No barrack was to be situated at a distance of more than 3.5 kilometres from the men's work. In the first instance, it was not possible to make any estimate of the number of buildings needed on a contract involving 70 millions of cubic metres of earthworks, and thus at first only eleven sites have been chosen, with accommodation for one thousand nine hundred and fifty workpeople, the sizes of the barracks varying from three hundred to fifty beds. By reference to drawings, the Author describes in detail certain of these structures. The minimum cube contents per bed was fixed by the Government Sanitary Department at 12 cubic metres. The buildings are all constructed with timber, boarded inside and out. The apartments are in all cases warmed and ventilated. The cost of each barracks-dormitory for one hundred workpeople is approximately 14,000 marks (£700); living-rooms, dining-hall, and premises for staff, 20,000 marks (£1,000); canteen, 1,800 marks (£90); latrine, 1,000 marks (£50); door-keeper's hut, 300 marks (£15), and dust-hole, 250 marks (£12 108.). The two hospitals, each with twenty beds, and their arrangement, are also described by reference to plans; they consist of three large wards, each with six beds, and a smaller one with two beds; the space per bed being 30 cubic metres. G. R. R. Hydraulic and Physical Effects of the Canalization of Rivers. By B. SANTINI. (Giornale del Genio Civile, 1889, p. 269.) The most notable hydraulic and physical effects arising from the canalization of rivers and improvement of waterways occur when by diminishing the width of the channel the depth of water is increased, by either deepening the bed or raising the surface-level of the water. If the bed is not changed in any way the alteration of the water-level is permanent, but if either by dredging or by the erosive action of the water itself the bed is deepened, the raised water-level is only temporary, and gradually disappears, leaving the surface little, if at all, above its natural point, and, indeed, in cases of considerable and continued erosion, distinctly lowering the water-level. The Author, therefore, considers the subject under three heads:-(1) Channels with unchanging beds, i.e., on a hard stratum unaffected by scour; (2) channels where the soil is acted on to a moderate extent by the current until the increasing depth of the restricted section restores the original velocity and consequent stability of physical conditions; and (3) channels in very loose or soft soil, where the work of erosion goes on continually to an extent which it is practically impossible to estimate or to regulate. With each of these cases he analyses as far as possible the conditions affecting the flow of water, giving formulas for estimating the depth of water, extent of erosion, variation of level, and velocity of current. As affecting the navigable conditions of any waterway, especially with regard to up-stream traffic, it is to be noted that the advantage derived from the increase of depth of the channel may be more than counterbalanced by the increase of velocity of the current. It may also be taken as a general maxim of practical hydraulics that although canalization in the form of channels of restricted width may beneficially affect navigation, it is not calculated to improve the physical features of any river course; in fact, that the variable water-level is rarely of advantage and often distinctly injurious. Even for the benefit of navigation, it is well to limit works of canalization to channels capable of easy erosion, otherwise the advantages and disadvantages are so closely balanced that it is often difficult to say which will predominate. The Author then proceeds to apply his formulas and deductions to an examination of a project for the canalization of the Tiber for a length of a little over 19 miles, from Alberobello to near Porte Galera. The engineer of the works estimates that the scouring of the current will deepen the bed to the extent of 17 feet, entailing a corresponding decrease of 10.36 feet in the surface of the water, while the Author considers that the erosion of the river-bed will not exceed an average of 3.75 feet, and that no appreciable difference of the water-level is to be anticipated. He concludes, therefore, that while no hydraulic advantage is to be expected, there will be an appreciable improvement for purposes of navigation, as the depth is considerably increased without any increase of velocity. P. W. B. The Improvement-Works on the Brenta and Bacchiglione. (Giornale del Genio Civile, 1889, p. 313.) Previously to the year 1840, the Brenta, which brings down a great quantity of alluvial deposit, discharged its waters into the Adriatic, about 2 miles north of the estuary of the Adige; but in the year mentioned its course was shortened by a lateral cut into the southern end of the Lagoon of Chioggia, its