490 REPORT OF OFFICE OF EXPERIMENT STATIONS. 



not be disregarded when it is found necessary to undertake drainage 

 operations. 



A clear account of methods of draining which are applicable to 

 such cases really involves a description of the surface and particularly 

 the physical features of irrigated tracts in widely separated localities 

 where special methods of draining have been employed, not omitting 

 the difficulties which present themselves when such reclamation is 

 attempted. 



To those who are accustomed to draining lands in the humid sec- 

 tions the arid soils present some striking differences in structure and 

 in the manner in which they become w^et, as well as in the effect which 

 continued saturation produces on vegetation. Arid soils are usually 

 a mass somewhat uniform in character and without subsoil, as we 

 understand the term in humid sections. With the exception of the 

 adobe class they contain but little clay, but are made up of disinte- 

 grated rocks, or in some localities of volcanic ash, sometimes inter- 

 spersed with gravel, which changes their density and physical condi- 

 tion. They are not laminated or stratified, as are those in the rainfall 

 regions, so we often find them fairl}^ uniform in structure and fer- 

 tile to considerable depths. The presence of hardpan interspersed 

 at irregular intervals in some localities breaks up this homogeneous 

 character, and, W'here found, is an important modifying factor in both 

 irrigating and draining, AVliile these are the general characteristics 

 which distinguish them from soils in the rainfall belt, there are any 

 number of difi'erences peculiar to arid soils which give nearly as 

 great a variety of conditions as we find in the humid areas. 



CAUSES WHICH PRODUCE SEEPAGE. 



The cause of seeped or oversaturated land is the w^aste from irri- 

 gation and leakage from canals and laterals. The skillful irrigator 

 may insist that if no more water is applied than is needed for grow- 

 ing and maturing the crops, and that if the canals are so constructed 

 that no substantial amount of water escapes into the earth, no land 

 Avill become too wet for farming purposes. It is true that in many 

 instances irrigators have been unduly prodigal in the use of water, 

 particularly when the land is first subdued and watered. The art of 

 economical irrigation is usually learned only when scarcity of water 

 compels its less lavish use. In any event, under methods that we may 

 expect will prevail, some waste of water will occur under the best of 

 management, making draining in many places essential to profitable 

 farming. For these reasons an account of drainage conditions in dif- 

 ferent localities and the methods of treating them, together with the 

 results which have followed various drainage operations, will be of 

 interest to the holders of irrigated farm lands. 



