On an undeveloped sandy beach, coastal erosion and restoration is an endless natural process. During storms, large swells remove sand from the frontal dunes and shift it offshore. The sandbars created or enlarged by this process dissipate wave energy, helping to reduce further beach erosion. In calmer weather, smaller waves move some of the sand back up onto the beach, rebuilding the frontal dune. Often this process is seasonal, with harsher winter storms tearing away beach sand and gentler summer waters nudging it back.
How much this process is aggravated, or even triggered, by human activity is a matter for debate. Some geologists and coastal engineers claim onshore development—buildings, parking lots, and erosion control structures themselves—speeds coastal erosion. Others say offshore coastal engineering practices, such as dredged navigation channels, breakwaters, groins, and jetties, are the worse culprits. Where a structure is—onshore or offshore might be less important than how it affects the migration of sand.
Still, most experts agree on three things. First, coastal erosion—much of it, anyway—is a natural process. Second, it wouldn’t be nearly the problem it is today if houses, roads, and other structures hadn’t been built so close to the ocean on what is essentially a constantly moving line of demarcation between land and sea. Third, since these structures do exist in places they probably shouldn’t, we somehow have to find ways to protect them.
As Martha Mitchell points out in her May 1999 article in Erosion Control, treatments for shoreline erosion fall into three broad categories: hard (sea walls, groins, breakwaters); soft (beach nourishment and bioengineering); and preventative (zoning changes to prevent intrusive development from triggering or speeding up natural erosion). Coastal communities around the country are trying—and often combining—all three.
A Soft Solution Gaining Ground
Beach nourishment, an increasingly popular option, is the practice of adding material—from offshore or inland—to restore coastal areas lost to erosion and to protect landward structures. Done well, it is more than simply dumping sand onto the beach. It increases beach width or elevation, taking into account beach cross-section, shape of the offshore profile, present erosion rate, wave parameters, dune height, grain size of the imported sand (coarser is generally better), sediment characteristics, and many other factors. Sand can be placed directly onto the beach or seaward of the existing beach to create a sandbar or a submerged mound; bars and mounds reduce wave height and energy and are created with the expectation that the sand they contain will eventually be deposited onto the beach. The conditions that led to a net loss of sand before nourishment took place will likely continue, however, and maintaining a beach in this way is usually an ongoing process.
First used at Coney Island in 1922 and common in places where beaches are vital for tourism, beach nourishment has both powerful supporters and vociferous opponents. “Beach nourishment is really the only option for shoreline protection that results in a beach when you’re finished,” states Richard Seymour, head of the Ocean Engineering Research Group at Scripps Institute of Oceanography in San Diego, CA. “If you are faced with a naturally eroding coastline, and the edge of the beach is defined by structures —houses, roads, improvements of any kind—and you want to maintain a beach, then the only economic solution is adding sand.”
Seymour was the chair of the National Research Council’s Committee on Beach Nourishment and Protection. The committee’s influential report, published by National Academy Press in 1995, supports well-designed beach nourishment projects on beaches where the erosion processes are well understood. Because dredging or importing sand specifically for beach nourishment is expensive, the report urges communities to coordinate nourishment projects with already-planned dredging projects. It also supports the use of such hard-armor structures as jetties and sea walls in conjunction with beach nourishment in certain cases.
Not everyone agrees. Those who practice beach nourishment are “living off the problem and not solving it,” claims Dick Holmberg, president of Holmberg Technologies in Sarasota, FL, which offers an alternative method for reversing coastal erosion. “They keep pumping sand and it goes away, and the problem keeps getting worse. So they pump more sand. They’re not solving the problem, but they’re making a lot of money, and the destruction continues.”
Ocean City, MD, located on a barrier island, has been nourishing its beaches for more than a decade. It has been the focus for much of the controversy, with both opponents and supporters of the process citing it as an example. Dunes and beaches restored by nourishment in 1990 and 1991 were reduced by severe storms almost as soon as they were completed, and the $11 million needed to once again restore the area drew sharp criticism from some members of the public and the media. The Maryland Department of Natural Resources, however, estimated that damage to the developed area behind the nourished beach could have reached $93 million had the beach not been there to act as a buffer.
