method singly. The prevision of the flood-rise of a main river, like the Seine, at Paris, is obtained from the maximum rise of each of its affluents, by multiplying their mean by a coefficient; but, probably, a nearer approximation to the actual results would be obtained by taking into account the duration of the flood on each tributary, owing to the different times at which floods of the various tributaries reach any given point on the main river, or by varying the coefficient in proportion to the size of the basin of each tributary. By taking as abscissas the sums of the rises of each flood at the several places of observation on the upper river or tributaries, multiplied if necessary by predetermined coefficients, and as ordinates the height of each flood at the place for which a prediction of floods is desired, a series of points is obtained by means of which a mean curve can be drawn, which gives the height of the flood at the place in question for any observed rises at the points of observation above. This graphical method is then applied by the Author to the floods of the Yonne, at Sens; the Seine, at Bray; the Marne, at Damery; and the Seine, at Paris, as examples of the system; and the results are discussed, from which the following conclusions are drawn. (1.) A graphical method, representing each flood by a point, and giving curves of prevision, may advantageously replace numerical formulas. (2.) The total flood-rise measured on the gauges may often serve as a basis for previsions, in place of the actual rise. (3.) The seasons generally affect the prevision of floods; and it is possible to specify the resulting numerical corrections. (4.) Lastly, the daily prevision of the heights of a river, which is the ideal aimed at, can only be roughly approximated to in the existing state of the investigations on the subject, but will doubtless be rendered more accurate by further researches. Several numerical tables relating to floods, and their prediction from day to day, at places in the Seine basin, are appended to the article. L. V. H. Submarine Works of the Outer Harbour of La Pallice at (Le Génie Civil, vol. xvi., 1889, p. 1, 6 woodcuts.) The north and south jetties of this harbour were first carried out from the shore to low-water of average spring tides. They were then connected by a dam constructed by tide-work, 984 feet long, along low-water mark; and the enclosure thus formed having been pumped dry, was excavated down to 16 feet below the lowest tides. Beyond this, the south jetty had to be extended 1,004 feet, and the north jetty 410 feet; and rock had to be excavated under the sea in the space between the jetties, and in the approachchannel outside. Two movable caisson diving-bells, provided with compressed air, were employed for founding dry, in the open sea, [THE INST. C.E. VOL. XCIX.] 2 F twenty-four blocks under water, each occupying a space of 1911 square yards, and the highest containing 1,504 cubic yards. The intervals, of 6 to 10 feet between the blocks, were spanned by little masonry arches. Each caisson was 72 feet 2 inches long, and 32 feet 10 inches wide; its working-chamber, at the bottom, was 5 feet 11 inches high; and there was a watertight chamber of equilibrium above, 6 feet high, on the roof of which an iron scaffolding was placed, 23 feet high, supporting a platform, 523 feet by 13 feet. This platform communicated with the workingchamber by four vertical shafts, of which two were provided with ordinary air-locks for the passage of the workmen, and smaller side-locks for the supply of materials; whilst the other two shafts, for the removal of the excavations and the introduction of stone, were surmounted by air-locks for the materials with automatic arrangements. Some Schmid compressed-air motors, for working the winches, were placed on the air-locks, being fed by compressors from the shore. Each caisson weighed 110 tons, and carried a permanent load of 220 tons of masonry on its lower platform. The caisson was built on land, taken down an inclined plane at lowwater, floated at the following high-water, and towed into position, drawing 11 feet of water when the equilibrium-chamber was full of air, and the working-chamber full of water. The caisson is adjusted to its exact position by the winches acting on its mooring cables, attached behind to the jetty, and in front to buoys; and it was then grounded, either merely by the falling of the tide, or by filling the equilibrium-chamber with water in deeper places. The caisson was weighted with 220 tons of pig-iron on the upper platform, to counterpoise the 400 tons of upward pressure produced