Living shorelines: Engineering that mimics nature

Sussex sites test new style of storm protection
October 2, 2015

When Marianne Walch practices tai chi, she abides by a basic rule of martial arts: Don't reflect, redirect.

Walch knows if she stands her ground against a powerful hit, she's going to get knocked out. But if she can absorb and redirect that energy, she can overcome the attack.

“It's a principle of biophysics that softer things withstand energy better than hard things, which tend to break,” she said.

It's a concept that also applies along Delaware's coastlines. That's why Walch, as the science and restoration coordinator at the Delaware Center for the Inland Bays, said she hopes living shoreline projects will gain popularity compared to seawalls, bulkheads, rip-rap or other hard structures.

“Hardened shorelines are the traditional way of stabilizing erosion,” she said. “Unfortunately, hardened shorelines decrease the natural habitat value. They result in the scouring of the near-shore areas, reduction of vegetation and underwater grasses, fewer fish and invertebrates. Over time, it significantly degrades the water quality in our bays.”

Walch and other coastal experts say a shift from hardened shorelines to living shorelines could provide more benefits than just storm protection by helping a marsh rebuild. By using natural materials including oyster shells, coconut coir fiber logs, wooden stakes and, in some cases, oyster castles and pine logs, living shorelines promote the growth of habitats for grasses and marine life and help restore marsh lost to storms and erosion. Hardened structures stunt biological processes by cutting off the natural interface by land and water, and by reflecting storm energy resulting in more erosion of near-shore areas.

“They help keep pace with sea level rise because they help buffer and restore our shores,” she said. “They're more resilient overall than hardened shorelines.”


How living shorelines come together

In late spring, Moody gathered a group of colleagues and volunteers and went on a rescue mission. They were looking for fallen clumps of spartina, a native marsh grass with a close relationship with local mollusks that act like an anchor for a marsh.

As sea level rise outpaces a marsh's ability to accumulate more sediment, spartina and the intermingled ribbed mussels are doomed to die as clumps break off and fall to the side. Spartina and the mussels, which extend fibers throughout the plants' roots, love tidal areas.

So along came Moody and his team, who gathered the doomed plant and mollusk partners and brought them to a new home, in a place where the grasses and mollusks are already poised for successful growth because they're used to the environmental conditions of the nearby site.

“You always want to make sure there is a living component to the shoreline,” Moody said. “Not only should it contain biological materials in the construction of them, but it should provide an ecological uplift to the area around them.”

Those natural clumps of grass and mussels are used alongside coconut coir fiber logs, which are strategically placed along eroding marsh shorelines, such as the one along the Lewes-Rehoboth Canal, just across the water from the Lewes Harbor Marina.

Moody and his volunteers work in knee-deep mud along the logs, which are held in place with wooden stakes. The logs must be installed first, and are later surrounded by salvaged spartina and spotted with young spartina plugs.

As the tide comes in and washes over the coconut logs, sediment is left behind, building up the marsh's elevation. In a few years, the coconut fiber logs will disintegrate, but a new marsh environment will emerge, full of sediment, grasses, mollusks and other marine life.

“We work with nature, not against nature,” Moody said.

Nature knows best

Each day, the Delaware Bay estuary loses nearly one acre of tidal wetlands.

The loss of sloppy, mushy terrain may not seem like a big deal to some, but those wetlands play a critical role in local ecosystems along with providing storm and flood protection.

Marsh estuaries provide vital breeding grounds for marine life, offer food for migrating shorebirds, improve water quality by absorbing and filtering nutrients and pollutants and can act as natural sponges during flooding events. They also are the first line of natural defense for coastal infrastructure including buildings, water treatment facilities and roads.

But natural erosion and sea level rise are outpacing the capacity of the marsh to accumulate sediment to absorb that water, especially in the face of coastal storm surges. The marshes are drowning.

To address the needs of diminishing marshes, experts with the Delaware Department of Natural Resources and Environmental Control, Partnership for the Delaware Estuary and the Delaware Center for the Inland Bays are using demonstration sites to illustrate that when it comes to coastal engineering, Mother Nature really does know best.