The project had lesser economic benefits as well. Bruce Nichols, a district conservationist with the Natural Resources Conservation Service in Snow Hill, MD, participated in the 9.5 mi. of dune restructuring in Ocean City. “The great thing about the dunes is that you can trap the sand, which is a liability when it blows inside town. It actually tears up property and has to be removed, sometimes at great expense. It’s not uncommon for parking lots to spend $2,000–$3,000 after a windstorm to remove the sand. That’s one thing a sea wall doesn’t stop as efficiently as the dunes.”
As the National Research Council committee recommended, project coordination for beach nourishment is improving. “There’s quite a bit of coordination with the Army Corps now,” Nichols observes, citing harbor dredging and beach restoration activity at Dewey Beach in Delaware. But beach nourishment has potential drawbacks as well. The salinity of some dredged material may be so high that it temporarily hinders revegetation projects. And some source material is of a wrong particle size—finer than the sand already on the beach and therefore more susceptible to erosion. “It may be smarter to use it as a deterrent to whatever degree it is instead of depositing it where it can’t be of benefit,” says Nichols. “But in Ocean City we’re creating an island in an area that was navigable in my memory. The island just grows and grows and reduces the ability of people to use it for boat traffic. This might be a result of the Ocean City dredging out activity and some of the particle sizes that were used there. Or it may be that it would have formed anyhow.”
Hard Line of Defense: Do Sea Walls Cause Erosion?
Unlike the ongoing financial commitment a beach nourishment project requires, a sea wall takes one big investment upfront—as much as $6,000/ft. Of concrete, stone, timber, or steel piling, a well-designed sea wall is extremely effective at protecting the structures immediately behind it. A poorly planned structure can cause its own demise, though, as the wave energy it reflects scours and undermines its foundation.
Hard barriers like sea walls and riprap encounter opposition for two reasons. First, they do nothing to protect the land in front of them. If erosion was occurring before the barrier was constructed—and if it hadn’t been, there would have been no need for the barrier—the shoreline will probably continue to move landward, and the area of beach in front of the sea wall will eventually disappear. This is a definite disadvantage for a community trying to maintain a public beach. Many people also claim that hard barriers increase erosion on adjacent areas of the beach, either by reflecting wave energy or by trapping sand that would otherwise move horizontally along the beach. Several states—Maine, North Carolina, Oregon, Rhode Island, and South Carolina—severely restrict or prohibit sea walls and other hard barriers. Others, including Texas, limit their use.
In addition to its nourished beaches, Ocean City has about a mile of sea wall and an inlet on its south end. Assateague Island, a major public recreation area, lies to the south of Ocean City. “We’re trapping that sand,” Nichols points out, “and it’s not going into the national park area of Assateague Island and everything located south of there. So now the north part of Assateague Island is vanishing. We’ve probably created some protection and sand accumulation by forming the inlet structure for boat traffic, but we also have led to the deterioration and accelerated erosion of Assateague’s north end. Everything you do is going to create a reaction.”
Seymour maintains that sea walls do not of themselves cause erosion or increase it. However, he explains how they prevent the beach from recovering after a storm—and why in some cases it no longer matters. “When you put in a sea wall to protect an existing structure, you are definitely for all time impounding whatever sand was behind that sea wall from being involved in the beach processes. Dunes provide a kind of a surge capacity for accepting punishment when you have a really big storm. The dune will be ripped up by the waves, and the sand will move offshore, but eventually it will come back again. It provides that supply of sand to rebuild the beach. If you build a sea wall at the very front of the beach and deny that sand to the beach, then the beach will take a very, very long time to recover, or it might not recover. So sea walls only make sense where for other reasons—usually stupidity—we have already tied up that sand and can’t let it go back on the beach. We pave over it to make parking lots, we build houses on it, and we build a road there. In that case, if the sea wall simply protects a structure we’re going to insist stay there anyway, then it by itself doesn’t impound any sand, nor does it aggravate the erosion on the beach.”
Combining Treatments in Texas
Galveston, TX, with just under 60,000 residents, is the largest city in the United States located entirely on a barrier island. In the late 1800s it was the largest city in Texas and the richest—the “Wall Street of the Southwest.” Then on September 8, 1900, a hurricane known today as The Great Storm killed more than 6,000 of Galveston’s 38,000 residents. Still the worst natural disaster in US history, the storm brought 120-mph winds and tidal surges that destroyed a third of the city.
