Water levels in the Chetco River after the elimination of foliage in the Chetco Bar Fire last summer shouldn’t be an issue, said Ronan Igloria of the consulting firm GSI Water Solutions.
The issue was brought up in part by Brookings City Councilor Dennis Triglia, who asked in a city council meeting this week when the development plans for Borax’s Lone Ranch development north of town changed to indicate it would be using city water and not on-site water as originally proposed.
Of concern to Triglia was the amount of water in the river that can be taken for municipal use by both Brookings and Harbor and the predicted ramifications of the wildfire on the river.
The Burned Area Emergency Response team said last fall water could see dramatic increases of silt and debris in the Chetco River this summer, possibly hampering port activities and compromising water quality.
Neither happened, but that doesn’t mean it won’t when the area gets a significant rain event, as the foliage in the burned area helped hold water back and prevented erosion and flooding, scientists said. They are also waiting to see if anticipated surges of water happen after rain storms.
“Based on our review of historical data, namely the Silver and Biscuit wildfires in the watershed, the recent wildfire events do not appear to have led to measurable change in runoff of ‘flashiness’ at the USGS (water gage),” Igloria wrote in a memo to Brookings City Manager Gary Milliman. The gage measures water levels in the river throughout the year.
Igloria does acknowledge, however, because they have limited field data to confirm the potential impacts, further monitoring would be prudent.
“Theoretically, the wildfire could change the infiltration characteristics enough to further reduce the naturally low summer flows in the watershed,” Igloria wrote. “The significance of that needs to be monitored and studied over the long term — especially in light of its relative impact compared to general climate change impacts on precipitation patterns.”
Glen Leverich, a senior geomorphologist and geologist with Stillwater Sciences, agreed.
“We didn’t detect any changes to annual runoff that could be directly attributed to the two past wildfires,” he said in response to Igloria’s comments. “And we haven’t yet seen fire-related changes in the gage records since the Chetco Bar Fire.”
He said that might be because the majority of trees in the fire scar remain “intact” and last winter’s storms were moderate, leading to less-than-predicted decreases in infiltration and increases in runoff and erosion.
“I agree with Ronan that continued attention to the landscape and river flows will be necessary during the next three to five years to assess whether runoff and water availability is changing in a way that … could impact the city’s water supply,” Leverich added.
Neither scientist was asked to address how any fluctuations in water flow in the river this summer might affect the problems Harbor has had in recent years with saltwater intrusion into its municipal supply. That situation has occurred when low water levels, often timed with extreme high tides in the ocean, bring saltwater into Harbor’s water collector, which is located closer to the sea than Brookings’.