1906 



FORESTRY AND IRRIGATION 



375 



eastward from the line above located 

 to a north and south boundary defined 

 by Westminster, Whittier, and Mon- 

 rovia. While the central section in- 

 cludes the area lying to the east of this 

 as far as San Bernardino and San 

 Jacinto. 



Completed tables giving the facts 

 concerning the wells throughout this 

 region are included in the reports. 

 They show the yield of each well, the 

 capacity, and depth at which water 

 occurs, as well as the cost of operation. 



With reference to the supply of the 

 entire region the report states that in 

 all of the important basins there has 

 been during the last ten years a gen- 

 eral reduction in the yield of the ar- 

 tesian wells. The last ten years have 

 constituted a period of low rainfall, 

 and as a result the ground water sup- 

 ply has been diminished, and it is evi- 

 dent that there should be no further 

 increase of the drafts upon the under- 

 ground resources. The rate of this 

 decrease even under the influence of 

 the great development that has taken 

 place has been very slow, and while 

 it is probable that in some basins some 

 of the favorably located wells will 

 never cease to flow, the shrinkage must 

 continue in other places unless there 

 is a concerted effort upon the part of 

 the irrigators to be economical in the 

 use of water. 



The summary given by the author 

 of these reports, Mr. Walter C. Men- 

 denhall, is as follows : 



The supply is large, since it consists 

 of the water saturating all that part of 

 the coastal plain gravels within about 

 250 feet from the surface over an area 

 of 600 or 700 square miles. 



The annual additions to the supply 

 are large, consisting of a part of the 

 flood waters of the San Gabriel, Los 

 Angeles, and Santa Ana Rivers, to- 

 gether with the return waters from 

 irrigation and the local rainfall. The 

 drafts upon this supply are also large 

 and seem certainly to be in excess of 

 the supply in certain parts of the re- 

 gion. 



With present developments the 

 water plane must be expected to de- 

 cline slowly and the artesian to shrink 

 until drainage is checked by this 

 shrinkage to a point where it no longer 

 exceeds the supply. This decline 

 should not prove serious if present de- 

 velopments are not increased, but so 

 long as this development continues at 

 a rate which increases the output, the 

 shrinkage will also continue. 



The lowering of the ground water 

 level and shrinkage of artesian areas 

 will no doubt be interrupted by periods 

 of rising water levels. 



The shrinkage of an artesian belt 

 will be manifest along its northern 

 edge, and the effect farther south will 

 be rather a decrease of flow and a les- 

 sening of pressure. 



Shallow artesian wells will gener- 

 ally be affected earlier and to a more 

 marked extent than the deeper ones. 



One of the maps included in this 

 series of reports shows the artesian 

 areas and the shrinkage which has al- 

 ready occurred. For example, the 

 great artesian area running along the 

 coast from a point west of. Los An- 

 geles to a point south of Santa Ana 

 already shows a shrinkage along its 

 northern and eastern borders equal to 

 about one-fourth of the original area, 

 while that south of Pomona shows a 

 shrinkage of approximately 10 per 

 cent. The San Bernardino area has 

 likewise been reduced about one-half, 

 and that north of San Jacinto shows 

 a shrinkage along its northern bor- 

 der equal to about one-fifth of the origi- 

 nal artesian area. 



These reports should be consulted 

 by every irrigator along the coastal 

 plain. They give most potent warn- 

 ings concerning the loss of water sup- 

 ply which, it appears, may be avoided 

 if intelligent measures are adopted. In- 

 asmuch as this garden spot of North 

 America has been developed solely as 

 a result of irrigation by ground waters, 

 it appears that the inhabitants of the 

 region can do no better than to or- 

 ganize and adopt such measures as are 

 recommended in these reports. 



