290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



regime, to promote pergelation or depergelation as desired. Generally 

 the former is diflScult near the southern margin of permafrost. If the 

 existing climate is not cold enough to insure that the permafrost re- 

 main frozen, serious consideration should be given to artificial freezing 

 in those places where permafrost must be utilized as a construction 

 material. Techniques that were used at Grand Coulee Dam (Legget, 

 1939) or on Hess Creek (Huttl, 1948) can be modified to fit the situa- 

 tion. It should be borne in mind that the refrigerating equipment 

 need be run only for a matter of hours during the summer after the 

 ground has been ref rozen and vegetation or other means of natural 

 insulation have been employed. Bad slides on roads and railroads, 

 settling under expensive buildings, loosening of the foundations of 

 dams, bridges, towers, and the like probably can be treated by re- 

 freezing artificially at less cost than by any other method. In fact 

 the day is probably not far off when airfields of Pycrete (Perutz^ 

 1948) or similar material will be built in the Arctic where no con- 

 struction materials are available. 



Where seasonal frost (active layer) is involved in construction, the 

 engineer is referred to the annotated bibliography of the Highway Re- 

 search Board (1948) and to such reports as that of the Corps of 

 Engineers (1945, 1946, 1947). 



Wafer suffly. — Throughout permafrost areas one of the major 

 problems is a satisfactory source of large amounts of water. Prob- 

 lems encountered in keeping the water liquid during storage and dis- 

 tribution or in its purification are beyond the scope of this report. 

 Small amounts of water can be obtained generally from melted ice 

 or snow. However, a large, satisfactory, annual water supply in 

 areas of continuous permafrost is to be found only in deep lakes 

 or large rivers that do not freeze to the bottom. Even then the 

 water tends to have considerable mineral hardness and organic con- 

 tent. It is generally not economical to drill through 1,000 to 2,000 

 feet of permafrost to tap ground-water reservoirs beneath, although 

 artesian supplies have been obtained under 700 feet of permafrost 

 (Dementiev and Tumel, 1946) and under 1,500 feet of permafrost 

 (Obruchev, 1946). 



In areas of discontinuous permafrost, large annual ground-water 

 supplies are more common either in perched zones on top of permafrost 

 or in nonf rozen zones within or below the permafrost (Cederstrom, 

 1948; Pewe, 1948b). 



Annual water supply in areas of sporadic permafrost normally is 

 a problem only to individual householders and presents only a little 

 more difficulty than finding water in comparable areas in temperate 

 zones. 



Surface water as an alternate to ground water can be retained by 

 earthen dams in areas of permafrost (Huttl, 1948) . 



