Abstract:
The focus of this study is the drainage history for the Smoky Hill River in central Kansas. The present interpretation is that during early Pleistocene time the Smoky Hill River flowed southward into the Arkansas River Basin through a bedrock channel known as the McPherson Valley. During mid-to-Iate Pleistocene the Smoky Hill River was diverted into the Kansas River system by a capture event resulting from incision and headward erosion by the Kansas River. The purpose of this study was to use Geographic Information Systems (GIS) techniques to understand more thoroughly the geomorphic history of the Smoky Hill River and capture events that have affected its course. A bedrock topography map was constructed from well logs in Kansas Geological Survey (KGS) Bulletins and Water Well Completion Records (WWC5) to search for bedrock channels marking previous positions of the Smoky Hill River and to study the influence of bedrock topography on present and past drainage patterns. Field studies were conducted to establish the positions of high-terraces
along the Smoky Hill River Valley that correspond to previous positions of the channel. Correlations between high-terrace deposits and modern soil map units were used to plot paleo-flow directions and postulate previous stream positions.
Results from this study suggest that the ancestral Smoky Hill River connected to the Arkansas River during late Pliocene/early Pleistocene. Highterrace deposits of fluvial origin were found throughout the study area. The elevation and composition of these terraces suggest that the ancestral Smoky flowed at a higher elevation than at present. The elevations of the terraces were compared to the bedrock divide (McPherson Ridge) that separates the modern Smoky Hill River from the Little Arkansas River. It was found that the terraces were approximately 50 m (165 ft) higher than the bedrock divide that is approximately 407 m (1335 ft) above mean sea level. Some geologists have suggested that the McPherson Channel was actually formed by glacial meltwater from the Kansas River Basin. This study may suggest glacial meltwater from the northeast to be an invalid explanation for the erosion of the paleo-channel. The apparent lack of exotic pebbles such as Sioux Quartzite in high-terraces and Equus Beds sediments disagree with this interpretation. Also, elevation differences between the spillover point (McPherson Divide) near Lindsborg of 407 m (1335 ft) and the glacial dam at 320 m (1050 ft) across the Kansas River Valley suggests that the connection between the two valleys was not the result of a glacial meltwater lake, but more likely a result of the ancestral Smoky Hill River flowing southward through the McPherson Valley.
