The Johnstown Local Flood Protection Project, part of the Pittsburgh District, U.S. Army Corps of Engineers, is the longest paved channelization project in Pennsylvania and one of the largest in the United States. Congress authorized its construction through amendments to the federal Flood Control Act of 1936, and it was built between 1938 and 1943 to handle river flows equivalent to those experienced in Johnstown during the 1936 St. Patrick's Day flood. Flood protection improvements included deepening and widening the channels of the Conemaugh, Little Conemaugh, and Stonycreek rivers and constructing concrete side slopes and floodwalls. The project is a specialized engineering structure eligible for listing on the National Register of Historic Places. Over six decades it was overtopped only once, during the exceptional 500-year flood of 1977, and through 2002 it provided over $803 million in flood damage prevention benefits.