With sea levels rising, coastal landmasses have been placed on a collision course with Mother Nature. Worldwide, coastal regions are highly populated, and coastal real estate is very desirable and very costly. At the same time, severe coastal storm events have resulted in loss of life and destruction of coastal structures and land masses.
Sea level rise history is very clear, and scientists worldwide are in agreement that this trend will continue. Globally, sea levels rose approximately 10 inches from 1880 to 2011. And, alarmingly, the rates are accelerating. Along the East Coast of the United States, for example, current sea level rise estimates vary, with a range of 1 to 5 feet predicted by the year 2100. Such projections are, of course, not popular. In some cases, reactions have included outright denial. However, the scientific community is in agreement that sea level rise will continue to threaten vulnerable coastal landmasses.
Coastal erosion, of course, is a natural and ongoing process. Our coastlines themselves have been carved and shaped by erosion. In addition to sea level rise and storm events, our coastlines are shaped by tidal action, rivers and streams, long-term erosion, geology, and human land management practices and intervention.
Against this backdrop, coastal erosion control practices and technology have moved more and more to the forefront. The demand for solutions has increased dramatically. Traditional practices have in many cases been called into question. Hard-armor solutions such as sea walls, groins, and revetments have been employed to mitigate coastal erosion for centuries. Such solutions have proved very effective in many cases. Unfortunately, these hard-armor structures can accelerate erosion or interfere with natural littoral drift or sand movement.
Without a doubt, coastal erosion control practices have been heavily influenced by the low-impact development movement. For years, land was developed with no regard for the impact on adjacent property. When large land areas were paved and covered with other impervious surfaces, the predictable result was increased site runoff volume and negative impacts on downstream real estate. Low-impact development stresses the need for more responsible site development with a goal of limiting discharges to historic levels. This can be done and is being done.
In effect, today’s land developers are asked to do the opposite of what they did 50 years ago. Yesterday’s goal was to drain all sites as quickly as possible; today’s is to slow down offsite flows to minimize their negative downstream impacts.
Therefore, it is not surprising that the most effective and promising coastal erosion control practices and technological innovations attempt to work in harmony with nature and not against it.
Sand Dunes
In 1969, the late Ian McHarg published Design With Nature, a book that today remains extremely influential with land-use planners. Of particular note is a chapter in the book titled “Sea and Survival.” In that chapter, the author describes natural processes that occur along seashores and the importance of close observation and study of natural processes. In his opening remarks, McHarg points out, “The people of the Netherlands have been engaged with the sea for two millennia.” Ultimately, he shows that the historic Dutch dikes are flexible and effective because they mimic the performance of natural sand dunes. McHarg adds, simply, “In their long dialogue with the sea, the Dutch have learned that it cannot be stopped but merely directed or tempered, and so they have always selected flexible construction.”
Modern designers have taken note, and sand dune preservation and restoration efforts have accelerated.
In an article published in Land and Water magazine (March/April 2013) titled, “A Dune, a Dune! My Kingdom for a Dune,” author Bill Young discusses the impact of Superstorm Sandy (October 29-30, 2012) on the New Jersey coastline. He discusses the areas of devastation and contrasted them with less impacted locations, stating, “Some areas right in the impact area were left less damaged. Less loss of property, less damage from flooding. They lost power and had some downed trees. These protected areas had one thing in common: dunes.”
In Design With Nature, describing another devastating New Jersey coastal storm event, McHarg had some particularly harsh words regarding land-use practices that preceded the storm. In his words, “While all the principles are familiar to botanists and ecologists, this has no effect whatsoever upon the form of development. Houses are built upon dunes, grasses destroyed, dunes breached for beach access and housing; groundwater is withdrawn with little control, areas are paved, bay shore is filled and urbanized.”
Overall, dunes provide much more than just a line of defense against coastal flooding. They provide nesting areas for migrating birds and food and habitat for countless other plant and animal species. And, as Young points out in his article mentioned earlier, the relatively low cost of dune creation and maintenance is dwarfed by the cost of restoring and reconstructing infrastructure in unprotected areas.
