Living Shorelines Meet Rising Seas
Volunteers plant marsh grasses along a "living shoreline" on the South River in Anne Arundel County, Maryland. This native vegetation can protect shores from erosion and wave damage and create habitat for wildlife. Photograph: David Harp
MOST OF THE SHORELINE along the Chesapeake Bay's tidal reaches is composed of highly erodible soils — and it's also mostly privately owned.
The question of what to do about the effects of sea level rise hits many waterfront property owners right in their own backyards as valuable real estate is lost to higher tides and storm surges are amplified by rising sea levels and a changing climate.
Until recently, the options for homeowners were limited — and decidedly of the brute force variety. Steel vertical bulkheads and stone riprap have been the choice of thousands who wanted immediate control of erosion.
But these days, some homeowners are choosing "living shorelines," using a suite of techniques that employ strategically placed plantings and rock sills that attenuate wave energy while at the same time allowing the building — or rebuilding — of plant communities that resemble fresh or saltwater tidal wetlands. The states of Maryland and Virginia and other organizations have backed this approach.
But, in the face of uncertain rates of sea level rise, are living shorelines a stopgap measure, or are they a good investment for property owners?
The answer is: it depends.
It depends on the site's conditions and how the project is designed. For many properties, the space available for building a living shoreline is constrained by existing structures and neighboring properties. And questions remain about whether these engineered living shorelines will perform effectively over the long term.
"Some sites are better suited to living shorelines than others," says Scott Hardaway of the Virginia Institute of Marine Sciences (VIMS).
Hardaway has been designing living shorelines for three decades. As a coastal manager, he says, he's been dealing with sea level rise the whole time. The formation and destruction of coastlines and beaches is a continual — and natural — process, and understanding these processes is key to evaluating sites and developing designs that can adapt to rising sea level.
"It's all about the energy coming at the shore — how much, from what direction, with how much fetch?" Hardaway says. In most locations, the installation of a living shoreline requires moving some earth to change the slope of the beach to allow a sufficient width of constructed shoreline so that the sand, rocks, and plants attenuate the wave energy.
One Family's Living Shoreline
John and Ruth Martin's home in Norfolk backs up to a stretch of the Lafayette River that is flanked by waterfront homes. Their backyard is a small peninsula dotted with live oaks and Virginia pines that provide welcome shade and native habitat for birds and wildlife.
In 2006, when the Martins returned from living overseas for seven years, they were shocked to see how much of the marsh that had flanked their property on three sides had disappeared. Aerial photos from earlier decades confirmed the loss. That persuaded the Martins it was time to take action — to build a living shoreline.
They brought in 400 tons of rock, 600 cubic yards of sand, and 5,000 plugs of panic grass and smooth cordgrass. Today, healthy stands of marsh grasses grow behind short sections of rock structures, or revetments. They were designed as the living shoreline's first line of defense from waves generated by powerboat wakes and storms. The revetments were also intended to help maintain the remaining wetlands that existed on the Martins' property before they began the project.
The total cost ran in the tens of thousands of dollars, driven up by the need to deliver the sand and rock by barge. The Martins also invested a considerable amount of sweat equity.
"To begin with, we decided upon a living shoreline for the erosion control," Ruth Martin explained. But as she and her husband explored alternative designs, they realized that they could build the revetments high enough to provide protection from sea level rise as well, at least for a time.
Because living shorelines are designed for specific sites, it can be difficult to compare costs between these more natural systems and other erosion control methods like bulkheads and riprap. And finding an experienced marine contractor to do the work is still a challenge, though efforts to expand the knowledge base are bearing fruit as more property owners ask for alternatives to traditional hardening of shorelines.
A Movement toward Living Shorelines?
Interest in living shorelines has grown. The state of Maryland has been encouraging living shorelines for three decades, and enacted legislation in 2008 requiring homeowners to use living shorelines to protect waterfront property. Homeowners can get a waiver allowing them to use alternate erosion protection if a living shoreline is not feasible. (Maryland will consider whether the area is subject to excessive erosion or heavy tides or the surrounding waterway is too narrow.)
Virginia, too, has legislatively stated a preference for living shorelines and is putting the finishing touches on a general permit designed to streamline the process of obtaining necessary permission from local wetlands boards and state agencies.
The Chesapeake Bay Trust has funded numerous public demonstration projects around the Bay that include living shorelines — some of which have been around for almost 30 years. These projects have been very resilient in storms, says Jen Wijetunga, a civil engineer with the Trust. And an increasing number of designs accommodate sea level rise in the choice and placement of plants.
