the top, but it was found by thus diminishing the size of the passages, the efficiency of the scour was also considerably diminished, and moreover openings of that size were unable to pass through them all the large timber, wrack, and brushwood which an Indian river brings down in times of high flood. It was therefore attempted, in Orissa, to increase considerably the size of the sluice-openings in the wear in the Mahanuddy River, and shutters on the plan adopted by French engineers in the navigation of the Seine were constructed.

*

The objection to this plan was that the upper shutter was raised by the stream with such velocity and force that the chain-ties supporting it frequently gave way, and the shutter was carried off its hinges. It was also necessary that the shutter should be self-acting, as to opening itself to let a flood pass through the sluices, and it was to meet these two requirements that Mr. Fouracres's self-acting shutters were invented. Figs. 30, 31, and 32 show three views of these shutters in different positions, and Figs. 33 and 34 show two sections which will further assist in explaining the arrangement. Fig. 30 shows the sluice "all clear," with both shutters down, lying on the floor, the floods being supposed to be running freely between the piers, which are 8 feet in height. When it becomes necessary to close the sluice, and shut off the water flowing through it, a clutch worked from a handle from the top of the pier is turned, which frees the shutter from the floor, and it then floats partially up from its own buoyancy, when the stream, impinging under it, raises it to an upright position with great force, shutting up the sluice-way. But if a shutter 20 feet long were allowed to come up with such pressure it would either carry away the pier or be carried away itself. destroy this shock, Mr. Fouracres has contrived six hydraulic buffers or rams, which also act as struts for the shutter when in an upright position. These rams are simply pipes with a long plunger inside; (see enlarged section, Fig. 35;) the pipes fill with water when the shutter is lying down, and when it commences to rise the water has to be forced out of them by the plunger in descending, and as only a small orifice is provided for the escape of the water, the ascent of the shutter forced up by the stream is slow and gentle, instead of being violent.

To

The water is now shut off effectually, as shown in Fig. 31, but, without other means being taken, it would be impossible to open the sluice again, as it could not be forced up stream. Another shutter is therefore provided below it, as shown in Figs. 32 and 34, this lower shutter being arranged so that it can be lifted up by hand and placed upright, as shown in Fig. 32. The water is then allowed to fill the space between the two shutters, and the upper one can then be thrown down on the floor again, but the lower one is held up by ties which are hinged to it at one-third of its height, and by this means it is balanced, and resists the pressure on it until the water rises to its top edge, when it loses its equilibrium and falls over, thus opening the sluice again. The shutters can be left to fall of themselves if the river rises in the night, or, if it is not thought expedient to let them fall, they can be made fast by a clutch on the pierhead, as shown. By these expedients these large sluice-ways, 20 feet broad and 8 feet deep, can be shut off or opened as required, with the greatest facility and expedition, and the whole set of 25 sluices can be opened in a few minutes, and when opened they can pass through them anything that the river brings down without danger to the wear. It has been proposed to bridge over the piers with a light iron foot-bridge to enable a man to work the clutches of the shutters more easily.

It will be seen from the above that in the sluices of the Mahanuddy dam the openings are 50 feet in width, and are closed by seven shutters of each kind, giving a width of a little more that 7 feet to each shutter, while in the Soane dam each opening is 20 feet wide and is closed by a single shutter.

CHANOINE WICKETS.

In the Annales des Ponts et Chausseés, tome 2, 1861, there is a very complete memoir on one kind of movable dams, prepared by MM. Cha

noine and De Lagrené, of the Corps des Ponts et Chaussées. This memoir gives a full detailed description of what is known as the Chanoine system of wickets.

It should first be stated that the dams, principally on the Seine and Yonne, to which these wickets have been applied, consist of a lock, a pass for navigation whose sole is about even with the bottom of the river, a pier, a weir whose sole is about 3 feet above the river-bottom, and an abutment.

The Chanoine wickets are shown in Figs. 37 to 45. Figs. 37, 38, and 39 represent the wicket of a navigation-pass; Figs. 40, 41, and 42 the wicket of a weir; and Figs. 43, 44, and 45 show the manner of raising the wickets by a boat, provided with a windlass and other suitable equipments.

The Chanoine wickets are of two kinds, automatic for the weir and non-automatic for the pass for navigation, or chute. They differ from the shutters previously described in having the axis of rotation at from one-third to five-twelfths the vertical height from the foot of the wicket. This axis is supported by a small iron horse, which is itself movable up and down stream around its foot. The head of the prop rests on a pin, passing through boxes fastened to the cap of the horse, and its foot rests against a heurter. To throw down a wicket the foot of the prop is pushed away from the heurter by the projections of an iron rod worked from the abutment. These projections are so spaced that the wickets are thrown down in succession. This arrangement is adopted from the Thénard system, which has already been described. To permit this movement, the hole at the head of the prop is larger than the pin, which connects it with the horse.