abandoned bed being utilized for a neighbouring stream, the Bacchiglione, the former bed of the latter, in its turn, being now known as the Canal Morto, and serving to collect part of the drainage of the flat tract of land to the southward. On account, however, of the silting up of the lagoon at the outlet of the Brenta threatening the harbour of Chioggia itself, and also on account of the liability to frequent floods where the waters could not be cleared off by the tortuous, shallow, and weedy channel which had gradually formed-conditions alike urgently affecting health, navigation, and surface drainage it had been found imperatively necessary to cut off the Brenta once more from all communication with the Lagoon of Chioggia, and to take it direct to the sea, near to its old outlet. It was not practicable to re-connect it with the channel now used by the Bacchiglione, at the old point of transfer, primarily because the latter, a more sluggish and level stream, flows here at a slightly lower level than the Brenta; and as the greatest difficulty is already experienced in securing efficient drainage for the district, the surface of the ground being but slightly above the sea-level, and about 68 square miles of the country being entirely dependent on incessant pumping for any drainage whatever, it was impossible either to raise the level of the stream on which this drainage is dependent, or to subject the land to the additional risks of floods from the Brenta. It was therefore necessary to keep the two rivers separate, side by side, to a point about 3 miles from the sea, where they could be united safely in one common channel. The works on the Brenta commence at Santa Margherita di Calcinara, about 10 miles from the sea. Above this point, for some distance, the sectional area of the waterway averages 4,024 square feet, and the width of the river 240 feet. At Santa Margherita the width of the new channel has been commenced at 260 feet, the old bed being followed for nearly 2 miles to Conche, where it approaches the Bacchiglione. From this point a new cut has been made to Le Tresse, 2 miles 7 furlongs in length; whence, to Ca' Pasqua, a distance of 2 miles, where the width of the cut is increased to 330 feet, the former bed of the river has again been utilized. For this length, and mostly parallel with the preceding, a new cut has been made for the Bacchiglione. Below the confluence of the two rivers the width is increased to 490 feet; at the confluence with the Gorzone, a stream flowing in from the south, 11 mile further on, the width is 590 feet; and passing Fort Brondolo, by a new straight cut through the sandhills, a length of about 2 miles, the outlet into the Adriatic is 660 feet in width. The course of the Bacchiglione, between Palate and Ca' Grassi, has not been enlarged, the channel-which formerly belonged, as noted, to the Brenta-being of ample dimensions; but the dykes have been strengthened and improved on the whole length. After the details for the works on the Brenta had all been settled, there occurred the heaviest flood ever known in the district, in consequence of which the whole design was revised; and it is considered that, with the present dimensions and with the straight outlet to the sea, in the place of the old deteriorated channel, there will be no difficulty whatever in dealing with any emergency of floodwaters. At Santa Margherita the dykes are 2 feet 6 inches above the highest flood-level; at Le Tresse, 2 feet; and at Brondolo 1 foot. The regulation top-width of the dykes equals their height; but in bad ground this is considerably increased, and in some places is used as a roadway. In cutting through the sandhills between Brondolo and the sea, the excavation to the full section was carried down to within 10 feet of the bottom, to which latter a gulley 105 feet in width was cut, the remainder being left to the erosive action of the water itself. The total amount of excavation for the river beds was 5,655,000 cubic yards, of which 2,314,000 cubic yards were used in forming new dykes and strengthening old ones, the remaining quantity being taken by barges or trucks to a distance from the works. At Conche, a siphon under the Brenta enables the drainage of the district of Sesta Presa to be still discharged into the lagoon. There are three bridges over the united channels of the Brenta and Bacchiglione; the first, at the point of confluence at Ca' Pasqua, having a length of 354 feet over the former river, and 197 feet over the latter; the second at the mouth of the Gorzone, with a length of 512 feet; and the third at Brondolo, 590 feet in length. These bridges are constructed of iron girders on brick piers, on a pile foundation; and each is provided with a central opening-span of 33 feet 10 inches. One of the most important considerations in connection with the new works, and the absorption of the