The shadow of Oroville Dam crisis: District strives to maintain dams

Tom Conning
Public Affairs Office

The openings in the spillway, shown releasing water, are the regulating outlets on Detroit Dam. Regulating outlets are the primary method typically used to pass water through a dam. Detroit Dam and Reservoir is located on the North Santiam River between Linn and Marion counties, Oregon. (Corps of Engineers photo)

The openings in the spillway, shown releasing water, are the regulating outlets on Detroit Dam. Regulating outlets are the primary method typically used to pass water through a dam. Detroit Dam and Reservoir is located on the North Santiam River between Linn and Marion counties, Oregon. (Corps of Engineers photo)

Tumultuous winter storms have tested and stretched the limits of infrastructure in the western United States, as the recent Oroville Dam crisis has shown. However, these aging and massive structures still provide a multitude of benefits to local communities. And although they may not seem complex they do have a variety of densities – figuratively and literally. One density is how a dam releases water. There are four ways dams can release water: powerhouses – if the dam has hydropower, regulating outlets, spillways or low level outlets.

Dams need constant maintenance and upgrades, including the mechanisms that are used to release water. This is the case for seven of the 13 dams Portland District operates in the Willamette Valley, as well as several other District dams. Jeff Ament, Portland District project manager, is part of the current assessment process to determine which dams need regulating outlet repair and which outlets should have priority.

“There is limited funding available to support projects like this,” said Ament. “We can’t just go in and upgrade all the regulating outlet systems at once,” Ament explains. “Therefore we need to determine several things, one – which regulating outlets are in the worst shape, in order to prioritize them based on condition. Two – which projects have the most impacts if a regulating outlet were to fail. And, three – what needs to be done at each project and what funding is needed to support that.”

Regulating outlets are the primary method typically used to pass water through a dam. Powerhouses are a secondary means of passing water but are not always available due to maintenance outages or other restrictions. Spillway gates are generally used only to pass large flows.

Logan Negherbon, Portland District hydraulic engineer, explained there could be several failure scenarios.

“If we need to pass flow through an RO but cannot, this could result in drying up the river downstream of the dam, and in the right circumstance, we could be forced to fill the reservoir and use the spillways to pass flow. In the flood season, dams depend on a low reservoir pool to ‘catch’ runoff from rain events and slowly release that flow downstream. Conversely, if a regulating outlet cannot close, we may end up draining the reservoir pool, which is not good either,” said Negherbon. “Scenarios like this could be bad for fish, cause flooding, reduce recreation opportunities or reduce power generation.”

According to Ament, the assessment process is almost complete and the next step is to use the assessment data to make funding requests for priority projects. Other projects included in the assessment include dams in the Rogue River Basin and the Willow Creek Dam. The District has already repaired regulating outlets at Blue River and Cougar dams and is in the process of repairing outlets at Fall Creek Dam.

Portland District is also upgrading spillway gates at many of its projects to ensure the dams function as intended. The Corps determined the spillway gates were a higher priority for replacement because of a higher risk of failure.