Alluvial Aquifers—Fairbanks, Alaska In the area of Fairbanks, Alaska, the Chena and Tanaua Rivers have alluvial deposits up to 800 ft (240 m) thick. The alluvium consists of interbedded gravel, sand,...

Alluvial Aquifers—Fairbanks, Alaska

In the area of Fairbanks, Alaska, the Chena and Tanaua Rivers have alluvial deposits up to 800 ft (240 m) thick. The alluvium consists of interbedded gravel, sand, and silt. The floodplains are interspersed with terraces from 3 to 25 ft (1 to 8 m) in height. The distribution of permafrost in the area is irregular. Permafrost is absent or nearly so in the alluvium beneath the river channels. Thin permafrost may be found under islands. The youngest, low-terrace deposits are underlain by unfrozen alluvium, with some isolated permafrost bodies up to 80 ft (24 m) thick. Higher terraces have more continuous permafrost, which can be 200 ft (60 m) deep. The older terraces have nearly continuous permafrost up to 280 ft (85 m) deep (Williams 1970). Permafrost thickness increases beneath progressively older terraces. Wells in the alluvial valley obtain water from unfrozen areas or, if there is permafrost, from either above or below it (Cederstrom 1963).