2 BULLETIN" 190, U. S. DEPARTMENT OF AGEICULTUEE. 
Drainage practice in the arid section differs greatly from that in 
the humid region. The nature of the land requiring drainage is 
different, and the methods applied are unlike those employed in the 
humid section. In fact, there is little in common between the two 
situations, and drainage experience in the humid section avails little 
in dealing with the problems of draining irrigated lands. For this 
reason literature on the general subject of drainage should be used 
with caution, as the difference in conditions between the arid and 
humid regions has been clearly recognized only within the last few 
years. 
MANIFESTATIONS OF POOR DRAINAGE CONDITIONS. 
Injury wrought by overirrigation manifests itself in several ways. 
In some cases the lands are literally swamped, and ponds, bogs, and 
tule marshes are dominant features. In others the ground is merely 
waterlogged, and the injury is shown by the wet condition of the 
soil, by the presence of alkali salt crusts on the surface of the higher 
spots of ground, and by any vegetation that may have survived the 
inhibitive conditions. Very often, however, there is no visible 
sign of wetness, and the only marks of the injury are the incrusta- 
tions of alkali salts, the presence of highly alkali-resistant plants, or 
the absence of all vegetation in the worst-affected areas. 
SPECIFIC OBJECTS OF DRAINING. 
It is important, at the outset, to understand the specific results 
which it is proposed to accomplish by draining. These may briefly 
be stated as follows: (1) To lower the ground-water table to such a 
depth that the moisture and air conditions within the root zone are 
properly balanced; (2) to provide an outlet for percolating water, 
so that fluctuations of the ground-water table within the root zone 
will be prevented ; (3) to effect rapid removal of the excess moisture 
resulting from spring thaws; and (4) to provide an outlet for the 
downward moving water used to dissolve out the injurious salts. 
PRELIMINARY INVESTIGATIONS. 
NECESSITY FOR KNOWLEDGE OF CONDITIONS. 
Having in mind the above-mentioned objects of draining, it is 
clear that the existing conditions must be known before work is com- 
menced, and that the system must conform to these conditions. Ran- 
dom procedure is manifestly poor policy where the objects aimed at 
are so definite. A little study and the application of judgment will 
often indicate how the drainage may be satisfactorily accomplished 
at comparatively small cost. On the other hand, it is quite possible, 
in the irrigated section, to install a system having many more lines 
than are necessary, and still meet with total failure. There are few 
projects so small and apparently so simple as not to warrant the 
