Subsidence is a drop in the surface level of land.  It sometimes occurs when groundwater is pumped from an aquifer. During this virtually irreversible process, cracks, fissures and sink holes can appear in the ground. 

The southern area of the Brazos River basin has experienced a great deal of subsidence.  To combat this problem, regulatory bodies known as subsidence districts were created by the State of Texas to begin lowering the use of groundwater and moving to a larger use of surface water in order to reduce groundwater pumpage and thereby slow the subsidence of the terrain near the Gulf of Mexico.

In addition, the legislature added language to the Texas Water Code explicitly recognizing groundwater conservation districts as the “preferred method of determining, controlling, and managing groundwater resources”(§36.0015)   By statute, the purpose of groundwater districts is to “provide for the conservation, preservation, protection, recharging, and prevention of waste of groundwater, and of groundwater reservoirs or their subdivisions, and to control subsidence caused by withdrawals of water from those groundwater resources or their subdivision …” (Texas Water Code §36.0015)

The photo at the left illustrates subsidence in the area thought to have experienced the worst amount of subsidence in the United States.  The signs posted on the telephone pole illustrate the altitude measurements for that location as it experienced subsidence.  (photo courtesy of the USGS.)