Alternatives that allow avoiding or minimizing sinkhole hazards are most numerous when a problem or potential problem is recognized during site evaluation. The number of alternatives declines after the beginning of site development. Where sinkhole development is predictable, zoning of land use can minimize hazards.

Numerous sinkholes resulting from declines in the water table due to ground-water withdrawals in carbonate terranes have occurred in the eastern United States and elsewhere. In Alabama alone, it is estimated that more than 4,000 of these sinkholes, areas of subsidence, or related features have formed since 1900. Almost all occur where cavities develop in residual or other unconsolidated deposits overlying openings in carbonate rocks. The downward migration of the deposits into underlying openings in bedrock and the formation and collapse of resulting cavities are caused or accelerated by a decline in the water table that results in (1) loss of buoyant support, (2) increase in the velocity of movement of water, (3) water-level fluctuations at the base of unconsolidated deposits, and (4) induced recharge. Damage due to sinkhole activity related to ground-water withdrawals has resulted in a variety of studies utilizing available scientific methods. These studies indicate that identifying the terrane in which the activity most commonly occurs and limiting large withdrawals of water from it will eliminate or minimize the problem. The terrane, youthful in nature, exhibits little karstification, is usually a lowland area, has a water table above or near the top of bedrock, and contains perennial or near-perennial streams.

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Large quantities of ground water and surface water are available in Washington County. Major sources of ground water are the Gosport Sand and Lisbon Formation undifferentiated, the Oligocene Series undifferentiated, the Miocene Series undifferentiated, and alluvium and low terrace deposits. The Miocene, the most productive source of ground water, will yield 0.5 to 1.0 mgd (million gallons per day) per well and is a potential source of larger supplies in most of the county. The quantity of potable water available is governed largely by geologic structures.

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