Engineering Heroes
Arrowrock Dam’s impact to the Treasure Valley involved many, but there were two engineers who played a key role in the construction of the former tallest dam in the world.
Francis T. Crowe, supervising engineer, developed a bucket-and-chute system to deliver concrete. Sand cement, gravel and water were mixed into concrete at the on-site concrete mixing plant and were conveyed and placed utilizing two Crowe cableways. This complex method for mixing and moving concrete proved very efficient; concrete for a good deal of the dam was placed this way. The concrete work was carried on in two eight-hour shifts, six days a week. This system was a first for the United States Reclamation Service.
Orville Hiram Ensign, was the chief engineer who designed the valve that was used at Arrowrock. The valves were activated by reservoir water pressure, eliminating the need for motors and electricity at the remote site. Two rows of 10 Ensign valves were originally installed on the upstream face of Arrowrock Dam at the entrance to conduits used to pass water to the downstream river. The lower row of valves were removed and replaced with clamshell gates between 2001 and 2004. The other row of Ensign valves remain in place and are rarely used.
