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Tracking watershed health

Tracking water quality in streams gives the city a better idea of the health of the local watershed


by: VERN UYETAKE - Delynn Clark, erosion control specialist with the city of Lake Oswego, finds a good spot to take a water sample from Tryon Creek in a culvert.City workers have ramped up water testing in hopes of providing a more complete picture of Lake Oswego’s watershed health.

While Lake Oswego has tested water samples from various sites for more than a decade, the relatively new Lake Oswego Watershed Health Index tracks more characteristics, such as riparian conditions and biological information, with data based on more frequent testing of some factors.

“It’s not just based on chemistry,” said David Gilbey, the city’s water quality program coordinator. “It’s based more on watershed health.”

Lake Oswego has separate stormwater and wastewater systems. That means rainwater that pours through street grates from the roads doesn’t get treated before flowing into the city’s streams and water bodies — even though as it runs over the roadways and other hard surfaces, it can pick up sediment and small pieces of litter, as well as microscopic bits of metal, oil, fertilizers and pesticides from people’s yards and more. The federal Clean Water Act, approved four decades ago, aims to limit the pollution stormwater can contribute to the nation’s lakes, rivers and streams.

by: VERN UYETAKE - Measurements are taken for a waterways oxygen content and conductivity.Lake Oswego’s stormwater management permit has long required the city to monitor its runoff for metals, nutrients, dissolved oxygen and pH. The last permit renewal added another substance to track: pesticides. It also required more frequent testing.

Here’s how it works: Water is taken from 14 locations in seven streams, or watershed areas, of the city and analyzed for a variety of conditions. The numbers in different categories are then crunched into a single score identifying overall watershed health.

Categories considered include physical or riparian attributes such as streamside vegetation and bank stability; water quality indicators like temperature, pH, turbidity and bacteria; dissolved oxygen and nutrient concentrations; and biological information about any aquatic insects that are present.

The biological information can be especially useful, Gilbey said.

“You can look at all the chemistry you want in a stream, but the biology really tells you watershed effects and watershed health,” he said. “In any urban system there’s a lot of sediment-tolerant taxa. Over time, as this is updated, are we seeing less and less or more sediment-tolerant taxa?

“We put a large amount of effort into our monitoring program, and for good reason.”

In addition to ensuring the city meets state and federal water quality standards, monitoring helps government officials and environmental professionals track watershed trends over time. The information can also help officials understand how effective “green” building and development practices are.by: VERN UYETAKE - Delynn Clark, erosion control specialist with the city of Lake Oswego, checks for oxygen content in Tryon Creek.

“If you build a rain garden or swale, you should see a response in the watershed,” Gilbey said. “The only way to look at that is to monitor results.”

Similarly, the results can help officials identify “where you’ll get the most bang for your buck” with stormwater infrastructure projects, he said. Overall watershed scores can help officials prioritize which public projects to fund with limited resources.

Still, it’s hard to say whether things are getting better or worse in Lake Oswego.

Officials have noted decreasing amounts of phosphorous in certain waterways; phosphorous levels typically spike between March and May, when people are fertilizing their lawns.

“But we still have some work to do in making that connection between actual infrastructure improvements or something else,” Gilbey said.

Although the city monitors streams that lead to Oswego Lake, it doesn’t monitor the lake itself; the Lake Oswego Corporation, funded by lake homeowners, handles Oswego Lake’s water quality.

And the watershed health index identified certain data gaps in the city’s stream sampling program. Those gaps can skew results. Some areas have riparian and biological information as well as chemistry, while others have information about just one or two of the categories.

Eventually, Gilbey hopes to partner with citizen advisory boards, watershed councils and maybe public schools to collect more water samples and provide better water quality data.

“The watershed index is by no means complete,” he said.




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