Five years on, Nisqually River dike removals showing results

Five years after the last dike near the mouth of the Nisqually River was removed, the freed delta is well into its rebirth.

The final stretch of river from Interstate 5 to Puget Sound, which for the century the dikes stood was 1 1/2 miles of fairly straight channel, is now a free-flowing, 21-mile network of winding waterways of various winding widths, which has vastly increased the habitat for juvenile chinook salmon.

When the tide comes in to submerge the mud flats, it brings with it the loose sediments the river carried into the Sound from upland. Over time, the sediments deposited back onshore and trapped by the newly growing vegetation are adding to the high ground. Because this land remains dry, it provides habitat for shore birds and land creatures.

This, scientists and observers say, is a portrait of restoration in action. The removal of eight-plus miles of dikes opened up 762 acres of coastal estuary. Today, federal and Nisqually Tribe officials are watching the project closely with two core questions in mind:

• Are the fish coming back in significant numbers?
• Is the sediment adding dry ground to the estuary fast enough to account for the rising sea level rise that climate change is expected bring?

The second question has, perhaps, wider implications for assessing the success of the dike removal, which ended in August 2011 and was the culmination of years of dike removals and other restoration projects. Total cost of the work was about $12 million.

If the seas rise faster than the sediments add to dry land, much of the restoration project will become new, shallow seafloor for the Pacific Ocean, welling up to a new dike within sight of traffic on Interstate 5.

Officials from the tribe and the U.S. Geological Survey are watching this aspect closely to see whether further engineering needs to be done to help the landscape become a more resilient estuary faster.

“What we’re seeing now, which was wholly expected, is basically a wide open mud flat,” said Melanie Davis, project manager for the Geological Survey.

Why this is important brings us back to the first question, regarding the fish population.

The dikes were pulled out of the delta, on the lands of the Nisqually tribe and the refuge, to help restore salmon runs, including the Puget Sound chinook salmon. Those salmon were listed as threatened under the federal Endangered Species Act of 1999. The river’s wetlands give juvenile salmon a home with invertebrates to feed on.

Increasing the amount of channel fish can use from 1 1/2 to 21 miles has a dramatic effect on the Nisqually’s capacity as a fish estuary, said Christopher Ellings, a biologist with the tribe’s salmon recovery program.

“At several of our sites, we routinely see almost a fish per square meter in these channels,” Ellings said, “and that’s a really high density.”

Salmon populations lost much habitat. Duck hunters built permanent blinds on some of the farm property. When the farms fell into disuse, the dikes low-lying landscape caused freshwater plants such as cattails and reed canarygrass to take over.

Then the tribe and the refuge gained control of the land and began an estuary restoration that took more than a decade.

“The tribe recognized that their ability to harvest their 50 percent share of the number of harvestable fish coming back was really dependent on the availability of the habitat that the fish depend on,” Ellings said.

A smaller area was diked in with a new earthwork near the refuge’s visitor center to preserve a freshwater marsh only a few yards away from the growing salt marsh. Removal of the old dikes wiped away the old vegetation and swept the canarygrass out to sea in immense mats.

“It's kind of like a bomb goes off when you open these up,” Ellings said, “because (when) the saltwater comes in, it kills all the freshwater stuff.”

The freshwater side is an established concern of lush greenery that helps support duck populations regularly harvested by seasonal hunting. The saltwater side still is being watched closely.

“We get a really neat mix of plant species,” said Isa Woo, a biologist with the Geological Survey.

With the plants above sea level come land-living invertebrates — think spiders and flies — that become links in the food chain to larger creatures. Some survey work has found promising signs: in 2015, a survey from a plane found 4,000 American widgeon ducks, a sign that the estuary is supporting a range of life.

Whether it is sustainable as a feeding ground for juvenile chinook salmon depends in large part on how well it weathers global climate change.

If the land remains a diverse delta of marshes and river channels, then the fish and the tiny invertebrates they eat will have a lot of territory. If rising ocean waters subsume the area, then salmon will lose the habitat.

Ellings said biologists hope to land steady funding to conduct thorough monitoring of the ecosystem. He estimated the cost at $250,000 a year.

“These large river deltas are totally pivotal to recovering Puget Sound chinook salmon,” Ellings said, “and it’s a shame not to learn everything we can from a project like this.”

This story was originally published September 2, 2016 at 3:45 PM with the headline "Five years on, Nisqually River dike removals showing results."