Case Study: Land Subsistence in the American Southwest

Case Study: Land Subsidence in the American Southwest

a) Land subsidence is the lowering of the land-surface elevation from changes that take place underground. Common causes of land subsidence from human activity are pumping water, oil and gas from underground. These places can be; reservoirs, sinkholes, collapse of underground mines, drainage of organic soils, and initial wetting of dry soils. This actually occurs in almost every state in the United States of America. More than 17,000 square miles in 45 states have been affected by subsidence.

b) Land subsidence causes many problems, such as the following: 

          - Changes in elevation and slope of streams, canals, and drains

          - Damage to bridges, roads railroads, storm drains, sanitary sewers, canals, and levees

          - Damage to private and public buildings

          - Failure of well casings from forces generated by compaction of fine-grained materials in aquifer systems.

          - In some coastal areas, the effects of subsidence has made tides move into low-lying areas that were previously above high-tide levels

c) If humans cut down on how much oil and other resources then less land subsidence will occur. In some areas where ground-water pumping has caused subsidence, it has been stopped by switching to surface-water supplies from ground-water. Reducing water usage will also minimize subsidence. Determining what locations for pumping will also help reduce subsidence.