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needful for the economical supply of gas to the Citizens. By Clause 60 of the Bill, the rights and powers of the Commissioners of Sewers of the City of London are reserved. There are other powers sought in the Bill, but the object is the same, namely, the supply of better and cheaper gas. The total area, including public way, scheduled within the City for the several projects reported upon is about 4| acres, which is very much less than has been scheduled annually for many years past. One of the Railways will materially interfere with the sewerage of the district through which it is proposed to construct it; but generally speaking the projects will not interfere to much extent either with the sewers or with the public ways; and very little of the public way is this year proposed to be absorbed by the Companies. From this state ment must, of course, be excepted the Corporation Gas Works Bill— which, if passed an I carried into execution, would involve laying mains throughout the entire City. Arrangements must be made before these Bills pass into law (should the Commission determine not to oppose them on other grounds) by which the sewerage in the City shall be altered or maintained in a fitting manner without loss to the Citizens, and when existing public ways are to be appropriated, that such an equivalent shall be given as * will most conduce to the public interest. For tho present, therefore, it is needful that the Commission should dissent from the whole of these projects so as to retain its locus standi before the Committees of tho Houses of Parliament, to which the Bills probably will be referred. 4- THE INSTITUTION OF CIVIL ENGINEERS. January 1868.—The Paper read was “ On the Relation of Fresh water Floods of Rivers and Streams, to the areas and physical features of their basins; and on a Method of Classifying Rivers and Streams, with reference to the magnitude of their Floods—proposed, as a means of facilitating the investigation of the Laws of Drainage.” by Lieut.- Col. P. P. L. O’Connell, R.E., Assoc. Inst. C. E. After referring to what might be termed the first stage of natural surface drainage, subsequently carried on and completed by rills, streams and rivers, the Author observed that streams draining largo areas were not subject to sudden floods caused by short smart showers, and that a lake, like the extension of the area of a drainage basin, was a moderator of the flood discharge, resulting from a given rate of rain fall. There were other natural moderators which were more or less effective, as, for instance, a porous, absorbent soil, and the foliage of dense forests, but the latter had apparently the property, in some situa tions, of increasing the actual amount of rainfall, which counter balanced its effect as a moderator of river floods. Snow might, according as it thawed slowly or rapidly, be a moderator or the reverse. Again, when a tributary in flood flowed into a large main river, the channel of the latter also acted as a moderator. If a series of natural basins could be found, increasing regularly in area, having physical features as to slope, soil, &c., all tending in the same degree to discharge the rain falling on them, and if the distribution of the rain were the same in all these basins, then, doubtless, tho rate of discharge in floods might be described graphically by some regular curve, the abscissae of which would denote the area drained, and the ordinates tho flood discharge per second. This curve would be concave to its base, and the tangent at its origin would have a value representing exactly the maximum rate of rainfall. Such, however, were the diversities of physical features in river basins, and in the distribution of rainfall in the world, that tho search after the desired scries of natural basins possessing exactly similar characteristics would probably be a vain one. This was to be regretted, for rivers .small and great, might alike be ..referred to some such curve, and classified as flood discharges, according as they took up positions near to or distant irom the curve. To supply the place, as a classifier, of this unknown curve, the author suggested the use of the common parabola, as follows : Let x, the abscissa of a point in the curve, represent the area in square miles drained by a river, and y, the ojdinate of the same point, represent the number of cubic yards discharged per second by that river. Then, in the common parabola, y =,M. a;, where M might bo termed the modulus of the river, or of its drainage basin, as a flood producer. When M was large, it would indicate that the physical features were such as to slope, soil, total amount and distribution of rainfall, as to give the river and its drainage basin a high place in the classification. When M was small, it would, on the contrary, show either that but little rain fell on the basin, or that it possessed some of those physical features which tended to moderate floods. With the view of illustrating how far this method of classifying rivers as flood producers was likely to prove useful, reference -was made to some facts respecting the Mississippi and its tributaries, as recorded in the report on that river, by Capt. Humphreys and Lieut. Abbot, which tended to show, in the author’s opinion, that the method might be usefully, if cautiously, applied. Certain exceptional cases of river floods were next alluded to, and regret was