Bacchiglione into the new cut, was the provision for the drainage of the southern district already referred to, comprising originally the districts of Foresto, Fossa Monselesana, and Fossa Pultana; to which were added later five other districts situated between the Canal Roncajette and the Canal di Battaglia, viz., Pratriarcati, Savellon di Bagnarolo, Paludi Cattaio, Due Carrare, and Retratto Monselice; a territory about 25 miles in length, extending from the Canal dei Cuori to the foot of the Euganean Hills. This drainage converges to Le Tresse, where it passes by a siphon under the two rivers direct into the lagoon, thus reducing the length of the outlet channel by 5 miles, and giving a corresponding advantage in the fall. The siphon at Le Tresse is one of the largest works of the kind in Italy. It is in two distinct parts, a distance of 552 feet intervening between the two rivers. The siphon under the Bacchiglione is 262 feet in length from face to face, and that under the Brenta 428 feet. Each comprises five parallel openings or tunnels, 14 feet 9 inches wide, with elliptical invert and roof. The sectional area of each opening is 135 6 square feet, giving a total water area of 678 square feet. In the horizontal length the clear height of the siphon, from invert to crown, is 10 feet 6 inches; this is increased by bellmouthing to 15 feet 5 inches at the upper end of each slope. The invert and roof curves are all easy and flowing, so as to offer no impediment to the ready passage of the water. Under the Bacchiglione the horizontal tunnel is 154 feet 10 inches in length, and each of the inclines 53 feet 7 inches. The piers and arching are all in brickwork on a foundation of concrete, 4 feet thick under the horizontal portion, and 5 feet on the inclines; the invert being 10 inches thick, and the arch 2 feet 1 inch for the middle two-thirds, and 2 feet 7 inches over the haunches. A concrete filling is carried up to 1 foot 4 inches above the crown of the arch, and covered with a g-inch layer of cement. The facework is of ashlar masonry, from the quarries of Istria. At the commencement of the outlet channel are sluice-gates, corresponding in span and water-area to the siphon. The gates, which are of wrought-iron, are intended to close the streams against the inflow of high tides in the lagoon, and close automatically with the rise of the tide, and may if necessary be fixed in the closed position. The angle of closing is 112° 38'. The gates measure 19 feet 8 inches in height, by 9 feet 10 inches in width, and are hung on piers 5 feet 11 inches in thickness and 24 feet 3 inches high, built on a foundation of concrete 4 feet 2 inches in thickness. Much trouble was experienced in the foundations from the inflow of a great quantity of water, which it was found extremely difficult to check, and which on two occasions necessitated the suspension of the works. It was found that the water came from the lagoon, filtering through a distance of some 800 feet under the intervening bed of the river. The soil (the nature of which had been carefully ascertained by preliminary borings) was sandy from the surface to a depth of 5 feet; then came a 6-feet 6-inches layer of loam, below which was a 5-feet bed of peat, reaching to about 12 feet 6 inches below the mean sea-level. Below this, for an indefinite depth, was the finest sea-sand, in which the excavations had to be carried to a depth of about 28 feet below sea-level. At a depth of about 11 feet 6 inches were found the remains of an ancient forest, the decayed mass presenting serious obstacles to the driving of piles. Owing partly to the large area to be excavated for the gates, the catchment-basin and the siphons, as compared with the area to be built upon, and also to the available time and the cost, it was decided not to adopt caissons, but to carry on the work in well-timbered excavations, depending upon sufficient pumping-appliances and rapid execution of the work. The Author explains at some length the principles upon which the details of the structures were calculated and specific dimensions assigned, and gives a detailed schedule of the quantities and the cost of these outlet-works. P. W. B. Prevision of Floods. By E. ALLARD. (Annales des Ponts et Chaussées, vol. xvii., 1889, p. 629, 1 plate.) The height of a flood may be reckoned in two ways; either the height of the flood may be measured above the zero of the gauge, corresponding approximately with the summer water-level of the river, which is the absolute or total flood-rise, or its height may be taken above the level at which the river stood when the flood commenced, which is the actual rise. A prevision can be made either by obtaining a relation between the total rises, or the actual rises; and sometimes one method is preferable to the other, or sometimes the use of both methods gives a better mean result than either |