Back to nature – combatting climate change with coastal restoration

Special from Wood plc

At Prime Hook, Wood performed shallow-draft hydraulic dredging to create tidal channels and used historical tidal channel patterns to modify the existing water control structures and allow for free flow of water
At Prime Hook, Wood performed shallow-draft hydraulic dredging to create tidal channels and used historical tidal channel patterns to modify the existing water control structures and allow for free flow of water (photo: Wood plc)

Creating and protecting thousands of acres of valuable habitat to restore an ecosystem.

A small, sand-coloured bird about twice the size of a sparrow.

It may be petite, but the Piping Plover’s recent breeding success symbolises the success of a USD 38 million restoration project at the Prime Hook National Wildlife Refuge in Delaware, one of the largest and most complex ever seen in the US.

The bird, a threatened species not seen on the refuge’s 10,000 acres for years, has returned, and is breeding. And it’s not alone.

Thanks to the multi-agency effort at Prime Hook, newly restored habitats are attracting migratory birds that have returned after decades; freshly dug and restored channels attract new types of fish including the herring, American eel, hickory shad and perch, and horseshoe crabs are coming back in record numbers.

Plus, the restored saltwater marsh is once again home to native species of plants and grasses, including smooth and saltmarsh cordgrass, bulrush and seashore mallow.

Importantly, the approach taken to bring about this renaissance is set to be a bellwether for national, if not global, efforts to protect our coastlines in the face of rising sea-levels and climate change.

Restoration and rebirth
The Prime Hook National Wildlife Refuge protects more than 10,000 acres of valuable habitat. Originally established as a migratory bird sanctuary in 1963, portions of the refuge were impounded and managed as a freshwater system in the 1980s.

During a decade of severe storms culminating in Hurricane Sandy in 2012, the dunes along the beach were breached, causing salt water to flow through, leading to beach erosion and flooding.

Sudden salt water inundation caused significant loss of freshwater vegetation, creating huge swathes of open water and reducing the available habitat for birds. At the same time, the higher water levels at the inland edge of the marsh increasingly caused flooding in neighbouring farmlands.

The U.S. Fish and Wildlife Service considered a range of options and concluded the best solution was to return the habitat back to its original state: a tidal marsh.

The expertise behind the renaissance
Wood supported the federal government agency in restoring 4,000 acres of damaged marshland as part of a wider effort. Three other restoration and rehabilitation projects took place on the site at around the same time, all designed to mitigate the damage caused by storms and improve resiliency against future damage.

These comprised two beach dune rehabilitation projects lead by the U.S. Fish and Wildlife Service and the U.S. Army Corps of Engineers, and a bridge installation fronted by the Delaware Department of Transportation.

Creating resilience in the face of climate change
Wood’s USD 17 million project focused on creating a sustainable, resilient ecosystem. Here, the U.S. Fish and Wildlife Service had modelled potential redevelopment scenarios, and tasked Wood with executing the construction.

Lytle Troutt, President in Wood’s Environmental & Infrastructure Solutions business says, “We were aware of the significance of this project from the beginning. We knew the refuge was a critical sanctuary for migratory birds, as well as being home to many threatened and endangered species.”

“We were committed to restoring the site in a way that benefitted the local ecology for wildlife and people – visitors and neighbours – alike, while setting the standard for future coastline preservation projects across the US, and beyond. We brought together a team of experts to make that happen.”

“First, we conducted shallow draft hydraulic dredging to create tidal channels, modified two water control structures, then installed around one million native plants. Finally, we treated invasive plants such as Phragmites, thus creating room for more of the native plant species to recover,” Troutt continues.

Phase one – creating thousands of acres of new habitat
Phase one included digging out channels to allow the free flow of water from canals that access the Broadkill River in the south to Slaughter Canal at Fowler Beach in the north. Dredging 20 hours a day, six days a week for much of the project created tidal inundation allowing the salt water to move through the channels with the tide. The resulting mudflats created the optimal habitat for native marsh grass to grow.

And what was interesting about this approach was the method of spray casting of dredged material, a fairly new approach at the time, brought its own benefits.

Typically, dredged material is collected, dewatered and landfilled. At Prime Hook, by casting it back out into the marsh, Wood was able to build up the marsh, and over time, as an added benefit, created thousands of acres of new habitat.

“Future colonisation of these new areas by native marsh grasses will immensely improve the area’s resiliency to storms. Furthermore, re-using this material meant an estimated 500,000 cubic yards of waste didn’t end up in a landfill,” adds Troutt.

But the dredging also posed one of the project’s biggest challenges. The mechanical dredges were huge, two weighed more than 100,000 pounds, and had to be dropped into the water via crane. These imposing machines also required constant maintenance. This meant careful planning to ensure the logistics and maintenance plans were in place to keep the project on course.

Added to that, the teams didn’t know what they would be dredging through on any given day, from old oyster beds and sludgy soil to rubbish blown into the marsh by the storms.

However, technology proved invaluable.

GPS-guided dredging contributed significantly to the level of precision, allowing operators to see their progress in real time with the proof being that only about 1% of the nearly 1,200 cross sections measured needed to be reworked to meet design specifications.

Phase two – tackling the worst affected areas
Most of Wood’s work took place in one of the worst-affected parts of the refuge, where nearly all of the marsh had been destroyed by salt water from the bay after storms had breached the coastline. As such, phase two, conducted by the U.S. Army Corps of Engineers, involved rebuilding 7,000 feet of beachfront north of Prime Hook Beach with 1.1 million cubic feet of Delaware Bay sand and constructing more than 10,000 feet of sand fence in three rows to provide stability.

Wood further supported these resiliency efforts with the planting of 20 acres of salt water-resistant Spartina, commonly known as cordgrass, to protect the reserve.

And this is where things get really interesting: where the lessons learnt have changed the way Wood will approach similar reconstructions in the future.

Thanks to the multi-agency effort at Prime Hook, newly restored habitats are attracting migratory birds that have returned after decades
Thanks to the multi-agency effort at Prime Hook, newly restored habitats are attracting migratory birds that have returned after decades (photo: U.S. Fish and Wildlife Service)

Troutt explains, “The fundamental theory behind the U.S. Fish and Wildlife’s approach to incorporate resiliency into the design was based on their observations that the wider and more heavily vegetated areas of the breached dune were able to repair themselves naturally. Narrower, less vegetated areas continued to deteriorate.”

“With this principle front of mind, the repaired breach was built far wider than standard practice in coastal reconstruction. Around 600 feet of the 900-foot-wide dune formed the back-barrier platform that sloped gradually into the marsh. So far, this approach has been successful at increasing the resiliency of the coastal dunes to the elements and may shape the standard approach to this type of reconstruction in the future,” Troutt adds.

Protecting the protectors
With healthy tidal marshes proven to be effective coastline protectors by reducing the impacts of coastal flooding and stabilising soil erosion – will others follow suit and create similar counters to climate change and rising sea-levels?

Time will tell.

But, with reports such as those from the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) that say climate change, alongside land degradation and habitat loss, is a top threat to wildlife globally, the importance of such measures is clear, not least for the likes of the Piping Plover.