National Water Center, Eureka Springs, Arkansas
National Water Center, Eureka Springs, AR
Updated: April 2014 Contact: Contact: NWC
Contents ©1999-2014 by National Water Center. All rights reserved worldwide.
Since people first came to the Ozarks, there has been a great deal of mystery surrounding the water systems. Within this mystery lies many misconceptions concerning springs, water, and the earth in the Ozarks, Some examples are:
1) Spring water is naturally filtered.
2) Spring water has traveled for hundreds of miles.
3) Sinkholes are caused by cave roof collapse.
4) The land is a uniform structure.
5) The surface of the land and the subsurface are totally separate.
6) If you want to get rid of something nasty, just bury it, or dump it into the nearest river or lake.
To deal with these misconceptions, and to begin to answer the questions about Ozarks water, let's go back in time a few million years when life on earth began. Much of the bioregion was covered by a shallow sea. Sea creatures and vegetation went through their life cycles to finally be deposited in many layers on the sea floor. After millions of years of deposition, these layers became fossilized into deep layers of limestone, dolomite chert, and sandstone. Geologic events took place causing the formations to uplift and fracture until a huge dome, known as the Ozark Domal Uplift, was formed.
Today, hundreds of millions of years later, the effects of the elements of the atmosphere and time on the landscape are visible. On the surface, the effects can be seen as huge stream valleys, dry river beds, sinkholes and high bluffs. In the subsurface, fractures, pores, and caves of varying sizes have formed.
The rocks that exist under our hillsides are of two kinds: soluble (easily dissolved) which are limestone and dolomite and insoluble which are chert, shale, and sandstone, and as it has through the centuries, the rock is continuing to dissolve from the abundant rainfall (about 40 inches per year). In these underground rock formations lies the bioregion's most precious treasure: groundwater.
These water-bearing formations are called aquifers, and are filled by rain filtering down from the earth's surface through the earth's surface (recharge zones). There are two types of recharge systems in the Ozarks: discrete and diffuse. Water entering the subsurface through the discrete recharge zone moves quickly into sinkholes (collapsed cracks in the surface) fractures, caves, and losing streambeds (in which water flows for a short distance only to disappear through rock fractures). This water receives little or no cleansing or filtration. The second type of recharge zine, diffuse, allows the water to enter the subsurface very slowly through overlying soils on ridge tops, valley floors, and hillsides. This water receives some effective cleansing.
A large portion of the water that falls as rain, as much as 75%, enters the groundwater system, with 25% remaining in the soils and vegetation to be eventually lost due to evaporation and transpiration (moisture passing from leaves of vegetation). Of the 75% that enters the groundwater system, approximately 75% enters by way of discrete groundwater recharge. The remaining 25% becomes diffuse groundwater recharge.
A walk through the Ozark woods during a summer thunderstorm can reveal some interesting findings. Much of the water can be observed to flow but a few feet before disappearing into the subsurface, with the rest running in the surface valleys, hills, and hollows. Obviously runoff in the Ozark landscape is more vertical than horizontal in movement. But what keeps the water from going downward endlessly? The answer is that every aquifer is underlain by a relatively watertight layer of rock (shale). This creates a two-part groundwater system known as storage water and transient water. Storage water is a deep and irregular level of water of which all permeable rock and voids are filled. There is little or no movement. Storage water is mostly recharged through diffuse recharge, and is consequently filtered and cleansed. The second part, transient water is characterized by rapid movement into and out of the subsurface, recharged mainly through discrete recharge zones.
A phenomenon that is common in the Ozarks are it's many springs. A spring is transient groundwater that intersects the land surface. The tale that springs flow underground for hundreds of miles and appear pure and pristine has been proven wrong. Since most water entering the spring systems is from discreet groundwater recharge, it has received little or no filtration or cleansing. Therefore there is great potential for contamination. Care has to be taken in not dumping, flushing, or burying wastes into the environment.
So once the delicate relationship between the land and the water in the Ozarks is realized, the responsibility of the inhabitants is obvious.
What is a Spring? On the nature of groundwater in the Ozarks. Danny R. Halterman, Sept., 1982.
Arkansas Water: Why Wait for the Crisis? Jeanne L. Jackson and Dr. Leslie Mack, 1982.