Karst groundwater is an incredible natural resource. It provides drinking water for many of our residents, beautiful springs to feed our waterways and habitat for many unusual underground species. The quality of the groundwater is dependent upon how we use the land and how well we protect the quality of groundwater recharge.An old adage is that whatever goes up comes down. In karst areas, whatever goes down, comes up--up through a cave, a spring or a well.
About three quarters of the water that reaches the major rivers in Missouri's karstlands has passed through groundwater systems for at least some distance. Karst is a landscape where underground water follows dissolved out channels in the rock. Sinkholes, springs, and caves are among the common features in karst areas.
Water that moves from the surface into the groundwater system is called groundwater recharge. Groundwater recharge replenishes wells, cave streams and springs.
Some groundwater recharge seeps and oozes through the subsurface, and in so doing receives fairly good natural cleansing. Other groundwater recharge occurs through a vast network of localized openings that are able to rapidly transport both water and contaminants. Water that seeps and oozes through the subsurface is called diffuse recharge. That which flows through localized openings is called discrete recharge.
From 1966 to 1973 I directed a watershed study for the U.S. Forest Service on Hurricane Creek south of Winona. Surface flow from Hurricane Creek enters the Eleven Point River while most of the underground flow from this basin discharges from Big Spring and flows into the Current River south of Van Buren.
We found that only about 25 percent of groundwater recharge was diffuse recharge; the remaining 75 percent was discrete recharge and was, therefore, not effectively cleansed.
Natural cleansing can be a misleading term--in many cases the underground openings are larger than the bacteria or parasites that cause waterborne illnesses in people and animals. Some discrete recharge zones cannot even filter out large materials such as acorns, walnuts, cans and pieces of styrofoam.
Sinkholes, which are depressions in the land's surface that have underground drainage, are abundant in some Missouri karst areas and rare in others. Their shapes are variable and range from bowl-shaped or elongated depressions to steep-sided natural funnels that may lead directly into cave passages and underground streams. Regardless of their shape, all sinkholes provide a direct connection between surface water and groundwater.
In a study in southern St. Louis County we simulated intense