Construction crews are picking apart a chunk of Idaho history. The Ensign valves on the backside of Arrowrock dam are slowly being removed piece by piece.
Removal of ten 88 year-old water control valves is the last stage of a three year, $15 million construction effort at the Bureau of Reclamation's dam on the Boise river.
Reclamation engineers and construction crews began replacement of the valves in 2000. Now three years later and over a quarter mile of steel pipe lining, the job is almost complete. The construction replaced the original Ensign valves installed in the dam back in 1915 with more efficient clamshell gates designed to extend the life of the 88-year-old structure.
"This year we are working on the upstream side of the dam, removing the Ensign valves that were installed in 1915. There are ten of those altogether - we removed the first three, now we are working on second group of four," said Don Rosbaugh, Bureau of Reclamation Resident Engineer.
Rosbaugh expects that all ten will be removed by February, 2004.
Since September, crews have carefully removed the old 30-ton Ensign valves piece by piece. Once removed, workers will attach the bell mouths, a horn-shaped intake that aligns with steel linings that run straight through the dam.
From the beginning said Don Rosbaugh, Bureau of Reclamation Resident Engineer, removal of the valves has been a real challenge.
"They've got 88 years of rust and corrosion to break apart and 25 tons of solid iron to break loose -it's a big job and a time consuming one at that, "observed Rosbaugh.
The 10 new clamshell gates went on-line in this summer and will be used exclusively for water releases through Arrowrock Dam.
Mounted on the downstream side, the clamshell gates have stainless steel control gates and are operated hydraulically. The new gates open and close like two halves of a clamshell.
According to Rosbaugh, the clamshell gates will be tested again in the spring of 2004.
Source: Bureau of Reclamation
