Alongshore

Barrier Islands and Beaches —
Bulwarks of the Land

By Tamia Nelson
tamia@paddling.net

February 3, 2004

My oldest memory of the ocean is of a family outing to the New Jersey shore. I was three years old, and I played happily in the hot sun, molding a rather shapeless sculpture in the wet sand of the foreshore. I wasn't the only little engineer on the beach. Farther down the strand, some unknown artist had built an elaborate sandcastle, only to abandon it to its fate when the tide turned. I watched in amazement as the intricate battlements and soaring towers were gradually swallowed up by successive waves.

Then my mother headed for the water. As she waded out through the surf, it appeared to my horrified eyes as if she were being consumed by the hungry sea, just like the doomed sandcastle. I was terrified. Long after my father had quieted my screams and my mother had emerged from the waves to stand beside me, the image lingered in my memory. From that day on, I never doubted the sea's power to sculpt and scour, to level structures and rearrange landscapes with impunity. Even today, I need only close my eyes to see the walls of the sandcastle crumble and fall into the sea, and to watch my mother's head disappear beneath the relentless waves.

As the years passed, I learned a lot more about the ever-shifting, fluid boundary between land and ocean that we call the coastline, and in time, I came to know more about the sea's many moods. As my understanding increased, my fears diminished. I never forgot the lessons of that first day on the New Jersey shore, however. I knew that waves and wind were always probing and pounding the land, plucking away individual sand grains, tumbling clods of earth into the sea, sending entire cliff faces crashing down, and wiping even the largest human edifices completely off the map.

But I also knew that whenever the sea takes, it gives back in equal measure. Sand and gravel that have been torn away from the land at one place will, sooner or later, be redeposited somewhere else. And sometimes the predatory sea turns guardian, building walls to protect the same treasures it once plundered so avidly. Fittingly enough, these walls are known as barriers: barrier beaches and barrier islands, to be exact. (Sand spits — narrow finger-like beaches that often sprout from headlands or extend across the mouths of sluggish rivers — can act as barriers, as well, but for some reason geographers class them separately.)

Such barriers can extend for miles, but they all grow one sand grain at a time. Currents carry quarried sediment along the shore, dropping their burden as their force diminishes. Beaches extend, stretching out in the direction taken by the current. In time, a barrier is born.

What distinguishes a barrier beach from other beaches? Simply this: narrow and long, and rising only slightly above the high-water mark, barrier beaches are hiding something. Behind each barrier beach is a sheltered body of water, a shallow, landlocked lagoon. Barrier islands are long and narrow, too. But they are islands, separated from the mainland. The lagoons that shelter behind them communicate directly with the open sea. Barrier islands are also wider than barrier beaches, and they're usually higher as well. Many boast dunes and vegetated slopes, and some conceal protected saltwater marshes in their lee.

I'm oversimplifying, of course. The origins of barriers are much debated in the literature. But whatever their genesis, they're easy enough to spot. Take a look at the map of North America in any good world atlas. You'll see a bulwark of barriers extending from Long Island all the way down the Atlantic coast to Florida, and continuing westward along the Gulf of Mexico. The Outer Banks of North Carolina are barriers. And Cape Canaveral, the spaceport on Florida's east coast, perches on one. Don't think that barriers are exclusively American, though. More than ten percent of the world's coastlines are guarded by barrier islands, and many large freshwater lakes have barriers of their own.

No matter what their nationality, barriers and lagoons are inseparable companions, and because the barrier shelters its partner from all but the worst of the sea's assaults, lagoons play host to a startling variety of extraordinarily diverse ecosystems. Some lagoons — those protected by barrier beaches — are landlocked, but many are extensions of the sea and subject to the rhythm of the tides. Water pours in and out through tidal inlets, nourishing salt marshes and tidal flats.