The wickets for the navigation-pass are hinged at five-twelfths the vertical height from the bottom, and are provided with a fixed counterweight at the foot. In vertical height they vary from 8 feet 10 inches to 10 feet 2 inches, and when in position are inclined down stream under an angle of 15°. The portion of a wicket above the axis of rotation is called the chase, and that below the axis the breech.

The wickets of the weir are smaller than those of the pass, and are hinged at about one-third the height above the bottom, so that when there is a flow over the top of more than 8 inches in depth, the pressure above the axis of rotation exceeds that below it, and the wicket swings into a position nearly horizontal, thus opening a passage for the water. The weir-wickets are provided with movable counterpoises, in addition to the fixed ones, with the expectation that after being swung they will close of themselves when the water recedes. As will be found further on, this arrangement did not work satisfactorily. These wickets, like those of the navigable pass, could be tripped by an iron rod, worked from the abutment, whenever a great flood made it desirable to throw them down flat, on the top of the weir. It was not thought desirable to make the wickets of the navigable pass automatic for fear lest they should be thrown down by floating bodies, which might become entangled, and, by preventing the wicket from lying flat, make a dangerous obstruction to boats.

The wickets of the weir varied in height from 5 feet 5 inches to 6 feet 7 inches, and their axes were placed about an inch and a half higher than one-third the total height above the sill. All wickets are made about 4 feet wide to facilitate maneuvering.

To raise the wickets a boat 30 feet long and 8 feet wide was used, which was worked from above the dam, and was provided with ropes, fenders, and windlass. To raise the wicket nearest the bank the boat

was placed along the upper side of the abutment, at right angles to the current, with its bow projecting half the width of a wicket. By means of a boat-book the attendant seized the handle on the lower end of the wicket. As soon as this was done his assistants commenced winding in a rope, fastened to the lower end of the boat-hook, and passing thence around a pulley in the bow to the drum of the windlass. The wicket was thus raised into a horizontal position, and the current pressing down on the breech swung it into place. As soon as one wicket was raised the boat was pushed forward the width of a wicket, and the operation was repeated until the pass was entirely closed. There is always an interval between the wickets of a little less than two inches, and by inserting keys in the intervals between the wickets already raised, and by using fenders and a cable fastened to the abutment the boat is securely held in place throughout the maneuver. of the weir are raised in the same way.

The wickets

COMPARISON OF THE PÓIRÉE, CHANOINE, AND DESFONTAINES SYSTEMS.

In tome xi, Annales des Ponts et Chaussées, 1866, M. de Lagrené, engineer desP onts et Chaussées, makes a comparison of the different methods of constructing movable dams, and the following is an abstract of his article:

At the present moment dams are in course of construction, not many miles apart, that differ essentially; thus on the Seine, below Paris, the needle-dam, invented in 1833 by Inspector-General Poirée, has been adopted; above Paris the dam with movable wickets, invented in 1852 by Chief Engineer Chanoine, has been chosen; while on the Marne the movable dams of the Upper Seine are used, but under different conditions, and with the addition of the drum-wickets invented in 1864 by Inspector-General Desfontaines.

These three systems are those which he compares. As the Poirée needle-dam has been fully described already, also the Chanoine wickets, only his conclusions will be given in regard to these two systems, but a full description will be given of the Desfoutaines drum-wickets, (hausses à tambour.)

The Poirée needle-dams were first designed for heights of 5 feet, but they have gradually been heightened to 10 feet 10 inches.

And as, in fact, a dam on any system whatever is always an obstacle to navigation, it was natural to limit their number as much as possible, and, in consequence, to give to each one the greatest height compatible with its location and details of construction. It will at once be understood that if a sudden flood should come, or even a simple artificial wave, the foot-bridge for managing a needle-dam might be submerged before there was time to remove the needles, and serious accidents might happen either to the dam, to navigation, or to riparian property. An endeavor was made to avoid this danger by means of a permanent weir connected with the pass, having a needle-dam ; thus at the Epineau dam, whose pass is 230 feet wide, with a sill 16 inches below low water, M. Poirée added a masonry weir 403 feet long, raised to 3 inches below the level of the pool; at the Bezous dam, consisting of an open pass 158 feet in length, with its sill 24 feet below low water, and a higher pass 155 feet in length, with its sill 16 inches below low water, a permanent weir has been added 1,411 feet in length, and at an elevation of 16 inches below the level of the pool; but such a weir, admissible for small lifts, becomes very costly when the lifts are great. Moreover, in certain cases, the submersion of the needles and trestles can still occur in spite of it.

