INSTITUTION OF CIVIL ENGINEERS.

New Zealand Times, Volume XXXIII, Issue 5317, 11 April 1878, Page 3

INSTITUTION OF CIVIL ENGINEERS.

(From The Times, January 21.) The first meeting of this institution after the Christmas recess was held on the 15th instant, when the newly-elected President, Mr. John Frederick Bateman, F.R.S.S.L. and E., delivered an inaugural address. The following extract from the address will be read with interest at the present time, when public attention is directed to the question of water supply and rainfall ; —“ The President next adverted to a question which was of the highest importance in that branch of the profession to which his attention had been more particularly directed —viz., the rainfall of this country.and the quantity of water which flowed off the ground—available for the use of man if properly utilised, or destructive when uncontrolled and permitted to cause floods or torrents. The variation in the rainfall was great. For instance, on the east coast of England and Scotland the average did not exceed 20in. per annum; on the south and west coasts it was 35iu. or 40in. ; on the Penine chain of hills forming the backbone of England the quantity ranged from 40in. to 60in.; in the highest parts of Wales, Cumberland, and Westmoreland, a fall of from 60in. to Sffin. was reached ; while in some parts of the lake districts it amounted to upwards of 150 in. The observations of Mr. J. F. (afterwards Dr.) Miller, of Whitehaven, made principally to ascertain the fall of rain upon the high mountains of that district, and the increase, due to elevation, were referred to, and his deductions quoted. The general conclusions were, that the maximum density of the rain cloud was at about 2000 feet above the sea level, although local circumstances exercised an important influence upon the quantity of rain which really reached the earth ; that the greatest deposition of rain might he expected on that side of a mountain exceeding 2000 ft. in height, upon which the rain cloud impinged, but on the opposite side when the mountains did not rise so high ; and that in a succession of ridges and valleys, without intervening mountains of a sufficient height to arrest the progress of the rain cloud, the greatest fall of rain would be in the first trough. In illustration, numerous observations were given on the rainfall in Lancashire and Yorkshire ; and it was mentioned that the same results were observed in the lake districts of Dumbarton, Stirling, and Perthshire. _ As the quantity of rain varied in every district, and depended not only upon elevation, but upon the physical and geographical features of the country, nothing could be more fallacious than to attempt to determine by any fixed ratio the amount of rain which would probably fall in any district, unless there were some corresponding one, similar in elevation, in proximity to the sea, in exposure to the wind, and in other external circumstances, with which to compare it. Only extended observation and judgment could enable an estimate to be formed of the probable rainfall in any district. The proportion of this very varying rainfall, which would flow off the surface, depended largely upon the geological character of the rooks, their elevation and declivity, and the manner in whicli they were clothed with vegetation. The water passed off partly in_ floods and partly in perennial springs ;‘ that issuing from springs varying according to the physical features or lithological character of the district. Absorbent rocks yielded the greatest abundance ; next, loosely stratified rooks, and least of all the closely bedded slate rocks and the primitive formations. From extensive observations, it had been found that, generally, in the coal measures, the millstone grit, and the primitive geological formations, the quantity of spring water in the driest seasons would vary from about to ■) of a cubic foot per second per 1090 acres ; \ a foot per second per 1000 acres being an average quantity in a dry season. The quantity formed, however, but a small portion of that flowing off the ground in times of flood, which might and would vary from 200 cubic feet per second from the same area to 400 and 500 cubic feet per second, so that the floods were from 500, 600, times greater than the quantity of water in dry seasons. The amount of flood waters_ was an important consideration in all engineering operations, as upon it depended the supply of large storage reservoirs for canals, for water power, and for the use of towns ; the openings of bridges spanning rivers, the construction of water courses, the drainage of lauds, and the effect in “ scour ” upon the beds of rivers and upon the mouths of harbors.”