To defend itself against future seaborne calamities, Galveston constructed a 17-ft.-high sea wall of granite, sandstone, and concrete. It also undertook an eight-year project to raise 500 city blocks by jacking up existing structures and pumping 4-6 ft. of sand beneath them—25 million yd.3 in all. Today the sea wall extends more than 10 mi.—almost one-third of the island’s length. The beach in front of the sea wall has eroded away, and the city periodically pumps sand from the Gulf of Mexico to re-create it.
Galveston’s sea wall is one of the few along Texas’s Gulf Coast, and until recently, its beach nourishment program was a rarity there as well. Although hard armoring is used extensively along the Gulf Intracoastal Waterway, where ships and barges travel in from the gulf and which has been battling erosion since its construction in 1905, sea walls and similar structures are prohibited on the gulf-fronting shoreline. “That is based on a principle that goes back to the period when Texas was an independent country, when it was recognized that the public has always used the beach as a transportation route and for recreation,” explains Bill Worsham, director of the Texas General Land Office (GLO) Coastal Projects Division. “It’s a public place. So even though a lot of these beaches are privately owned, the owners can’t keep the public off of those sandy beaches. And building an erosion response structure is essentially doing just that, because if you build something like a sea wall and the shoreline continues to erode, eventually it erodes to the point where the sea wall is the shoreline, and the public no longer has the access that they’re entitled to.”
Texas is the only state in the US with an open-beach policy. Everything from the vegetation line seaward is public land and is managed by the Texas GLO. The problem for private landowners along the coast is that the vegetation line—that is, the area of vegetation closest to the ocean—keeps moving landward during storms. It’s known locally as the “rolling easement.”
Although private homeowners cannot build erosion control structures on the beach, county governments can, and a few communities have tried sand-filled geotextile tubes and other devices. Nothing has worked consistently. “We’ve lost coastal highways. We’ve lost entire subdivisions, or at least four and five rows of houses that were formerly beachfront houses. We’ve lost a lot of our park lands and wildlife refuges,” says Worsham.
Beach nourishment has not been used extensively in Texas, but a 1999 agreement between the Coastal Coordination Council of Texas and the Army Corps of Engineers is changing that. As the National Research Council report recommended, the agreement ensures that all federal maintenance dredging within the state undergoes a “beneficial-use analysis” to see where the dredged material can best be used. Previously, the corps simply disposed of the material as cost-effectively as possible, usually dumping it offshore or in confined, levied-off areas onshore.
The amount of material in question is immense. The corps dredges more than 40 million yd.3 annually from 46 Texas navigation channels. After two years of analysis, says Worsham, “We’ve identified a number of projects where they can take material and put it to better use by building marshes or nourishing beaches.”
“Say the Corps of Engineers is doing a million dollars’ worth of dredging. We may have a place to put that material where it’s a benefit to everybody. It might cost an extra hundred-thousand dollars, and the state is now able to pay that hundred-thousand dollars and essentially gets $1.1-million worth of project. The million dollars’ worth of dredging was going to have to be done anyway. We’re simply taking advantage of that work.” Legislation passed last year allows the state to pay the difference. Worsham expects about six projects a year will make use of the dredged material.
The third means dealing with shoreline erosion—prevention—is also at work in Texas. “Since 1986, anyone who has purchased property anywhere near the beach has signed a disclosure statement acknowledging that they’re aware of the Open Beaches Act,” Worsham explains. “That doesn’t make it any easier when the beach moves landward and the houses end up on the beach. When that time comes, they generally don’t want to move.” The state can sue landowners to have the houses removed—even still-intact ones built on pilings. “In defense of the property owners, a lot of the erosion problems can be traced to navigation inlets and ship channels. You end up with channels dug out through the beach with jetties around them, and they stop the movement of sand along the beach. The coastal property owners and coastal communities are generally left holding the bag for upstream projects. There’s a very active ongoing dialog about the causes of shoreline erosion.”
Alternatives to Beach Nourishment: Undercurrent Stabilizers
Dick Holmberg has long opposed beach nourishment and the practice of offshore dredging or importing sand from distant beaches simply to provide beach fill material. “They’re treating symptoms,” he says. He has developed a technology called undercurrent stabilizers to restore eroding coastlines. Holmberg Technologies installs the product on coastlines and lakefronts around the world. Placed underwater perpendicular to the shoreline, the geotextile tubes are filled in place with concrete or sand. By altering the dynamics of the currents, Holmberg explains, the stabilizers encourage sand deposition to rebuild the eroding beach or lakeshore. “I restore coastlines to a self-building capacity so that they never have to be touched again or need any work done on them.”
