INVESTIGATING EVIDENCE FOR STORM-INDUCED OVERWASH DEPOSITS IN A POND ALONG THE JAMES RIVER, VIRGINIA

Models predict that tropical storm frequency and intensity will increase along with increasing global temperatures. Understanding of long-term storm frequencies and impacts may aid in prediction and mitigation of storm-related damages. Geologic records that preserve overwash deposits answer questions about past storm frequency, magnitude and sediment transport, and play a role in predicting localized storm surge impacts. Here we present data from sediment cores recovered from a small (2500 m²), low elevation pond located 25 m from the James River estuary near Williamsburg, VA. The pond is fed by a small stream with a steep-sided, forested catchment and is only ~1 m above the elevation of the river. The composite sediment record is 1.1 m long, and we analyzed changes in sediment lithology, magnetic susceptibility and organic matter properties. Analysis of historical maps show that the pond likely formed from the damming of the creek in the mid to late 1800s, and that our record represents at least 100 years of deposition; however, analysis of short-lived isotopes (²¹⁰Pb, ¹³⁷Cs) is ongoing and will provide chronologic control. Preliminary analyses show that the core contains several distinct peaks in magnetic susceptibility and changes in organic matter properties that could be attributed to storm surge overwash or intense precipitation events. These events could wash sediment from the sandy beach into the pond and/or transport catchment-derived sediment and terrestrial vegetation to the basin, changing sediment properties. Storm surge models show that inundation of the area likely occurred during at least three major hurricanes over the past 100 years. New chronologic data from our site will constrain the timing of sedimentary changes and potentially correlate them to these historic events. Our preliminary results suggest that analysis of sediment from low lying lakes, ponds and wetlands around the estuaries of Virginia’s major rivers can provide useful long term, local storm frequency records.