Living coastline project to restore tidal salt marsh at Humboldt Bay

By Matt Baun

A flock of Pacific black brant geese fly-off at Izembek National Wildlife Refuge in Alaska. Nearly the entire western population of black brant stops at Humboldt Bay NWR to feed on eelgrass during migration. Photo Credit: USFWS

Fresh, brackish and salt waters mix within the landforms around Humboldt Bay, setting up the various physical and biological processes that form the mosaic of habitats that allow aquatic life to thrive.

These types of areas are called tidal marsh and they are among the most complex and productive landscapes in the world supporting a variety of organisms. One of the habitats that make Humboldt Bay’s ecological network tick is salt marsh, an area of salt tolerant vegetation that is regularly flooded by seawater. Here, vegetation will grow in the shallow, sunlit water, amidst soils and nutrients that ebb and flow in the Bay’s ever-shifting tides.

Since the 1850s, 90 percent of the California’s eelgrass
acreage has been destroyed. When eelgrass is
destroyed, populations of fish-including threatened
salmon, rockfish, and shellfish—are affected and
shorelines are left vulnerable to erosion.
Source: NOAA

The end-result of all this energy is an impressive and interconnected system that teems with rich, diverse and abundant plants and wildlife – literally hundreds of species of algae, plants, insects, crustaceans, fish, shorebirds, and migratory birds.

But salt marsh features along Humboldt Bay have been significantly altered. Over the course of the last century, salt marshes were converted to agriculture and were impacted by urbanization, population growth, and development. Today, barely 10 percent of original salt marsh remains around Humboldt Bay.

Salt marsh, and associated tidal sloughs, are important because they offer vital habitat for many creatures, including, and perhaps most notably, those which live at the bottom of the food chain. These are extremely important areas to Humboldt Bay’s food web. Only certain types of vegetation can grow and tolerate these dynamic landscapes including eelgrass.

Eelgrass provides smaller fish and crustaceans shelter from larger prey and some species such as black brant depend on eelgrass as a key food source in their life cycle. Salt marshes are also important for water quality and they act as filters to take nutrients and particulates out of the water column.

The U.S. Fish and Wildlife Service is leading a relatively large-scale restoration project on a portion of the Humboldt Bay National Wildlife Refuge working with local and state partners. Eric Nelson, the refuge manager and Conor Shea, a geomorphologist and engineer with the Service’s Coastal Program, developed and designed the project.

Eric Nelson (left) and Conor Shea of the U.S. Fish and Wildlife Service survey work on a "living shoreline" project at Humboldt Bay National Wildlife Refuge. Nelson, the Refuge Manager, and Shea, an engineer with the Coastal Program, designed the project with the help of state and local partners. Photo Credit: Matt Baun/USFWS

“Salt marshes provide habitat for fish, crabs and aquatic insects to grow and when they move out to the larger estuary, fish will feed on them, and then the ‘bay birds’ will eat the fish,” said Shea. “The benefit from salt marsh restoration isn’t seen only in the marsh – but is seen throughout the larger ecosystem.”

While the refuge staff does manage areas that contain much of the remaining salt marsh around the bay, they are also always looking for opportunities to restore some of the diked former tidelands as well. In that vein, the good news is that the groundbreaking for this salt marsh restoration project got underway on refuge lands last fall, with work set to resume this summer.

Mud flats and Eelgrass beds provide a myriad of intertidal
habitat for fish, shellfish, and herring, and black brandt.
Intertidal areas provide habitat for clams and oysters. A living
shoreline project ongoing at Humboldt Bay National Wildlife
Refuge will restore salt marsh habitat on a portion of the Bay,
which would further benefit the ecosystem.
Photo: Tupper  Blake/USFWS

The project site itself is unfolding in front of thousands of people a day as they zoom by it along U.S. Highway 101, the primary thoroughfare that skirts Humboldt Bay and connects communities north-to-south.

Nelson said he hopes this aspect of the project, given its visibility in the community, could serve as an important educational tool and demonstration project on the importance and need for more "living shorelines.” The project also meets multiple refuge objectives. Not only will salt marsh habitat be restored, but a failing system of dikes and levees that make the freeway vulnerable to inundation will give-way to a more natural system that uses plants and earthen materials to provide shoreline protections.

“The living shoreline is a concept being used many places around the world and in the United States to create resiliency and to deal with sea-level rise and shoreline changes,” said Nelson. “What we are doing is filling a subsided wetland with dirt with the intent of grading the material out and then breaching the dikes when the project is done so the area is once again tidal salt marsh.”

Current land surface elevations at several locations between the bay and freeway are now regularly overtopped with “King tides” and storms which makes inundation of diked lands and the freeway a regular threat.

