Man-Induced Land Subsidence
How would you feel if your land had sunk 9 m in the past 50 years because of human activity? It happened in the San Joaquin Valley. In fact, land subsidence has been caused by man’s activities in at least 37 of the 50 states of the United States and affects more than 40,000 km2 in this country alone. Data from a few sites where economic impact is documented suggest a total annual cost to the nation of more than $100 million; worldwide, the total economic impact is astounding and growing. These nine papers, dedicated to Joseph Fairfield Poland's life work, constitute a major contribution to measuring and understanding this problem. They are arranged in three categories: (1) fluid withdrawal from porous media; (2) drainage of organic soil; and (3) collapse into man-made and natural cavities.
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.