DAMAGE BY FLOOES IN RIVERS PREVENTION. 635 
than on the up-stream end; then had no option but to 
flow the wrong way; so that the river with its winding 
course ceased to act, as all the reaches overflowed at their 
higher loops, the long reaches having now a surface-gradient 
of 1 in 2000; therefore, the flow could not follow the course 
of the river, which would give a gradient of only 1 in 9000. 
The effects of fioods are also greatly influenced by the 
depth of the river; and the difference in depth of rivers is 
difficult to understand. Thus, the Amazon, Parana, 
Yangtse, are very deep; but the Mississippi, Ganges, 
Hoangho, Volga, are shallow. ~ The cause cannot be 
the geology of the countries which the rivers flow 
through, because rivers like the Amazon and Mississippi 
flow through every sort and condition of country, 
neither can the extent of level plains through which 
the lower parts flow be the cause. The Mississippi 
flows through extensive plains, and so does the Parana. 
The same thing is also seen in Tasmania, where the lower 
18 miles of the Gordon is about 100 feet deep; and the 
King and Pieman rivers are very deep at their lower parts. 
Some parts of the Amazon are 500-feet deep below sea- 
level, while the mouth is over extensive shoals only 12 or 
18 feet deep. 
As regards the effect of depth on the floods—taking the 
case in China, the deep Yangtse causes no trouble, al- 
though it rises about 50 feet in spring and summer, while 
the shallow Hoangho is called “ China’s Sorrow,” and in 
1837, 1,600,000 people were drowned by a flood in it; and 
again in 1901, immense numbers of people and cattle were 
drowned by the bursting of the banks by floods. The City 
of Glasgow was afflicted with floods long ago, but since the 
deepening of the Clyde no floods ever affect the town. 
_ As stated above, the nature of the banks is generally the 
measure of the crookedness of the river; and of course the 
crookedness of the stream aggravates the destructive effects 
of the floods. The river canno: be permanently straightened 
unless the banks are artifically protected, which is generally 
impracticable, from the magnitude of the work involved. 
But if the river is straightened and prevented from eating 
away its banks, it will at once commence to attack its 
bottom, which action is generally beneficial in every way, 
as tending to abate the height and shorten the duration of 
floods. 
In the course of the operations to improve the Mississippi, 
the river is said to have been shortened about 260 miles 
by cutting through bends, the tendency of which is, of 
