Karst, Sinkholes, and Land Subsidence

MODFLOW is the USGS's modular hydrologic model. MODFLOW is considered an international standard for simulating and predicting groundwater conditions and groundwater/surface-water interactions. MODFLOW 6 is presently the core MODFLOW version distributed by the USGS. The previous core version, MODFLOW-2005, is actively maintained and supported as well.

Karst terrain is created from the dissolution of soluble rocks, principally limestone and dolomite. Karst areas are characterized by distinctive landforms (like springs, caves, sinkholes) and a unique hydrogeology that results in aquifers that are highly productive but extremely vulnerable to contamination.

Groundwater is the largest source of fresh water on Earth - it's kind of a big deal. The USGS monitors, tests, and studies groundwater resources to assure one of our Nation's most precious resources remains viable for future generations.

More than 80 percent of known land subsidence in the U.S. is a consequence of groundwater use, and is an often overlooked environmental consequence of our land and water-use practices. Increasing land development threatens to exacerbate existing land-subsidence problems and initiate new ones. Subsidence detection and mapping done by the USGS is needed to understand and manage our current and...

Regional groundwater availability studies enable information about groundwater to be integrated and consistent, so that this resource can be analyzed and understood on an aquifer–wide scale. These studies provide decision–makers with a better understanding of the status and trends in the Nation's groundwater availability.

Stream, river, and lake bed sediment are reservoirs for many contaminants. These contaminants include some “legacy” contaminants, like DDT, PCBs, and chlordane, and chemicals currently in use, like the insecticide bifenthrin and many flame retardants. Learn about techniques used to study sediment-associated contaminants and their importance to aquatic biota.