INTRODUCTION 7 



sured only when the draft from the wells is balanced by inflow 

 to those wells. The remedial measures undertaken to date 

 have involved reducing the draft or increasing the inflow to 

 the developed area, or both. Many areas of overdraft are small 

 in extent, and many also are in humid regions, where addi- 

 tional water supplies are available at no great distance. 



It has been easy to reduce the draft by tapping other sources 

 of water, and many cities and industries have developed 

 stream, lake, or reservoir sources as they have outgrown the 

 facilities of ground-water reservoirs in the vicinity. Others 

 have tapped other ground-water reservoirs or even the same 

 reservoir at some distance from the area of overdraft. Con- 

 tinued pumping in disregard of declining water levels has 

 tended to reduce the yield from individual wells, though also 

 increasing the rate of inflow to the area of overdraft by steepen- 

 ing the hydraulic gradient from the recharge area. In such 

 cases, however, the water is obtained at progressively greater 

 cost. 



In order to obtain increased supplies without excessive 

 pumping lifts and particularly without contamination by 

 ocean water, the natural recharge has been increased in several 

 places by the use of spreading areas, ponds, and recharge wells. 



The watercourse problems result from pumping wells along 

 rivers, where the ground water is so closely related to the water 

 in the stream that pumping from wells depletes the stream 

 flow. Diversions from the stream for various purposes may in- 

 crease the amount of ground water at one place and reduce it at 

 another. The intimate relation between surface and ground 

 water is also shown at some river cities where protection from 

 floods requires not only protection from a rise in the river but 

 also protection from the simultaneous rise of ground-water 

 levels under the city. 



Many problems have arisen as wells along watercourses 

 have been pumped: some because the pumped water is not 

 readily replaced from the stream; others because it is readily 

 replaced but the stream water is either needed downstream or 

 is unsuitable for use. Some wells close to streams produce 



