Construction crews supervised by the US Bureau of Reclamation (USBR) have installed 10 new clamshell
gates replacing the 89-year-old Ensign valves that had been in continuous operation since the dam was first
Installation of the new gates required holding the reservoir behind the dam at record low levels in order to ensure the safety of the work crews. The new outlet works will provide flood control benefits to the Treasure Valley.
USBR collaborated with irrigators, fishery biologists, recreation interests and the US Army Corps of Engineers to manage flows during construction in order to ensure adequate water for all interests.
The Arrowrock dam is a 106m high, 350m long concrete thick-arch structure with an overflow spillway with six large drumgates, 20 ensign valves, and five sluice gates.