Some of the intense wildfires that occurred during late summer of 2020 in Oregon happened along streams that were being monitored by the USGS. As a result, the USGS was able to measure how water-quality was affected by those wildfires.
USGS Measures the Effect of Recent Wildfires on Water Quality in Oregon
The wildfires began around Sept 7-8, with specific dates varying by watershed, in response to an extreme wind event. The wildfires caused significant damage to above ground equipment and communications at eighteen real-time monitoring installations. As a result, monitoring for stream depths and flow amounts at these sites were lost for a period of time. However, seven of the sites had water quality instruments that were submerged and and logging data internally. The surviving water-quality monitors were deployed at the following locations:
- the Clackamas River within the Riverside Fire;
- the North Santiam River within the Lionshead Fire;
- the Blue River, South Fork McKenzie River, and the McKenzie River within the Holiday Farm Fire; and
- the North Umpqua River within the Archie Creek Fire.
The map below shows the locations of those seven water-quality monitors.
The locations shown on the map can be classified as minimally regulated, regulated, and unregulated with regards to the influence of upstream reservoir operations. Although there was no rainfall during this warm, dry event, emergency flow releases from some reservoirs may have occurred, which could affect the water quality patterns observed downstream. Here we have compiled the data from the three minimally regulated sites - and what we've found has provided insights into how streams are affected by wildfires. Below are some of our preliminary findings.
- The water-quality parameters we measured responded rapidly and tended to be affected for several days. Having this information may help us narrow the window for when the fires were apparently most intense (to within a few hours or less).
- Over the short term water temperature dropped as fires came through, which we think might have been due to the wildfires drawing cooler air down the riparian corridor.
- Turbidity responded rapidly but moderately, and typically with increases less than 5 FNU. The return to background turbidity levels took several days, however.
- Specific conductance increased rapidly, then remained high and sometimes experienced a secondary increase. We think this might be due to solutes being mobilized in groundwater or might reflect the influence of ash and soot deposition.
- Dissolved organic matter increased rapidly and remained elevated for days. We think this might be due to carbon being mobilized in surface or subsurface runoff, or from soot deposition.
Below are some water-quality results for those three minimally regulated sites, which are located on the Clackamas River, the MacKenzie River, and the North Umpqua River.
This photo shows the impact from the Riverside Fire at this location. Click on the image to obtain a higher resolution version.
This graph shows the preliminary water temperature, turbidity, and specific conductance measurements at this location during the Fireside Creek Fire between September 7 and 12, 2020. Click on the graph to obtain a higher resolution version or click here to explore the data in the plot.
The photo shows the impact from the Holiday Farm Fire at this location. Click on the image to obtain a higher resolution version.
The graphs below show the preliminary water temperature, turbidity, specific conductance, and dissolved organic matter fluorescence (fDOM) measurements at this location during the Holiday Farm Fire between September 7 and 12, 2020. Click on one of the graphs to obtain a higher resolution version. Click here to explore the data in the water temperature plot and here to explore the data in the dissolved organic matter fluorescence plot.
This photo shows the impact from the Archie Creek Fire at this location. Click on the image to obtain a higher resolution version.
This graph shows the preliminary water temperature, turbidity, and specific conductance measurements at this location during the Archie Creek Fire between September 7 and 12, 2020. Click on the graph to obtain a higher resolution version or click here to explore the data in the plot.
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