30 
LOSSES FROM CANALS BY SEEPAGE. 
cases a thin layer is sufficient to check the leakage very 
much. 
LOSSES AT DIFFERENT FORMATIONS. 
The effect of different strata is shown in the measure- 
ments of the seepage increase of streams. In the case of 
the Cache a la Poudre there are several stretches in which, 
notwithstanding the large gains in the river as a whole, 
there is an apparent loss of water. 
In the Rio Grande river in Colorado marked losses 
were found for a portion of its length in the San Luis val- 
ley, amounting to 75 cu. ft. per second in a distance of 15 
miles. The loss was noticed in 1896 and verified in 1897. 
Similarly in the case of the Arkansas river, a loss is 
found in several places, but of less amount than found in 
the Rio Grande. 
EFFECT OF PREVIOUS CONDFITON ON LOSS. 
d'he previous conditions of the bed of the canal, or 
stream, will materially affect the loss experienced in the 
canal or river bed. If the bed has been dry and has become 
heated as well, the amount of water which is absorbed by 
the bed when water is turned into the canal, is surprising to 
one who is not acquainted with the peculiarities of the flow 
of water under such conditions. The layer of dry soil ab- 
sorbs the water with avidity. It will take up about one-third 
of its volume of water, and the amount of water thus ab- 
sorbed is in addition to the amount which is flowing through 
the soil under steady conditions. The effect is to greatly 
increase the time required to send water through a ditch 
after having been dry, and on the longer ditches days may 
be taken to send water through the ditch, while when al- 
ready soaked up a very slight change at the headgate is 
quickly felt throughout the length of the canal. It is be- 
cause of the loss from this source that the attempts to run a 
moderate amount of water through streams with sandy beds 
have not been successful. 
On the other hand, with falling water, a considerable 
amount of saturated soil is exposed. Water oozes from the 
banks and the supply thus received retards the fall of water. 
Sometimes when the banks are gravel, the outflow appears 
in streams and is so rapid and abundant that it may cause a 
slipping of the bank. Experienced canal men have a well 
founded objection to lowering water suddenly and consider- 
ably and though some, mistakenly, think that the pressure 
