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Floods with a Purpose by Tim Hyatt, fall 2003

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This article was written by Tim Hyatt, Hydrologist and former SFEG board member, after the 2003 floods on the Skagit River. Its message seems as timely today.

The recent floods on the Skagit River and elsewhere reminded us all that rivers are dynamic systems with harsh penalties for humans and fish that can’t adapt to occasionally extreme conditions. But whereas humans have the option of moving uphill, fish have to either find a refuge somewhere in the river system or else be swept downstream, often to a premature death. While it’s clear from the counts at the Mount Vernon smolt trap that high floods greatly reduce salmon egg-to-fry survival, floods also create and maintain the habitats on which salmon and other fish, plants, and animals depend.

High flows provide ecological benefits by maintaining ecological diversity and productivity. A dynamic patchwork of different habitats—in mainstems, side channels, tributaries, estuaries, sloughs, braids, and wetlands—is necessary for fish to find the habitats they need at different stages of their life cycles. So the mainstem this year may be the side-channel or slough next year, and it is the flood flows like we had last month that trigger these shifts in habitat. Over time the off-channel areas— especially side channels and sloughs–change in character and develop a higher diversity of plants, insects, and habitat types. This higher diversity is often linked with higher productivity as well. After a few years or decades the side channels may once again become the main channel, but in the mean time they have provided some very valuable spawning, rearing, and refuge habitat. Without floods these side channels more quickly become colonized by trees and shrubs, and eventually become blocked or filled or otherwise useless as fish habitat. Maintaining these off-channel habitats, and their connectivity to the mainstem, is crucial for wild salmon to survive.

High flows cause the gravel and fine sediment in the riverbed to move around, in both favorable and damaging ways. Floods inevitably move, re-arrange, and sort the gravel, creating high-quality spawning beds free of fine sediment. Spawning gravels that fill up with fine sediment either suffocate the eggs or trap them in place before the salmon fry have a chance to emerge. Stirring up and sorting the gravel also encourages growth of the aquatic insects upon which salmon and trout feed. Depending on the timing, floods can destroy the eggs that have already been laid, but here too the fish have evolved a mechanism to partially withstand such assaults. Recent studies in the Nooksack basin are showing that egg damage during floods is much less likely in the off-channel areas than in the mainstems, so again the habitat-forming mechanism at work during floods is more important than ever.

High flows, if allowed to function in natural systems, have numerous other ecological benefits. Most of the plant species one finds on river banks are adapted to life in areas with frequent floods, and many of these plants, namely cottonwoods, often can’t get established without barren, wetted areas free from competition— exactly what is left behind after a flood. Floods draw big and small trees and logs into the channel, and it is this large woody debris that, when incorporated into the channel, provides most of the high-quality rearing habitat necessary for young salmon and trout. Floods rejuvenate the floodplain (in both wild and agricultural areas) and encourage the growth of healthy streamside plant communities. Floods clear new areas where noxious weeds can easily take hold, but they also prevent non-native species (both plants and fish), that are not adapted to frequent flooding, from getting established.

Floods have always been with us and always will be. The challenge seems to be to recognize and accept the inevitability of floods and get out of the way. Frequently the most cost-effective means of flood control is to allow the river room to shift and expand. This not only cuts down on revetment maintenance, it also makes for better fish habitat. Trying to limit large floods by increasing dam storage, and trying to limit damage by putting levees close against the low-flow channel, not only deplete tax coffers and destroy fish habitat but often fail as well. Floods like the ones this fall undoubtedly destroy many salmon redds, but they also create and maintain off-channel habitats. So floods may actually be a good thing, if we have the wisdom to let them function naturally.

A flooded field

The flooded East Fork Nookachamps restoration site in fall 2003

Adventures at Ennis: A Snapshot of Salmon Surveys in the Field

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While explaining work as a SFEG Spawner Survey Intern, I’m usually met with one or a combination of three faces: blank confusion, bewildered support, or instant intrigue. Most people would imagine being bundled up in multiple layers, out in the frigid winter weather, and hiking some nebulous trail along a random stream counting fish. To a certain extent, they wouldn’t be wrong.

 

The temperature most days settles around the high 40’s, but often feels much colder under the canopy of trees. Truth be told, I hardly feel the cold regardless of the knee-high glacial melt and frigid air once we get moving. It’s the one day I look forward to every week, rain or shine.  Once a week, there’s a chance to catch a glimpse of salmon spawning in their native stream.

