Mar. i, 1924 
Movement of Water in Irrigated Soils 
669 
soluble substances brought in by the irrigation water, together with 
those set free by soil disintegration, must accumulate to the point of 
harmfulness. Thus it may be said that for continued successful irriga¬ 
tion farming there must be a cumulative downward movement of water 
through the soil. 
In the preceding chapters attention has been given to certain factors 
which contribute to a condition of the soil which hinders or prevents the 
normal downward percolation of water. There remains to be considered 
another situation which is equally effective in preventing such move¬ 
ment. This is the situation that exists when the subsoil is supersaturated 
with water. A large part of our irrigated land lies in the valleys of rivers 
where it is most convenient to divert water for irrigation. These valley 
lands are very commonly made up of sedimentary deposits from the 
main stream or its branches or from material eroded from adjacent high 
land. Only a part of the stream water is carried in the open stream bed. 
Another part, and often a very substantial part, is carried as underflow 
below the stream bed and under the adjacent valley lands. This under¬ 
ground water may occur as a continuous body extending to great depth 
and moving perceptibly though very slowly downstream, or it may be 
confined to certain underground channels of more permeable material, 
such as gravel or sand, which lie between islands of clay or fine silt in 
which no free or moving water is found. The diversion of stream water 
and its application to the valley lands very often results in adding to 
the supply of underground water to such an extent that the natural 
underground drainage ways are inadequate to carry it away. This 
results in raising the level of the saturated zone and necessitates opening 
new drainage channels if complete water-logging of the land is to be 
prevented. 
In connection with a leaching experiment made on the Newlands 
Experiment Farm, Nev., in 1922, some observations were made which 
bear on this point. The field in which this experiment was conducted 
was divided into plats of approximately half an acre each. These plats 
were separated by parallel borders 85 feet apart. A large tile drain 
had been installed some years earlier along the south side of this series 
of plats, so that one end of each plat was just above the drain and the 
other end was less than 300 feet from it. There was a free discharge of 
water through this drain and the tile was seldom submerged. At the 
beginning of the leaching experiment the water in the sand box of the 
drain at the west end of the series of plats stood at 3,955*8 feet above 
sea level. At the east end of the series it stood at 3,955*5 f ee t* Though 
the drainage discharge varied somewhat during the experiment, the 
height of the water in the sand boxes changed but little. The ground 
surface in the plats ranged from just below 3,960 to 3,961 feet above 
sea level. Thus the water in the drain was about 5 feet below the ground. 
The ground-water conditions within the plats were observed by means 
of open wells set in the borders between the plats. There was one line 
of wells across the north ends of the plats and another line across the 
south ends. These wells were cased with galvanized iron tubing 3 inches 
in diameter. Being set in the plat borders they were protected from 
direct filling when the plats were irrigated. During the progress of the 
leaching experiment it was possible to observe the height of the ground 
water as it was shown by these wells and to take samples from time to 
