The Tennessee Valley Authority has had a second leak at an impoundment at a coal-fired powerplant, this time from a gypsum pond at its Widows Creek Fossil Plant in northeast Alabama. The incident prompted Sen. Barbara Boxer (D-Calif.) to announce on Jan. 13 that she plans to seek federal regulation of coal-ash ponds across the U.S. Shifting gypsum dislodged the cap covering a 30-in. pipe once used to drain water from the gypsum pond into an adjacent settling pond, says John Moulton, a TVA spokesman. Once the cap came off, water in the gypsum pond flowed into the settling pond,
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.