Page 332 - Moving the Earth_ The Workbook of Excavation

LANDSCAPING AND AGRICULTURAL GRADING

7.26 THE WORK

FIGURE 7.18 Concrete lining in irrigation canal. (Courtesy
U.S. Department of Agriculture.)

FIGURE 7.19 Damage to land from canal seepage.

Damage from leaking canals is not confined to the water loss and the breaking down of the
canal structure. Farmland near the leaks may be rendered unusable by excessive water and resulting
alkali deposits, unless subdrainage is provided. (See Fig. 7.19.)

Pipes. Either ditches or pipes may be used to distribute the water from the canal. Ditches are more
economical to construct, but cut up the land, are expensive to maintain, form breeding spots for insect
pests, are a hazard for children, and may allow substantial water losses by seepage and evaporation.
Pipes may be concrete, glazed tile, plastic, steel, or some composite material. The first two
sometimes separate at the joints when filled with cold water, either after lying empty or being used
to carry warm water. Iron pipes may corrode rapidly due to alkalies in either the soil or the water.
Various methods have been developed of joining concrete and of treating iron pipes, which
reduce the difficulties mentioned. On the whole, pipes require less maintenance and waste much
less water than ditches. However, they must be laid on steeper grades to prevent silting. If they
become blocked, they are very expensive to clean.