108 OUR USE OF THE LAND 



It may take several years for people who live along the 

 rivers to realise what is happening. In any case, unless the 

 run-off at the headwaters is checked, /they are in for serious 

 trouble. The nature of this trouble depends on the type of use 

 to which the river water is put. 



The users of river water can be divided into several groups. 

 First there are those who depend on rivers for their domestic 

 water supply. This means water for drinking and washing. 

 About three-quarters of the population of the United States 

 which is served by water systems depend on surface water. 7 

 When the stream bed fills with silt, it is more costly to clean 

 the water. If the flow of water is uneven, coming down in floods 

 in the wet season and shrinking to a trickle in dry periods, the 

 water supply will be endangered. Floods overwhelm the water 

 systems, frequently putting them out of commission. During the 

 Ohio-Mississippi floods in 1938 many towns along those streams 

 had to import water by railroad and truck because the water- 

 supply plants were under water or washed out. In the dry 

 season there may not be enough water. Also, when a stream 

 flows slowly it does not carry off impurities such as sewage, so 

 that the problem of purifying the water is increased. 



Similar troubles afflict the industrial users of river water. 

 They are unable to use the silt-laden flood water. The reduced 

 flow of the dry season does not provide them with enough 

 water for the manufacturing processes or for carrying away in 

 dustrial waste. 



Those who use river water to produce electric power find 

 that their power dams are silted up in the flood season, if they 

 are not completely washed away. In the dry season the water 

 supply may be too small to turn the turbines. 



During the periods of flood, river transportation must stop. 

 Low water means that the channels may not be deep enough 



7 National Resources Board Report, op. cit., p. 330. 



