1. That, in the first section, Auxerre to Laroche, the 8 dams have lifts varying from 4 to 8 feet, and an average lift of 6 feet. The two locks of the Gurgy cut-off have each a lift of 8 feet. The 9 pools between the mouth of the Nivernais Canal and the La Gravière Dam have lengths varying from four-fifths of a mile to four miles, with an average length of one mile and a half.

2. That the Epineau pool is common to the first and second sections, and has a length of two and one-half miles.

3. That, in the second section, from Laroche to Monterean, the 17 dams have lifts varying from 2 feet 10 inches to 7 feet 5 inches, and a mean lift of 5 feet. The two cut-off locks have lifts of 10 feet 8 inches and 12 feet 9 inches. The 16 pools between the Epineau and the Cannes Dams have lengths varying from seven-eighths of a mile to six and one-third miles, and an average length of three miles.

4. That the distance of two miles between the Cannes Dam and the Montereau bridge is a part of the first pool of the Seine, which ends at the Varennes Dam.

The width of the floor of the navigation-passes of the new dams, with wickets, is from 23 to 33 feet, measured in the direction of the current. The thickness is at least equal to the lift of the dam, and seldom less than 64 feet.

Between Auxerre and Joigny the body of the floor rests directly on solid rock or chalk; the masonry was laid dry in coffer-dams. Between Joigny and Montereau the main body is composed of a bed of beton, poured into an inclosure of piles and plank. On this the floor of the sole, consisting of cut and hammered stone, was placed after the water was removed.

In the masonry floor anchors, iron rods, and cast-iron anchoring-plates are imbedded, in order to bind solidly to the masonry the wooden sill against which the breeches of the wickets rest.

The floor of the weir of the new dams has generally a width of 13 feet and minimum thickness of 63 feet. It is entirely of masonry, or formed by a wooden box filled with beton and covered by a pavement of heavy stone.

The weir lies between a masonry pier 10 feet thick and 20 feet long, which separates it from the pass, and a masonry abutment, which is connected with the bank by two wing-walls.

Below most of the dams there is an apron, formed of heavy riprap of natural or artificial stone. At some of the dams this riprap is held in place by piles driven in quincunx order. The passes of the twenty-two new dams on the Yonne are closed by movable wooden Chanoine thickets, 4 feet wide, with 2-inch intervals. During the season of low-water these intervals are covered by planks to make the dam tighter.

It is well known that each wicket is movable around an axis forming the cap of the horse, which itself turns around its sill, whose journals are held in two boxes fastened in the lower face of the sill of the pass. The wicket, when upright, is inclined at an angle of 15 from the vertical, and laps 3 inches against the upper face of the sill. The top is even with the surface of the pool. The axis of rotation of the wicket is so placed that the height of the breech above the sill is 5 of the total height, and consequently that of the chase is 7. The cap of the horse passes through an eye in the head of a prop, whose foot is supported, when the wicket is up, against a cast iron heurter fastened in the sole of the pass. When the wicket is down the prop is retained in a slide, of which the heurter is the head. When it is desired to lower a wicket, the foot of the prop is tripped by a corresponding projection on the tripping-rod, which is moved horizontally on the sole by means of a wheel and gearing placed in the pier or in a wall of the lock, for each pass is managed by two tripping-rods, each of which acts upon one-half of the wickets, beginning at the middle of the pass.

On the other hand, the wickets, when down, are raised by a boat-hook, worked from a boat furnished with windlass and other appliances.

It is quite evident that the trestles, the props, and the tripping-rods are of wrought iron; the slides and the heurters of cast iron.

The weirs of the fifteen new dams between Laroche and Auxerre have been, since their construction, supplied with automatic wickets, with movable counterpoises, on the Chanoine plan. These wooden wickets are 4 feet wide, with 2-inch spaces between. The weir can be made tighter by applying joint-covers over the open spaces between the wickets.

Each weir-wicket is movable, like a pass-wicket, around a horse, which carries a prop; and for each wicket there is a heurter and slide. M. Chanoine had even added tripping-rods, which, however, he did not regard as very necessary. The axis of rotation of a weir-wicket being only 2 inches above the one-third the height of the wicket, it was only necessary that the water in the pool should rise from 4 to 6 inches above the top of the wicket to make it swing; the movable counter-weight placed at the foot of the breech, which kept the wicket up when the pool was at its ordinary level, slipped to the chase when the wicket swung. If the level of the pool fell a certain distance the wicket would swing back, and the counter-weight would fall back to the foot of the breech.

