Water Supply Problems in Alaska— Alter 223 



probably does not exceed eight feet. However, much of the 

 storage space in a lake is unusable when a thick ice cover 

 exists. The majority of lakes would probably not provide ade- 

 quate storage for a community of more than a few people. Lakes 

 which are fed by underground springs or receive an appreciable 

 amount of shallow subsurface drainage may provide an ade- 

 quate supply of water. A thorough study of lake depths, tem- 

 peratures and geological features is obligatory. Many lakes are 

 deceiving in that they are principally the result of retarded 

 drainage through permafrost rather than evidence of a large 

 source of water. 



Broad, treeless expanses of permanently frozen water sheds 

 tributary to streams in much of the low temperature areas allow 

 rain water to run rapidly into the principal streams. In general 

 300-400 square miles of watershed are necessary to maintain 

 continuous flow in a stream. Facilities are necessary for storage 

 of water on small streams if a constant source of supply is main- 

 tained. Both conventional and underground dams have been 

 used to provide storage. 



Annual precipitation is very small in many parts of the 

 low temperature areas and cistern water supplies are usually 

 inadequate. 



Water which percolates down into the soil collects in the soil 

 at the top of the permafrost or permafrost table. In the south- 

 ern sector of the permafrost zone, where there is a continuously 

 thawed stratum between the seasonally frozen layer and the 

 permafrost table, appreciable amounts of this "supra-perma- 

 frost" water collects. Many shallow wells draw water from this 

 source. Such shallow sources are not dependable and usually 

 do not provide sufficient quantities of water for a community. 



Hot springs and other spring water supplies which issue from 

 below the permafrost may be found in some places. These 

 sources may be detected at unusually warm areas of a lake or 

 stream or may exhibit themselves as water within the perma- 

 frost (intrapermafrost water). Extensive icing or mounding at 

 the surface of the ground may also indicate the location of a 

 spring source. Deep spring sources with appreciable discharge 



