From Watts Up With That?

Guest Essay by Kip Hansen

On the U.S. Atlantic Coast and the Gulf Coast, we find Barrier Islands:

“Barrier islands are a coastal landform, a type of dune system and sand island, where an area of sand has been formed by wave and tidal action parallel to the mainland coast. They usually occur in chains, consisting of anything from a few islands to more than a dozen. They are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish. A barrier chain may extend for hundreds of kilometers, with islands periodically separated by tidal inlets.”

There are several important things to know about barrier islands: 

1)  There are made of sand.  Often on the ocean side they have sandy beaches and sand dunes,  behind which are flatter areas of sand leading to the semi-enclosed lagoon. 

2)  They have been formed by wave and tidal action, and are re-formed by the same natural forces.  (There are several theories of how the come into existence.)

3)  They are subject to change – by the very same forces that created them:  waves, currents, and storms.

Barrier islands, when left to their own devices, make wonderful places to visit – by car if there are roads and by boat when there are no roads.

They seem so nice, in fact, that beach loving humans have even building entire cities on them for more than a century. 

Now, a reasonable person might think that building a city on a low-lying spit of sand at the ocean’s edge is a rather foolish thing to do.  After all, barrier islands are by definition “subject to change”.  That is, the sand both washes onto the barrier island and washes away from the barrier island.   The wind and waves remove parts of barrier islands and move them elsewhere.   Whole islands can move along the shore in what is known as longshore drift.

The USGS’s Earth Resources Observation and Science (EROS) Center has a very well-done illustrative series of satellite images showing the changes of the barrier islands off of Chatham, Cape Cod, Massachusetts.  Check the link and click through the images in time order.  Then imagine, instead of bare sandy beaches, the island had been covered, like so many others are, with homes and businesses.

The island, as its name implies, is a barrier between two bodies of water – the ocean/sea and an enclosed (semi-enclosed) body of water.  The backshore (facing the continent) semi-enclosed bodies of water have many different names such as “bay”, “river” (incorrectly), “sound” and “lagoon”.  Not all barrier islands are strictly islands, are not entirely surrounded by water, some have minor connections to the main body of land and a larger number have been connect to the main shore with causeways and bridges.

Sea level, slowly and steadily rising in most parts of the world at the present time, is not a major concern for barrier islands.  This is true despite the clamor of alarm from the climate crisis crowd.  The tiny annual rise of the sea’s surface, measured in single digit millimeters, goes entirely unnoticed by the dynamical system that creates and destroys barrier islands. 

Remember:  “They [barrier islands] are subject to change during storms and other action, but absorb energy and protect the coastlines and create areas of protected waters where wetlands may flourish.”  [ source ]

Barrier islands do not protect the coastlines on purpose – nor do they create wetlands.  The protection is a byproduct of the dynamics of the energy of ocean waves, tides, and storms (increased energy) that builds the barrier island.  Wetlands develop on the backshore of the islands and on the shoreline behind barrier islands as the sediment from the land builds up along the shore and is no longer washed out to sea by waves and strong tides – both prevented by the existence of the barrier island.

But the same forces that build barrier islands also alter and destroy them – one piece at a time.

The greatest U.S. disaster involving a barrier island was the Galveston Hurricane of  1900.   “Galveston  [Texas] is built on a low, flat island, little more than a large sandbar along the Gulf Coast. …. development activities on the island actively increased its vulnerability to storms. Sand dunes along the shore were cut down to fill low areas in the city, removing what little barrier there was to the Gulf of Mexico.”  [ source ] Over eight thousand lives were lost (6,000-12,000) and the city was nearly totally destroyed.   Galveston, Texas did not learn its lesson, as evidence by the Google maps satellite view here.  Before that, the Texas city of Indianola was destroyed by a hurricane in 1875, rebuilt, and then destroyed again by a hurricane in 1886.  It is a ghost town today.

Ocean City, Maryland is said to have benefited from a massive storm in 1933:

“However, the most historically significant change in the storm-ravaged resort was the existence of a new 50-foot wide, eight-foot deep Inlet at the south end of town. The huge waves that pounded the east side of the resort combined with the massive amount of water that built up in the back bays conspired to cut the Inlet and separate the southern end of the town from what is now Assateague Island.” [ source ]

A number of homes and business were swept out to sea an the new inlet caused the loss of continuous access to the southern portion of the island creating what is today called Assateague Island.  The good news was that  the new inlet allowed the fishing community, on which the area  depended for income, to get their fishing boats from the bay to the ocean and return.  Before the storm, fishermen were forced to drag their boats with teams of horses from the oceanfront beach across the island to the bay. 