expressed, that data sufficiently extensive and accurate for the purpose of testing very rigidly any method of classification had not yet been collected. The author had, however, prepared a table, exhibiting a few of the physical features of some of the principal rivers of North America, Europe, and India. This table gave the area of the drainage basin of each river in English square miles, the flood discharge of the river in cubic yards per second, with the name of the authority for this statement, the flood discharge of the river in cubic yards per second per square mile drained, and the values of M in each case. The facts so collected were also exhibited in diagrams. After commenting upon the range in the values of M thus recorded, it was observed, that whereas, in the case of large rivers, the parabola expressive of the relation between the area drained and the discharge per second might without sensible error, be supposed to have its apex situated at the origin of the co-ordinates, in the case of small districts this supposition would lead to error. In ( the latter instance it became necessary to ascertain, at least approximately, what was the maximum rate at which rain fell in the district, and to place the origin of the co-ordi nates at a point in the curve -where the inclination of the tangent to the axis of x should correctly represent that maximum rate. For the sake of illustration, it was assumed, that a district existed in which the maximum rate of rainfall was 5 inches an hour, and the maximum value of the modulus M was 20. This required that the origin of the co-ordinate should bo situated at a point in tho parabola where its geometrical tangent was inclined to the axis of x, at an angle whose trigonometrical tangent was 120. If a/ andy' were the rectangular co-ordinates of the curve, measured from this point, its equation was /= 20 V the areas being measured in square miles, and 120’ the discharges in cubic yards per second. But as, for small districts, it would be more convenient to measure the areas in acres, and the discharge in cubic feet per second, the formula became, when adapted to these new measurement, ?/' = 21.4 x> -&• very nearly, or after the solution of this quadratic equation, y' = —45.797 + \/2097.28 4- 457.96 x. A table computed by this formula, was then given, showing the dis charge in cubic feet per second from districts increasing in size from 10 acres to [5 square miles; and it was stated, while the discharge from an area of 10 acres represented a rainfall of 3.56 inches an hour, that from a district having an area of 5 square miles represented a rainfall of only .36 of an inch. It was stated, that in rivers whose basins were by no means small, very extraordinary floods might occur in years not remarkable for large totals of rainfall; and in conclusion a few state ments and quotations were given, as affording examples of flood moderators. February, 1868.—The Paper read was on “ Floods in the Nerbudda Valley : with remarks on Monsoon Floods in India generally.” By Mr. A. C. Howdcn, Assoc. Inst. G.E. This valley was described as being bounded on the north by the Vindhya and on the south by the Sautpoora ranges of mountains, and as consisting principally of black cotton soil, which was renowned for its fertility. Tho drainage of the valley supplied nearly the whole volume of the waters of the Nerbudda River, which traversed it in a direction nearly due east and west. The river took its rise in the Vindhya Mountains, at an elevation of 3,500 feet above the sea; its fall to Jubbulpore, 190 miles distant, was 10 feet per mile, and thence to the Gulf of Cambay, the fall might be estimated at about 2 feet per mile, the total length of the river being 800 miles. The width at its source was only 1 yard, while a little above its confluence with the Towah, 360 miles down stream, it was 900 yards, and at its mouth upwards of 1 mile. In an ordinary monsoon the level of the water ’rose between 30 and 40 feet, but it had been known to rise nearly 60 feet, when it owerflowed the banks. Midway between the river and the Sautpoora Mountains, this valley for a length of about 270 miles was traversed by the north-eastern extension of the Great Indian Peninsula Railway, which crossed all the tributaries falling into the river on its southern bank; and it was the floods to which theese feeders were liable that formed the subject of the present paper. The floods of this region were divisible into two classes, according as they affected the plains, or the rivers. With regard to the former, it was remarked that the greater part of the Nerbudda Valley traversed by the railway was almost a level plain; and that although the average rainfall in the district, 46 inches, or 11| inches for each of the four monsoon months from June to September, could easily be provided for by tho natural watercourses, yet that as much as 10.50 inches fell in eighteen hours, in August, 1864, causing sudden and disastrous floods. It was observed that, in constructing a railway across plains of this description, great attention should be paid to the rainfall of this dis trict, and ample provision should be made for carrying off the maxi mum amount speedily, without allowing it to dam up ; as few embank ments (especially those formed of black soil) could withstand the immense pressure then brought upon them, although the period of danger might not exceed twelve hours during the year, and should an
