The maximum water level at Detroit Reservoir is being lowered this year to reduce the possible impacts of future earthquakes. The reduction in water levels could affect boat ramp access in dry years and is just one part of ongoing seismic readiness work there.
The reservoir spans the border of Linn and Marion counties on the North Santiam River near the city of Detroit and is a crucial source of drinking water for communities in both counties, including Salem. A 2020 seismic study there found that the current maximum water levels might “overstress the spillway gates during a large earthquake,” a news release by the U.S. Army Corps of Engineers stated.
To avoid this, the maximum height of the reservoir will be reduced by five feet, to 1,558.5 feet from 1,563.5 feet. While that may not seem like a lot, officials say it would significantly reduce the strain on the floodgates during an earthquake.
The move might impact boat ramp access during some years, however, as the waterline drops below ramp lines, especially during the driest part of the summer in August and September. The reduction is not expected to impact other recreation activities, like non-motorized boating, fishing, swimming and camping.
“Structural analysis has shown a possibility of the spillway gates buckling under the force of a full reservoir during a large earthquake,” the press release stated. While officials say the risk of a full breach of the dam is low, they say this reduction is necessary to avoid damage to the spillway gates.
The corps is holding a public meeting to discuss the new restrictions and get feedback from the public 5 to 7 p.m. on March 22. The virtual meeting will go over the larger projects planned at the dam, as well as the findings from a 2020 seismic study that indicated the need for improvements to the dam and reservoir. The online presentation can be accessed by visiting https://usace1.webex.com/meet/PDXCorps.publicmeetings.
Those wanting to listen in to the meeting can call 844-800-2717 on March 22. The access code is 199-430-8599. Public comments about the project can be submitted via email at DetroitPoolRestrictions@usace.army.mil.