In addition to buffering against sea level rise, living shorelines offer other advantages to homeowners and their communities. The plants help to improve water quality by taking up excess nutrients and trapping sediment. Because of their effectiveness in doing that, living shorelines can now be counted as a BMP — or best management practice — under the Chesapeake Bay TMDL cleanup plan.
"I think we're going to see living shorelines really take off once we figure out the nexus between all the requirements local governments have to protect water quality and address the impacts of sea level rise," says Kevin DuBois, an ecologist with the City of Norfolk and a strong proponent of living shorelines.
The marsh vegetation in a living shoreline also can provide nursery grounds for fish and habitat for other wildlife. Darcy and Brooks Stephan installed a 300-foot-long living shoreline by their house on the Lynnhaven River in Virginia Beach two years ago. "It has improved the habitat immensely," says Darcy, saying that her shoreline now teems with life. "We have raccoons, opossums, muskrats." And, of course, the herons: great blue, common egret, green night heron.
Keeping Pace with The Water
Evidence suggests that living shorelines do accomplish their intended purpose of controlling shoreline erosion. For a report published in 2006, Hardaway and colleagues at VIMS surveyed 36 living shorelines installed at various locations in the Virginia portion of the Bay between 1984 and 2003. The team found little to no signs of erosion in the upland areas behind all but five of these sites. (Some of those had rock sills sticking up less than one foot above mean high tide, leaving those shorelines exposed to large waves.)
In coming years, an important question will be whether these living shorelines can keep pace with the rising tides in a region that many call "ground zero" for sea level rise.
Patrick Megonigal from the Smithsonian Environmental Research Center and Matt Kirwin of VIMS have studied this question and concluded that the tidal marshes that defend a coastline's integrity can keep pace with rising seas, if they remain healthy and nourished with enough sediment to allow them to build upwards as sea levels rise. In any given area, Kirwan and Megonigal said in a study published in 2013, total wetland area may stay the same, even as portions of the marsh lose ground or are destroyed.
Several design factors influence whether a living shoreline can survive over time, says Pam Mason, a coastal resource specialist at VIMS. One is whether it can move or "migrate" inland as tides reach higher and higher. Another consideration, she says, is the length of restoration along a reach (or segment) of shoreline. Coastal processes are dynamic and specific to the topography — a living shoreline built between sections of shoreline protected by bulkheads may not be effective due to currents generated by the hardened sections.
Choosing and planting vegetation according to salt tolerance is another strategy to help keep pace with rising water levels. "We take this into account when we design living shorelines," says Sarah Picking, a landscape architect in Norfolk who has guided clients through the decision-making process. "We make sure that the more salt-tolerant species are planted in the tidal zone, the less salt-tolerant species are planted in the upland regions," to mimic how they are found in nature.
However, sea level rise and climate change are expected to change the Bay's salinity over time, and it is unclear by how much in particular locations.
Another strategy for building a living shoreline that persists is to build its rock "sill" higher than necessary in anticipation of future sea level rise. The additional cost is not always one that homeowners are willing to bear.
And some restoration professionals wonder what will happen to those rock sills during the high tides of the future. In 50 or 75 years, the living shoreline's vegetation may be inundated and die because of rising sea levels, says Joe Fehrer, who works with The Nature Conservancy in Virginia and Maryland. What if all that's left is an underwater pile of stones, he wonders?
Other people advocate augmenting the living shoreline's first line of defense using another kind of natural tool. They want to develop oyster reefs on top of the rock sills by setting spat or by relying on nearby oyster beds to help populate new habitat there.
Researchers have studied the vertical reef growth of oyster reefs in high salinity environments in North Carolina's coastal bays, and the results are promising. In April 2014, Antonio Rodrieguez from the University of North Carolina reported that accretion rates of intertidal oyster reefs have the potential to surpass all other coastal ecosystem engineers and to keep up with rising sea levels as they grow ever taller — and wider. Like marsh vegetation, oyster reefs also help to improve the Bay's water quality.
Although questions remain about their effectiveness, living shorelines may offer one creative solution for protecting shorelines from erosion while maintaining, restoring, and even enhancing the natural habitat, at least in the short term.
More Information About Living Shorelines
Maryland and Virginia have different processes for approving living shorelines. Learn more about them: