Summary appraisals of the Nation's ground-water resources; Alaska

Abstract

Alaska has enormous surface-water resources, but many of the streams are frozen for most of the year and most contain glacial silt that makes them unacceptable for human use. These factors lend special significance to ground water as a water-supply source, even though perennially frozen ground (permafrost) profoundly modifies ground-water flow systems in much of Alaska north of the maritime southern coast and southeastern panhandle areas. Frozen ground is a virtually impermeable layer that restricts recharge, discharge, and movement of ground water, acts as a confining layer and limits the volume of unconsolidated deposits and bedrock in which water may be stored. Ground water is an untested resource in most of Alaska, but in many areas potential development of ground water far exceeds current use. Alluvium of major river valleys, such as the Yukon, Tanana, Kuskokwim and Susitna Rivers, probably contains the most extensive aquifers in the State. Large amounts of ground water are also stored in glacial outwash aquifers that underlie coastal basins and valleys, such as those at Kenai and Anchorage in the Cook Inlet lowland. Individual wells yielding more than 1,000 gallons per minute have been developed in the Tanana River valley, Cook Inlet lowland, and the coastal valleys at Seward and Juneau. Comparable yields should be possible in other areas that have similar geohydrologic environments. No major aquifers have been identified in glacial and glaciolacustrine deposits of interior valleys or in deltaic deposits. Major bedrock aquifers have been identified only in carbonate rocks of the Brooks Range and on the north side of the Alaska Range. Springs issuing from the carbonate rocks of the Brooks Range have discharges as great as 16,000 gallons per minute. Most ground-water recharge occurs beneath reaches of stream channels that are losing flow to the ground-water system. Most ground-water discharge also takes place along reaches of stream channels. This discharge augments streamflows during summer and maintains low flows during winter when there is no surface-water runoff. On the basis of a streamflow hydrograph separation technique and using the 60 percent flow-duration value as an indicator of ground-water discharge, it is estimated that 25 percent of the total volume of streamflow in Alaska (exclusive of coastal, maritime environments) is contributed by ground-water discharge. The thawing of frozen ground in the permafrost regions of Alaska causes construction and engineering problems. Disturbance of the ground surface disrupts the natural thermal equilibrium and tends to thaw part of the permafrost. Thawing can cause loss of strength, a decrease in volume, and an increase in erosion potential, particularly if the frozen ground is fine grained and poorly drained. Present deficiencies in the ground-water information base are obvious limiting factors to ground-water development in Alaska. There is a need to extend the ground-water data-collection network and to pursue special research into the quantitative aspects of ground-water hydrology in cold regions, particularly the continuous permafrost zone.