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Raising the levels: Seattle City Light’s work to keep the Skagit River communities safe

Ross Dam

Ross Dam

The Skagit Hydroelectric Project is responsible for more than 30% of the clean electricity produced by Seattle City Light. Situated near the North Cascades National Park Complex, the Skagit Project uses three dams: Gorge, Ross and Diablo and three reservoirs (or lakes) of the same name to maintain the water flow that feeds into the Skagit River.

Every day, City Light’s Power Marketing team, located in downtown Seattle, works with multiple departments and agencies including City Light’s System Control Center and the U.S. Army Corp. of Engineers. During potential upcoming rain events, the team connects with these agencies before, during and after flooding occurs on an hourly basis. This careful monitoring and oversight are mandated by federal, state and local government agencies as well as tribal considerations. These agreements are vital to the survival of threatened species, the protection of the surrounding environment, both public and personal property all along the Skagit River’s course through the surrounding communities of Skagit County.

During the daily staff meeting before a significant weather event is forecasted to strike the region, the team decides when and where to maintain the optimal elevation levels among the three reservoirs strategically. This is done to limit potential flooding contingencies. The decision is dependent on the number of sidestream inflows in the current state and the forecasted impact of incoming rain or snow into the mountain streams and creeks that naturally flow into Skagit’s bodies of water.

Diablo Lake and the Diablo Dam

Ross Lake, the most northern reservoir, is drawn down to absorb the increased water levels from the side streams. Diablo is set up to gather as much side stream as possible while limiting any increase in spill or discharge flow patterns. Gorge Lake, the reservoir that feeds into the Skagit River through the Gorge Dam, can be reduced down 5-10 feet and can serve as the last line of defense for the area. As long as the Skagit projects can limit the impact of discharge and absorb a significant amount of inflow in the process, they hold back that amount of water that would typically compound the flooding downstream of the projects.

The amount of river flow is measured at the town of Concrete. If the river flow reaches a certain cubic foot per second, the U.S. Army Corps of Engineers can take control of the project to assist in reducing the amount of water flowing downstream.

These measures are a crucial mitigation practice to prevent increased flooding into the Skagit Valley. In November 2017, portions of the Skagit River experienced the highest flood levels the region had seen in more than a decade. The constant rain compounded with the already drenched soil created a significant threat to both property and loss of life.

“What could have happened would have been very likely catastrophic flooding,” U.S. Army Corps of Engineers’ Senior Water Manager Ken Brettmann said in an interview with Q13 FOX. “[The flooding] would have swamped the towns of Mount Vernon and Burlington.”

Because of precise planning and the proactive systems in place, City Light mitigated the flood risk, easing the burden of the other dams while maintaining the flood levels downstream.

City Light was lauded by for their decisive actions as the flooding downstream in Lyman and Mount Vernon was approaching historic levels.

This measure also plays a vital role in City Light’s efforts to protect the threatened chinook and steelhead spawn populations across the Skagit Watershed. Power Marketing works closely with members of City Light’s Environmental, Land and Licensing team to adjust the amount of river flow to align with the life stages of the spawning salmon from incubation to their journey back downstream.

Salmon along the banks of the Skagit River

While this is only a facet of the work of City Light’s Power Marketing team, its impact radiates throughout the Skagit River and beyond.

“It is City Light’s mandate to safeguard the ecosystem and communities, including Marblemount and Concrete from rising water levels” explains John Clarke, Chief Power Marketer/Power Operations and Marketing Manager.

“The uniqueness and unsurpassed beauty of the Skagit River Basin demands an unprecedented level of commitment on the part of all Seattle City Light’s employees. A responsibility gladly shared by those who serve, understand, and are firmly bound as stewards to such an important natural resource.”