 

On an offshoot of Highway 9 is one of the most important tributaries in the Samish Basin. It’s the spawning ground to one of the state’s most iconic organisms and a cultural touchstone of the Pacific Northwest: salmon. At first glance, Ennis Creek can easily be overlooked. It’s a sight that is representative of thousands of other streams all over Washington State that are currently or once historically salmon-bearing streams. It might not even occur to you to wonder if salmon make the 1000-mile trip to this very creek to ensure the life cycle continues.  Ennis Creek is merely one of the dozens of streams SFEG monitors through their volunteer program to determine the success of restoration efforts and evaluated by the WDFW for escapement forecasting.

 

Ennis Creek, a site my field partner, Casey, and I survey, is more than 0.7 miles of hard terrain changing frequently due to seasonal windstorms and natural hydrological processes. Starting in October, we bundle up in SFEG provided gear – an assortment of thermal wear, raincoats, life jackets, reflective vests, waders, and gloves – before we begin the long hike to our designated endpoint, a waterfall which is the natural end of salmon access in this waterbody.

Despite following the same stretch of stream to a fixed destination, every week is a new adventure with new challenges. It’s amazing to watch the stream change in these short periods of time. In climate weather will cause alterations to the stream. Windstorms can fall trees into the stream, providing natural woody debris to alter the streamflow and streambed. Intense rainfall and natural flooding can completely change the topography of the stream channel.

 

Weather and stream changes aside, our main goal is to document the presence or absence of salmon spawning within these select sites of the Skagit and Samish watersheds. With the data collected during the course of these surveys, SFEG is able to determine prospective restoration sites and monitor the success of past efforts.

Each week we climb over new treefalls, cut through dense native plant thickets along stream banks, and side-switch with careful consideration to these potential new redds. When female salmon find locations suitable for harboring offspring, they dig these gravel nests called redds. For several weeks, we find no presence of salmon. However, keep our eyes peeled for the first tell-tale signs of fish. This could be a flash of movement cutting through the water, an inexplicable dark shadow hovering in the stream, or evidence of gravel nests that can’t be explained by natural stream hydrology. Granted, looking for these signs pales in comparison to actually counting salmon, but it’s a critical period to establish baseline channel characteristics before salmon arrive.

It’s not until several weeks later, at the start of November, that we will see the first signs of coho at the mouth of the creek. Our flutters of excitement accompany the vibrant red bodies of coho, nearly hidden within the shade of the bridge at the starting point. From absolutely zero fish from the week before, suddenly there were hundreds.

Historically, thousands of coho once used Ennis Creek to spawn. The Ennis Creek site remains as one of the main spawning grounds of the upper Samish River Basin. Despite its significance to the local salmonid population, Ennis Creek has suffered significant habitat degradation from straightening, dredging, inadequate culvert placement, and redirection into a roadside ditch in the past. SFEG and affiliated agencies have restored the historical channel and re-established the channel across a major fish barrier into the Samish River.

 

As we conduct our survey, I can’t help but feel a sense of awe walking along the streambanks. We eagerly log of the number of fish, both live and dead, and their redds. Already, we are recording significant increases of salmon at Ennis, and other locations, in comparison to past years. It’s yet to be determined if populations will surpass historic milestones, but 2021 appears to be promising.

 

There’s something both humbling and impressive about being immersed in habitats used by these anadromous fish. We have witnessed their resilience while acting upon millions of years of instinct and genetic memory to ensure the next generation of offspring is successful. It’s endlessly rewarding to see firsthand the effects of restoration efforts made by organizations like SFEG; effects that make a difference toward a species with long lasting impacts on both humans and the larger interconnected ecosystem. This is an experience I have been incredibly lucky to both participate and contribute through SFEG’s Spawner Survey program. I would eagerly recommend the program to anyone interested in the Skagit Watershed, salmon ecosystem and population restoration, or community planting parties.

When the roads are rivers, where do the salmon go? by SFEG Intern Elizabeth Kimberly

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On November 15th, 2021, the Skagit River in Mount Vernon crested at a height of 36.98 feet, just five inches short of the previous 1990 record. Across the county, rivers replaced roads, riparian zones became stream beds, culverts filled to the brim, and homeowners’ backyards and living rooms were inundated with water. The culprit? A succession of atmospheric rivers that brought several days of heavy rain to the region. As we drove past fully submerged Christmas tree farms, kayakers paddling downtown roads, and cars flipped sideways, I grieved for the widespread damage and loss, but I also couldn’t help but think of the salmon. What does this massive flood event mean for them? Where do they go? Will they survive?

