Examination of the Relationship Between Longitudinal Profile and Sediment Mobility within a Fluviokarst Stream System

The complex drainage systems within karst settings can result in atypical longitudinal profiles. Features, such as cave entrances, can be expressed as anomalous ‘bumps' in the longitudinal profile of a stream if down-cutting has continued behind the area in which the water is pirated to the subsurface. Horn Hollow, a fluviokarst valley located in Carter Caves State Park Resort in northeastern Kentucky, was examined for these types of features. The hypothesis of this work is that anomalous areas along the longitudinal profile will correspond to differences in sediment movement potential and that these anomalous sections will have different sediment sizes and cross-section shapes. In addition, these data, anomalies, sediment size, and cross-section shape, will aid in the identification and in the differentiation of areas of cave collapse and natural downcutting. To address the hypotheses, the longitudinal profile of Horn Hollow, including both surface and subsurface stream segments, and 22 cross-sections were surveyed. Armor point counts were performed at cross-sections unless the section was dominated by bedrock. Although Horn Hollow's waters have been predominantly pirated to the subsurface, the longitudinal profile of the system is similar to that of a stream near equilibrium. The conventional view of grain size decreasing (statistically significant) along the longitudinal profile was affirmed, with the exception of sediments directly downstream of cave passages. Grain sizes following cave passages were larger than the preceding cross-section; however, grain sizes at subsequent cross-sections followed the conventional trend. The preliminary analysis implies the sediment mobility is correlated to grain size, indicating a change in flow dynamics following cave passages. All of the data may be of use in identifying cave collapse or natural downcutting, but is not intrinsically definitive.