244 



THE IRRIGATION AGE. 



One of the results of this work has been to show 

 the importance of keeping canals in good condition, 

 and to emphasize the benefits resulting from diminish- 

 ing as far as possible the losses by percolation. Meas- 

 urements show that the loss from seepage and evapora- 

 tion in ditches and canals varies from 15 to 70 per cent 

 of all the water taken in at their heads, and that by far 

 the greater part of this loss is due to seepage. Formerly 

 many believed that most of the loss was due to evapora- 

 tion, and was therefore beyond the power of man to 

 remedy. Now that it has been demonstrated that the 

 water disappears through the sides and bottoms of 

 ditches and canals, steps can be taken to improve these 

 channels and the loss stopped to a great extent. Im- 

 provements of this character will increase the area 

 which can be irrigated, and save much land for pro- 

 ductive agriculture which would otherwise become 

 swamps and marshes. 



The difference between the high and low duties 

 obtained under practically the same conditions shows 

 that where water can be had in abundance the natural 

 tendency is to use too much, resulting in a reduction 

 in the yield of crops, a temporary injury to the land, 

 and a limitation of the area which can be irrigated 

 with the available water supply. 



In many localities a lavish use of water has con- 

 verted areas' once arid into alkali marshes, of which the 

 only product is cat-tail flags, and made drainage neces- 

 sary at a cost fully as great as was required to provide 

 the water supply in the first instance. The need of this 

 drainage might have been avoided in many cases had 

 canals been constructed with more care and the evil 

 results of overirrigation appreciated at the outset. 



The soils of the arid regions are rich in mineral 

 ingredients. This is due in part to their origin and in 

 part to the scanty rainfall, which has not been sufficient 

 to wash out the soluble elements, as has been the case 

 in humid regions. Because of this there are large areas 

 which are highly charged with alkali. The tendency of 

 irrigation is to leach these salts out of the higher 

 grounds and concentrate them in the lower lands. 

 Evaporation tends to bring them to the surface, where 

 they accumulate in such quantities as to kill vegeta- 

 tion. The remedy is to be found in drainage, and this 

 investigation has been called upon to assist in solving 

 the larger engineering and legal problems connected 

 with the formation of drainage plans. As some of these 

 districts embrace in the aggregate many thousands of 

 acres, in which not only the alkali but the water plane 

 has risen until it has reached the surface, it is necessary 

 that the plans should be comprehensive, and must in- 

 clude provision for removing the surplus water as well 

 as the salts which are to pass with it. Drainage studies 

 must include the causes of their being flooded and a de- 

 termination of the source and volume of the water to 

 be removed. Drainage and irrigation are a part of one 

 whole, and their investigation should be carried on to- 

 gether. The office is now engaged in this work in Col- 

 orado and California. 



The publication and circulation of the facts being 

 gathered regarding the injuries resulting from exces- 

 sive losses in distribution or wasteful use will go far 

 to prevent a recurrence' of such injuries in other locali- 

 ties where irrigation is yet in its infancy. Another re- 

 sult will be the reclamation of more land than would 

 otherwise be possible. 



(To 'be Continued.) 



THE PRIMER OF IRRIGATION. 



COPYRIGHTED, 1903, BY D. H. ANDERSON. 



CHAPTER XIV. 



THE SCIENCE AND ABT OF IRRIGATION INFILTRATION 



OR SEEPAGE. 



(Continued.) 



Irrigation by infiltration or seepage is effected, fol- 

 lowing the configuration of the soil, by means of flowing, 

 or sleeping water seeping or soaking into the soil from 

 ditches, canals, or other waterways at or beneath the 

 surface of the land. The water spreads, soaks, seep& 

 out fanlike into the soil from the sides and bottom of 

 the ditch or canal, and descends in pursuance of the law 

 of gravity, or ascends in accordance with the law of 

 capillary motion toward the surface, where it evaporates 

 unless its course is stopped by breaking up the soil. 



Water descending by the force of gravity continues 

 on until it meets with what is commonly called "ground 

 water," with which it mingles. If it does not encounter 

 ground water, or a water table, it expends its energy by 

 descending as far as it can as water, then it is converted 

 into moisture and begins making its way to the surface 

 through capillary motion. Infiltration rests upon the 

 principle of the permeability of the soil, and hence, this- 

 method of irrigation is not always so beneficial as those 

 which have been already mentioned, for it consumes a 

 large quantity of water without supplying the soil with 

 a uniform humidity. There is this exception, however; 

 when the flowing water in the trench, ditch, or under- 

 ground conveyance reaches the intended root zone and 

 there spreads out or seeps into soil where it can be di- 

 rectly utilized. This is one of the advantages of sub- 

 irrigation, a system which can not be ignored for many 

 reasons. 



SUB-IRRIGATION. 



Sub-irrigation is a variety of infiltration which pos- 

 sesses many advantages, over surface irrigation where 

 wastage -of water is an object to be avoided. By this 

 system, land too elevated to be reached through other 

 means is transformed into fertility. In the case of hill 

 land it is admirable for cereals, and also on lands where 

 weeds abound. It lends an invaluable aid to special 

 plant cultures, such as grapes, olives, oranges and citrus 

 fruits generally, and in gardening. It enables steep 

 lands to be cut into terraces which irrigation water could 

 not reach or in which it could not penetrate to a suf- 

 ficient depth. In addition to these advantages, the ap- 

 plication of underground water to arid or waste land 

 covered with gravel or sand, permits the propagation and 

 cultivation of productive plants which would otherwise 

 perish through dryness of subsoil. Finally, a well ar- 

 ranged system of sub-irrigation operates as a drainage 

 system, and thus a double purpose is served. 



The nature of the soil is of more importance than 

 the configuration of the land in sub-irrigation. In this 

 respect, hard, impenetrable soils, and those too open 

 and porous should be avoided for general infiltration 

 purposes. Experience alone is able to guide the irrigator 

 in establishing any system of deep ditches, the main 

 point to be attained is always to provide for moistening 

 the soil uniformlv. 



