Aquifers

Most area wells draw water from water-bearing layers (aquifers) recharged by precipitation on the hills surrounding Fairbanks. Only 10% to 25% of the 12-inch annual precipitation reaches the aquifers to become available for use. The rest is lost through evaporation and runoff.

Slope, vegetation cover and soil permeability all determine how much water penetrates. Ridgetops are most effective because of the low slope and permeable soil largely from decomposed rock. Many of the slopes are deeply covered by relatively impermeable wind-blown silt (loess). Worst are the water-saturated frozen soils, totally impermeable. Buildings, roads and similar constructs of man also inhibit recharge of the ground water aquifers.

Plant covering tends to inhibit runoff, but it also increases evaporation. Light rainfall collects on leaves or tree needles and then evaporates. Water penetrating to the roots is carried back up the plant and later evaporated. For the most part recharge of ground water seems to occur only during prolonged heavy rains and during the spring melt.

Because water supply is an important local problem, the University of Alaska's Institute of Water Resources is actively trying to learn more about the nature of and how to better identify prime recharge areas.