Water column: Slow flow, Part I

Water column: Slow flow, Part I

The dog days of summer are here at last, giving us a great excuse to simply hang out by the Dungeness River.

The gurgling of cold, clear water over cobblestones is the perfect accompaniment to a sultry afternoon and invites a dip in the shallow, braided stream.

For Sequimmers, the Dungeness is our home river and we can be grateful for easy access at county and tribe parks so we can enjoy this classic summertime experience — as the S’Klallam People have done for thousands of years.

As the river calms and soothes the casual visitor, they wouldn’t have any idea how many people focus a part of their professional lives and mental energy on that flow.

First, there’s probably a dozen salmon biologists working on the North Olympic Peninsula who track very closely the flows in the Dungeness and other local rivers year-round, watching for signs that flow conditions are trending poorly for salmon at various life stages.

And of course, there are several dozen farmers whose livelihoods depend on irrigation water conveyed to their crops and livestock from the Dungeness. When salmon are in trouble so are these farmers, since they and irrigation managers have agreed to divert less water in extreme low-flow years, for the benefit of salmon.

Third, between here and Olympia several hydrologists are watching river flows in addition to snowpack in the mountains and water levels in wells, as leakage through the river bottom provides about 25 percent of the recharge to underground aquifers tapped for people’s water supplies.

Fourth, there’s climatologists and emergency managers who are keeping an eye on storm flows in the winter in case a flood warning is needed.

Finally, there’s hundreds (thousands?) of men and women who love to go fishing in the fall months — and catch fish (Dungeness coho salmon from the hatchery). They watch for the flow to rise from a rain shower that might entice migrating salmon to swim upstream. They can also tell from the flow level whether it the river is safe for wading or too high.

For all these people I suspect the Dungeness still has the power to mesmerize, but their reaction is probably a little more diagnostic and slightly less romantic.

By the numbers

Rivers and streams are easily measurable. River “stage” means the height of the water surface on a large ruler (“staff gage”) stuck in the streambed, usually (in our region) reported in hundredths of a foot.

Flow is harder to measure since you need the depth and width of the stream as well as special tools that measure the velocity of the water passing by. Flow is reported in cubic feet per second, or cfs, and can be calibrated to heights on a staff gage.

The Dungeness has two permanent flow gages with telemetry, so their stage and flow numbers are transmitted and available online within minutes. The upstream gage at River Mile 11.2 is managed by the U.S. Geological Survey out of Tacoma; the downstream gage at RM 0.8 is next to the Schoolhouse Bridge, managed by the State Department of Ecology in Olympia.

For the Dungeness River, flow is generally between 100-500 cfs. When it drops close to 100 cfs it’s considered extremely low and is problematic for spawning salmon.

August and September are the “critical period” for salmon when river watchers are keeping an eye on the weather for hot spells that could completely melt out snowpack reservoirs in the mountains, or for rain that might boost flows by 10 or 20 percent.

Wintertime flows on average are 300-500 cfs, but storms can radically change that by 10 or 20 times.

When flow rises above about 2,000 cfs, the Dungeness River’s gurgle is replaced by the booming of cobblestones crashing into one another at the river bottom, re-braiding the stream channel. A flood watch starts if rain predictions indicate the river flow could rise to around 4,000 cfs, or to a gage height of 7 feet.

Obviously, extreme high flows cause problems for human development, and it’s no different for salmon: their egg nests (called “redds”) built in shallow cobble can be destroyed when high flows scour the streambed and change the shape of the channel.

Who needs what?

In the past, irrigation companies and districts would have diverted well over 60 cfs of Dungeness River flow in July and August since they have senior water rights from the state to do so and plenty of farmers needing to maintain their crops through the height of summer.

However, in 2012, farmers and irrigation managers agreed to never take out more than half the flow amount reported at the upper stream gage — and to never cause the in-stream flow in the Dungeness to drop below 60 cfs (e.g., when the gage reads

120 cfs, the irrigators decrease their diversions to 60 or less).

According to biologists, Dungeness salmon need at least 105 cfs to migrate upstream, and ideally more.

As of Monday, Aug. 17, the Dungeness River is flowing at 172 cfs with a gage height of 2.76 feet.

We’re well into August now and I already mentioned that critical period flows descend to 100 cfs or less in many years. Will this year’s snowmelt keep the flow above that level and, if not, will late summer rain showers raise it enough for salmon to migrate?

If not, what do you suppose happens then? Stay tuned, until next time …

May we all be students of water and look at our lovely river with a little more information.

Geek moment

The temperature at elevation 4,000 feet in the upper Dungeness watershed (Silver Creek) was 88 degrees Fahrenheit yesterday (Aug. 16). Today’s (Aug. 17) streamflow in the Dungeness River is about 10 percent higher than the past two, a reflection of that heat and indication there’s still snow to be melted up high!

Anyone can watch the flows change at the USGS website: waterdata.usgs.gov/nwis/uv?12048000.

For the 2020 Water Year (started Oct. 1, 2019):

• Rain in Sequim at the Sequim 2E weather station (sea level): Total rainfall to Aug. 17 = 19.2 inches; High temperature = (August data unavailable, but 82 degrees Fahrenheit on July 30); Low = 20 degrees Fahrenheit in November.

• Cumulative precipitation at the Dungeness SNOTEL station (elev. 4,010 ft.) = 34.4 inches (79 percent of normal).

• River flow at the USGS gage on the Dungeness River (Mile 11.2): Highest maximum daily mean = 1,880 cfs on Feb. 1; Low = 98 cfs on Dec. 16. Range for the past month = 160-350 cfs.

• River flow at the state Ecology gage at Mile 0.8: On Aug. 17 = 140 cfs.

• Bell Creek flow entering Carrie Blake Park: 0 cfs; at Washington Harbor = about 2 cfs.

Ann Soule is a hydrogeologist immersed in the Dungeness watershed since 1990, now Resource Manager for City of Sequim. Any opinions expressed are those of the author and do not necessarily represent policies of her employer. Ann’s concerns about water in the Dungeness watershed can be represented by a moniker other than “Water Matters,” so she asked the Gazette to rename this space the “Water Column” last month. Reach Ann at columnists@sequimgazette.com or via her blog at www.watercolumnsite.wordpress.com.

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