Trees in the town of Osoyoos, British Columbia, surrounded by floodwaters on May 15. Credit: Tamara Morgan
Heavy snowpack in the Pacific Northwest and mountainous areas to the east is leading to flooding and flood risks along the Canada-US border, though the severity depends on how quickly it melts.
Floodwaters Hit Osoyoos Lake for Second Year in a Row
For people who live and work around Osoyoos Lake – located at the border of central Washington state and British Columbia – flooding from a heavy mountain snowpack upstream was worse than last year’s flooding event.
The US Geological Survey (USGS) reported 2018 water levels on the lake reached 279.29 meters (916.32 feet) on May 18, higher than last year’s peak on June 2, 2017 (278.84 meters, or 914.88 feet) and the second-highest peak recorded at the Osoyoos Lake gage since the 1972 peak lake level of 279.49 meters (917.11 feet).
Prior to the establishment of the Osoyoos Lake gage, a high-water level of 280.03 meters (918.8 feet) in 1894 was documented from a floodmark on the old Okanogan Hotel Building in Oroville, Washington. In part, this year’s peak was due to the early and rapid melt of a heavy snowpack along the mountains and waterways of the basin. The snowpack is only one, albeit major, component of the flooding problem though. The layout of the waterways in the basin severely limit how much dam operators can do to mitigate flooding, according to Brian Symonds, International Osoyoos Lake Board of Control member and retired director for British Columbia’s Ministry of Forest, Lands and Natural Resource Operations.
As the snow melts, Okanagan Lake should have room available to store a portion of the runoff volume without worsening flooding downstream and around Osoyoos Lake. Since the storage capacity in Osoyoos Lake is relatively small when compared the amount of water that enters the lake during the spring freshet, Symonds said it’s not viable to operate Zosel Dam to significantly reduce the water level by making room for anticipated snowmelt as is done for Okanagan Lake.
Zosel Dam is subject to an IJC Order of Approval for its operation and maintenance. Operation of the dam is overseen by the Osoyoos Lake Board of Control. Okanagan Lake has its own dam to control flows out of the lake; while the Okanagan dam isn’t subject to IJC orders its operators work with water managers downstream to effectively control the water flow. Okanagan Lake has snowpack in the mountains that could potentially feed into a large freshet, but water managers there anticipated this during the winter and let out as much water as they were allowed in preparation, Symonds said.
During spring freshet, high flows in the Similkameen River can impact how much water flows from Osoyoos Lake. The Similkameen, which joins the Okanogan River just downstream of Osoyoos Lake, also has seen a near-record amount of snowfall in the surrounding mountains. If a large amount of water from the Similkameen River enters the Okanogan River in a short period of time, it can reduce the amount of water that can physically pass through Zosel Dam, exacerbating high water levels on Osoyoos Lake.
All the gates on Zosel Dam were opened in March, said Kris Kauffman, board of control member and consulting engineer in Washington state – effectively taking it out of the control system. Kauffman said the dam was designed with specific control limitations in mind, and the high water levels the area has seen in 2017 and 2018 exceeded those. Kauffman said water managers at Okanagan Lake have worked hard to hold back as much water as possible to prevent the Osoyoos region from being overwhelmed.
“There’s simply more water than their systems and our systems can deal with,” he said.
The International Osoyoos Lake Board of Control regularly updates water levels through its website, and the town of Osoyoos maintains an emergency page for floods and other dangerous conditions, including where to find sandbags and what should go in an emergency kit. USGS maintains a real-time water level trackerfor Osoyoos Lake as well, placed against the water level target range dam operators attempt to maintain.
With the slope of the Okanagan River Valley downstream of Osoyoos Lake being less than 0.42 meters per 1.6 km (1.4 feet per mile), Kauffman said, even a small increase in the water level around mid-May can cause problems for communities throughout the area. South of the Zosel Dam, there has been a “fair amount” of shoreline flooding, though the major north-south road in the US hasn’t had any interruptions. As of May 15, the Confederated Tribes of the Colville Reservation reported road closures along the Okanogan River, and closed it to recreational activities for safety.
To deal with floodwaters, Osoyoos board member and mayor of the town of Osoyoos Sue McKortoff said sand and sandbags were distributed to homes and businesses along the waterfront thanks to assistance from volunteers, provincial and town staff, and the regional Emergency Operations Center. The town also deployed “Tiger Dams,” or large bladders filled with water that serve as a temporary dam.
Floodwaters from Osoyoos Lake come precariously close to a surface street near the waterfront May 15. Credit: Tamara Morgan
As a resort town, Osoyoos officials stressed to visitors that there are still activities available during the flooding, but the town temporarily banned motorized vehicles on the lake, as the waves could cause water to shift onto additional property.
Kootenay Lake Water Managers Prepare for Worst
The area around Kootenay Lake has seen an above average snowpack this winter season – around 130 percent of the normal snowpack, according to Gwyn Graham, secretary for the International Kootenay Lake Board of Control. Combined with high water conditions, the potential is there to see flooding as spring continues.
But whether or not the region will see flooding is still up in the air as of early June, due in part to the reservoir capacity in the system and from weather conditions. Current conditions are available through FortisBC, the power company that operates the Corra Linn Dam downstream of Kootenay Lake. FortisBC maintains a water level chart for Kootenay Lake, and runs an email list to notify people of fluctuations with the Kootenay Lake water levels.
Graham said flooding could be averted or mitigated based on how temperatures play out and how much rainfall the region gets through May and June. As of May 29, water levels on Kootenay Lake reached 534.07 meters (1752.2 feet) above sea level, and as of June 5 levels were declining.
Flood Events and Risks Elsewhere
Other transboundary regions have seen some flooding during the spring. The Milk River, which runs through Montana and Alberta, had moderate flooding in late April along the US portion of the river due to snow melting along the lower elevations of the basin.
The Red River and Souris River basins didn’t see any substantial flooding this spring, due in part to ongoing drought conditions and dry weather. In the Rainy-Namakan Lakes watershed, water levels have remained within the IJC’s rule curves.
To the east, rain and melting snow brought Lake Champlain and the Richelieu River into its flood stage in early May. The IJC has a study underway looking at causes of flooding in the region and potential solutions to mitigate related damage.
Water levels along the Great Lakes are still above their long-term averages, and some storm-driven flooding occurred off western Lake Erie April 15 in Ohio, Michigan and Ontario. No major flooding is anticipated this spring, however.
Kevin Bunch is a writer-communications specialist at the IJC’s US Section office in Washington, D.C.