This ingenious system was striking in its simplicity, and was accepted at once after the isolated experiments made at a single dam, while specially pre-occupied in devising means for rapidly passing a flood, without exhausting the pool above or injuring the passage of river-craft; but a great disappointment was experienced when the continuous navigation on the Yonne and Seine, between Paris and Laroche, came to be tested. An official order of May 4, 1868, in approving the provisional regulations for the new method of navigation, authorized the engineers to put in operation the dams built on the Seine and the Yonne, between Paris and Laroche. The official order recommended that this delicate work should be undertaken with all the precautions necessary to prevent injury to navigation. The dams on the Seine were raised between the 18th of May and the 7th of June. The first four dams on the Yonne were closed between the 8th and 10th of June, but the rais ing of the thirteen others was only finished by the 5th of September, after the closing of the canals. A difficulty immediately arose on account of the co-existence of the artificial floods of the Upper Yonne, whose waves came twice a week, and swung a certain number of weir-wickets, which wickets, although called automatic, would not raise themselves until there was a fall of 34 feet in the pool above, from which circumstance navigation was much hindered. Thanks to the zeal and activity of the engineers, to the careful watch of the conductors, and to the devotion of the lock and dam tenders, it was possible to master the situation during low-water. With boats and different expedients devised by those in charge of the navigation success was obtained in raising the wickets with sufficient rapidity, and the improvement of the new system was finally apparent and conceded by all. But in the month of August the waters discharged from the canals, and those from violent storms, increased by the artificial flood-wave, produced disturbances in the pools that extended to Paris. In consequence of this experience, care was taken to empty several of the upper pools before the arrival of the artificial flood-wave. On the 22d of October a little rise of 8 inches from the Armançon River arrived at Laroche without being announced, and consequently without the precautions prescribed for an artificial flood-wave having been taken below. A complete derangement resulted at all the weirs and in all the pools from Laroche to Paris. Immediately the engineers proposed to establish above each weir, with movable wickets, a foot-bridge, which, with the aid of a windlass and chains, would permit the management of the wickets and the regulation of the level of the pool above; meanwhile all the dams were opened, and the system of artificial flood-waves was continued freely as formerly. A board of three inspector-generals of Ponts et Chausées, charged with an examination, heard those interested at Joigny, at Sens, at Montereau, and at Paris. They adopted the propositions of the engineers, which, as advised by the General Council of Ponts et Chausées, were approved by an official order of December 28, 1869.

In consequence, during the two seasons of 1869 and 1870 foot-bridges for maneuvering were built above each weir with so-called automatic wickets; and but for the unhappy events at the close of 1870, continuous navigation would have been established between Paris and Laroche by the month of September, 1870; which, however, could not be until the 1st of September, 1871, a year later. Each bridge for maneuvering is composed of wrought-iron trestles, like the trestles of Poirée dains, movable around a horizontal axis at right angles to the axis of the weir. Each trestle is opposite the middle of a wicket. These trestles are connected at their caps by two clamp-bars, which fix the width of the bridge. Between these bars is a wooden flooring, which is raised 20 inches above the level of the pool. The two clamp-bars are the rails upon which rolls the truck that carries the hoisting-windlass. Finally, to this windlass reach two chains, one attached to the head of the chase, and the other to the foot of the breech of each wicket. By the help of the windlass, solidly fastened to one or two

trestles and the two chains, every maneuver necessary to regulate the level of the pool-raising lowering, or swinging the wickets-can be performed without fatigue and without danger. In times of flood the trestles of the foot-bridge fall into a recess nearly on a level with the crown of the weir. The planks, the clamp-bars, and the windlass are put in store. The counter-weights have been removed from the weirwickets as no longer required.

This system has succeeded perfectly. At night each lock-tender is warned of the change in the water-surface above his dam by an alarm, put in motion by a float. Soon all the dams will be connected by telegraph, and the system thus completed will prevent surprises..

