The San Lorenzo River.
(Kevin Painchaud / Lookout Santa Cruz)

CZU fire not impacting water quality — plus other highlights from the State of the San Lorenzo River event

One post-fire debris flow was observed, no ongoing water quality impacts from the CZU fire.

The CZU Lightning Complex fires created an unprecedented event, and the impacts are still being felt throughout Santa Cruz County.

Now, environmental leaders are trying to understand how the fire impacted the San Lorenzo River, and how best to prepare for the wide range of climate change effects — from fire to flooding — already affecting the watershed.

Local water managers, scientists, and the public gathered virtually on Saturday for the State of the San Lorenzo River Symposium. The symposium is an annual event, hosted by the City of Santa Cruz Water Department, the County of Santa Cruz, the Coastal Watershed Council, the Resource Conservation District of Santa Cruz County, and the San Lorenzo Valley Water District.

Local scientists, policy makers, and other river experts convene at the symposium to share information on the past, present, and future of the river.

The theme of this year’s proceedings was “Recovery and Resilience” in the aftermath of the CZU fires. Santa Cruz Mayor Donna Meyers began the proceedings with a look back at the importance of the river in the city’s origin story.

“The San Lorenzo River is the source of water for over 100,000 people, and protects endangered fish and wildlife species, and it is really the foundational element of why the city of Santa Cruz really got started,” Meyers said. “Everyone that came here, primarily in the native communities that were here first, they knew that this river was very powerful.”

Meyers congratulated the fast-moving stewardship and watershed protection that happened in the aftermath of the fire, as homeowners, the California Conservation Corps, and others moved to remove debris and hazardous waste from the burn scar that could contaminate the river.

“We are now going to need to be stewards moving into [dealing with] climate change,” Meyers said, acknowledging that fire frequency, changing storm patterns, and other consequences of climate change will put added stress on the river.

Following Meyers, scientists and local policy makers gave updates on the state of the river and river monitoring programs. Here are a few key takeaways:

Water quality not a major concern following the fires

Dr. Marilyn Underwood, the director of Environmental Health for Santa Cruz County, said that water contamination was a top priority following the fire. Underwood’s division was especially concerned with runoff from the 1,400 homes and other structures that burned. Buildings “have a lot of toxicity,” Underwood said. “Our homes are filled with toxic material, and it only becomes worse when it burns.”

Because the river watershed was impacted by the fire, “we knew that we needed to take some steps, even as the fire was still happening,” Underwood said. The county requested help from the state to begin a toxic runoff control program, and received funding and manpower from the California Department of Water Resources, California Conservation Corps, and mutual aid from neighboring counties. Their work focused largely on removing toxic materials and creating barriers to prevent runoff.

This work appears to have been largely successful. “We’re not seeing ongoing impacts on water quality from the fire,” Underwood said.

A summary of toxic runoff efforts led by Santa Cruz County post-fire.
(Dr. Marilyn Underwood/Director of Environmental Health for Santa Cruz County.)

Volatile organic compounds, one class of contaminants that was a concern post-fire, weren’t elevated in samples tested by the county, though about 13% did have bacterial contamination, probably from damages to septic systems during the fires.

One post-fire debris flow was documented during January’s storm

Debris flows — fast moving torrents of mud, trees, and other debris — were a major safety concern this winter. Fire-scarred landscape doesn’t absorb water well, so intense storms can trigger these disasters. Hundreds of households in or near the burn scar area were evacuated in January when an atmospheric river passed over Santa Cruz.

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Dr. Amy East, a research scientist at the USGS Pacific Coastal and Marine Science Center, has been working to calibrate predictions of when debris flows will happen in the CZU burn zone. The storm between January 26-29 was of particular interest in refining these predictions.

“Although there was concern just before that storm that it could have produced large debris flows based on the rain conditions we ended up getting we would expect sediment runoff and small debris flows,” East said, “and that is in fact what we got in the CZU burn area.”

One “true” debris flow was observed, on the coast facing side of the mountains, in a moderate-to-severely burned area on private property. The flow carved a canyon between three to six feet deep for a distance of over 600 feet. It was a small flow, according to East, but if a person or structure had been in its path, “it would have been very dangerous.”

An image of a debris flow triggered by a January storm.
(Dr. Amy East/USGS)

A difficult aspect of post-fire debris flows is that it’s difficult for meteorologists to predict ahead of time exactly where intense rain bands will fall, and where they could stall — which is what happened in Big Sur during the January storm, when intense rainfall triggered a debris flow that destroyed part of Highway One.

“We were lucky,” to have escaped major damage during that storm, East said. Now, she said vegetation in the burn scar is starting to recover, but the risk of debris flow from the CZU fire could remain elevated for several years.