SLACKWATER DEPOSITS AND PALEOSTAGE INDICATORS AS EVIDENCE OF PALEOFLOODING ALONG THE BLUE RIVER IN SOUTH-CENTRAL INDIANA

The Blue River in south-central Indiana provides a probable location for paleoflood investigations in that it is a bedrock river with many likely locations for preservation of slackwater sediments and other high water indicators. Features associated with flooding mark a minimum flood stage within which sediments were deposited and/or erosion occurred. Using the flood stage, and reasonable velocity estimates, it is possible to calculate discharges and compare them to historical records of flooding.

Along the Blue River, several locations were identified as potential flood stage indicators. Site 1, an erosional scarp in alluvium/colluvium, is within the area influenced by the Ohio River. The Ohio is in a permanent slackwater flood state due to the locks and dam system at Cannelton, about 40 miles downstream of the research area. Site 2, an exposed bedrock bluff with horizontal gaps, is located upstream of the area permanently backflooded by the Ohio. Sediments with the proper morphology and occurrence were located 25-30 feet above the streambed at Site 2. Preliminary evidence suggests that these possible paleoflood sediments are 5-10 feet above the 23-foot maximum flood stage recorded on the Blue River at White Cloud, Indiana, upstream of the research area. The elevation of the sediments falls within the realm of the historic flood regime along the Blue River. Paleodischarges calculations would require not only stage, but velocity measurements. At present, we can only estimate velocities based on historic records. Using the velocity recorded during the 23-foot flood stage, and assuming a stage of 30 feet and a width limited by the confines of the stream valley, yields an estimated minimum discharge of 37,854 cubic feet per second.

Paleoflood data observed in the course of this research could prove useful in ascertaining more realistic flood histories for the Blue River.