Not all lagoons support salt marshes, of course. They require gently shelving shores, conditions that are common enough along the Atlantic and Gulf coasts of North America, but rare in the active tectonic landscape of the Pacific, where no more than one-fifth of the shoreline is suitable. Even on the Pacific coast, however, salt marshes can be seen in protected bays and sheltered coves, on Alaska's arctic slope, and along the Baja peninsula. And wherever natural lagoons and salt marshes are found, you can bet wildlife will be found there, too. Salt marsh grasses anchor the sediments from which they spring. When the grasses die and wither, their remains accumulate as a fertile organic mulch. Over time, this mulch becomes peat, sustaining a living community of incredible richness in the process. Tidal flats attract an army of crawling and burrowing invertebrates. These, in turn, attract larger predators. Shore birds and land animals scavenge along the flats when the tide goes out. Fish swim in the tidal waters and graze among the roots of the grasses in the salt marsh. It's a marine Garden of Eden.

Unfortunately, Eden is under siege. People flock to America's beaches in order to escape the coastal cities' stifling summer heat, and more and more of them are deciding they don't want to leave when the sun goes down. Oceanfront property is the hottest seller in an already superheated real estate market, and a small swathe of North America's dwindling stock of salt marsh is lost to development every day. It's death by a thousand cuts — agonizing, slow, and sure.

And people aren't the only threat. The hungry sea still waits just outside the barrier, eager to stake its own claim to a piece of Paradise. No barrier island can withstand the full force of an ocean storm without sacrificing something of itself. When the sea attacks the shore, the land has no choice but a fighting retreat. Hurricane-force winds and plunging surf tear away at the fabric of the barrier. Storm surges dredge inlets where none existed before, making barrier beaches into islands, and opening landlocked lagoons to the action of the tides.

But even in the fiercest hurricanes, the sea gives as well as takes. Storm waves wash over the crests of barriers, quarrying sand and gravel from the beaches on the seaward side and dropping it to leeward. These "overwash sediments" actually increase the height of the barriers and prolong their life. Without overwash, the barriers would eventually sink below the rising sea. Global warming's not to blame for this, by the way — at least it's not the only culprit. The sea has been rising since the last continental ice sheets started to melt. We're just hurrying things along. That's enough, though. A lot of oceanfront property is going to get wet feet in the coming decades.

Lagoons are shaped by the sea's tough love, too. Each storm increases the burden of silt and sand borne by local streams and rivers. Much of that runoff ends up in lagoons, where it's trapped in the salt marsh grasses. As storm follows storm, the shoreline builds outward, encroaching on the shallow waters. In time, the whole lagoon may be transformed into a salt marsh. Eventually, that too will fill in.

The sea giveth, and the sea taketh away. Nothing lasts forever, and the continents' seaward defenses are no exception. When extraordinary storm swells breach or overwhelm barrier islands, the coast stands naked, exposed to the full power of the ocean. Catastrophe then becomes commonplace. We humans find this hard to accept. We fall in love with barrier islands and beaches. We build homes on them, savoring the sweeping views and salt air, and we tell ourselves that these will always be ours to enjoy. But we're doomed to disappointment. Once a barrier is surveyed, platted, paved, and built, it loses its ability to retreat. It can no longer roll with nature's punches. It can only stand and take each blow on the chin. The result is certain. Only the length of the match is in doubt. The sea wins every bout on its card.

As a child playing in the sand, I got my first inkling of the power of the sea. Later, as a geologist, I learned to question the seeming certainty of solid land and embrace the constancy of change. Later still, now a paddler making her first tentative forays along the coast, I caught glimpses of the richness and majesty of the living ocean. And I saw how much had already been lost.

Nothing lasts forever. I know this. So do you. But barrier islands and beaches, along with their lagoons and inlets and salt marshes, are essential parts of the coastline's intricate, elastic armor. They absorb the force of the waves' knockout blows, and tame the wildness of the raging seas. They offer shelter to all manner of creatures, and safeguard the ocean's legacy of life. They also bring pleasure to millions of people who are content to visit and then leave: beachcombers, birdwatchers, sun-worshippers, surfers, and kayakers alike. That's no small thing, even if the dollar value of "quality of life" continues to elude the economists.

Yes, change is inevitable, but change that comes too quickly can overwhelm. We live for the moment, and our moment is brief. The sea's time is not our time. It has infinite patience. It tests the coast's armor every day, and every day it finds the armor weaker. One day it will strike, giving no quarter and granting no parole. No coast is safe, no bulwark perfectly secure. This much, at least, is obvious, even to little engineers: If you don't want to see your work swallowed up by the hungry sea, be sure you build all your sandcastles well away from the farthest reach of the waves.

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