CORRESPONDENCE. THE CONSERVANCY OF RIVERS
Minutes of the Proceedings of the Institution of Civil Engineers
299 been heavy rain for the three days preceding this date, and no Mr. Jacob. doubt all the subsoil drains were discharging freely. Moreover, it was probable that the fall of rain for a few hours immediately preceding the time of maximum flood was much heavier than the average rate of fall for the whole twenty-four hours. Mr. Rawlinson's remarks regarding the relative advantages of dredging and of embanking were well worthy of attention. Evidently there was a limit to the amount of dredging
... unt of dredging that could bc executed through districts in which the margin of the river was bounded by large and costly buildings ; for any interference with the foundations or footings of the walls would certainly be attended with danger to such structures. One of the most formidable difficulties to be contended with as regarded the dredging of the Irwell had been to find suitable and sufficient places of deposit for the material. At a seaport the material could be sent out to sea and dropped in deep water, but this was impossible in many localities, and the only remedy was to improve the sections of the stream, both cross and longitudinal, so that a velocity would be obtained which would carry the silt down to the estuary. The removing or reconstruction of existing weirs, and the straightening of the river's course, combined with the formation of substantial and sufficient embankments, would undoubtedly accomplish the desired end. Proceedings.] CORRESPONDENCE ON THE CONSERVANCY OF RIVERS. 301 who appeared to take the latter view should give at least some Mr. Browne. ground for their opinion. The Rev. J. C. CLUTTERBUCK remarked that the frequency of J. c. floods, and the damage caused by them, had been put forth in proof Clutterbuck. of the necessity of placing the rivers, as main arterial drains of the watersheds of England, under Boards of Conservancy, armed with legal powers to carry out remedies for acknowledged evils. It was obviously impossible to devise a scheme by which all rivers and their watersheds could be dealt with alike. Take the watershed of any river, and it would not be found practicable to calculate the flooding capabilities with reference to its measured surface area, due to its geological condition. In the chief rivers finding their outfall in the Wash, as in all cases, the geological condition varied. So, in a remarkable way, the Thames in its upper district gathered its waters from the springs of the chalk, and oolitic, and liassic strata, and the surface waters of the Gault, Kimmeridge, Oxford and Lias clays. These latter were to a great extent covered with sand and gravel, in which the water accumulated, from the surface of which it would not flow, and whence floods were not augmented except in some instances of artificial drainage. Downloaded by [ Purdue Univ Lib TSS] on [19/09/16].