6 
LOSSES FROM CANALS BY SEEPAGE. 
over the surface of the canal, lost in one day, rather than in 
per cent, of the water in the canal. The losses from differ- 
ent canals are then more easily compared, and cases of un- 
reasonable loss sooner recognized. In ditch management 
the tendency is to express the loss in per cent, in which case 
the loss suggests nothing as to the economy of water. To 
say, without other information, that a canal loses 25 per 
cent., gives no indication whether the carriage is economi- 
cal or not. In a long canal the managers could congratu- 
late themselves that it is no more; in a short canal it might 
be excessive and should set the officers to determining the 
location of the losses and to seek a remedy. 
For those unaccustomed to this form of calculation, it is 
convenient to remember that the amount of water given by 
one cubic foot per second in 24 hours is enough to cover 
two acres one foot in depth (correct within less than i per 
cent.l , and hence a daily loss of two feet over an acre would 
require the constant flow of one cubic foot per second to 
make good. The deeper the water in the canal the more 
rapid is the leakage, but with our ignorance of the exact re- 
lation we neglect the depth and consider only the surface 
of the canal. In the table full data is given and if the con- 
nection is subsequently determined, the data should be suffi- 
cient for the later investigations. It would doubtless be 
better to consider the wetted area of the canal rather than 
the width as a factor. As the canals are shallow and broad 
it matters little whether the surface area of the canal or the 
wetted area is used. 
EVAPORATION RELATIVELY SMALL. 
In considering the losses from canals, it is common to 
consider the loss from seepage and evaporation together. 
In most cases the evaporation is small in comparison with 
the loss from seepage. In ten years record of an evapora- 
tion tank freely exposed to the sun and wind, at the State 
Agricultural College, Fort Collins, Colorado, the annual 
evaporation has averaged but 41 inches.* 
The temperature of the water surface in the tank 
is, however, lower than in many of the canals. As evapo- 
ration increases with the temperature of the water, the 
evaporation from some canals would be correspondingly 
*Annual reports Colo. Atrricultural E.vpe'iiiient Station, 1889 and 1890. 
Monthly evaporat’on ^iven in full, table 4. p 18, bulletin 45, on Lospes from Res- 
ervoirs. 
