New study provides information about ice jams on Osoyoos Lake

Ice jams are accumulations of ice that partially block water from flowing downstream and can cause challenges to the operation of control structures such as the Zosel Dam at the outlet of Osoyoos Lake. Ice jams form at the shallow outlet of Osoyoos Lake during certain winter conditions. A new U.S. Geological Survey (USGS) report, prepared in cooperation with the International Joint Commission (IJC), provides an analysis of when and why these ice jams occur. The findings will help the IJC's International Osoyoos Lake Board of Control (IOLBC) better understand the conditions that lead to ice jam formation and support future lake-level management decisions. The IOLBC is responsible for overseeing the operation of the Zosel Dam in compliance with the IJC's Order of Approval.

Osoyoos Lake staddles the Canada-United States border and is connected to the Okanagan/Okanogan River which flows through both countries. Ice jams can have significant implications for both countries, with undesirable impacts on Osoyoos Lake and the Okanogan River. By drastically decreasing streamflow in the river, ice jams may dewater the gravels where salmon eggs are incubating, taking away their oxygen supply and exposing them to freezing air. Ice jams can also cause short-term rises in lake level, which may affect shoreline infrastructure. Impacts from ice dams on the lake and the river can affect communities on both sides of the border.

The IOLBC is responsible for overseeing the management of lake levels in Osoyoos Lake. Concerned by the impacts of ice jams, IOLBC initiated a scientific study of the phenomenon, conducted by the USGS. The results of the study are now available as a USGS Scientific Investigations Report: Historical Ice Jams and Associated Environmental Conditions on Osoyoos Lake.

To determine how often ice jams occur, researchers compiled more than 80 years of data, including streamflow, lake levels, and air temperature. They also reviewed satellite imagery from Landsat 8-9 and Sentinel2 to visually confirm ice accumulation at the lake outlet when satellite imagery was available during more recent ice jams. Calibration of confirmed ice jams with daily mean streamflow and lake level allowed them to identify days impacted by persistent ice jams on Osoyoos Lake in the past. Using these combined datasets, the team identified 16 ice jam events spanning 31 days total during the period examined (1942-2024). Notably, 13 ice jam days occurred in the past decade (2014-2024), more than in any previous decade of record.

Statistical analyses revealed a specific range of environmental conditions under which ice jams form. Ice jams were more likely to form when:

• Winds blew from the west or northwest near or above 10 kilometers per hour
• Minimum daily air temperatures were near or below -9.4 °C

Identified days with ice jams persistent enough to impact daily mean streamflow and lake level occurred only under the conditions stated above. While the report does not evaluate mitigation strategies, its findings provide the Board and other water managers with a clearer understanding of the conditions that lead to ice jam formation. This information may support future efforts to anticipate ice jams, inform lake-level management decisions under the IJC's Orders, and guide the development of potential mitigation approaches.

Contacts 

Sarah Dunn, U.S. Secretary 

Martin Suchy, Canadian Secretary 

International Osoyoos Lake Board of Control

To contact the board by email, use the Contact form on the board's website. 

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