PALEOHYDRAULIC RECONSTRUCTION OF A LATE QUATERNARY STREAM FROM ALLUVIAL DEPOSITS IN SOUTH-CENTRAL PENNSYLVANIA

Furnace Run in South-Central Pennsylvania was used in a paleohydraulic reconstruction to determine the flow needed to transport sediments in two late Quaternary alluvial deposits. Forty of the coarsest clasts in Furnace Run were identified and measured, with the intermediate axes having a mean value of 16.3 cm and a standard deviation of 9.2 cm. Slope was measured at two stream reaches and determined to be 1.0 degree. Stream dynamics were assessed using two equations: (1) Competent flow depth using the Knox equation D= 0.0001 A^1.21 S^-.057 and (2) Velocity using the Williams equation V= 0.65 d^0.5. Forty of the coarsest clasts were collected from the younger of the alluvial deposits. The intermediate axes had a mean value of 14.0 cm and a standard deviation of 10.4 cm. Competent flow depth was calculated to be 83 percent of the competent flow depth of the modern Furnace Run. The mean paleovelocity of the younger sediment was determined to be 93 percent of the velocity of Furnace Run. Forty of the coarsest clasts were collected from the older of the two Late Quaternary alluvial deposits. The intermediate axes had a mean value of 11.5 cm and a standard deviation of 6.0 cm. Competent flow depth was determined to be 66 percent of the competent flow depth of Furnace Run. The mean paleovelocity of the oldest sediment was calculated to be 84 percent of the velocity of Furnace Run. These flow reconstructions suggest variation in flood hydrology and hydraulic geometry at the site, either in response to individual flood events or longer term climate trends.