SEASONAL AND STORM EVENT VARIATIONS IN SPRING DISCHARGE AND WATER QUALITY AT THE FOREST 44 KARST AREA

The Forest 44 Karst Area is located in southwest St. Louis County on the edge of the Meramec River floodplain. The best-known karst feature is Sinking Creek Spring that flows approximately 500 feet, before disappearing completely into the Williams Creek stream bed. Several other springs are located within the Williams Creek watershed. These perennial springs provide important sources of water for wildlife and horses at adjacent ranches.

This study recorded the variations in rainfall, spring discharge, and water chemistry (pH, conductivity, hardness, temperature, and turbidity) of the Sinking Creek Spring. This information was used to infer properties of the source aquifer.

Rapid recharge and discharge of storm event water was observed, along with significant changes in water quality parameters. Based upon the coefficient of variation (CV) for conductivity and base to storm event discharge ratios, this component of the aquifer is dominated by conduit flow, and considered hypersensitive to contamination. This indicates rapid entry of surface water into the conduit system at points close to the spring. This water may bypass mixing in the regional conduit system and represents the short-term storage component of the aquifer.

Seasonal changes were also noted in flow and water quality of the perennial base flow. The wet season base flow was in the 300 to 400 gallons per minute (gpm) range, and dry season base flow was about 150 gpm. This perennial flow represents long term storage in the aquifer and may contain a significant component of diffuse recharge and flow. The recharge area for the perennial flow may cover several square miles, based on a previous dye trace that connected one of the study area springs to a losing section of Williams Creek. The distance of this trace was approx. 2.4 miles.

It is hoped that future dye tracer studies can be conducted to include Sinking Creek Spring and further delineate the recharge area.

Limited floral and faunal surveys were also completed at some of these springs. The typical flora was watercress. The fauna includes sculpins, long-tailed salamanders, and macroinvertebrates.