Unlike traditional groins, undercurrent stabilizers taper as they get farther from shore. The stabilizers are designed to reduce wave reflection and turbulence to create a “low-energy beach.” Calmer waters allow more sand to be deposited, and as sand accumulates and the nearshore areas become shallower, wave energy is lessened even more. Holmberg has a fundamental disagreement with many coastal engineers about the source of beach sand. While the traditional model has sand moving along the beach —meaning that structures capturing and retaining sand in one area are depriving it from another—Holmberg maintains that the primary source of beach sand is the offshore shelf, and therefore undercurrent stabilizers do not deprive adjacent beaches.
The National Research Council report recommends that all such alternative methods be thoroughly researched and tested by coastal engineers—some of the very people with whom Holmberg has had an ongoing debate. Seymour says of such methods in general, “Structures that are sold on the basis of impounding sand are ineffective because they do not create sand. If they have any effect at all—which they usually don’t—it simply is robbing sand from someplace else on the beach and saying, ‘OK, I’ve got mine, guys. The hell with you.’ This is true of offshore breakwaters as well as all the mystery devices that are supposed to mess with the currents and keep the sand from moving offshore.”
Holmberg recently installed undercurrent stabilizers near an oil refinery in Saudi Arabia. Fourteen-foot-high sea walls surrounded the structure. At Holmberg’s suggestion, several-hundred feet were removed, but the rest was left in place and the stabilizers were installed in front of both areas. Just five weeks after installation, Holmberg says, “We had elevated 6 feet of sand across the whole zone. The offshore had no sand in it, and now it’s accumulating sand. The bottom habitat zones were coming back to life. Bivalves and things that couldn’t exist when there wasn’t any sand came back in.”
On this project, the undercurrent stabilizers extended 300 ft. from shore. Holmberg explains, “Some areas call for a greater distance than that because the pathways the currents have developed are very wide. Sometimes there are several currents moving together parallel to the coastline, and you have to be able to slow those currents down. The only way you can do it is to get under them. I also create an upgrade—I’m turning gravity around on them. We put a new elevation and profile into a bottom, and we’re actually slowing those currents down. You get deposition of soil and build beach.”
Bioengineering: Parachutes and Oyster Shells
Edward Seidensticker, a resource conservationist with NRCS in Baytown, TX, on the Galveston Bay, has pioneered some much-needed erosion control methods for the backbay area. “We’ve got a lot more erosion going on back there than we do on the front beach or on the open gulf,” he points out. “Those get the most attention, but there are places in the bay where we’re having as much as 6-10 feet of erosion a year.
“My job is in demonstration and development,” states Seidensticker. He has innovated several bioengineering solutions. For sites where revegetation efforts are underway, he has protected smooth cord grass plantings by constructing temporary wave barriers from surplus military cargo parachutes. Three-ft.-wide strips from the parachute canopy are fashioned into fences. “Cargo parachutes are different than standard parachutes in that they have openings or slits,” he explains. The slits allow air to flow through the parachute canopy and prevent it from ripping out when descending with a heavy piece of cargo or equipment. The cargo chutes work the same way in the water. “It doesn’t stop the wave energy, it just slows it enough to allow the plantings to establish themselves.” Once the vegetation is established, usually within two years, the fences are removed. “That’s about as long as the parachutes last,” he adds.
Seidensticker’s recent projects involve a more permanent solution: creating oyster reefs for erosion control. “The reefs, in conjunction with the shoreline, act as a natural wave break. Even though the reef is subsurface, it trips the wave energy enough before it impacts the shore that you can get vegetation started on the shoreline,” he describes. By dissipating wave energy, the oyster reefs also encourage the deposition of sand.
A 1,700-ft. reef in Dickinson, TX, and a 2,000-ft. reef in East Galveston Bay both show promising results. The Dickinson project started in 1997. “We’ve cut the erosion rate in half over there, even with the oyster reef just starting to function. We’re waiting now until the reef gets well established and colonized with oysters, then we’ll start planting vegetation,” Seidensticker reports. Conditions in East Galveston Bay allowed planting to start immediately after the reef was built. “We’ve gotten a stand of grass already and essentially stopped the erosion.”
