NC MILL PONDS: A NEW ARCHIVE FOR POST-COLONIAL STORM EVENTS?

Extreme storm events and their widespread socioeconomic effects have been well documented in recent U.S. history, but prior to 1870 few measurements are available. Previous reconstructions have been attempted based on lake and tree-ring records, but these are only possible in a limited number of locations, limiting their utility for forecasting models and regional planning. In the Eastern U.S, however, millponds were extremely widespread from the colonial period until the early 1900’s. In this study the potential use of sandy event layers within millpond sediments as storm proxies has been investigated. Grain size variations are used to identify coarser (sandy) event layers, opposed to the “background” pond sediment which is relatively fine-grained (silt and clay). Changes in the clastic grain-size distribution of these sediments may indicate fluctuations of inlet and outlet stream discharge, primarily as a result of large precipitation events.

Millpond sediments were examined along stream banks and in piston cores from six sites in Wake and Johnston Counties, North Carolina, and the presence and thickness of sandy event layers were documented. In the laboratory, grain size variations were measured via laser particle size analyses. The age of the sediments was determined by a combination of tree ring chronology, historical records, and Pb²¹⁰ analysis. GIS was used to map the types of soils surrounding the millponds that would have been sources of clastic material. In areas were the source material is coarser, sand layers are typically thicker as opposed to areas where the surrounding soils are generally finer.

This study has identified graded storm layers at multiple millpond sites that indicate extreme hydrologic events. Some of these layers correlated with storms in the historical record, but many do not. The identification of storm layers in millpond sediments may lead to reconstruction of storm histories in many other areas.