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Corps anticipates insufficient water year

Portland District
Published April 20, 2021
A pier at a lake of water, with hills and a blue sky in the background.

Due to recent dry weather, Cottage Grove Reservoir is four feet below what would be expected this time of year.

The U.S. Army Corps of Engineers, Portland District is anticipating an insufficient water year as it refills its 13 Willamette Valley and two Rogue River Basin reservoirs for the upcoming recreation season.

Both the Willamette and Rogue reservoir systems, which depend on rainfall to fill, are experiencing a dry spring that is hampering refill efforts at most of the reservoirs.

Year-to-date precipitation across the Willamette was 80% of normal, as of April 19, but most of this rain fell prior to the start of refill season or fell as snow. The Rogue saw worse precipitation at 64%, most of which fell before refill season, too.

“We’re monitoring forecasts and updating our modeling on a daily basis,” said Salina Hart, Reservoir Regulation chief. “We rely on spring precipitation to fill the reservoirs, which with this year being so dry, most Corps reservoirs are not able to fill to their maximum conservation pool levels,” she said. “Current modeling of the long-term forecast is predicting an insufficient water year for this conservation season, but we are working with partners to reduce dam releases based on the available storage within the reservoirs.”

The snowpack is 109% of median for the Willamette and 70% of median for the Rogue. Snowmelt helps keep reservoir elevations up in the summer if it lasts and matches outflows – but it only accounts for roughly 10% of each system’s storage.

The Corps manages reservoir inflows based on a “rule curve,” or the authorized maximum elevation on a given day to balance flood risk and storage for authorized purposes.  Both systems’ reservoirs are kept lower in the winter to reduce downstream flooding and refilled in the spring to prepare for recreation and adequate flows for fish.

The public is encouraged to visit the Portland District website to check the “teacup diagrams” before heading out to recreate.

As of April 19, the below information represents current conditions at both locations.

Willamette Valley Project: The Willamette Valley Project’s 13 reservoirs are currently 58% full. System-wide reservoir storage are 27% below the rule curve. Year-to-date precipitation in the Valley is 80% of normal. Willamette Basin snowpack is currently 109% of median. View the Willamette River Basin teacup diagram: https://www.nwd-wc.usace.army.mil/nwp/teacup/willamette/ or http://pweb.crohms.org/nwp/teacup/willamette/.

Rogue River Basin Project: The Rogue River Basin Project’s two reservoirs are currently 70% full. System-wide reservoir elevations are 24-feet below the rule curve. Year-to-date precipitation in the Rogue Basin is 64% of normal. Rogue River Basin snowpack is currently 70% of median. View the Rogue River Basin teacup diagram: https://www.nwd-wc.usace.army.mil/nwp/teacup/rogue/ or http://pweb.crohms.org/nwp/teacup/rogue/.

Portland District’s 150th Birthday: Portland District is one of the nation’s most comprehensive and diverse civil works programs and has been supporting the people of Oregon and southwest Washington since 1871. Throughout its 150-year history, the District has been operating locks and dams along the Columbia River, managing flood risks in the Willamette Valley and Rogue River Basin, maintaining Oregon's coastal waterways for navigation, and leading the Nation in hydropower generation. The team of more than 1,400 civil servants manage these missions all while ensuring equal attention is paid to environmental protection and restoration, fish and wildlife enhancement, and world-class recreation opportunities.

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Contact
Tom Conning
503-808-4510
edward.t.conning@usace.army.mil

Release no. 21-020