Effect on Lake Roosevelt of Adopting Modernized Columbia River Treaty Interim Measures

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Published: Tuesday, 10 December 2024 21:06

On December 4 and 6, the U.S. Army Corps of Engineers and Bureau of Reclamation hosted virtual meetings to review “interim measures” being put into effect while the United States and Canada seek to finalize and adopt a modernized Columbia River Treaty. These measures, said the Bureau of Reclamation’s Roland Springer, “generally reflect the Agreement in Principle” reached by both countries in July to modernize the treaty.

The need for interim measures reflects a strong desire to avoid potential changes to U.S. Columbia River reservoir operations and associated impacts. As part of the original Treaty, the United States agreed to pay Canada in advance for assured flood space in the Canadian Treaty dams for a 60-year time period that ended in September 2024. The agreement in principle includes 3.6 million acre feet of pre-planned flood risk management space at Arrow Lakes in Canada through 2044. Arrangements have been made with Canada to make this space available for operating year 2025.

Key components of interim measures include the U.S. and Canada agreeing to a combination of pre-planned Flood Risk Management storage in Canada’s Arrow Lakes Reservoir and coordinated power operations.

The expected changes and timing to Lake Roosevelt are:

-- In “dry” to “average” years (which occur 60% of the time) there will be little to no difference to how much and when lake levels will change during the year.

-- In “wet” years (which occur 10% of the time and when runoff from Canadian snowpack and dangers of downstream flooding are highest), the changes and timing of lake level changes are also similar to previous years. As community members know, wet years mean the reservoir (lake) can be drawn down up to 30 feet more than average in the spring and impact protecting cultural resources, supporting fisheries and recreation, supplying water for irrigation, and operating the Inchelium-Gifford Ferry. This reality gets no better or worse with the adoption of interim measures. 

-- The graph shows what is expected in “moderately wet years,” or 30% of the time. 

• The blue line “Before September 2024” shows the historical trend of lake level changes. 
• The orange line “Coordinated Power & 3.6 MAF Preplanned FRM” shows what is expected with interim measures. From March through May, Lake Roosevelt may be lowered up to an additional 7 feet compared to the historical average. Federal agences will continue to work with tribes and resource managers to address cultural, fishery, recreation, Banks Lake management, and ferry impacts.