CORVALLIS - An Oregon State University research review and survey of water systems in many Oregon cities suggests that modern forest management can be compatible with a high quality and quantity of water, and challenges common assumptions about the impact of logging and other forest practices.
The report looked at both research studies and 30 major municipal water systems in the state that are served largely by forested watersheds, including those of Portland, Eugene and Salem. Sponsored by the Oregon Forest Resources Institute, it will be presented on Aug. 23 in a public forum at Ashland, Ore.
"When people raise concerns about impacts of forest practices, one of the first things they mention is water quality," said Paul Adams, an Extension watershed specialist in the OSU Department of Forest Engineering. "In this report we tried to separate the facts from the myths to better understand how we get clean water."
One myth, Adams said, is the notion of pure water emerging from pristine forests.
"There is no such thing as pure H2O unless you buy distilled water at the grocery store," Adams said. "And while it's true that forested watersheds usually do deliver a very high quality of water, there's a wide variation even in nature. The Flynn Creek watershed in the Coast Range has been used as a control in research because it's a relatively pristine forest, but even there the suspended sediments have ranged from near zero to about 2,000 parts per million, when the water looks about like a chocolate milkshake."
Another myth, he said, is that trees store and release water to streams. Actually, a heavy forest canopy in most cases causes a net water loss of 15-20 inches a year in water volume. Trees consume water like any plant - it's actually the forest soils that store and filter the water, releasing it slowly like a sponge.
Adams said that protecting forest soils is the key to water retention, filtering and quality, and that from a water perspective the importance of forest cover is largely in protecting and nurturing the soils. Occasional timber harvest should not interfere with this process if done carefully with modern methods and good stream buffers.
Because much of the research on the effects of forest practices was done years ago, it can give an incomplete picture of the benefits of management tools and techniques now commonly used or required by law, Adams said. But this earlier research did help guide us toward these improved methods, he noted.
"Keeping forest lands intact is vital, but in general we've found that advanced harvesting practices with proper reforestation has little impact on water quality and quantity for municipal supplies," Adams said. "If you want to protect watersheds, the key is to protect the soils."
Among the other findings of the research review and survey:
- The quality of water from forest lands in Oregon is generally very high, although some dissolved, particulate and biological constituents are often present.
- Natural erosion can be an important sediment source and difficult to distinguish from management sources.
- Changes in forest cover may increase or decrease stream flows, but only if this occurs on a large portion of a watershed within a short period.
- Stream buffers during logging and other activities, as now required by law, can prevent many water quality problems.
- Forest roads can increase landslide and other erosion in steep terrain, but improved design, location and maintenance can greatly reduce problems.
- Logging and road construction between 1980-91 on 13 municipal watersheds in western Oregon did not result in sustained increases in turbidity at the water treatment facilities.
- Agricultural, urban and suburban areas in the Eugene and Salem watersheds have become major sources of sediments.
- High quality and safety of municipal water supplies are required by law, including careful treatment and frequent monitoring for contaminants.
- City personnel who manage major water systems in Oregon have significant concerns about wildfire risk in their watersheds, as well as water quality, sedimentation and the effect of agriculture, forestry and urban use.
Among the most serious concerns at the moment, Adams said, is the potential impact of major wildfires, especially on watersheds like Portland's Bull Run or Bend's Bridge Creek - in each case, these water sources have no filtration systems to remove sediment. Some of the highest erosion and sedimentation levels ever recorded on forest watersheds have occurred after major wildfires.
And despite Oregon's reputation for perpetual rain, Adams said, maintaining an adequate water supply is becoming an increasing concern in many areas. The Ashland forum to outline the findings of this report will be open to the public. It costs $15, which includes lunch. Information about registration and the agenda can be obtained by calling 541-737-4966 or on the web. Among the topics are the survey results; social issues in drinking water, forests and watersheds; fire ecology and hazard reduction in forested watersheds; and a tour of the Ashland watershed.