The U.S. Army Corps of Engineers has begun rehabilitation of one of two spillway gates at the 80-MW Green Peter hydroelectric project on Oregon's South Santiam River.
Intended to improve the dam's ability to reduce flood damage on the South Santiam, work is to include strengthening the gate face; replacing the gate's arms, trunnion pins and wire ropes; and replacing or refurbishing electrical controls, gearboxes and other systems.
The Corps' Portland District awarded a $3.5 million contract in 2013 to Knight Construction & Supply Inc. for the tainter gate rehabilitation work. The work is similar to that performed on spillway gates at 40-MW Foster Dam in 2008-2009.
The Corps said public restrictions to the Green Peter Dam area would begin with mobilization of construction crews Sept. 15.
Crews are to pin the spillway gate face in place to hold back water, but Corps reservoir regulators are aggressively to manage the reservoir's elevation to keep the gate unwatered as much as possible. That might result in higher flows for longer durations downstream following significant rains. The Corps said its goal is to keep the river below flood stage.
Green Peter, one of 13 Corps dams in the Willamette River Basin, underwent a special stilling basin survey in 2011. With total capacity of 428,000 acre-feet, Green Peter is third to 120-MW Lookout Point and 110-MW Detroit dams in its ability to store Willamette Basin flood water.
Green Peter prevented the South Santiam from rising eight additional feet at the Waterloo gage during a January 2012 storm and is estimated to have prevented more than $17 million in damage to downriver communities during the 2011-2012 flood season.