Living shorelines have been installed at four Sussex County locations within the last two years to demonstrate how natural shoreline stabilization can restore marshes, rebuild lost habitat, increase water quality and provide added protection against coastal storms and flooding.

The four demonstration sites at the Mispillion Harbor near Milford, the Lewes-Rehoboth Canal, the Indian River Marina and Loop Canal on Salt Pond near Bethany Beach, use natural materials to stabilize receding shorelines and jump-start marsh growth.

Yet it may take a few years to see the significant impacts of the living shorelines, said Josh Moody, restoration coordinator at the Partnership for the Delaware Estuary.

“It usually takes a couple years to see a big difference,” he said.

So far, he said, everything is going as planned: Grasses and coconut fiber logs have not been washed away, which tells scientists their engineering plans were correct. This year, Moody hopes to see an increase in elevation as the shorelines trap sediment, which rebuilds the marsh.

“It's not a mold or a one size fits all,” he said. “Sometimes it takes a little bit of time to see a change.”


In the face of a storm

When Superstorm Sandy slammed the East Coast in 2012, it left behind billions of dollars in damage from the landfall backlash of record-setting wave surges and winds that reached more than 100 miles per hour.

As debris piled on bulkheads and floods washed out access roads, a small strip of coastline at Matt's Landing along the Maurice River in New Jersey was almost completely undamaged after the massive storm.

A small living shoreline, installed in 2010, withstood the surge, while a nearby bulkhead protecting a parking lot and small building were severely damaged. The crab shacks behind the living shoreline were among the only buildings in that area left intact after Sandy passed.

That has experts at the Partnership at the Delaware Estuary convinced are on the right track.

Sandy was the spark that has led residents and civic leaders to take a closer look at the benefits of natural systems and living shorelines, Moody said, generating more interest in using natural materials instead of hardened structures to protect coastal infrastructure.

“They saw how badly things fared behind what they would typically consider very protective,” Moody said.

Since Sandy, more funding has flowed to pilot living shorelines projects, but more funding is still needed for long-term monitoring and comparison studies to show how living shorelines fare compared to natural shorelines and hardened structures.

“That's when money started becoming more available to pilot these living shoreline ideas,” he said.

For Moody and his team, though, the focus is not solely on proving the success of a specific living shoreline project. It's on what they can learn from living shorelines to drive technical development and policy that can protect vulnerable estuaries.

“It's also important how you define success or failure,” Moody said.

Another living shoreline near the Matt's Landing site had been abandoned by the Partnership when they thought it wasn't progressing as it should. But Moody recently discovered that it was thriving compared with other regularly monitored projects.

“One of the challenges in collecting living shoreline data is you don't get a lot of money to monitor for a long period of time,” he said. “But it may turn out that if you really want to see how successful they are, you have to expect to be involved for a certain number of years.”


Value of the shoreline

While living shorelines mimic natural systems, they do have similar financial investments to their artificial counterparts.

It's not about the upfront cost, but the return on investment, Moody said.

“Everybody wants a hard number of acre-per-acre, pound-per-pound,” Moody said. “But when you can quantify those numbers better, there's going to be no contest. Living shorelines are by far the best economic choice.”

At a glance: Loop Canal project impact

350 linear feet of shoreline protection

0.4 acres of tidal wetland restoration

About 225 pounds per year of nitrogen reduction

About 60 pounds per year of phosphorous reduction

Chris Bason, executive director of the Delaware Center for the Inland Bays, agreed. The benefits of ecosystem services and goods – water quality, habitat, pollution control – that are provided by a salt or tidal marshes far outweigh the costs of installing a living shoreline.

“The investment is a very good one for the long term,” Bason said.

Bason said he hopes the statewide initiative sparks a policy change similar to what is already instituted in Maryland, which requires living shorelines to be used instead of hardened structures when feasible. Bason said he thinks Delaware is only a few years away from having a policy in place that starts shifting coastal engineering designs away from structures that some say cause more harm than good.

“Our shorelines in the bays are a critical interface between water and land,” he said. “Dumping rock kills the habitat. Living shorelines are going to change all that.”

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