Case Study: Land Subsistence in the American Southwest

Using the links provided as well as your own research, answer the following questions in full sentences.

a) Describe the causes of land subsistence in the American Southwest and explain why it is getting worse over the past few years. (4 marks)

Common causes of land subsidence from human activity are pumping water, oil, and gas from underground reservoirs; dissolution of limestone aquifers (sinkholes); collapse of underground mines; drainage of organic soils; and initial wetting of dry soils (hydrocompaction). Overdrafting of aquifers is the major cause of subsidence in the southwestern United States, and as ground-water pumping increases, land subsidence also will increase.

b) Describe the potential impacts of land subsistence. (4 marks) 

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

- damage to bridges, roads, railroads, storm drains, sanitary sewers, canals

- damage to private and public buildings

- failure of well casings from forces by compaction of fine-grained materials in aquifer systems

c) Outline ways to prevent further land subsistence. (This will require you to think on your own) (4 marks)

- switching from ground-water to surface-water supplies

- reducing water use and determining locations for pumping and artificial recharge that will minimize subsidence

- monitor water uses; such as preventing too much water use for people's yards or inside people's homes