KENTUCKY KARST
Figure 1: Geologic map of Kentucky. Note box around study area. Introduction and Geology
The dye trace was performed in Lexington, Fayette County, KY, in the Inner Bluegrass Region, which is underlain by highly-weathered, Middle Ordovician limestone (Figure1).
The study sites are in the Grier Member of the Lexington Limestone Formation. The unit is approximately 55 m (180 ft) thick, containing up to 15 cm (6 in) thick beds of fine- to coarse- grained limestone with interbeds of shale approximately 5 cm (2 in) thick (Blair, 2009). The geology and climate of the region is conducive to the development of karst features, such as sinkholes, springs, and conduits.
The study area is located within a single karst drainage basin area of approximately 12 km2 (4.6 mi2) in Lexington, Kentucky (Spangler, 1982; Currens, 1996; Norris, 2016). Project locations include the dye-injection location, informally known as the “Campbell House Sinkhole” and a monitoring location at McConnell Springs (Figure 2).
After briefly surfacing at McConnell Springs before again sinking, water ultimately daylights at Preston’s Cave Spring, where it then flows as surface water to Wolf Run and thus eventually into Town Branch. Though karst drainage basin studies have been conducted in this area (Spangler, 1982), detailed measurements of conduit-flow velocities were not recorded.
In our preliminary study (Norris et al., 2016) we measured the conduit distance from the Campbell House sinkhole to McConnell Springs as 1.9 km (1.2 mi). The topographic relief over the study area is 21.4 m (70’), the highest elevation being 295.7 m (970’) and the lowest at 274.3 m (900’). The differ- ence in elevation between the Campbell House and Preston’s Cave Springs is 12.2 m (40’) over the conduit path of 3.2 km (2 miles), making the stream gradient 6 m per 1.6 km, or 20’ per mile. Regional bedrock dip is 3°-5° NE. While no faults are evident directly in the flow path, the study area lies within the vicinity of several major fault systems: the Kentucky River and Lexington Fault systems, the Cincinnati Arch, and the Jessamine Dome (Black, 1989; McFarlan, 1943). Tectonic activity from these geologic structures has resulted in joint- ing and fracturing in the local bedrock, opening new paths for groundwater to travel freely and quickly: caves and sinks
Figure 2 - Sinkhole and spring locations. The thick black lines represent the surface watershed drainage divides. Note that water traveling underground transgresses surface water basins in some locations. Thus Campbell House Springs and Preston’s Cave Spring are in a different surface drainage basin from McConnell Springs, though all aforementioned sites are on the same subterranean flow path.
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