Flooded Skagit River in downtown Mount Vernon WA

Flooded Skagit River in downtown Mount Vernon WA on November 15, 2021

A major consequence of climate change in Western Washington, and the Skagit Watershed in particular, is an increase in flood frequency and intensity in the winter months. As temperatures warm, our atmosphere can hold more moisture. As we urbanize our landscape through paving and development, we increase run-off volumes into streams and rivers, and decrease our resilience in the face of significant precipitation events. As more precipitation falls as rain in the upper reaches of our watershed, streamflow increases more rapidly. While the November 15th event was rare and anomalous, climate change models project that these intense winter flood events will become less rare in the decades to come. Floods that have historically reoccurred every 50 years will likely start to happen at 20, 15, and even 10 year intervals. How will the salmon fare?

Flooded stream bank

This picture, taken four days post-flood shows the new Pressentin Park channel at near capacity. Some plants were buried under sediment, some potted plants redistributed, and our new salmon viewing station was partially destroyed. Hundreds of pink salmon spawned here in the weeks leading up to this flood; many nests may have been lost

While salmon adapt to their local flood regimes and minor flooding can actually be beneficial for salmon (i.e. new habitat, clearing of sand and silt, wood recruitment, and new food sources), they are not yet adapted to the anomalously large flood events that we’re seeing with increased frequency in the Skagit Watershed. In their hydrologic model, researchers Mantua and Tohver (2010) found that Western Washington’s historic 20-year flood return frequency will experience the most substantial flood increases in December and January. Unfortunately, these early winter months coincide with the spawning season for several salmon and trout species, when salmon are in their earliest life stages and thus most vulnerable to flood disturbances.

During spawning, salmon deposit and bury their eggs in gravel nests in the stream substrate. These nests, called redds, protect the eggs from high flows and other environmental threats, like predators or sediment build-up. However, there is a water velocity threshold at which the eggs are washed downstream and unable to survive. Additionally, climate change-induced high flow events can mobilize and transport large volumes of sediment atop the eggs and suffocate them. Because the depth of redds varies across species, certain species will be more greatly impacted by these peak flows. Smaller fish, like pink salmon, are unable to bury their eggs as deep and prefer to build their redds in smaller gravel than other salmon species, and are thus more vulnerable to being washed away through streambed scouring.

Humpy salmon under the water

These pink, or humpy, salmon are spawning in September 2021 in the Cascade River, a major tributary to the Skagit River. Photo courtesy of Jess Newley

 

Flooding can also threaten fish by displacing them in floodplains and isolating them from their river channel habitats. High flows have the potential to flush salmonids downstream and into estuaries or marine water bodies. The draw backs of this are two-fold: if the juvenile salmon rearing in freshwater aren’t killed by the great forces of the flooding Skagit on their way downriver, they can be washed into salt water before they are physiologically prepared for saltwater life stages and perish as a result. Furthermore, increased stormwater runoff can incorporate toxic contaminants into freshwater systems, which is especially deadly for coho salmon. Finally, high precipitation events, like the mid-November storm, trigger landslides and mudslides, which add detrimentally large sediment loads to streams and rivers. These sediment influxes can clog gills, impact feeding, and bury salmon eggs. In extreme cases, landslides can block entire streams or rivers. For example, the 2020 Big Bar landslide blocked a critical migration route in the Fraser River in B.C., and threatened to decimate local sockeye and chinook populations.

The negative impacts of climate change are great, but there are greater reasons to continue the pursuit of salmon population enhancement and environmental restoration. In their 2007 study, researchers Battin and others used models of the nearby Snohomish River to study salmon responses to climate change. While their model’s projections for summer streamflow and winter peak flow don’t bode particularly well for Chinook populations, they acknowledge that their models are unable to take into account the remarkable adaptability of salmon. They speak to potential for salmon to adjust to higher winter peak flows by changing the timing of their egg laying. If salmon deposited their eggs just a month or two later in the winter, would flood mortalities be significantly reduced? In their paper, they encourage research that examines the likelihood of these evolutionary or behavioral responses to climate change, as they’re not yet well-understood.

On an optimistic note, they also speak to the promise of restoration efforts – like floodplain connectivity and riparian planting – as an effective means to further buffer the detrimental impacts of winter flood disturbances for our salmon populations. SFEG and other organizations implement these types of restoration projects every year. Pacific Northwest salmon have co-existed with active volcanoes, earthquakes, and dynamic, ever-changing river systems. With our help and continued efforts, perhaps they can withstand climate change as well.