Clearing up Muddy Waters

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[Steven Sobieszczyk] You are listening to episode 14 of the USGS Oregon Science Podcast for Tuesday, January 11, 2011.

For this month’s episode we discuss the water-quality parameter turbidity. More than just a way to measure dirty water, turbidity can serve as a useful indicator of the ecological health of a watershed. Join us, as we sit down with USGS scientist Heather Bragg to discuss differences in how turbidity is measured, how the data are used, and where you can find real-time turbidity monitoring here in Oregon, only in this month’s episode of the Oregon Science Podcast.

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[Steven Sobieszczyk] Hello and welcome. I'm Steven Sobieszczyk. Today, I'm pleased to be joined by USGS hydrologic technician Heather Bragg. Heather has been monitoring turbidity in Oregon for the last 10 years and has published numerous reports on the subject. The most recent report came out in 2010 and focused on using turbidity as a surrogate to estimate suspended-sediment budgets in the North Santiam River. Thank you so much for joining us today, Heather.

[Heather Bragg] No problem, thanks Steve.

[Steven Sobieszczyk] First off, can you describe what turbidity is?

[Heather Bragg] Basically, turbidity is a measurement of the muddiness or cloudiness of water. Now one thing to keep in mind when you’re measuring turbidity is that you're generally measuring something that's in the water rather than the water itself.

[Steven Sobieszczyk] How do you go about measuring turbidity?

[Heather Bragg] Turbidity sensors work by shining a beam of light into a water sample and then measuring the amount of light that gets either reflected at an angle or transmitted straight through the water. Now there are hundreds of turbidity sensors on the market, and they don't all measure turbidity the same way. Some of them use a white light source; some of them use infrared light; some of them have a detector at 90 degrees from the light; where some of them might have a detector at 45 degrees. It's important to note that there is no universal standard for how to measure turbidity. So, in order to address this problem, in 2004 the USGS published guidelines for classifying different turbidity sensors. These are primarily based on the kind of light used and the angle of the detectors. These distinctions are really important if you're comparing turbidity. You want to make sure that the instruments you're comparing are measuring turbidity in the same way.

[Steven Sobieszczyk] Regardless of what instrument is used or how it is measured, what is turbidity data used for? 

[Heather Bragg] There are all kinds of uses, actually, for turbidity data. It can be used to assess or even regulate water clarity for, say, drinking water or aquatic life. You can use it as a direct surrogate for something like suspended-sediment concentration. You can also use it for the contaminants that are associated with sediment transport. One of the things that people most are interested in now are the effects of land development and other human-related activities. And turbidity can be a good indicator of that kind of activity. 

[Steven Sobieszczyk] If people are interested in finding out more about turbidity or about on-going projects in Oregon that use turbidity data, where might they look?

[Heather Bragg] For information of the measurement of turbidity I would suggest going to the USGS national field manual chapter on turbidity. People can learn about the different measurement units that we use and some recommendations for how to measure and publish turbidity data. As far as turbidity data collection in Oregon, there are projects on the North Santiam River, the Tualatin, the Clackamas River, and on Johnson Creek. So if people want to look at some actual turbidity data and how it’s being used, they can go to those projects, which are all listed on the Oregon Water Science Center website.

[Steven Sobieszczyk] Lastly, to wrap things up, what do you think is the important thing to know about turbidity and its usefulness?

[Heather Bragg] When you're measuring turbidity, be sure you know what you're measuring. A lot of turbidity sensors are not going to produce comparable data, and secondly, turbidity is a very good for an overall assessment of water quality and watershed health. 

[Steven Sobieszczyk] Well, that's all the questions I have Heather, thank you so much for joining us today.

[Heather Bragg] Sure, thanks for having me Steve.

That's all we have for today's show. Thank you so much for listening. You can check out related links from today's podcast in our show transcripts. You can find them at our website: or.usgs.gov/podcasts. If our monthly podcast doesn't feed your need for USGS-related news here in Oregon, you can follow us daily on Twitter at “USGS_OR.” As always, if you have any questions, comments, or even complaints about the USGS Oregon Science Podcast, please feel free to email us at oregonpodcast@usgs.gov. To hear more about other research the USGS is doing around the country or even around the world, check out any one of our other USGS social media outlets at usgs.gov/socialmedia. There you can listen to other USGS podcasts, as well as find links to USGS on Twitter, YouTube, Facebook, and Flickr.

Until next time. I'm Steven Sobieszczyk.

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This podcast is a product of the U.S. Geological Survey, Department of the Interior.

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