The Missing Legacy of Middle Creek Lake: Implications of Legacy Sediment Erosion

Elaine Langone Center, Terrace Room

Erosion of legacy sediments from Middle Creek Lake, south of Selinsgrove, PA, contribute to pollution in the Susquehanna River and Chesapeake Bay. In the last two centuries, at least 4 different dams have operated on Middle Creek. Two adjacent grist mills, operating simultaneously, were located on the creek throughout the 19th century, and later, in the 20th century, two small wooden hydroelectric power plants: one in 1906 and a larger, replacement dam in 1936, operated until 1992, when it was removed. Each of these dams allowed sediment to accumulate in the lake as legacy sediment. Recently, the Middle Creek Lake Basin was examined to better understand the anthropogenic legacy sediment record. Though the lake underwent nearly 163 years of sediment deposition, much of this record is now believed to have been removed by erosion. In 1992, the PA Fish and Boat Commission (PAFBC) estimated 760,000 m3 of total sediment within the lake. With the breach of the dam in 1992, they also estimated a potential loss of 57,000 m3 of silt to be transported away, to the Susquehanna River and beyond. Based on recent examination of the lake sediments, we estimate a total of 789,000 m3 of sediment was deposited in the lake basin, with 436,000 m3 representing actual legacy deposits. Artifacts exposed at the surface of legacy sediment today, range in age from the 1940’s to the 1970’s, suggesting that much of the sediment deposited from 1936 to 1992 has been eroded. Additionally, the silty loam representing this time interval (56 years) is very thin throughout the basin, averaging 0.15 m. We approximate that nearly 3 to 4 times as much sediment estimated by the PAFBC has been lost from the lake basin due to erosion since 1992. This study suggests earlier estimations of sediment volume were imprecise and too low, and a greater amount of sediment likely made its way into the Susquehanna River and to the Chesapeake Bay.