ur it into a flume that runs
back over the land. At some places engines are used to pump the
water from the stream and lift it to the desired height.

[Illustration: FIG. 115.--IRRIGATING AN ALFALFA FIELD, ARIZONA]

Generally, however, another method is employed: the water is taken
out of the stream in an artificial channel dug in the earth. But
in order to get the water at a sufficient height to make it flow
over the fields, it is necessary to start a ditch or canal at a
favorable point some distance up the stream, perhaps miles from
the garden.

The ditch is made with a slope just sufficient for the water to
flow. The slope must be less than that of the river from which the
water is taken, so as to carry the stream, at last, high enough
to cover the lands to be irrigated.

Visit almost any valley in the West where agriculture or fruit-growing
is being carried on, and you will at once notice the lines of the
ditches, apparently level, as they wind around the hillsides. At
convenient distances there are gates to let out the water for the
orchards and fields.

The ground may be moistened in different ways. The first method is
that employed by the Mexicans, who, if we except the Cliff Dwellers,
were the first to introduce irrigation into our country. This consists
in dividing the land into squares by embankments and allowing the
water to flood each in succession. The method is known as irrigation
by checks, and can be used conveniently only upon nearly level
land.

In many orchards a series of shallow furrows is ploughed between
the rows of trees, and the water is allowed to flow down these
until the soil is thoroughly soaked. In alfalfa fields the water
is often turned upon the upper end and permitted to work its way
across until it reaches the lower edge, soaking the ground as it
goes. The slopes must in every case be so gentle that the current
will not be strong enough to carry away the soil.

Once in every two to four weeks throughout the spring and summer,
the exact period depending upon the rapidity with which the ground
dries, the wetting is repeated. If the soil is light the water
must be turned on more often and a larger supply is required.

It frequently happens that the stream from which the water is taken
so nearly dries up in the summer, when the water is most needed,
that the cultivated lands suffer severely. During the winter little
if any irrigation is necessary, but at that time the streams are