by filling the working-chamber with compressed air. The bottom was first levelled, and then excavated down to the calcareous stratum on which the blocks were founded. As the masonry proceeded, the caisson was raised by twenty-four long jack-screws. Stormy weather often interrupted the work; and then the caisson was lowered on to four large masonry pillars, built up on the block to the roof of the working-chamber. When the block reached 5 feet above the level of the lowest tides, advantage was taken of the next high tide, rising up to 173 feet above the zero, to float the caisson into its next position, after having removed the load of pig-iron, readjusted the six moorings, and forced the water out of the equilibrium-chamber. This operation, which was easy in fine weather, became difficult in bad weather, so that sometimes it was delayed five or six weeks. The caisson was reached from the jetty, the erection of which followed about 164 feet behind the blocks, the intervening space being crossed by a foot-bridge, resting upon a light firm scaffolding, over which the little trucks with materials ran. The excavation of the 170,000 cubic yards, for obtaining the requisite depth in the entire harbour, was effected in the dry by constructing four additional blocks across the entrance, and filling up the space between them with masonry so as to form a second dam, and also closing up the arched intervals between the blocks of the jetties, thus forming an enclosure of about 31,750 square yards. This enclosure was pumped dry, and the first dam removed; and the excavation was then carried out in the ordinary manner. The four supplementary blocks were founded 10 feet below zero, and a dam was raised on them up to 33 feet above zero; whilst two sluiceways, furnished with paddles, enabled the water inside to be drawn off at low-water down to 12 foot above zero. The arched spaces between the blocks of the jetties were closed at each side by panels, composed of frames, 1 to 13 foot high, formed of wrought-iron plates and angle-irons, and connected across by screw tie-rods. A vertical shaft had been constructed in each arch, so that, with the blocks and panels, a regular little caisson was formed, which, as soon as the panels had been lowered on to the layer of stone and clay filling the base of the spaces, was filled with compressed air, and a little wall built under the bottom of each of the panels, 13 foot high, and the material excavated to this depth. Two other little walls were then built under the first ones, and the next layer of material excavated, and so on by successive steps till the rock was reached. As soon as the space had been filled in up to 31 feet above zero, the panels were removed till the next site. The rock excavations outside, amounting to 13,100 cubic yards, were effected under water, by aid of Beaumont's rotary diamond drills; the 4.20-lbs. dynamite cartridges, inserted in the holes thus formed, were fired by electricity; and the débris were removed by a hopper dredger, and deposited out at sea. L. V. H. Quay-wall at the Government Harbour of Ruhrort. By - HAUPT and ROHNS. (Zeitschrift für Bauwesen, 1889, p. 255.) This work forms an extension of an older quay, constructed about the year 1870, and extends for a distance of 311 yards, following the bend of the harbour, and laid out with a curve of 985 feet radius. The coping is at a level of 20.50 (above Ruhrort gauge datum), the bed of the harbour being 4.10 feet, the lowest water-level 0.15 foot, and mean water-level + 8.20 feet. natural ground is of strong clay, overlying compact gravel. The After considering five different modes of construction, which included three in ironwork, viz., wrought-iron screw-piles and cast-iron plates, wrought-iron piling with clinker backing, and a platform supported on cast-iron columns, it was concluded that a wall founded upon masonry wells would be more suitable and economical than either of the ironwork designs or of masonry on a continuous foundation of concrete laid within sheet piling. The wall, as constructed, is founded upon thirty-six wells, 26 feet 3 inches apart, centre to centre. These wells measure, externally, 13 feet 2 inches x 16 feet 5 inches (the latter being the dimension, at right angles, to the line of the wall), their bases being sunk to a level of 8.20 feet, and the lowest portion, for convenience in sinking, being battered 1 in 10 for a height of 8.20 feet, above which the well-walls are vertical-excepting on the harbour-face, where the batter is continued up for the whole height, whereby the portion of wells above datum is reduced to 11 feet 6 inches, leaving