It’s called “first flush,” the rain that fell last week upon the scars of recent wildfires and threatened to wash into local streams whatever ash, debris or contaminants had been left upon the landscape.
From fire retardant to heavy metals to organic byproducts and exposed sediment, anything left behind by the flames was at risk of being swept into storm drains and streams during the season’s first substantial rains, experts said.
Public agencies are hopeful that a feverish effort to deploy thousands of straw wattles and other barriers around burned structures, charred hillsides and storm drain inlets prevented some pollution from occurring with storm runoff.
But strategic stream testing will help measure their success as water quality engineers and experts gear up for what will be a long-term campaign to protect water resources and restore scorched watersheds into the rainy season and beyond.
“Healthy watersheds mean a healthy environment, and right now we have a very unhealthy watershed,” said Sonoma Clean Power Director of Programs Cordel Stillman, who is helping to coordinate county and municipal watershed recovery projects in the wake of the wildfire disaster.
Flames torched 137 square miles of Sonoma County during a series of wind-driven fires that broke out the night of Oct. 8. One, the Tubbs fire, is now ranked as the most destructive wildfire in California history. The larger Nuns fire, part of which burned in Napa County, is listed as sixth most destructive. The third, smaller blaze was known as the Pocket fire.
Each burned in rugged, mountainous terrain above creek and river banks, including 617 streams that drain into the Russian River watershed that were affected by Sonoma County fires, water regulators said. Still more fire-impacted streams drain into the San Francisco Bay.
The fire left behind toxic materials and debris but also incinerated plants and forest litter, removing material that helps stabilize steep hillsides and slow water absorption, preventing erosion. In addition, very hot flames can leave the soil unable to absorb moisture, causing streams to accumulate water much faster when it rains.
Multiple agencies are now coordinating a wide array of projects addressing concerns such as flooding, debris slides, aquatic habitat and water quality for more than a half-million North Bay consumers whose drinking water comes from the Russian River watershed, officials said.
The Sonoma County Water Agency and smaller water systems are conducting mandatory testing of treated water from the watershed, “out of an abundance of caution,” said Katharine Carter, a senior environmental scientist with the North Coast Regional Water Quality Control Board.
Instruments also are being put in place to measure rainfall and stream flows around the area as part of early- warning systems for flooding and mudslides, for instance, Stillman said.
As it prepared for first flush, the North Coast Regional Water Quality Control Board had a team out in the rain last Wednesday night collecting samples from four creek sites expected to reflect the scope and severity of pollutants in the runoff.
The results, expected to be available next week, will be compared with samples taken a week earlier from the same locations and will help guide future remediation efforts, Carter said.
Water quality studies from past wildfires offer clues to what they might expect: elevated heavy metals, phosphorous and other nutrients distilled from flame retardant, pesticide residues, byproducts from burned organics, and other chemicals, Carter and others said.