Three dams on the Columbia River system need something other than simple maintenance work. They will be replacing the downstream navigation lock gates starting in December. Scott Clemens with the Army Corps of Engineers says that is why the river will be closed. The work will cost more than $50-million. The Dalles and the John Day dams on the Columbia and the Monumental on the Snake River will be closed through next March for replacement of navigation locks. Usual river traffic will be put on trucks and trains.