FLOODING IN KARST REGIONS OF THE VALLEY AND RIDGE PHYSIOGRAPHIC PROVINCE OF TENNESSEE

Flooding in karst terranes is a geo-hazard. It causes damage to properties, businesses, and roadways. It can lead to the formation of cover-collapse sinkholes and groundwater contamination. Three types of flooding or their combinations are related to karst in the Valley and Ridge province of Tennessee.

1. Recharge-related sinkhole flooding. This type of flooding occurs when a sinkhole's drainage capacity is not adequate to transfer the stormwater runoff to the subsurface. The sinkhole in-take or throat may be plugged by trash disposal, soil and debris eroded from the drainage basin. Human construction may increase the runoff rate to a sinkhole so that the rate of recharge exceeds the acceptance capacity of the sinkhole drain.

2. Flow-related flooding. Karst development in the Valley and Ridge Province is predominantly controlled by the geologic formations and structures. In the karst aquifer water can move quickly to an area with smaller flow-through cross-section or where water is coming in from other tributaries in the same drainage basin. Flooding will occur when the in-coming flow rate exceeds the flow capacity of the conduits in the aquifer. Excessive sedimentation, rock fall, or human activities including sinkhole remediation during construction can reduce the flow capacity of the conduit.

3. Discharge-related flooding. This type of flooding occurs when groundwater discharge is reduced due to an increase in water levels at discharge points. The groundwater flow can even be reversed from its normal flow direction. Construction of dams in surface water to which the groundwater discharges can reduce the discharge rate from the karst aquifer.

Understanding of the type of flooding is essential to solution of the flooding problem. Areas prone to karst flooding should be recognized, and restrictions and laws on land use should be implemented. Runoff and erosion control plans should address the unique characteristics of karst features. Digging out clogged sinkholes, creating retention basins, or installing Class V Injection Wells are possible solutions to improve drainage of storm water. However, solutions to flooding problems in karst areas should also be coordinated with the water quality control to prevent groundwater contamination.