Some of the greatest troubles arose from, on the one hand, excess of water in the rivers owing to floods, and, on the other, from inadequate supplies of water due either to droughts or to shallows. The liability to floods will be at once apparent if the reader considers the extent of the areas from which rain water and the yield of countless springs, brooks, and rivulets may flow into the principal rivers. In the Report of the Select Committee of the House of Lords on Conservancy Boards, 1877, there was published a list which showed that the 210 rivers in England and Wales had catchment basins as follows:-- 1000 miles and upwards 11 500 " to 1000 miles 14 100 " " 500 " 59 50 " " 100 " 24 10 " " 50 " 102 ----- Total 210 The rivers having catchment basins of 1000 miles or upwards are given thus:-- AREA OF TRIBUTARIES. {151} NAME. COUNTY. LENGTH. Basin. United length. Miles. sq. miles. No. miles. Humber York 37 1229 2 55 Mersey Lancaster 68 1707 6 188 Nen Northampton 99 1055 1 11 Ouse York 59½ 4207 11 629 Ouse Cambridge 156¼ 2894 8 212 Severn Gloucester 178 4437 17 450 Thames -- 201¼ 5162 15 463 Trent Lincoln 167½ 3543 10 293 Tyne Northumberland 35 1053 6 154 Witham Lincoln 89 1052 4 75 Wye Hereford 148 1655 9 223 In times of heavy storms or of continuous rainy weather, rivers which drain up to 5000 square miles of country may well experience floods involving a serious impediment to navigation. The Severn, which brings down to the Bristol Channel so much of the water that falls on Plinlimmon and other Welsh hills, and is joined by various streams, draining, altogether, as shown above, an area of 4437 square miles, is especially liable to floods. In a paper read before the Institution of Civil Engineers in 1860, Mr. E. L. Williams stated that floods had been known to raise the height of the Severn 18 ft. in five hours, and they had not infrequently caused it to attain a height of 25 ft. above the level of low water. The Thames and the Trent, also, are particularly liable to floods, and so, down to recent years, when considerable sums were spent on its improvement, was the Weaver.