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Hydrology Road Trip of Rockcastle County, Kentucky
PHYSICAL SETTING AND CAVERN DEVELOPMENT
Field Trip: Hydrology of the Crooked Creek Region.
By: Gary O'Dell, NSS 10278
Rockcastle County is located roughly at the intersection of three distinct physiographic regions; the Bluegrass, Mississippian Plateau, and the Cumberland Plateau.
The Crooked Creek basin is contained within the latter province and occupies about eight percent of the county. The western edge of the Cumberland Plateau has been deeply dissected by surface streams and has a rugged and mountainous terrain. In the study area, as for much of the region, ridges of up to 150 meters (500 feet) in height are separated by narrow valleys. These ridges are generally composed of soluble limestones of Middle and Upper Mississippian age capped by Lower and Middle Pennsylvanian sandstones. Major groundwater movement is characterized by conduit flow, with extensive cave systems having developed in the Newman Limestone composed of the Upper member, the Ste. Genevieve and the St. Louis limestones. The cave-forming limestones occupy the middle sections of the ridges, with less soluble rocks comprising the lower portions and the present valley of Crooked Creek.
Consequently, cave systems are generally developed well above the valley floor. Characteristically, cave entrances occur at the base of limestone cliffs that outcrop 10-30 meters (35-100 feet) above the valley floor. These represent former, abandoned levels of conduit flow. Older cave passages generally parallel contour lines and thus trace the approximate outlines of the ridges containing them. Sasowsky and White (1992) have proposed that this configuration, according to their research on the Cumberland Plateau Escarpment in Tennessee, may represent cavern development along stress-release fractures. According to this hypothesis, valley walls fracture outward due to loss of support during stream entrenchment. Virtually every ridge contains one or more caves, and almost without exception cavern morphology conforms to the model suggested by Sasowsky and White. However, explorations have shown that, for many caves in the Crooked Creek area, there exists a network of cross-connections located above those passages that parallel the valleys. These nonconforming, high level cave passages may represent an era of cave development that predates valley entrenchment. The various caves in the study area range from fragments a few meters long to very extensive systems as much as 24 kilometers in extent. Among the largest cave systems in the Crooked Creek basin are Goochland Cave (24.0+km/15.0+miles), Precinct 11 Cave (8.0+ km/5.0+ miles), Miller's Cave (3.3 km/2.0miles), and Smokehole Cave (3.0+km/1.85 miles).
Present-day stream flow in these cave systems results from a process of secondary development. The abandoned upper-level passages often appear strongly influenced by local joint orientation. These passages are usually large and dry, and pierced by active vertical shafts that carry water running off the sandstone caprocks to the lower, active levels (those carrying present-day stream flow). Morphology of the lower levels appears less influenced by joint sets, often displaying a meander pattern similar to that of surface streams. Active passages also pierce the less soluble Borden formation, mainly in the Renfro member, though such passages are usually very small and sinuous and difficult to follow. Many of these stream passages in the Borden can only be inferred, being blocked by rubble at the bottom of shaft drains.
Springs are common throughout the basin, where contemporary conduit flow resurges at surface valleys. These springs are usually found at the southern edge of ridges and at the mouths of tributary valleys; underground conduit flow appears to parallel surface stream flow. Some of the larger springs function as a distributary, where several springs are clustered together and discharge water from a single underground stream. Where conduits are developed in the St. Louis limestone, outlets often form cave entrances. Impressive springs often flow from these caves; an example is the huge Goochland Cave entrance, roughly 30 meters (100 feet) wide and 15 meters (50 feet) high with a base flow of 55-85 liters/sec (2-3 cubic feet/sec). Springs emerging lower in the stratigraphic sequence seldom exhibit visible cave passage, usually flowing through rubble or appearing as seeps. Entrances high above the valley floor represent former springs in the Ste. Genevieve/Upper member or passages in those formations exposed by valley entrenchment.
Minor tributary valleys above these springs are dry throughout most of the year, carrying flow only after storm runoff. Several of the major valleys tributary to Crooked Creek also carry no surface flow except after very heavy precipitation. Examples of these are the Dry Fork valley (drainage area 6.0 square km/2.3 square miles) and that of Barnett Valley (drainage area 8.3 square km/3.2 square miles). During rainfall events, runoff into the Dry Fork and Barnett valleys generally sinks gradually into the stream beds or abruptly into well-defined swallets along the stream courses, so that continuous flow for the full valley length occurs only when the stormwater infiltration capacity for these inlets is successively exceeded. Stormwater is thus carried below or parallel to the dry surface streambeds. The entire Barnett Valley drainage is apparently discharged from the Precinct 11 Cave springs at the end of the ridge southeast from the valley, approximately 395 meters (1,300 feet) downstream from the intersection of the dry valley with Crooked Creek. For the Dry Fork Valley, however, discharge into Crooked Creek apparently occurs at a point remote from the Dry Fork valley mouth, approximately 2.8 km (1.75 miles) down Crooked Creek, emerging from the Arthur Singleton Cave spring. These hypothesized connections have not yet been demonstrated, but planned dye-trace studies during 1992 are expected to establish flow routes for the major springs.
Under base-flow conditions, the flow of Crooked Creek is lost in several locations. Particularly just above the Precinct 11 Cave spring and also above the Arthur Singleton Cave spring, where the stream flow disappears underground for short distances and then reemerges. Beyond the Singleton spring, surface stream flow is usually continuous for Crooked Creek to its intersection with Roundstone Creek. Due to the interception of surface runoff into underground conduit systems and the inferred presence of under flow along the Crooked Creek streambed, there appears to be a localized buffering effect on storm runoff. This effect produces a delayed and lessened flood peak, while extending the period of flood recession for Crooked Creek. Flood hazard is thereby reduced for the Crooked Creek basin, in contrast to non-karst areas in eastern Kentucky where similarly steep slopes and narrow valleys have resulted in frequent severe flooding with high costs in terms of human lives and economic losses.
Scanning and OCR work done by Lea Spokane
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