The mud flats and marshland to the west of the Washington Monument (on the left side of this image) were called the Potomac Flats for most of the 1800s. In 1870, the Army Corps of Engineers began dredging the Potomac to remove silt and to deepen the ship channel to improve access to Washington by water. Dredged material was dumped onto the tidal flats along the Washington waterfront. The work continued until August 30, 1911, when contractors had moved over 12 million cubic yards of material from the river to create East and West Potomac Parks and the Tidal Basin.
Library of Congress Prints and Photographs Division. View original.
The Flats were the wetlands to the west of the Washington Monument and southwest of Constitution Ave. The land was transformed into Potomac Park and the Tidal Basin