2015 Stormchaser Event
Would you believe that this is the 9th storm we have documented with Stormchasers!? This wouldn’t be possible without YOUR help, so thank you! Because of your dedication, our knowledge about the water quality of our coastal streams continues to grow each year. Unfortunately, due to funding cuts this year we were only able to look at turbidity. In past storms we have examined turbidity, nutrients, and E.coli to name a few parameters. We are hoping to secure enough funds to continue collecting this valuable information into the future.

We sampled 87 sites across Curry County from 2:00-4:00 PM on December 3rd, 2015 with 39 brave volunteers!

We have included the results for the 2015 storm, sorted by location from North to South and upstream to downstream (Click on North and South to see the data values). Site Names include the watershed name first, such as “Chetco River: Jacks Creek: Hamilton Creek at Mouth.”

There is some technical information discussed hereafter. Please feel free to call us if you have any questions or would like to further discuss the information below. While going through the results I was trying to think of a simple way to show the impacts of turbidity on water quality, and I found this lovely picture.

Turbidity Measurements

Turbidity is a measure of the cloudiness of water, and during our winter storm runoff, it is caused primarily by soil particles. These soil particles are also known as fine sediments or suspended solids. Turbidity is measured using a nephelometer (aka turbidity meter!). This electronic meter measures the amount of light scattered by the water sample. Higher concentrations of soil particles scatter more light, which the meter records as higher nephelometric turbidity units (NTUs). If anyone is interested in observing the tests or assisting, samples are tested at the watershed council office after each Stormchaser event.

To give some perspective, distilled water reads 0.1 - 0.2 NTUs, and typical summer readings on our rivers are less than one to two NTUs. On the high end, we once measured turbidity levels that exceeded the scale of the meter at 1000 NTUs – from North Fork Indigo Creek, after a storm that likely eroded landslide deposits and included runoff from the Biscuit Fire (charcoal was visible). During our first Stormchaser event (2004), values ranged from 6.5 to 494 NTUs. As a reference, the highest level we measured previously from Rogue River at the Lobster Creek Bridge was 105 NTUs (also after the Biscuit Fire).

Because the range and distribution of turbidity results is different for each storm, we have included “Turbidity Distribution” graphs. You can easily compare the results from your sites to all other sites. If you sampled a site that was particularly high, we are interested in your thoughts about the cause(s). Watersheds with differing geology, topography, and soils naturally have different water quality characteristics. Turbidity levels vary between streams draining watersheds with high clay versus low clay soils. Clay particles, due to their small size, are suspended in the water longer than the larger silt and sand size particles. Also, soil that is rich in clay is more susceptible to deep, slow-moving earthflows, which deliver sediment to streams by gullies and toe slides.

Turbidity Effects

Elevated turbidity may have physiological, behavioral, and habitat effects on fish. As turbidity increases, predators must be closer to their prey in order to feed. Active feeding is more energy intensive than drift feeding, so that elevated turbidity has been correlated with decreased growth rates. At turbidity levels exceeding 20 NTU, coho salmon were found to be less successful in capturing prey and decreased their feeding rate. Studies also showed effects on fish food sources; both macroinvertebrate density and diversity declined significantly with increased turbidity. There are also physical effects caused by suspended particles, such as gill abrasions. Because fish get oxygen from the water, fine sediments coating the gills can cause suffocation. Fine particles also interfere with flow through salmon redds (nests), needed to supply oxygen and remove wastes from the eggs.

Interpretations of Results

Because rainfall intensity was not uniform over the entire county, valid comparisons may be made of sites within a watershed and between adjacent watersheds, but not between north and south. We are collecting rainfall and temperature data from official stations and unofficial observations. It is essential to be cautious when associating causes with high turbidity levels – sometimes the most obvious land disturbance is not connected to the stream. In other cases we may have only part of the whole picture – if anyone has thoughts about what may be causing some sites to have lower or higher turbidity levels, please let us know.

At times, minor erosion of banks or small slides can increase turbidity for a short time, particularly on small streams. If there is a small, short-term cause, the variability between storms will be high. This is one reason why it is important for us to sample multiple events. If turbidity is consistently high at one site (and soils are similar to adjacent sites), it will need further investigation to determine the cause.

Some watersheds include areas influenced by large, slow-moving deep landslides (known as earthflows). The type of clay associated with these features produces high turbidity values. It may be possible to isolate the effects of some earthflows, or areas of intensive land use (and disturbance), by sampling upstream and downstream.

In order to measure natural differences, we located eight reference watersheds (where human disturbance is relatively low), four with soils of high clay content (labeled Hi) and four with soils of low clay content (labeled Lo). Figure 1 compares the two sets of streams for two storms, showing the effect of high clay soils on turbidity. 

One final, but most important note - please respect the watershed council’s intent to use these data only for providing landowners with the resources and technical expertise to address sources of sediment (NEVER to play “Gotcha”). Please let us know if you think additional locations should be sampled in the future, by you or another Stormchaser. And think about joining our Email List to get important updates about your watershed!
Thank you for another great Stormchaser Year!