Public response to the project has been enthusiastic. “The oyster reef in itself is excellent habitat. In Galveston Bay we’ve lost a lot of our shallow oyster reef habitat because of subsidence and a lot of other things. And coincidentally, that’s when our big erosion process started—when we lost that habitat,” he notes. Grants from the National Estuary Program, the US Environmental Protection Agency, the National Fish and Wildlife Foundation, and the Shell Oil Company Foundation have helped fund the projects.
A-Jacks: Interlocking Concrete
Port Fourchon, a large Louisiana port serving the offshore oil industry, is one of the southernmost points in a state that is losing about 35 mi.2 of land each year to coastal erosion. Stone barriers along the beach and rock breakwaters offshore have failed to stop the beach’s retreat around Port Fourchon. After the damage from Hurricane Andrew in 1992, a segmented breakwater was constructed by lining up and sinking 14 salvage barges at 300-ft. intervals along the beachfront and filling the barges with stone. Then Hurricane Georges hit in 1998, damaging the barges, scattering some of the stone, and claiming still more of the beach.
With Federal Emergency Management Agency funding to restore the beach, the Greater Lafourche Port Commission decided to try another tack. Seven of the barges—about 1,400 ft. altogether—were topped with double rows of interlocking concrete units, called A-Jacks, produced by Armortec of Bowling Green, KY.
“You can see 3- to 4-foot waves going into the face of these 10-foot A-Jacks, and when they hit the barrier they dissipate down so just a little surge of water comes through the back side, really not even a wave,” describes Russell Reeves, owner of Mid-South Erosion Control Systems Inc. in Golden Meadow, LA, which furnished the A-Jacks. “They’re doing a fantastic job of dissipating the energy of the wave. And that increases with the number of rows that you have in place.”
Each A-Jacks unit is cast in two pieces. Named after the children’s toy jacks, which they resemble when the two halves are put together, the six-pointed A-Jacks rest on three points and interlock, creating a much more stable line than riprap. “Rock has been our main source of hard armoring for years, and rock has a tendency to be displaced with fairly light wave action,” says Reeves. “And of course now rock has gotten very expensive.” Louisiana has imported rock for coastal erosion control projects from Arkansas, Kentucky, Tennessee, and Missouri.
Two- and 4-ft. A-Jacks are commonly used for streambank reinforcement, and 6- and 8-ft. units have been used for coastal and streambank applications, but to date Port Fourchon is the only site where 10-ft. units have been used. The project originally called for 8-ft. units. “We were trying to reach a specific elevation above mean sea level with the top of the A-Jacks,” recalls Reeves. Rather than stacking the A-Jacks or trying to elevate them, he suggested creating larger units. Because each 10-ft. unit weighed 5 tons, Reeves’s crew built the forms and did the casting locally. The entire project required 575 A-Jacks.
“The A-Jacks have about a 40% open area. It allows for the small shrimp and so forth in the estuary behind the shore protection to continue to develop, which wasn’t possible with other types of hard armoring, such as sheet piling or continuous rock barriers. The fisheries here in Louisiana and the state parks department have been very receptive to them for that reason,” says Reeves.
Economics and Other Considerations
“If we can be smart in our development of the coastal areas—avoid the areas with higher probability of losing our infrastructure and manage the dunes with more natural habitats—economically it’d be to our advantage,” notes Bruce Nichols. “Here we’ve already got the infrastructure in Ocean City, and we’ve got to protect it. But if this area ever goes out because of a hurricane, we should consider not building it back there.”
But those who have watched the sea claim their property understand the continuing pursuit of ways—economically sound or otherwise—to hold back the waves. Richard Seymour describes the scene of an impending hurricane in the Cayman Islands, where beachfront dwellers were filling garbage bags with sand. “Just black plastic garbage bags, and they tried to sandbag in front of their house. Well, of course the bags lasted about 30 seconds. People were throwing garden rocks out there and even pushing dirt from their garden out in front of the house, assuming that’s going to protect them from hurricane waves. It’s pretty sad. But I don’t know what you do when your house is going away. You don’t want to lose it, but you have no resources.”
Editor’s note: This article appeared in a previous edition of Erosion Control magazine and has been checked for accuracy.
Janice Kaspersen
Janice Kaspersen is the former editor of Erosion Control and Stormwater magazines.
