Land Subsidence – a Gradual Enemy
The continuing drought in California has led to accelerated groundwater pumping from San Joaquin Valley aquifers. This is nothing new for this part of California, but the intensity of the pumping during the last few years is unique.
Pumping groundwater from the San Joaquin Valley began in 1926 and some areas have seen land subsidence in excess of 28 feet. Today the experts are sounding the alarm because subsidence is now one foot per year in many areas. See a Photo from on U.S. Geological Survey site showing the extent of Land Subsidence
What is Subsidence?
Land subsidence (or subsidence) is the settlement (reduced elevation) of the ground’s surface. It is usually due to the movement or removal of soil, minerals, or water from under the surface. Most subsidence is “man-made,” however, some cases can occur naturally from sinkholes, thawing permafrost, or natural compaction.
How does Subsidence affect Texas?
The soil in the southeast portion of Texas is comprised of clay, sand, and water. When the water is removed the land sinks. This is the nature of the geology of the area. When the land sinks, ground faults are created and/or expand. Soil movement – sinking or settlement – damages foundations, buildings, water lines, and pipelines.
Perhaps the most dramatic example of subsidence in Texas has occurred in the Brownwood subdivision of Baytown, Texas, twenty miles east of downtown Houston. It is a subdivision of 448 homes, most of which are sitting in 10 or 15 feet of seawater of Crystal Bay. It is the result of the aggressive groundwater extraction of the southeast Texas Evangeline and Chicot aquifers that began in 1943.
In a 1974 Texas Monthly article the author states that over 20,000 acres of land area around Galveston has or will soon sink into the Galveston Bay and it estuaries. He also pointed out that over $100 million in property has been lost and that in Texas City and Pasadena the storm sewers have water flowing in the wrong direction.
This Texas Monthly article also states that more than 1000 miles of faults can be “activated” by the threat of subsidence – which in turn threatens residential, commercial, and industrial buildings. The Woodlands has recently seen problems with faults and some homes are being literally torn apart by fault lines that widen every year. We discussed these Texas faults in an earlier blog post.
Currently, the northwest corner of Houston is one of the areas experiencing the greatest subsidence. Home owners and home buyers should be aware of the long term risks associated with land subsidence.