SENSITIVITY IN SPRING DISCHARGE TO CHANGES IN PHYSICAL AND HYDROLOGIC PROPERTIES OF A CONDUIT DOMINATED KARST AQUIFER SYSTEM

Karst aquifers are essentially a natural storm drainage system where conduits help drain the surface of fluids and solutes that will travel to and be discharged from an outlet spring. Using the EPA’s Storm Water Management Model (SWMM), the role of the conduit geometry and the role of hydraulic parameters on controlling transport dynamics in karst aquifers were assessed. Properties and parameters specifically addressed were: changes in the length of the conduit system, the cross-sectional area of the conduits, the slope of the conduit system, the roughness of the conduits, and the ratio of the amount infiltration to the amount of pirated surface water.

The implications of this work confirm that the lack of knowing the internal system of a karst aquifer limits the effectiveness of pipe-flow models. The routing of flow through a karst system is intrinsically linked to the geometry of the system. When minor changes (+/- 10%) in the length and width of a conduit are made, a significant response occurs in the fluid flow. Changes in the height of the conduit do not produce a significant response to routing of the flow in conduits that are not full. Although important in accurately predicting the movement of water through the system, larger variation in the values of the slope of the system and the conduit roughness can be made in comparison to the geometric values. Both the slope and roughness can be varied by 10% and still produce flows consistent with the baseline system. The role of infiltration in routing flow is also important; however; differences in the infiltration rate of up to one magnitude still route flow in a similar fashion.

The use of SWMM to simulate flow and solute transport through a karst aquifer system produced good results. Although SWMM was used in this work, it may not be a universal solution to modeling karst system. The pipe-flow model approach used to simulate flow and solute through the conduits provides a reasonable solution to a system when the internal geometry and physical properties are known. However, inaccurate values for the length and the width of the conduits will generate model results that are not consistent with actual behavior.