Water Column: Slow flow, Part II

Water Column: Slow flow, Part II

Wow. What a difference two weeks makes.

(Bear with me as this is a deep dive into the very shallow – but fascinating – Dungeness River…)

At the time of my last column two weeks ago, the Dungeness River flowed close to what biologists would consider good conditions for salmon spawning this time of year. By the numbers, that is a flow of 180 cubic feet per second (or cfs).

In terms of actual water, this time of year that flow is mostly going to be snowmelt from high in the mountains, with periodic flushes of rain that spike the flow rate temporarily.

In the past two weeks streamflow dropped by over a third and is now approaching the number that is considered extreme low, but passable, for salmon to migrate and spawn in: 105 cfs.

In “Slow flow, Part I,” I wondered whether this year’s snowmelt would keep the flow above that level and, if not, would late summer rain showers raise it enough for salmon to migrate?

That 60-70 cfs drop is bad news — the price paid for lovely hot weather which melted the snow fast.

I also asked this question: What do you suppose happens when the flow level approaches or drops below this critical lower limit?

Answer: A lot of people look for rain in the forecast.

Indeed, if you were here five years ago you may have heard that 2015 was the worst snowpack in recorded history, with barely any snow in the mountains to melt. The river flow was in critical territory by the end of July.

During the months of August and September, anticipating continued decline, multiple field crews placed inflatable dams and moved cobbles around in areas where the braided river flattens out, to funnel water into the deepest channel. Their purpose was to assist migrating adult chinook as well as pink and coho salmon.

At times, workers watched pink salmon shoot past them as soon as they stepped away.

That year, a few well-timed late summer rainstorms helped the flow but it was October before it stabilized.

What about farmers? When extreme low flows are predicted they coordinate closely to determine what alternatives they have to diverting water from the River, to help salmon out. As explained last time, irrigation managers agreed years ago to “share the pain” and take no more than half the flow even if they have state water rights for much more and previously used it.

At some farms a well could be an alternative for a short period, but other customers have to be prioritized and may not get what they need. Perennial crops like berries and orchards are vulnerable to water shortages and vegetables may not be quite ready to harvest, whereas growing another set of hay or alfalfa is sometimes optional — provided those farmers can get state assistance to purchase livestock feed they otherwise would have grown with river water.

As you might imagine, non-commercial crops — green lawns — are low priority and that’s why irrigation companies and districts are now asking those customers to conserve or completely stop irrigating.*

Rain, rain, come again

Our brief shower Sunday night washed off the dust but didn’t change the situation in-stream. Unfortunately, as of this writing there is very little rain in the two-week forecast (or beyond) so the river will likely drop further.

This year may resemble 2005, when flow was 103 on August 31st and dropped another 30 cfs during September because of a lack of rain. If — or when — flow goes below 105 cfs this year it will make five of the past six years to do so during the critical late summer period.**

At this point, irrigation managers are checking flow gages every day. They check the USGS gage in the upper River, where it exits a canyon and enters the lowlands, to determine what half the flow is before they coordinate operators of the five diversion headgates.

Indeed, as I write, the upper River gage is reporting 114 cfs of flow; taking exactly half for irrigation would leave 57 cfs in the stream.

But the math doesn’t stop there. The other agreement irrigators made is to leave at least 60 cfs in the River. So, since 114 minus 60 is only 54, they can’t take quite half the flow today.***

This story is not meant to be about gages, numbers, and calculations. The point is that there are many people paying close attention to the River, its salmon, and local farms – and how to balance all those needs.

Farmers can’t grow our food without water any more than fish can swim without it. One can’t “tighten the belt” on a water budget, and our income of snow and rain is disappearing.

Now the question becomes, “What can we do about it?” First, we can conserve water. Beyond that, stay tuned for “Part III.”

*Grass can go dormant without dying, but for further information on outdoor water conservation contact Clallam Conservation District at clallamcd.org.

**Further statistics for years with flows as low as 105 cfs: Six of the past 20 years, and just 12 of the past 90 since recording at the USGS gage began.

***In addition to the five irrigation outflows (three on the east bank and two on the west) there is also outflow from seepage into the water table below, plus inflows from the water table and tributaries including Canyon, Bear, Matriotti, and Hurd Creeks. Irrigation managers have a lot of experience in judging how large these factors are in the overall flow picture.

Geek moment (more, that is)

Did someone say 180? With the apparent regularity of extreme low flows around 100 cfs, how did biologists come up with 180 cfs as the “minimum” decent flow?

According to state Department of Ecology staff, in a nutshell, a lot of science went into the discussion but in the end the number was negotiated.

First, a team of biologists analyzed the results of a study presenting the month-by-month relationship between streamflow and habitat quality. This was done for each life stage of each type of salmon in the Dungeness. For example, adult chinook spawners and tiny pink fry each benefit most from a certain flow that’s not too shallow and slow or too deep and fast — for them.

For the months of August through October the team settled on a flow level that would maximize benefits for all: 180 cfs (though a number three times that was proposed at first). It was agreed and accepted that 180 cfs doesn’t have to happen every year for three straight months, but it is the amount needed to benefit the river’s species and ecosystem as long as it happens “often enough.”

You don’t have to be a scientist to understand there’s a troubling trend in the mountain snowpacks feeding the Dungeness, and “often enough” may not be happening.

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

• Rain in Sequim at the Sequim 2E weather station (sea level): Total rainfall to Aug. 30 = 19.4 inches; New high temperature = 83 degrees Fahrenheit on Aug. 15; Low = 20 degrees Fahrenheit in November.

• Cumulative precipitation at the Dungeness SNOTEL station (elev. 4,010 ft.): 34.5 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 = 114-240 cfs.

• River flow at the state Ecology gage at Mile 0.8: On Aug. 29 = 60.6 cfs.

• Bell Creek flow entering Carrie Blake Community Park: 0 cfs; at Washington Harbor = 1-2 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. Reach Ann at columnists@sequimgazette.com or via her blog at www.watercolumnsite.wordpress.com.

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