Impacts of Early American Mill Dams and Stored Legacy Sediments on the Chesapeake Bay
Dorothy Merritts and Robert Walter have been researching geologically recent and historic sediments of the mid-Atlantic region since 2003. By examining historic maps from the 18th and 19th centuries, air photos dating back to the 1930s, and outcrops along streams, Walter and Merritts have determined that tens of thousands of mill dams once existed in Pennsylvania, Maryland and orther mid-Atlantic states. Each dam formed a slackwater pond that trapped sediment over a period of 2 to 3 centuries. Water-powered mills are long gone, but obsolete, derelict dams gradually breach or are removed, releasing sediment and attached nutrients to be carried downstream, some of it ultimately reaching the Chesapeake Bay.