The Keystone XL pipeline—an approximately $7-billion project that complements the original Keystone Pipeline and nearly doubles the size and capacity of the system with an extension to the Gulf Coast—has been in the planning stages since 2008. This additional energy source from our North American Free Trade Agreementneighbor should be built. One of the key objectives to securing the nation's long-term economic security is the need to expand our access to safe, secure and sustainable sources of energy. The security of the U.S. and other leading economies in the world will remain threatened as long as we continue to derive
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.