Rip-rap. Bulkheading. Revetments. Seawalls. Whatever you call it, they all mean and do the same thing: create a hard, unnatural barrier between water and the shoreline. And wherever they are placed, they destroy the shoreline’s ability to do its job.
On a recent sunny day, I paddled my kayak down the lower Wicomico River towards the Chesapeake Bay. Most of the shoreline was populated with houses, many of which also had docks sticking out into the river, with or without boats attached. And more than half had some kind of bulkhead or shoreline armor between their property and the water. I understand their reasoning. This part of the Chesapeake Bay is experiencing sea level rise faster than almost any other part of the Atlantic Seacoast.
That Sinking Feeling
During the last glacial period, about 15,000 years ago, Chesapeake Bay, a drowned river mouth, was under thousands of feet of ice, which compressed the sandy, silty alluvial sediments. After the glaciers receded, the land rebounded, “springing” back up to higher levels. But since then, it has begun to subside again, historically at a rate of about six inches per century, but over a foot in the last 100 years; about half of that is due to withdrawal of groundwater, causing the soils to compact [1]. Sea level in the southern Chesapeake Bay is rising at a similar rate, so the relative sea level (including both subsidence and sea level rise) is rising at about 4 mm/year, or almost 16 inches per century, but may increase by another meter before 2100 [2]. Some areas in the Chesapeake Bay, such as Smith Island and Tangier Island, are sinking so rapidly that they may not be habitable by 2050 and may disappear completely by the end of the century. People who live on those islands, however, don’t believe this. They prefer to believe that the loss of shoreline and higher frequency of flooding is just due to erosion and hope the government will help them out by building a giant rock seawall around the whole island.
Natural shorelines around the Chesapeake Bay are home to submerged aquatic vegetation (SAV) like seagrasses (Zostera marina) and widgeon grass (Ruppia maritima), sedges, cordgrasses (Spartina alterniflora), and reeds (Phragmites spp) [3]. These form a natural buffer to waves, absorbing and dampening their force against the shore. The plants offer hiding places to juvenile fish and crabs, which eventually become bigger fish and crabs. In natural areas, rainwater and runoff is absorbed by the ground like a sponge and released slowly, preventing floods. Soft shorelines allow rainwater to percolate out into tributaries gradually. Shoreline vegetation captures and recycles nutrients (nitrogen and phosphorus) draining from cropland and septic systems and may absorb other pollutants coming down river from upstream industries, all of which improves water quality and prevents algal blooms and oxygen depletion [4]. Living shorelines also offer access pathways between the water and land for turtles, raccoons, birds, snakes, muskrats, and other animals that move between these environments. And, let’s face it, the beauty of a living shoreline, and all the plant and animal life it supports are major reasons people choose to live here.
Hard Shorelines Disrupt Ecosystems
Solid bulkheads do none of that. Bulkheads and seawalls are hard structures built to protect land or houses from erosion, wave runup, overtopping and flooding. They are semi-permanent objects (typically designed to last 50 years) placed into a dynamic, moving environment. Seawalls and bulkheads have many negative environmental consequences. They destroy the ecological services provided by living shorelines as well as the view. If placed behind an eroding beach, erosion will continue until the beach disappears completely. If placed at an angle, they can interrupt sand supply to the downstream side. Bulkheads and seawalls channelize the flow of groundwater into funnel-like areas that increase runoff speeds, causing more scouring and erosion. Seawalls, revetments, or rip-rap have replaced over 1,700 miles of shoreline in the Chesapeake Bay, or about 10% of the entire shoreline [5].
Hard shorelines offer no shelter to juvenile fish or crabs and turn a living shoreline into a biological desert. While they may protect the shore and homes temporarily, they eventually succumb to wave action. Waves hitting vertical walls are reflected back into the water, concentrating their energy and amplifying incoming waves. This creates turbulence that disturbs the sediment and aquatic organisms living there and may intensify undercutting of the bulkhead. Loss of SAV in Chesapeake Bay is one of the major reasons that crab and fish populations are struggling. Hard shorelines degrade the environment that attracts people to live near the water [5].
