DAMAGE BY FLOODS IN RIVERS PREVENTION. 643 
effects brought about prevent all our Sffarta to control the 
floods in this way. 
Although the inclination of the bed of the river is not 
the same as that of the surface of the water at all parts 
and in all states of flood, yet it is of course the measure of 
the average inclination of the surface. Now from’ this it 
is inferred that the character of the material of which 
the river-bed is composed determines the inclination of the 
bed and of the average surface-inclination. 
Thus, near the mouth’of a great river the sediments may 
be mud or soft sand, and at such parts they are so easily 
scoured that the inclination of the bed may have no refer- 
ence whatever to the mclination of the surface of the river ; 
that is, the river may be very deep while its mouth may be 
very shallow. But as we ascend the river, we find the sedi- 
ments getting heavier and coarser, andthe inclination of the 
bed approaching more to that of thesurface of the water, untal 
we reach the state of things found in many New Zealand 
rivers, where the sediments being shingle and heavy boul- 
ders the inclination of both bed and surface of the river, 
may be from 40 to 60 feet-a mile. Yet even with such 
heavy sediments, the river is continually raising its bed, 
until being elevated above the surrounding country, it 
suddenly breaks through into lower ground and commences 
raising it; so that the strange phenomenon is seen over a 
hundred miles of plains with a uniform slope towards the 
sea of from 20 feet a mile near the sea to 60 feet a mile 
near the foot of the mountains. 
In a case of this kind there are two factors which 
govern the inclination of the plains and the river, one being 
the weight of the sediments or deposits, and the other the 
size and volume of the river; accordingly, we find the slope 
of the plains from sea to mountain with a steep fall, and 
getting gradually flatter towards the sea. But we also find 
that the larger rivers, where they come out of the mountains 
on to the plains, flow in deeper beds than the smaller 
rivers, the latter not having the weight and body of water 
to cut down the heavy shingle which the larger rivers have. 
Thus, given the weight of the deposits and the size of the 
river, the inclination is fixed; and a fine example of this 
was seen in the Otira River, in New Zealand, where during 
a great storm a vast “shingle slide,” as it is called, slipped 
from the lofty mountain-side bodily into the river. The 
flood distributed this shingle for many miles down the 
river, raising the bed from a foot or two to about 20 feet in 