In consequence of the experience obtained in 1868 on the working of the twenty-nine movable dams between Laroche and Paris, it was decided to improve the navigation of the Yonne between Laroche and Auxerre, with passes opened and closed by movable wickets and weirs provided with foot-bridges and needle-dams. An exception in the ar, rangement of the weir was made at the Ile-Brulée Dam, near AuxerreWhich was provided with large shutters, 114 feet wide, the invention of M. Girard These shutters, movable around a horizontal axis at the foot, placed on the upper crest of the weir, were supported by props, which were the piston-rods of the same number of inclined pumps, firmly fastened to the floor. These pistons are put in motion by the water which comes by pipes under water, communicating with a reservoir supplied by a turbine, which is itself put in motion by the fall at the dam. Finally the dam of La Chainette, at Auxerre, at the head of river-navigation, has a stationary weir, and a pass only closed by a needle-dam.

To sum up. Of the 25 movable dams established on the Yonne between Auxerre and Montereau three are on the Poirée system proper; there remains but one on the Chanoine system proper; 22 have passes with Chanoine wickets, but the weirs have different systems; 15 weirs have movable wickets with foot-bridges for maneuvering, 6 have needle-dams on the Poirée system, and 1 only has large Girard shutters. At present the working of all these dams is easily managed, without danger to the attendant, and surprises are no longer to be dreaded, thanks to the floats with alarms at each dam, and the telegraphic communication from dam to dam.

There are 26 locks between Auxerre and Montereau, while there are only 25 movable dams, because the Gurgy cut-off, just above the dam of the same name, has 2 locks. Of these 26 locks 23 are new, and their chambers have a width of 344 feet, and an available length [between chord of lift-wall and recess of lower gate] of 315 feet, so as to receive six canal-boats coupled two by two, and two rafts coupled together; 2 of the 3 old locks, those of Epineau and Port Renard, have chambers 27 feet wide, with an available length of 594 feet; they therefore can receive six canal-boats and two rafts one after the other; a single lock that at La Chainette, has a chamber 27 feet wide, with an available length of 304 feet. This lock receives three canal-boats or one raft; which is not inconvenient, for reasons given before.

The three locks of La Chaînette, Epineau, and Port Renard have the faces of their walls of cut and hammered stone; the river-wall has a thickness of 8 feet 2 inches. Thirteen of the 15 new locks below Laroche have only their extremities and the gate recesses in masonry with vertical faces; the rest of the chamber is bounded by two paved masonry slopes with 45° inclination. [These slopes were originally made of dry stone resting upon beton, but several accidents and slides caused the dry stone to be replaced by masonry, both here and for the upper surfaces of dikes.] This rockwork, of scabble-stone for 10 locks and rough for 3, rests on a mass of beton or masonry, founded on solid rock or sustained by a line of piles and sheeting; the dike which forms the river-wall of locks in the river has a thickness of 10 feet at the top, with an exterior slope of rubble on an inclination of three base to two perpendicular; the foot of the exterior slope is protected by a line of piles and sheeting, or by heavy stones, when it does not rest on rock. The top surface of the dike is covered with masonry. This dike, which is of earth, and contains a core 64 feet thick of puddled clay, is generally water-tight. The 2 locks of Péchoir and St. Martin have on the land side of their chambers a slope of 45°, and on the river side a vertical wall of masonry 8 feet thick, with an enlargement opposite the lower gate to contain the chamber in which are placed the wheels and pinions which work the tripping-rod of the press.

Of the 8 new locks between Auxerre and Laroche, two, those at Monéteau and Bassou, are on the same plan as those at Pêchoir and St. Martin. The 6 other locks have their chambers bounded by two vertical masonry walls, and for the 4 locks in the river, the river walls are 8 feet thick.

The cost of the forgoing works was as follows:

The reservoir des Settons

Francs.

Dollars.

One dam without lock between Sens and Monterean
12,715 meters (7.9 miles) of wide cut-off, at 238.45 francs ($45.30)
per meter...

One dam without lock between Laroche and Sens..
Seven locks and dams between Sens and Montereau, at 561,000
francs, ($106,590)..

One dam without lock between Auxerre and Laroche...
Eight locks and dams, between Laroche and Sens, at 462,000
francs, ($87,780).

Seven locks and dams, between Auxerre and Laroche, at 317,000 francs, ($60,230).

Miscellaneous work: protection of banks, dredging, damages, &c.

18, 152, 038

The total length of the Yonne, in its natural state, between Auxerre and Montereau, is 74.30 miles; the length of the improved river, measured by the cut-offs, is 67.28 miles; the cost per mile of improved river is, therefore, $51,261; but if the cost of the reservoir des Settons be deducted, the cost per mile becomes $48,998.