Hard substrates do, however, offer attachment points for marine organisms such as mussels, sponges, amphipods, and the larval stage of sea nettles. Bay nettles Chrysaora chesapeakei are abundant in this area after July both because it has the right temperature and salinity, but also because of the increasing amount of hard substrate for the larvae to attach. As much as I hate being stung by sea nettles, they do have an ecological role, which is to consume comb jellies, or ctenophores, that eat a lot of larval fish and compete with fish for other plankton (see E@L No. 7). Wooden docks don’t create as many problems; they don’t displace plants or have much of a footprint and may dampen incoming waves somewhat. But they do create shade and prevent plants from growing beneath them, and release toxic chemicals into the water.
I don’t begrudge homeowners their desire to protect their homes from erosion. But this is a classic case of the Tragedy of the Commons. Nobody owns the river, or the organisms living in it, so nobody has a reason to take care of those living along the shoreline. Everywhere a bulkhead is built, it destroys the ability of a small part of the shoreline to do its job. And when every house on the river is walled off from it, then the river has no natural boundary left, and will eventually become a sewer. This has already happened in many overdeveloped shoreline areas in Florida, and farther north. We need look no further than the bay side of Ocean City, Maryland, to see what happens when all of the shoreline is turned into heavily bulkheaded personal inlets for home and condo-owners to park their boats in. Water circulation is inhibited, oxygen levels are depleted, and harmful algal blooms become more common. Fortunately, there are still miles of undeveloped shoreline in my part of the Eastern Shore.
Coastal erosion due to sea level rise creates enormous economic damage. On North Carolina’s outer banks, homes are being lost to the sea every year. And when that happens, it costs communities and taxpayers to clean up the mess. It also causes our insurance rates to go up, as insurance companies redistribute the cost of their losses to the rest of us.
Living Shorelines Enhance Ecosystems
So, what can we do? I doubt we could outlaw building of bulkheads, as property owners would be up in arms. Bulkheads are necessary where businesses (shipyards, freight yards, etc) need access to the water. But insurance companies should charge much higher premiums for waterfront property (even here, most of it is not in a Federally declared flood zone). Local communities could enact laws requiring minimum setbacks to prevent people from building close to the water’s edge, or on land close to sea level, so bulkheads would not be needed. And we should also designate which kinds of shoreline protection are preferable and allowed. This may differ regionally, depending on the local environment and wave exposure.
But the best way to protect property and the environment is to create a living shoreline, a protected, stabilized coastal edge made of natural materials that grows over time. Living shorelines provide a low-maintenance green space that purifies water, buffers floods, reduces erosion, stores carbon, and attracts wildlife. They help protect shorelines from erosion, while enhancing their ecological function, and allowing natural processes to occur. Oyster reefs are the best sort of living shoreline, but they are scarce and difficult to recreate (that’s another story). A better method is to build a detached breakwater, essentially a row of rocks beyond the shoreline, that protects shoreline vegetation from wave energy. This may allow marsh grasses to grow right out to it, or it may trap sediment and create salients or tombolos, extensions of the shoreline from the beach to the barrier. Living shorelines have been created in a number of public areas, including Assateague State Park. We need to create incentives, legal or financial, for private landowners to create more of them.
Coastal engineering is a developing science, and old habits are difficult to change. As we learn more about the effects of hard shoreline stabilization, and see more evidence of climate change, we need to phase out traditional practices and replace them with methods that maintain and support ecological function. Shoreline communities must wake up to this problem and start taking action.
Someday I hope to be able to kayak the length of the river or the Bay, and see only beautiful, green living shorelines along its entire length.
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Sources for this Post
[1] J. Eggleston and J. Pope, Land Subsidence and Relative Sea-Level Rise in the Southern Chesapeake Bay Region, USGS Circular 1392. Reston, VA, 2013. 32 pp.
[2] D. Bosch (ed), Global Warming and the Free State: Comprehensive Assessment of Climate Change Impacts in Maryland. Report of the Scientific and Technical Working Group of the Maryland Commission on Climate Change, University of Maryland Center for Environmental Science, Cambridge, MD, 2008.
[3] C. P. White, Chesapeake Bay Field Guide. Atglen PA: Schiffer Publishing, 1989. 212 pp.
[4] W. C. Dennison et al., Shifting Sands: Environmental and Cultural Change in Maryland’s Coastal Bays. College Park, MD: University of Maryland Center for Environmental Science, 2009. 395 pp.
[5] D. Malmquist, Chesapeake Bay Explorers Guide. Lanham, MD. Rowman and Littlefield Publishing Group, Inc, 2021. 361 pp.