Muddy waters — Overactive year in natural turbidity stirs up challenges for river water monitoring

Photo by Patrice Kohl, Redoubt Reporter. Trees double over the Killey River as high waters discharge large amounts of mud and debris into the Kenai River on June 26. The Killey River is believed to have contributed to a spike in the Kenai River’s turbidity in the days following a rise in water levels after June 22.

Photo by Patrice Kohl, Redoubt Reporter. Trees double over the Killey River as high waters discharge large amounts of mud and debris into the Kenai River on June 26. The Killey River is believed to have contributed to a spike in the Kenai River’s turbidity in the days following a rise in water levels after June 22.

Patrice Kohl
Redoubt Reporter

The impacts of human activities on Kenai River water quality are not as clear as environmental regulators would like. So when the Kenai Watershed Forum failed to secure enough funding to continue the second year of a study measuring the river’s turbidity, state regulators stepped in.

Turbidity is the amount of dissolved solids, like mud and glacial silt, suspended in water. The results from turbidity research conducted by the Watershed Forum last summer suggest the amount of mud stirred into the Kenai River by boating activity may exceed environmental regulatory standards. To be certain, regulators require a minimum of two years of data. So when it looked like turbidity research on the Kenai River might not continue a second year, regulators dug into state coffers to support it.

“We truly believe the Kenai River is a great resource that we want to protect, so we felt it was necessary to find the funding to do this work,” said Tim Stevens, an Alaska Department of Environmental Conservation environmental programs specialist.

Without at least two years of data, regulators cannot define the river’s naturally occurring turbidity levels and, consequently, how much of the river’s turbidity is human induced. The Kenai River has naturally occurring background levels of turbidity, which generally stay within certain levels but occasionally spike due to natural events that carry large quantities of silt into the river over short periods of time.

Turbidity levels in the Kenai River can be erratic, since part of the Kenai watershed is glaciated and some of its tributaries, such as the Funny, Skilak and Killey rivers, can dump large amounts of sediment into the river over short periods of time.

“If they start acting up, the turbidity levels can change drastically,” Stevens said. “At this point we’re not sure we’re going to stop at two years. … It would be smart to get more years of data so we can get the wide variance.”

This summer may provide a prime example of the kind of erratic spikes in turbidity that natural events can cause on the Kenai River, said Robert Ruffner, executive director of the Kenai Watershed Forum. Around July 22, water in the lower Kenai River began to rise rapidly, carrying with it large quantities of debris and resulting in major spikes in the natural turbidity.

The sudden rise in the water level and turbidity were likely due do to a glacial-dammed lake that outburst above Skilak Lake and a large quantity of water that suddenly surged from the Killey River, Ruffner said. He said he did not know what caused the flow of water from the Killey River to suddenly rise, and that he had learned about it from people in the area who observed the phenomenon. Ruffner said that after July 22 a large number of trees had also begun to wash down the Kenai River.

Events contributing to this sort of spike in turbidity are unusual and could be both helpful and detrimental in the effort to understand the Kenai River’s natural turbidity once the second year of data collection is done. The unusual spike could provide helpful information about natural turbidity peaks, but may also skew results.

“We’re supposed to have a statistical measure of what happens out there and then when you have an event that happens once every 25 years and that’s the year that you happen to be measuring, it may or may not give a false sense of what’s out there,” Ruffner said. “(But) it’s a good thing, in that we have a relatively extreme event that occurred and can be put on one end of the spectrum of what natural conditions might be.”

Turbidity levels in the Kenai River are measured in NTUs (Nephelometric Turbidity Units). The point at which turbidity becomes noticeable in water is at about five NTUs. Under normal conditions, background NTU levels in the Kenai River range from the single digits to the mid-20s and natural events will typically push turbidity up into the 50s or 60s NTU.

Preliminary results of measurements being made on the Kenai River so far this summer suggest the events in late July may have spiked natural turbidity levels to more than 90 NTUs, Stevens and Ruffner said.

This summer, the Watershed Forum is measuring turbidity levels in the Kenai River at six locations. At three of the locations, turbidity-measuring instruments are measuring and recording turbidity every 15 minutes every day.

Measurements are made in three remaining locations on a rotational basis.

This year will mark the second year of turbidity data collection at Swiftwater Park and Eagle Rock. Swiftwater Park is upstream at river mile 23, where few human activities disturb the water, while Eagle Rock is downstream at river mile 11.5, an area of the river where the July peak of the fishing season results in heavy motorboat activity.

Last summer, departures in the turbidity data recorded at Eagle Rock and at Swiftwater Park seemed to make a clear connection between motorboat activity and increases in turbidity levels in the lower Kenai River. Data collected at the two sites tracked similar trends in turbidity from about mid-May to mid-June, with recorded NTUs ranging from the single digits to the mid-20s with some peaks in the low 50s due to discharges from the Funny and Killey rivers.

From mid-June through July, however, data from the two sites traced separate paths, with Swiftwater Park data indicating turbidity levels similar to those recorded in mid-May and mid-June, and Eagle Rock data indicating major spikes in turbidity levels that correlated with peak motorboat traffic periods. In the first two weeks of July, spikes in turbidity at Eagle Rock reached nearly 100 NTUs, and in the last two weeks of July reached up to 140 and 150 NTUs.

The impacts of increased turbidity on the ecological health of a river are a source of debate. But researchers worry human-induced turbidity may be pushing peak turbidity to levels that aquatic life might be poorly adapted to handle. As fishermen who have tried to lure salmon to bait in turbid waters will attest to, murky waters do not facilitate a salmon’s search for food. And while adult salmon failing to find bait may result in frustrated fishermen, biologists worry the impacts of turbid waters on juvenile salmon’s ability to find food could result in more severe consequences.

The turbidity data collected so far this year is still preliminary and could change once assessed for quality control. But Ruffner said it looks like some of the patterns in turbidity being measured this year are generally the same as last year. This year appears to be different from last year in that the river began the summer with clearer waters than it did the year before, and at the same time reached a higher spike in naturally caused turbidity. But in the lower river, high turbidity levels seem to be again correlating with high motorboat traffic.

Environmental regulators require measurements in NTUs to quantify the impact of motorboat wakes on water turbidity. But during the peak of the fishing season, the impact of motorboats on turbidity can also be observed with the naked eye. As the boat wake activity builds during a busy fishing day, so does the band of turbidity that grows from each of the river’s banks.

“At first you see it 6 inches or a foot away from shore,” Ruffner said. “And as the day progresses, pretty soon it’s 3 feet out and then it’s 10 feet out then it’s 30 feet out.”

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Filed under ecology, Kenai River, Kenai Watershed Forum

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