a space of 14 feet 8 inches to be spanned by the intermediate arching of brickwork, springing at a level of +8.20 feet. The thickness of the well-walls is 3 feet 3 inches, reduced at the base, internally, to 1 foot 3 inches, and the latter rest upon beech curbs of 3 to 4 inches thick, strengthened by angle-irons and bolted to the wells, the lowest thinner portion of which is of brickwork in cement. The masonry of the wells is of sandstone rubble set in mortar, composed of lime, trass, and sand, in equal parts. The interior of the wells was finally filled up to the level of +3.28 feet with cement concrete, and the remainder with rubble masonry; the portions of shore between the wells were trimmed to a slope of 1 to 1, and pitched with stone as a protection against wash. In the upper part of the slope, at the back of the arches, is driven a sheeting of old rails, through the gaps of which water can readily escape from the earthwork backing. The walling above the arching is 5 feet 4 inches thick at the base, and 2 feet 3 inches thick at the top, and is finished with a coping of basalt 10 inches thick. The wall face is protected by fender piles 26 feet 3 inches apart; there are mooring rings at every 39 feet 4 inches, and ladders at 157 feet 6 inches apart. Particulars are given of the manner in which the new work was connected with the old, also of the methods of sinking the wells, by excavating and by dredging, and of the cost of labour. With three men excavating in a well, the average depth sunk was 1 foot 10 inches, and the cost of labour 378. per diem. The cost of sinking with a vertical dredger was 268. per day, the mean depth sunk by this method being 11 inches per day. The total cost of the wall, 311 yards long, amounted to about £7,676 38., or £24 138. 6d. per lineal yard (exclusive of the value of the old rails, which would add, say, 188. 3d. per lineal yard), divided as follows, viz. : The amount of masonry and brickwork per lineal yard was 16 cubic yards. Details of the prices of materials, &c., are given. The works were commenced in August 1883, and completed in May 1886. D. G. New Timber Dry-Dock at the Brooklyn (New York) Navy Yard. (Scientific American, Nov. 30, 1889, p. 341, 5 woodcuts.) This dock, built by Messrs. J. E. Simpson and Co., of New York, on the principle introduced many years ago by their senior partner, is an excavated basin lined throughout with Georgiapine timber, with sides and inner end sloping to the floor. The outer end is open, and is provided with heavy sill and abutment timbers. An iron caisson fits this opening and acts as a gate. The general dimensions are as follows:-Length over all on coping, 530 feet; length over all inside caisson, 500 feet; width on top amidship, 130 feet 4 inches; width on floor amidship, 50 feet; width on floor at entrance, 53 feet; width on top at entrance, 85 feet; depth of gate-sill below coping, 30 feet 6 inches; depth of gate-sill below high-water, 25 feet 6 inches; depth at centre, 32 feet 8 inches. The general contour of the dock conforms in some degree to the outline of a ship. Around the perimeter of the dock-floor, which is 460 feet long by 50 feet wide, 8-inch tongued and grooved sheet-piling is driven, in the present instance, on account of quicksands, to a depth of 45 feet, though 7 feet will suffice in good ground. The enclosed area is studded with round piles 12 inches in diameter, driven in rows, 3 feet from centre to centre transversely, and 4 feet from centre to centre longitudinally. Each longitudinal row of piles carries a 12 by 12 inch square timber. Upon these rest timbers of similar dimensions spaced 3 feet from centre to centre. On the latter is spiked or bolted 3-inch planking. Special rows of piles are driven to carry the keel-blocks. A space 10 feet wide beneath the centre of the dock contains extra closely-spaced piling for this purpose. Under the floor, and surrounding the heads of the piles, is a bed of Portland cement concrete 5 feet thick at the centre, and rising towards each side to a maximum thickness of 6 feet. Any water runs down to the central axis of the dock, owing to this slope.1 From each side of the floor the walls rise in steps at an angle of 39°. They are lined with 10-inch timbers of Georgia pine, 1 The sectional view of the dock shows the concrete as flush with the under sides of the transverse timbers in the middle of the dock, and rising at an incline to each wall, where it is flush with the upper sides, the inclines ending on each side the keel-blocks in a longitudinal drain 1 foot deep, being the space between two rows of longitudinal bearing-timbers. |