Regulators behind the scenes keep reservoirs, rivers on target

By Scott Clemans, Public Affairs Office

The Willamette and Rogue “teacup” diagrams on Portland District’s website give a snapshot of current reservoir and river levels. (Corps of Engineers map)

The Willamette and Rogue “teacup” diagrams on Portland District’s website give a snapshot of current reservoir and river levels. (Corps of Engineers map)

When you woke up this morning, you probably took a quick look out the window or at your favorite news outlet to see how much rain to expect. For most, those few seconds of advance notice and planning is all we need.But a small team of engineers and scientists at Portland District headquarters has been watching that rain forecast for more than a week and calculating what to do as the rain runs off into the streams and rivers in the District’s area of operations.

They are the Reservoir Regulation Team, and their main job is to determine how much water to release from the Corps’ 13 Willamette Valley and two Rogue River Basin project dams, as well as John Day Project’s Willow Creek Dam. They’re on call 24 hours a day, 365 days a year, but most of the time they don’t attract much attention.

As we head into the November-January time frame, though, when most floods occur west of the Cascade Mountains, the spotlight often shines on our flood fighters.

“About 10 days out, we start to see rainstorms in the National Weather Service forecast,” said Reservoir Regulation Team Chief Laurie Nicholas. “Their radar and satellite imagery can pick the storms up over the Pacific Ocean and track them.”

“It seems like a long way out, but we really do start planning reservoir releases based on the 10-day prediction,” Nicholas said. “We evaluate our reservoirs’ actual and desired pool elevations; current and expected future downriver flows; what the weather’s expected to do in the meantime; required minimum and maximum flows for fish, water supply and other uses; and a variety of other factors.”

Regulators use a unique shared National Weather Service model that provides a real-time analysis of how different releases might affect reservoir and river levels and helps them understand the resulting depths and flows at various points downriver. The Northwest River Forecast Center’s official river flow forecasts, including any flood watches or warnings, are based on the model’s projections.

“Portland District and Northwestern Division have a special relationship with the National Weather Service,” said Mary Karen Scullion, Willamette Valley reservoir regulator. “We collaborate so that the Weather Service can send watches and warnings based on actual dam operations.”

The National Weather Service points to this relationship as the standard for how its regional river forecast centers should work with water managers.

Scullion explains that a daily schedule provides a pretty complete description of operations and restrictions, telling operators how much flow to release, which outlets to use, when to generate electricity, how quickly to change flows, how to manage downriver water temperatures and what kinds of activities are going on at and below the dam.

“Each season has specific goals: the goal during flood season is to keep the reservoir pool elevations at or below the rule curve, and the river levels below action stage,” Scullion said.

The rule curve for each reservoir shows the maximum desired pool elevation for any given day of the year, except during a flood fight when the reservoir is storing water to reduce downriver flood impacts.

The regulators’ overall strategy for handling a flood situation is fairly straightforward. They monitor river levels using a system of cooperatively managed gages to learn how much a river below the dam is rising from runoff. Correspondingly, regulators ask dam operators to reduce dam outflows to store water that might otherwise push downstream rivers above critical levels. When levels begin to subside, they increase dam outflows to get rid of the extra water and regain storage space for the next storm.

The devil’s in the details, though. For example, the gages don’t tell the regulators the whole story of how flows are affecting downriver communities. Regulators will work very closely with staff at the operating projects during serious storm events, sending spotters to known trouble spots to relay if releases are too high, or if there’s more room in the river than the gages indicate.

And, of course, flood storage in the reservoirs isn’t unlimited.

“Multiple back-to-back storm events can fill our reservoirs – especially the smaller ones like Cottage Grove – faster than we can draft them,” Scullion said. “Once that happens, there’s nothing more I can do except pass the water flowing into the reservoir, sending it downriver.”

And as often happens during a crisis situation, the people that usually do daily routine work are suddenly in the spotlight.

“The demand for information – from our own coworkers, leaders, partner agencies and the general public – goes up exponentially during a flood fight,” Nicholas said. “That, of course, is exactly the time the regulators most need to work undisturbed.”

So during a flood fight, sit back and let the “Res Reg” team do its job – but be sure to thank them later for keeping our reservoirs and rivers on target.

elevation and flow forecasts and other information are available for almost every stream gauge in the region on the Northwest River Forecast Center’s website.(Corps of Engineers image)

elevation and flow forecasts and other information are available for almost every stream gauge in the region on the Northwest River Forecast Center’s website.(Corps of Engineers image)