The Cowlitz River is flowing less than normal this summer and experts expect it to drop further over the next two months.
The lower water levels might be most visible in Kelso, where sandbars have appeared below the Allen Street Bridge. A nearby river gauge shows the water is about 10 feet deep, near the lowest level staked out on the wood pier measurer.
The river is flowing through Castle Rock at around 2,600 cubic feet per second, according to the National Weather Service’s river monitors. The normal rate for July is closer to 4,300 cubic feet per second.
Hydrologists say while the Cowlitz River does often reach these levels near the end of summer, it is more unusual to see these levels in July and indicates further declines are likely.
“The river levels are likely to continue a gradual decline until we see persistent precipitation start up again in the fall,” said Andrew Bryant, senior hydrologist from the National Weather Forecast Center.
Geoffrey Walters, hydrologist for the Northwest River Forecast Center, said rivers throughout Southwest Washington and much of the Pacific Northwest are running with below-average flows this summer. A healthy snowpack had built up during the winter throughout Oregon and Washington. The first extended burst of summer heat arrived in May, melting much of the snowpack into the river well before the extended dry months of the summer rolled around.
“That component of the natural river cycle we saw come and go sooner than normal, so we’ve seen a recession down into the summer flows faster and sooner than we typically do,” Walters said.
The hydrologists said there were no immediate dangers to Cowlitz County residents from the current state of the river. Bryant said the conditions could pose a danger to fish during a heat wave, as the shallower water will heat up faster than deeper streams.
As the summer continues, Bryant said the Cowlitz River might not see as much fluctuation or decline as smaller rivers because of its upstream management. The Mossyrock Reservoir and Mayfield Dam in Lewis County have to manage river levels to meet goals for hydroelectricity and environmental impacts.
The Cowlitz County Department of Emergency Management plans to use the low river levels to create a better map of the Cowlitz River. Department Director Larry Hembree said the county’s team will fly a drone over the river to map the river channels, silt buildup and some details about the riverbed.
The images and scans from the drone will be shared with county departments and agencies like the Northwest River Forecast Center to update their models about the river conditions.
