LOSSES FROM CANALS BY SEEPAGE. 
27 
Temp., F. 
Velocity. 
Temp., F. 
Velocity. 
32° 
1.000 
72° 
1.860 
42° 
1.195 
82° 
2.109 
52° 
1.403 
92° 
2.372 
62° 
2.109 
102° 
2.649 
In warm weather the loss is therefore greater than in 
cold, and the loss at 80° temperature of the water would be 
twice as much as if it was at freezing temperature; or the 
loss at 70° would be about one-third more than at 50°. 
LESSENING SEEPAGE. 
Of the conditions affecting seepage, the one which can 
most readily be controlled, and in fact the only one, is the 
character of the canal bottom or the bottom and sides. No 
soil is absolutely water-tight, but there is a great difference 
between the perviousness of the different soils, which range 
through all degrees of clay to sand and gravel. Clay of the 
quality known as adobe, essentially a clay from which all 
vegetable matter has been extracted by action of alkaline 
carbonates, is well known to be nearly water-tight. 
A layer of fine material, as of fine silt, makes the pass- 
age of water so much more slow and difficult, that its effect 
is well known and is shown in a number of cases in the 
measurements reported in this bulletin. Even water that is 
apparently clear contains enough matter to lessen the rate 
of filtering in a few weeks time in the large filters for city 
water supplies. 
The silt carried by canal waters is sufficient to greatly 
lessen, and in many cases to practically stop the seepage, 
but to do this the velocity of the water must be slow enough 
to permit the silt to be deposited. 
A constant current tends to prevent the settlement of 
sediment. If the current is swift enough to erode the bed 
then not only is the sediment kept from dropping and filling 
the pores, but the surface is swept and the losses will re- 
main large. 
Hence defective alignment of the canal, too sharp 
curves causing the current to strike and erode the banks, 
are conducive to losses. Some canals have found it desira- 
ble to straighten the line of their canal to lessen the troubles 
of maintenance, and in so doing have also lessened the loss 
from seepage. 
Any way in which the canal may be silted up, or be per- 
mitted to form a layer of silt, thin though it be, will tend to 
lessen the seepage. 
Hence checks which some canals have found it neces- 
sary to construct for water distribution, cause slack water 
