The U.S. Environmental Protection Agency on Dec. 29 sent a letter to the District of Columbia and six states in the Chesapeake Bay watershed and outlining new penalties if they do not meet more stringent requirements for cleaning up water pollution. Bay advocates have criticized federal and state efforts to clean up the bay in the past because although states have been encouraged to meet certain milestones in reducing water pollution from point and non-point sources, they typically have faced no penalties for failing to do so—until now. Penalties could include expanding National Pollutant Discharge Elimination System (NPDES) permits to
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.