Irrigated Agricueture in the San Luis Vaeeey 
9 
built, materially increasing the supply of water available during the 
irrigation season since they store water in flood times and hold it 
till times of normal slack stream flow. 
In the western and southwestern portion of the Valley, there is 
considerable artesian water. Owing to the very porous nature of 
the soils small reservoirs cannot be built economically and success¬ 
fully for storing the flow from these wells. There are between 
5,000 and 6,000 of these artesian wells. Roughly, the wells average 
a flow of 40 gallons per minute. This is much too small for direct 
application except on small acreages, such as garden patches. Some 
of the wells, however, have much heavier flows. Despite the aggre¬ 
gate flow of 450 second-feet the acreage irrigated is extremely 
small, totaling not over 2,000, mostly on gardens and small patches. 
Owing to the manner in which the wells have been cased—that is, 
for a short distance only—it is not feasible to cap the wells and 
stop the flow when the water is not needed for use. Consequently 
the discharge from these wells has created local swampy areas and 
has caused considerable trouble without furnishing very much 
direct benefit except in the way of water for domestic purposes. 
Data for 1912 show practically 300,000 acres irrigated by sur¬ 
face flooding. Sub-irrigation is employed directly on about 130,- 
000 acres or approximately one-fourth of the irrigated acreage. 
The sub-irrigated lands are almost exclusively those irrigated from 
waters taken from the Rio Grande, there being only about 5,000 
acres in other districts which are sub-irrigated. Furrow irrigation 
is used on 24,000 acres, principally for cultivated crops such as 
potatoes, beets and other roots, and also on lands toO' steep for 
flooding. The border and check methods are used on about 4,000 
acres. 
As stated above, the acreage watered directly by sub-irrigation 
methods is approximately one-fourth of the total irrigated acreage. 
However, there is no way of telling what acreage is indirectly in¬ 
fluenced by the sub-irrigation practice. The water level has doubt¬ 
less been raised over a very much larger area. Near the upper por¬ 
tions of the sub-irrigated belt the water table must be raised from 
20 to 30 feet each season to bring it into the root zone. This prac¬ 
tice has naturally resulted in an undue rise of the water table in 
lower lying lands and in seeping and swamping the lowest. Sub¬ 
irrigation can hardly be improved upon where ideal conditions of 
soil and slope obtain, but ideal conditions are very rarely encoun¬ 
tered. When only a few farmers were irrigating with sub-surface 
methods no bad results followed, but when large areas were so irri¬ 
gated it was found that sooner or later the farmer on the lower land 
was drowned out. Perfect control of the water level is impossible 
