Water that fills the void space between the particles of soil or rock and other more open spaces in bedrock is referred as ground water. The boundary between the saturated zone below (where all the voids are filled with water) and the unsaturated zone above (where not all the voids are filled with water) is called the water table. There are two factors that make ground water available for human use - porosity and permeability. Porosity is the measure of the volume of void space (pore space), their size, and number, and permeability is the measure of how easily the water moves from pore space to pore space through a body such as rock or soil or how well they are interconnected. Porosity will determine how much water is present and permeability how fast that water can pass through material. When both factors are large enough, the medium, like soil or rock, can produce enough water usable by humans to a well placed within it, such material is then called an aquifer.

The highest yielding aquifers are typically in unconsolidated sand and or gravel layers. Aquifers composed of highly porous sandstone or highly fractured rock can also make good aquifers. Contrary to popular belief most ground water is not found in underground lakes or streams. Such large open cavities or caves only occur under very restricted conditions based on the type of bedrock - an example is limestone when it becomes eroded forming what is called karst terrain. Some sedimentary rocks such as clay and shale, metamorphic rocks and massive igneous rocks can hold only small amounts of water and do not allow water to pass through quickly. These types of formations are called aquicludes or aquitards and usually will yield little to no water to a well or spring.

How Groundwater occurs in rocks and sediments

How groundwater occurs in rocks and sediments.


Howard, J.M., Colton, G.W., and Prior, W.L., eds., 1997, Mineral, fossil-fuel, and water resources of Arkansas: Arkansas Geological Commission Bulletin 24

A spring is a place where ground water flows naturally from rock, sediment or soil onto the land surface. Its presence depends on the nature and relationship of permeable and impermeable units, on the position of the water table and on the land topography. Springs are present throughout Arkansas and consist of two general types: perennial and seasonal. Perennial springs flow year round whereas seasonal or “wet weather” springs dry up periodically, especially during droughts or long periods of minimal rainfall. In Arkansas these conditions often occur during lat summer and early fall.

Most of the perennial springs in Arkansas with the largest flows are located in the Ozark Plateaus region. With an average flow about 150,000 GPM, Mammoth Spring in Fulton County has the largest yield of any spring in the state. In this region, springs have historically been important community water sources. Most north Arkansas communities have now begun to abandon natural springs as water supplies because shallow springs are susceptible to contaminants from the surface.

Discharge from a cave opening at Blanchard Springs. Flow can vary between 1,000 to 103,000 gallons per minute depending on local rainfall (see picture on the left).

Discharge from cave at Blanchard Springs

Perennial springs also occur in the Ouachita Mountains, most of these are considered “cold” (temperatures of less than 80 degrees F). Some of these cold springs are important sources of bottled water. However, there are areas of hot-water springs such as those of Hot Springs National Park where water temperatures average 143 degrees F. The quality or purity of spring water can vary from especially depending on which part of the state the spring occurs in, just like with surface water spring water from the Interior Highlands tend to be of higher quality than those that come from the Gulf Coastal Plain.

Mammoth Springs in Fulton County, Arkansas (see picture on the right).

Mammoth Springs in Fulton County

Data on Springs in Arkansas, 1937

This is an unpublished compilation of information on springs in Arkansas arranged alphabetically by county. The information was collected during the late 19th and early 20th centuries (approximately 1885 - 1935). This work should be of interest especially for its historical descriptions of springs and their use during this time period. The only authorship noted is that it was compiled under the direction of George C. Branner, the then State Geologist of Arkansas.

PDF Data on Springs in Arkansas, 1937

Howard, J.M., Colton, G.W., and Prior, W.L., eds., 1997, Mineral, fossil-fuel, and water resources of Arkansas: Arkansas Geological Commission Bulletin 24

Ground-water use in Arkansas is about 7.5 billion gallons a day (2005) of which 6.9 billion gallons is used for irrigation alone. There is some 4.7 million acres of cropland in Arkansas that is irrigated and of this 84 percent is irrigated with ground-water. The growth in ground-water use has grown by some 632 percent from 1965-2005 just for irrigation alone.

Comparison of ground water use in irrigation from 1965 to 2005 (see picture on the left).

Comparison of ground water use for irrigation from 1965 to 2005


Holland, T.W., 2007, Water use in Arkansas, 2005: U.S. Geological Survey Scientific InvestigationsReport 2007-5241