BEDROCK CHANNEL MORPHOLOGY IN CARBONATES VERSUS CLASTIC SEDIMENTARY ROCKS

Most studies of channel morphology have been carried out on alluvial streams, where morphologic variables are mainly a function of stream flow characteristics. Bedrock streams are fundamentally different from alluvial channels in that morphologic variables are highly controlled by bedrock resistance. Despite the importance of a resistant boundary in bedrock channels, researchers have shown that bedrock channels do exhibit some similarities to alluvial channels (e.g., downstream hydraulic geometry). In this study we examine channel morphology along Indian Creek, which flows over Ordovician limestone located within the Highland Rim physiographic province of Tennessee. High rock solubility results in a dry stream bed at baseflow along much of Indian Creek. Preliminary results from fieldwork indicate that boulder bars are regularly spaced along the channel at an average of 8 channel widths. These data suggest a spacing of bars, perhaps similar to pool-riffle sequences observed along alluvial channels. Along Indian Creek, boulder bars are typically separated by sections floored by smooth bedrock or a mix of bedrock and boulders. Channel slopes range from 0.000375 to 0.009454 and are steepest for mixed-bed sections.

We also measured valley and channel morphology variables along Clear Creek, which flows over Pennsylvanian sandstones of the Cumberland Plateau. Preliminary results show that valley width increases with drainage area along Indian Creek, located in carbonate rocks. However, along Clear Creek, which flows over sandstone, valley width decreases with drainage area as the stream becomes incised. These data point out fundamental differences in valley morphology, which appear to be controlled by bedrock resistance. More work needs to be done to examine the influence of bedrock on other channel morphological variables.