A METHOD FOR PALEOFLOOD RECONSTRUCTION USING SEDIMENTS DEPOSITED IN CAVES ADJACENT TO RIVERS

Paleoflood evidence is poorly preserved or non-existent in humid climates due to biogenic disturbance and erosion. However, flood records might be extended if paleoflood deposits in caves adjacent to rivers could be identified. This approach could be particularly useful in the eastern United States where paleoflood records are simultaneously sparse and of great practical interest. We identified several paleoflood deposits that lie slightly higher than the flood of record in a cave along the Greenbrier River, West Virginia, near the eastern edge of the Appalachian Plateau. The river is incised 115 meters below a limestone/shale upland, and has a drainage area of 3526 km2.

We mapped the cave, and conducted a precise leveling survey to position the deposits. We also surveyed Greenbrier River channel cross-sections both up and downstream from the cave. A step backwater model, calibrated using known stage and discharge values for the flood of record, yielded a minimum discharge of slightly greater than 2650 cms which is equal to the flood of record. However, evidence observed elsewhere in the cave suggests pipe-full conditions prevailed during the largest paleofloods. Revised model results based upon an assumption of pipe-full conditions in the cave yield a minimum discharge value of 3500 cms. This discharge estimate is 32 per cent larger than the flood of record. Using estimated paleo-discharges and the pending results of radiocarbon analyses, recurrence intervals for the Greenbrier River will be reported.