Beginning of end for landmark dam
The removal of Savage Rapids Dam begins in earnest next week, when Slayden Construction begins building a 26-foot-tall coffer dam to reroute the Rogue River away from demolition of the north side of the dam.
The 88-year-old dam on the Rogue River has been targeted for years for removal to improve fish passage, and beginning next month the Grants Pass Irrigation District will begin using 12 giant new pumps to deliver water to its approximately 6,700 customers.
“It’s a really exciting time for the Rogue River and the fishery,” said Bob Hunter, lawyer for WaterWatch and key proponent for dam removal for years. “This should really help boost salmon and steelhead runs, and open up another stretch of river for boat passage. It’s been a real long process to get here.”
The $40 million project should end by December with removal of most of the dam, leaving parts of both sides.
The river will be free flowing in early October when the north side coffer dam is breached.
“This is a big deal,” said GPID Manager Dan Shepard. “They’ve been scurrying around, testing the electric motors.”
In two weeks the pumps will be tested, and by early May irrigation should begin, Shepard said.
Meanwhile the construction of the north side coffer dam will take 25,000 cubic yards of fill, and involve pounding large sheets of metal into the riverbed. During the estimated three weeks of construction, no water will flow through the fish ladders, completely halting fish passage. The river will be lowered by opening radial gates in the middle of the dam. Fish are unable to get through those gates.
The river should experience a spike in turbidity when the gates are opened.
“This is the one time where ODFW concurred with temporary loss of fish passage,” said Dan Van Dyke, district fisheries biologist for ODFW. “It’s supposed to be a maximum of three weeks.”
He added that the timing is fairly good, because it is the tail end of winter steelhead migration and early for spring chinook.
Once the north side coffer dam is done, it should take about two weeks to knock out the dam’s bays one through six on the north side, using large trackhoes, said Slayden Superintendent Rick Blankenship. The project also requires smoothing out and removal of rebar and concrete on the river bottom, and plugging of structures on the north side.
A key issue is fish passage after the first coffer dam is done. Because all the flow will be pushed to the south side, the radial gates may have to be left partially open at flows above 3,000 cubic feet per second to lessen flow through the fish ladder, Van Dyke said.
That could create attraction for fish which will not be able to make it through the radial gate flow.
Slayden has placed 20 huge sand bags below the ladder to help direct fish into the ladder. Jump height has been lessened at the bottom and in one spot higher up in the ladder, Van Dyke said.
“ODFW wants this to succeed in 2009,” Van Dyke said. “This whole analysis is a reminder that it’s not a good situation for fish at Savage Rapids Dam.”
The river won’t be shifted to the north side until October, to mitigate disruption of migrating salmon. Once the river is running freely on the north side, a second smaller coffer dam will go up, and the south side demolition will occur.
The breaching of the north side coffer dam in October will send an unknown amount of sediment down the river at a time when summer steelhead fishing is peaking.
Van Dyke said some fall chinook spawning grounds will be harmed by sediment, but at the same time spawning could occur upstream where the former reservoir was.
• April 7: Build north side coffer dam.
• April 14-15: First “wet” test of electric pumps.
• Late April: North coffer complete, river pushed south.
• Early May: Irrigation begins with new pumps.
• May: Demolition of north half of dam.
• October: Breach north coffer dam.
• October: Build south coffer dam.
• Nov.-Dec.: Complete demolition of dam.