In-water work restrictions are so tight in the salmon-filled rivers of western Oregon that the Oregon Dept. of Transportation decided to employ a top-down bridge construction method to replace a section of Interstate 84 east of Portland. If all goes well, say ODOT officials, the method may be adopted on a more frequent basis.
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.