To diminish the danger of submersion, while at the same time avoiding the cost and inconvenience of a permanent weir, and also to facilitate navigation by artificial waves, the bars that support the needles have been arranged so that the lock-tender can easily disengage them. The needles of each bay are then carried away by the current, as the lock-tender successively opens the bays; but as the precaution is taken to fasten them to ropes, they are easily fished up from below the dam.

At the dams on the Yonne the escapement consists of an eccentric which permits the opening of 131 feet of pass in 15 minutes, while au hour used to be required with the old arrangements.

The Belgian method allows the needles of each bay to escape in a body, but the trestles remain standing. The French method drops each trestle as the needles attached to it, are loosened. By the Belgian escapement the heads of the needles must pass under the sheet-iron floor of the foot-bridge. The disadvantages of this arrangement will be shown presently. The employment of escapements does away with the necessity of raising the needles by hand, and thus permits the construction of higher dams.

METHOD OF MANEUVERING A NEEDLE-DAM.

Let us recall in a few words how a needle-dam, furnished with escapements, but without permanent wear, is managed.

Suppose it to be entirely closed. If the discharge is nearly that of low water, the filtrations between the needles can be reduced by throwing in grass just above them. If a rain should come sufficient to raise the level of the pool, the attendant makes a sufficient number of openings in the part of the dam farthest from the lock, by removing only a few needles from each bay, so as to divide the issuing current. As the discharge diminishes, the attendant gradually replaces needles that have been removed. When the rainy season approaches, the dam is prepared for opening. With this view he passes the ropes through each group of needles yet remaining between the trestles, and fastens them to the shore in the customary manner, and as soon as the lift of the dam is reduced to a height determined beforehand, he looses the escapements and lowers the trestles in succession, satisfying himself as he goes on that each one is well down and makes no projection on the floor. The same method of opening is used on the arrival of an artificial wave on the rivers where this method of navigation is in use. This maneuver must evidently be made at night as well as during the day, and, besides, the trestles must be laid down in winter, as soon as the first ice-cakes form. When the opening is completed the attendant can fish up at his leisure the needles which are floating below the dam at the end of the cable.

When the high-water season is passed, the attendant piles up the needles upon the walls, and prepares to raise the trestles; this raising is done when the water-surface has fallen to a previously determined level; the attendant then raises all or part of the trestles, places a few needles at intervals, and gradually increases their number so as to obtain and preserve the normal level of the pool.

OBJECTIONS TO NEEDLE-DAMS.

A needle-dam is evidently, as has been already shown, a work by means of which the level of a pool is regulated at will, and very simply, by removing or adding a certain number of needles, provided always that the placing and the removing or loosing of these needles cause neither danger nor too severe an exertion. It, therefore, seems to us that when the height of the lift is slight, these conditions are only partly fulfilled, and that they are not fulfilled at all when high trestles are in question. This is the case which we propose examining.

When the trestles are more than 8 feet high the needles assume such dimensions that their transportation from the store-house to the place where they are used is quite burdensome, (the Bezons needles are 13 feet in length and 3 inches square,) and their placing becomes dangerous and difficult, as much on account of their length and crosssection, as in consequence of the depth of the water, and its velocity. If a needle does not strike the sill against which it ought to abut, the attendant may be dragged overboard by it. Their removal by hand becomes impossible if the difference of level is great, and it is then necessary to resort to a system of loosing the supporting-bars, or to pull the needles one by one by means of a windlass. (A needle 13 feet long and 3 inches square weighs 20 lbs. when it is dry, and 29 lbs. when it has remained in water.)

Throughout the work of placing or removing needles or opening by escapement, the attendant is obliged to be on a narrow foot-bridge, and while there to use considerable exertion above a rapid current, no matter what the weather, and as often at night as by day; his work is certainly very dangerous.

Careful watching is necessary, at least at certain times and for certain rivers, for the least negligence may cause the submersion of the dam, and result in serious damage. As soon as the work of removing the needles of a dam is begun, the current sets toward the bays that are wholly or partly open; its strength increases with the number of needles removed, and if the pass is near the lock, boats may miss the entrance and be drawn against the trestles.

The removal of the needles, even if only partial, ends, at last, even when the open