8 CONSERVATION OF GROUND WATER 



water free of bacteria even though the stream is highly pol- 

 luted, but there has not been enough research to show quan- 

 titatively the effectiveness of aquifers in reducing bacterial 

 pollution. It is likely that the utilization of ground water 

 along watercourses will increase because of this reduced de- 

 gree of pollution and because of more uniform temperature 

 and quality of the ground water. Studies at a few places along 

 rivers indicate that large quantities of ground water are avail- 

 able, with the river as the ultimate major replenishing source. 



Many activities unrelated to pumping of ground water have 

 modified the storage of water below the land surface. Drainage 

 projects and irrigation projects have proved that it is possible 

 to manipulate the storage in ground-water reservoirs. Un- 

 fortunately, ground-water storage has been increased by irriga- 

 tion in some places until good agricultural lands have been 

 waterlogged and abandoned; and it has been decreased in 

 other localities by drainage to the detriment of agricultural 

 use of the land or municipal use of the water. Man has changed 

 the quantity of water stored underground by his structures 

 for storage of surface water or for protection against floods, 

 by improving channels for navigation, and by building cities 

 and providing them with storm sewers. He has damaged some 

 water supplies by discharging contaminated water into the 

 ground or into streams from which it enters ground-water res- 

 ervoirs; and also by puncturing protective layers, thus per- 

 mitting entry of sea water or other mineralized water into 

 aquifers. 



For the country as a whole, the greatest change wrought by 

 man has been the change from the original forest and grass- 

 land to cultivated or barren areas. This change has had a pro- 

 found effect upon the soil cover, as shown in areas of severe 

 gullying and wholesale removal of the soil and more extensive 

 areas where the soil has been eroded less markedly. That lost 

 soil now forms part of the sediment in many stream channels, 

 lakes and reservoirs, and ocean bottoms. Although the effects 

 of man's activities may be measured in millions of tons of dis- 

 placed soil, these effects are insignificant in comparison with 