One of the project worksites west of Highway 101 in Humboldt Bay. Photo Credit: USFWS

Once sea-level rise projections are factored in, many experts worry about long-term impacts to public safety and damage to the roads and other infrastructure adjacent to the bay. CalTrans, the state agency with responsibility for maintenance of Highway 101, is a collaborator on the project and is working with many partners toward long-term climate adaptation and resiliency at these locations.

To date the project has taken a lot of planning and designing.

“First, we needed a design of how to place the soil to construct a tidal marsh landscape that would have a lot of complexity and the correct form and shape to support a good functioning tidal marsh,” said Shea.

Plans and designs also were necessary to get the permits required to do this type of project. Shea said this was an enormous challenge, in part, because the permits required approvals from nine different entities.

With the project underway, the most challenging aspect is yet to come. The project requires a lot of dirt – not just any dirt, but the right kind of dirt, and the right kind of clean dirt. This requires locating enough clean and suitable fill material to raise the subsided areas to an elevation of about nine feet. This is achieved the old fashioned way – 20 cubic yards at a time, dump truck load by dump truck load.

Black-necked stilts, such as these, are among the many shorebirds and waterfowl found on the refuge. Photo: Tupper Blake/USFWS

Service staff from the Arcata Fish and Wildlife Office and the Humboldt Bay NWR have been on the look-out for as much locally sourced material as they can come up with. More than 240,000 cubic yards will be needed to complete the work and they anticipate needing two to three construction seasons – April thru October – to complete the project.

“A project of this size is only doable with partners, and the biggest partner to date has been the California Coastal Conservancy, which provided invaluable assistance in funding and project planning,” said Nelson.

A willet stretches his wings at Colusa NWR. These long-legged,
straight-billed shorebirds feed along beaches, mudflats, and
rocky shores and are common on most of  the Pacific  coastline.
Photo: Mike Peters/USFWS

Another partnership is with the Humboldt Bay Harbor Recreation and Conservation District and Pacific Gas and Electric Company to take about 10,000 cubic yards of dredge material to use next summer. While not a lot of volume, it is a pilot project and first step in the beneficial re-use of dredge spoil material, a process that could potentially be used in many other locations around the Bay.

Nelson and Shea both agree that the first phase of the restoration project went even better than expected. This past fall, about 50,000 cubic yards of soil was put in place. They noted that a silver lining in last year’s drought meant that construction crews could spend more time working in dry weather to complete the crucial first-steps of the restoration project – building a series of earthen ridges and roads in the area between the freeway and bay. These structures will facilitate the transport of more fill material next summer when the actual on-site restoration work will resume.

One of the other challenges this winter is watching to see the impact of winter and spring storms on the work completed to date. The entire California coast is experiencing high tide anomalies associated with El Nino. Tide levels in Humboldt Bay are running about one foot higher than predicted due to low pressure in the East Pacific and warmer water temperatures.

“The levees have been overtopped by high tides through the winter and we expect that this will continue through the spring,” said Shea. “The tidal ridges constructed last fall provided protection against catastrophic levee failure. If we do lose a section of levee, flooding will be limited to a small portion of the unit.”

Plans for work in summer 2016 are to bring in about 40,000 cubic yards of fill and stabilize two remaining weakest links, which will put the project on secure footing for completion as fill becomes available.

Sea Level Rise Projections and Restoration Projects

What does sea-level rise and climate change mean for restoration work? The White Slough Salt Marsh restoration project that is being undertaken at Humboldt Bay National Wildlife Refuge and Arcata Fish and Wildlife Office provides some answers.

Refuge manager Eric Nelson said that with climate change and sea-level rise, the "name of the game" at virtually all coastal refuges, ecosystems and landscapes is all about elevation and topography. This is true, he said, for conservation, restoration or migration of habitats, and protection of existing infrastructure.

“In some places migration will be the answer, but at many others like White Slough unit at Humboldt Bay NWR, restoration and protection are parts of the equation, and early projects like these are going to help answer societal questions about vulnerability, restoration, and the associated costs and benefits.”

Actual planning and design for restoration projects in coastal areas are also challenging due to the vulnerability to from sea-level rise due to a changing climate. The project designers from the US Fish and Wildlife Service worked with the California Coastal Commission to account for sea-level rise projections and provided a description of what is likely to occur in the project area over time.

The proposed project will initially restore salt marsh habitat on an elevational gradient that would culminate in upland-Riparian habitat. By 2050, the area would transition to a mix of mud flats, tidal marsh, and upland-Riparian. By 2080, the area would likely support a mixture of mud flats and tidal marsh.

The salt marshes of the Pacific coastline are essential habitat for shorebirds migrating the Paficic Flyway. Photo: Mike Peters/USFWS

Matt Baun serves as the Klamath Basin Collaborative coordinator for the U.S. Fish & Wildlife Service, based in Yreka, Calif.

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