196 CONSERVATION OF GROUND WATER 



treated sewage of Miami, there is also a danger of bacterial 

 pollution. 



Dade County (which includes Miami) is engaged in a 

 water-control program to prevent inflow of salt water 

 through drainage canals and encroachment into the aqui- 

 fers. Locks or other control structures are planned for all 

 the major canals discharging into Biscayne Bay and will be 

 designed to hold water on the upstream side during dry 

 periods as high as drainage requirements will permit, and 

 to have ample capacity for passing the flood flows during 

 wet seasons. 



The principal source of the water used by Miami and 

 other coastal cities is the abundant precipitation upon the 

 Atlantic coastal ridge, which infiltrates into very permeable 

 aquifers. Most of this water is discharged unused into the 

 ocean. The problems of salt-water encroachment are limited 

 to those areas where the water table has been lowered to 

 sea level by drainage or by concentrated pumping. 



Drainage is a major problem in many mines, and in some 

 places the cost of pumping water has become so great as to 

 cause abandonment of some workings. On the other hand the 

 water from some mines is of considerable value in several 

 areas in the West, where it can be used for irrigation, public 

 supply, or other purposes. For example, the waters from the 

 Ontario Tunnel near Park City and the Elton Tunnel near 

 Tooele, Utah, are used for irrigation. In the Iron River dis- 

 trict of Michigan, investigations of the ground- water phe- 

 nomena have been in progress for several years, with the ex- 

 pectation that the knowledge so gained will serve to reduce 

 the costs of mining caused by water in the mines. 31 



REGULATION OF POSITION OF THE WATER TABLE 



It has been possible in many irrigated areas to solve the 

 problems of waterlogging by drainage. In the earliest irriga- 



3i Stuart, W. T., C. V. Theis, and G. M. Stanley, Ground-water Problems of 

 the Iron River District, Michigan, Mich. Dept. Conserv., Geol. Survey Div. 

 Tech. Rept. 2, 1948, 58 pp. 



