Science & Environment

Clear-cutting forests near watersheds could threaten drinking water supplies, conservationists warn

By Alex Baumhardt (Oregon Capital Chronicle)
Oct. 18, 2023 1 p.m.
A  lumbered portion of Tillamook State Forest in northwest Oregon, on Friday, Oct. 13, 2023.

A lumbered portion of Tillamook State Forest in northwest Oregon, on Friday, Oct. 13, 2023.

Jordan Gale/Oregon Capital Chronicle

By August, residents of coastal Newport were put on mandatory water curtailment due to low stream flows. That same month, the city of Yamhill, 30 miles southwest of Portland, enforced water use restrictions on pools and lawns when Turner Creek, its primary water source, dropped to significantly low levels.


The blow of late summer drought could have been lessened and perhaps avoided if the forests around those watersheds that provide drinking water had been kept intact, according to Casey Kulla, a state forests policy coordinator at the nonprofit conservation group Oregon Wild. State forestry leaders say Oregon law is focused more on regulating logging to protect drinking water quality, rather than quantity.

“The number of trees of a certain age on the landscape, and the amount of logging that’s done in a watershed, directly affects the timing of water coming out of the stream at the bottom of the watershed,” Kulla said. Kulla accompanied the Capital Chronicle on a plane tour sponsored by the Colorado-based nonprofit environmental organization LightHawk, over logged private forests, the Tillamook Forest and the Siuslaw National Forest to show the impact of clear-cutting.

A recent study by the U.S. Forest Service found that about 90% of people in the West are served by public drinking water systems that rely on water that originates in national forests and grasslands, sometimes transported hundreds of miles from points of origin to flow into taps. The federal researchers found “unequivocally” that forested land provides the cleanest, most stable water supply of any land type.

But when there isn’t a forest buffer of diverse and mature trees to store and direct melting snow and rain or keep it from evaporating, what’s moving comes down quickly, Kulla said, leaving little water available when it’s most needed at summer’s end. Younger trees planted to replace older cut trees suck up more water than older stands.

Oregon law allows clear-cutting on a maximum of 120 connecting acres with 300 feet of trees left between each cut. While clear-cutting is less frequent on forests managed by the U.S. Forest Service and Bureau of Land Management, the Oregon Department of Forestry and private forest owners continue to clear-cut large swaths of public and private land.

Mike Wilson, state forests division chief at the state forestry department, said most Oregon timber laws are focused on protecting water quality, not quantity because there isn’t a large body of established science on logging impacts to hydrology and the flow of water in various types of watersheds.

“So that’s currently the focus of a lot of different research, and a lot of modeling work that’s going on, and I expect that will evolve in the future,” he said. “But our focus to date has always been around water quality.”

Today, from above, many parts of the Tillamook State Forest appear to have gone through a bad buzz cut. Large swaths are exposed to the ground, with patches of green where tree stands have been replanted or, rarely, left entirely alone. Dotting the bald spots are slash piles where limbs, leaves and pine needles burn and send up columns of smoke.


Logging watersheds

Oregon coastal communities that rely on drinking water from forested rivers and creeks have lost substantial old-growth trees and have been heavily logged during the last 20 years, according to a recent NASA analysis. In collaboration with Oregon Wild, NASA researchers found that between the late 1990s and 2023, logging took place on about one-third of the forested land across the 80 coastal watersheds in Oregon, representing about 600 square miles.

Some communities have experienced more loss than others. Logging has occurred on about 34% of forested land within the watershed serving Lincoln City with drinking water in the last 20 years. In Seaside, logging occurred on nearly 60% of the watershed, and in Rockaway Beach nearly 80% of the forested land in its primary watershed has been subject to logging. Rainstorms in 2016 caused erosion and landslides into a creek supplying drinking water to Rockaway Beach, requiring excavators to remove rock and sediment.

Looking for solutions

Hagg Lake, also known as Scoggins Reservoir, supplies water to Hillsboro in the summer. Officials there are trying to grow its capacity so it can store more water for late summer, but Kulla said the bulk of the forestland around it is owned and logged by the Stimson Lumber Company.

Kulla describes the area as “aggressively logged” during the last 20 years.

“Storage capacity is one way to deal with a higher water flow in winter and spring and a lower flow for the summer,” he said. “It’s not a complete solution, though, right? It’s expensive.”

A 2020 study by Oregon State University researchers published in the Journal of Hydrology found that the conversion of old-growth forests to farms of Douglas fir trees significantly affected streams in the Northwest. From July through September, stream flows in areas where old growth had been replaced with 34- to 43-year-old Douglas firs were half of what they were in basins with 150- to 500-year-old forests dominated by Douglas firs as well as Western hemlocks and other conifer trees.

Some cities have bought the forestland around their reservoirs to manage it themselves for logging and drinking water conservation. McMinnville Water and Light, a public utility in McMinnville, bought the forestland around the Haskins Reservoir to protect its water supply. In 2022, Arch Cape, south of Manzanita on the coast, bought 1,500 acres for $4.7 million to establish a public forest and protect its drinking water supply.

A 2023 state law created a $5 million fund for communities hoping to own or improve land around their source of drinking water. The Rhododendron Water Association in Rhododendron in the Mount Hood Corridor, which previously took out more than $100,000 in federal loans to pay a private timber company not to harvest in a vulnerable part of the community’s drinking watershed, is among the first groups to seek state funding.

This story was originally published by the Oregon Capital Chronicle.

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