The cutoff southern portion of the island is now the famous Assateague Island National Seashore, with fabulous beaches and roaming herds of wild horses.

Now, consider the consequences of such a natural event if it was to  occur today at a slightly different portion of what is Ocean City:

Like in Ocean City, sometimes the ecological outcome of a strong storm rearranging or cutting a barrier island has positive effects:

“Barrier islands like Fire Island are known as early successional habitats [pdf], which means they require regular disturbance events to keep their ecosystems in check. Under normal circumstances, Fire Island would experience disturbance events on an annual basis. However, engineers have gone to great lengths to stabilize the island, and now only powerful storms like Sandy are able to have a significant impact on the island’s ecosystem.”

“Barrier islands are very dynamic systems, they don’t stay the same from one year to the next. The species that inhabit them there are adapted to these changes, so if we try to keep these systems static, we are going to lose these species,” said Dr. Cohen [assistant professor at SUNY College of Environmental Science and Forestry ].“

The major threat to all of these cities built on low-lying barrier islands is storms with high winds and strong waves.   These forces wash away sand dunes, lowering the overall height of the island, and drive water through low elevation areas, often all the way across an island forming a cut.  Sometimes the water comes from the bay side of a barrier island, as a storm blows more and more water into the bay, the lagoon, on the shoreside of the island.  The excess water then seeks out a path back to the sea.  When it finds a downhill path to the sea, it runs through it, cutting away the sand, the land, faster and faster as the water flows through.  This is what happened at Ocean City, MD in 1933, which is clearly visible in the photo of the new inlet (far above).    The same occurred at Fire Island, NY. 

Not all long thin islands off the Eastern Seaboard are, strictly speaking, sand-based barrier islands.  Some, such as Miami Beach, are remnant limestone/coral reef systems subsequently covered with sand. These types of islands will suffer from waves and wind and surface erosion, but are unlikely to have new inlets created.

When we speak of a storm forcing water into a bay, we should think of New York City during the remnants of Hurricane Sandy, which raised water levels in New York Harbor and up the Hudson River by as much as 12-14 feet.   Many factors were involved in that event, among them the restriction of access of the rising water to the Meadowlands, the natural bioswale for the excess water.

Bottom Lines:

Almost all mass media outlets focus primarily on sea level rise when covering threats to barrier islands, with storms (hurricanes) secondary. This is, of course, a misleading picture.   Sea level rise is a slow minor issue. 

Storms, with their energetic wind and waves, push almost unbelievable amounts of water at high energy against the shore – whatever is there has to deal with all that mass moving at speed hitting those stationary objects.   

That water moves sand, soil, building, trees—whatever is there.  That water builds up in bays and lagoons and seeks release to a lower elevation – and it is this that cuts barrier islands, forming new inlets.  And it is then, when water is rushing into or out of a bay,  that major geomorphic changes occur.  One island becomes two, a long island is shortened, a short island is made longer, an entire island moves hundreds of yards up or down the coast or its end becomes a hook.  The human developments on those islands are of little consequence, unable to mitigate or resist the tremendous forces being applied.

Building permanent structures or infrastructure on impermanent, or ephemeral,  barrier islands is a serious societal error.  These islands should all be allowed to revert to their more natural states, used as beaches and National Seashores.  Rebuilding after storms should be forbidden.

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Author’s Comment:

This has all been said before.  The lessons of Galveston,  Ocean City and Indianola (Texas) have been ignored and cities built on the “here today, gone tomorrow” barrier islands of the U.S.’s Atlantic and Gulf Coasts. 

Historically, we are almost at the height of the Atlantic Hurricane Season, which statistically is the second week of September.

As I showed in a recent essay on Atlantic hurricanes, it is only a matter of time before a hurricane barrels ashore on one of our barrier islands covered with condominiums, homes, highways and businesses.  Hurricane strength and path, direction and speed of winds and state of the tide at landfall will determine the extent of the disaster. 

Thanks for reading.

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