NAVIGATION OF THE UPPER SEINE.

The Upper Seine extends from Marcilly, at the mouth of the Aube, to Paris; but the portion between Marcilly and Montereau is generally called the Little Seine, while that between Montereau and Paris is the Upper Seine proper.

During low water the depth of the Little Seine varies from 8 to 12 inches, and that of the Upper Seine from 20 to 24 inches. The greatest flood known had an elevation at Paris, above low water, of 23 feet.

The slope of the Little Seine in low water averages 14 inches per mile, and that of the Upper Seine 13 inches per mile.

On the Little Seine there is a continuous navigation between the mouth of the Aube, at which place the Upper Seine Canal enters the river, and Nogent, by means of the cut-off between Marcilly and Nogent and the two dams of Conflans and Nogent; but from Nogent to Montereau there are only four dams, which are used to give artificial flood-waves as far as Montereau. The navigation of the Little Seine is, therefore, not very important, but it is expected that, before long, the same improvements will be introduced here as on the main Upper Seine and on the Yonne. Although the navigation of the Upper Seine, between the mouth of the Yonne and Paris, has always been very important, until September, 1871, it was intermittent for three-fourths of the year and largely dependent upon the artificial floods from the Yonne. This condition of affairs has been ended by the establishment of 12 movable dams between Montereau and Paris.

In examining the question of improving this navigation, it was ob served that the effect of an artificial flood-wave was insufficient after it had traversed a distance of 19 miles.

In 1859, 3 dams, in accordance with plans of M. Chanoine, were ordered at Champagne, (one mile below the mouth of the Canal du Loing,) at Melun, and at Evry; and in 1860, 9 others were ordered at Varennes, La Madeleine, Samois, La Cave, Les Vives-Eaux, La Citanguette, Le Coudray, Ablon, and Port-à-l'Anglais.-(See the profile Fig. 52.)

The 12 large movable dams just mentioned were built between 1859 and 1864, after the system of M. Chanoine, that is, with movable wickets 4 feet wide for the pass, and

REPORT OF THE CHIEF OF ENGINEERS.

automatic wickets 4 feet 3 inches wide for the weir; the interval between two wickets was 4 inches; a single dam, that at Melun, retained for the weir the needle-dam which was already built across the right arm of the Seine. The navigation-passes, which are of masonry, vary in width from 132 to 212 feet; the wooden sills, solidly built into a floor 32 feet wide, are 10 feet below the level of the pool and 2 feet below low-water line. The new weirs are from 197 to 229 feet long; their sills are 20 inches above low water; the floor, 13 feet wide, is formed of a wooden casing filled with béton, with wooden ties on top, between which is inclosed a masonry pavement; each weir is contained between a pier 10 feet wide, which separates it from the pass, and an abutment which connects it with the bank.

The locks have chambers 39 feet wide, with an available length of 587 feet, so as to receive at least twelve canal-boats or four rafts.

The extremities and the gate-recesses of the locks are built of masonry; but the revetments of the chambers are simply of paving made with rough stones laid dry, resting upon a core of béton placed under water and inclined at an angle of 45°; the dike on the river side, which has a puddled core, is 10 feet wide on top; its outer slope is revetted with rough stone laid dry over riprap. The Port-à-l'Anglais lock has masonry walls with vertical interior faces. The miter-sill is placed at least 5 feet below the surface of the pool below, which is assumed as horizontal.

The upper surfaces of the dams aud of the locks are at least 16 inches higher than the surfaces of the pools above them.

The test made in 1868 of the continuous navigation, which has been mentioned before, in connection with the movable dams on the Yonne, had shown the unreliability of the automatic weir-wickets, and the lack of solidity of the revetments of the lockchambers, which had been made of rough stones laid dry, and often crumbling under the action of frost. The official order of December 28, 1868, approved of the complementary works which had been considered necessary, and which consisted chiefly1st. In lowering the lower miter-sill of the Port-à-l'Anglais lock, and in reconstructing the chamber of this lock.

2d. In the establishment of foot-bridges for maneuvering, made with trestles placed just above all weirs, with Chanoine automatic wickets.

3d. In the consolidation of the paved slopes of the lock-chambers.

4th. In the establishment of a line of telegraph between the dams.

The changes above mentioned were all made by September, 1871, having been delayed by the war and the communist troubles. All the works are firm and solid, and have succeeded perfectly.

The following table gives the principal dimensions of the dams and locks: