40 CONSERVATION OF GROUND WATER 



southern California, pumping is perennially greater than 

 replenishment. This basin is somewhat similar to Antelope 

 Valley. Recent studies indicate that current pumping is at 

 a rate of about 250,000 acre-feet a year, and about 43,000 

 acre-feet more than the average annual replenishment. 



Mimbres Valley, N. Mex.* The Mimbres Valley is a closed 

 basin in southwestern New Mexico. Beginning in 1923, 

 pumpage for irrigation has steadily increased to 10,000 acre- 

 feet in 1934, 21,000 in 1941, and 58,000 in 1948, when about 

 24,000 acres was irrigated by ground water. Water levels had 

 declined as much as 30 feet in some wells by 1939, and more 

 than 8 feet in an extensive area. From 1942 to 1949, water 

 levels have declined more than 10 feet in an area of 10 

 square miles, an accelerated rate that ties in well with the 

 increased rate of pumping. 



Some wells east of the Florida M ountains were abandoned 

 as water levels reached the base of the aquifer, but there is 

 still much ground water in storage in the rest of the basin. 



The natural replenishment comes chiefly from the 

 Mimbres River and has probably diminished in recent 

 years because of increased use of the stream for irrigation. 

 It has been estimated that the average annual replenish- 

 ment is about 10,000 acre-feet, and that in the wet year 1941 

 it may have approached 15,000. Thus, in the past decade, 

 the bulk of the water pumped for irrigation has been taken 

 from storage. 



Many ground-water reservoirs in arid regions are not re- 

 plenished in dry years. In the driest basins, the ground-water 

 reservoir may receive no recharge in a year of "normal" pre- 

 cipitation, because all the moisture is dissipated from the soil 

 zone. Recharge to these reservoirs occurs only during years of 

 exceptionally abundant rainfall, which may mean only one 



* Reference: Theis, C. V., Progress Report on the Ground-water Supply of 

 Mimbres Valley, New Mexico, N. Mex. State Eng. 12t/j-13r/j 

 Bienn. Rept., pp. 135-154, 1938. 



