242 CONSERVATION OF GROUND WATER 



with prospects of adequate replenishment from the river. Full 

 development of the potentialities of ground-water reservoirs 

 along some watercourses would also contribute substantially 

 to flood control. 



Many ground-water reservoirs receive the bulk of their 

 natural replenishment by infiltration of precipitation upon 

 the land surface. Increasing the natural replenishment in- 

 volves increasing the amount of downward percolation, 

 whether by spreading water from other sources, or by reducing 

 overland flow or other avenues of escape of the precipitation. 

 In the great soil groups forming the land surface of most of 

 the country (page 166), the rate of infiltration is influenced by 

 such factors as vegetative cover, tillage, slope, and organisms 

 and organic matter in the soil zone, and good soil-conservation 

 practices have demonstrably increased the rate of infiltration. 

 Where the chief purpose of good land-use practices is to pre- 

 vent erosion by minimizing the overland flow or to increase 

 the soil moisture for agricultural crops, the very fact of in- 

 creased infiltration is a mark of success. But any project in- 

 tended primarily to recharge a ground-water reservoir needs 

 more than that in order to merit, say, the financial support of 

 the well owners dependent on that ground-water reservoir. 

 Artificial-recharge projects should be based on a sufficient 

 knowledge of the reservoir characteristics and should be ac- 

 companied by tests to show quantitatively what happens to 

 the water applied for recharge. 



Artesian ground-water reservoirs are special cases, because 

 the artesian conditions indicate the presence of impermeable 

 material that impedes upward movement of the water and 

 also prevents recharge by downward movement from the land 

 surface. Where wells have depleted the storage in artesian res- 

 ervoirs, artificial recharge cannot be by infiltration and down- 

 ward percolation from the surface but must be through wells 

 that puncture the impermeable layer. The alternative is to 

 augment the recharge in the areas of natural replenishment, 

 but this may make no appreciable difference at the wells, at 

 least for a long time, particularly if they are several miles from 



