Retrofitting dams to generate electricity

Retrofitting dams to generate electricity seems like a no-brainer to me:

Only 3 percent of the 80,000 dams in the United States are used to generate power, according to Norm Bishop, a vice president at MWH, a water engineering firm. They were built for other purposes, like flood control, recreation, irrigation or water storage.

To expand the nation’s hydropower capacity, “We should be looking at the dams in the 97 percent range that have no existing power facilities,” Mr. Bishop said.