Artificial Reefs
Just as dune creation and restoration mimics a natural process, the same can be said for the creation of artificial reefs. Reefs, which have been labeled the rainforests of the sea, perform a particularly important coastal erosion control function, acting as natural breakwaters. Protecting shorelines from wave action, and in particular from surges caused by severe storm events, these natural erosion control devices provide an important first line of defense.
Wave attenuation devices are manufactured products designed to create artificial reefs. Cast from high-strength concrete, the devices are deployed underwater and have proven extremely effective in accreting sand and in restoring or expanding beaches. Success stories are plentiful. Quite simply, as artificial reefs, the wave attenuation devices collide with tidal surges and slow them down, with waterborne sand being deposited behind the structures. In a 2009 application in Negril, Jamaica, a wave attenuation device array resulted in a 60-foot gain in beach depth just 39 days after installation.
During World War II, in preparation for the Allied invasion at Normandy, Winston Churchill became fascinated with the idea of creating an artificial harbor on the French coast. In his sweeping 12-volume history of World War II, Churchill spends considerable time discussing this idea. Knowing that all the established French ports would be heavily defended by the Germans, the British Prime Minister resolved to build such a harbor in Arromanches, France, just east of the Allied landing sites at Utah and Omaha beaches. All the components for these structures were manufactured in England and towed across the English Channel.
More than a dozen ships were sunk to provide a first line of defense. A second breakwater was created by sinking reinforced concrete shells. Floating piers and steel causeways were also added. The remains of these innovative structures, which provided the safe harbor the Allies sought, are still visible to this day.
Beyond wave mitigation, reefs provide shelter and refuge for wildlife, along with spawning and feeding areas. Although reefs cover less than 1% of the ocean floor, they support an estimated 25% of all marine life, an incredible statistic. Wave attenuation devices take on these same characteristics, quickly being colonized by a very diverse group of organisms, including crustaceans, mollusks, and sponges.
Marine Mattresses
Marine mattresses offer yet another new technology option. Constructed with high-strength geogrids and geotextiles, the mattresses are then filled with stone. Functionally, marine mattresses resemble gabions, which are three-dimensional wire structures filled with stone. The flexible geosynthetic component of marine mattresses allows for easier conformity to land contours and irregular subgrade conditions, especially when compared with wire products, which are at once more rigid and can corrode. The high-strength cells of the mattresses can be overtopped with beach sand and planted with native vegetation. In other applications, above the high-water mark, mattresses have been filled with a combination of stone and topsoil, seeded, and then protected by a high-strength turf reinforcement mat. In such systems the vegetation itself is anchored within the mattress, while its root-and-stem structure is protected by the three-dimensional turf reinforcement matting.
Gabions
Gabions, as described above, have been utilized for coastal stabilization. After the three-dimensional baskets are fabricated, they are filled with stone. As is the case of marine mattresses, gabions are flexible and flowable, two desirable characteristics. Their wire construction is a legitimate concern, and in any marine application PVC-coated wire should be used.
Coastal Bluff Restoration
Much of the world’s coastline is defined by rock bluffs and cliffs, and it is easy to assume that such coastlines are indestructible. While not as vulnerable as sandy beaches, rocky bluffs do in fact erode. In response, rock restoration technology has been developed. At Pebble Beach Golf Course in California, such techniques have been used to restore fragile rocky outcroppings. With concrete and steel at the core, these structures are shaped, sculpted, textured, and colored to blend with existing rock.
Coastal rock restoration is further complicated by the importance of working around the tides, understanding local geology and wave patterns, and working closely with the appropriate regulatory agencies. These factors, and others, make coastal erosion control planning and engineering extremely complex, regardless of the technology or practices being employed. Virtually everyone involved with coastal erosion control planning admits to mistakes and lessons learned. In one case, during a rock restoration effort along a beach, the designing engineer chose to specify a stair-step design. This design actually accelerated wave splash and made the problem much worse.
Coir Fiber Logs and Mats
Coir fiber products are very commonly used in coastal erosion control projects. Coir, or coconut fiber, is a very tough and slow-degrading natural fiber. Coir fiber logs and mats provide building materials that are at once dense, flexible, and long lasting. This technology has seen extensive use in states and regions that discourage or have even outlawed the use of hard-armor structures.
Eight years ago, a contractor in Massachusetts developed coir fiber mats in the form of very large envelopes. Dave Lager, president of Netco Construction Project Managers Inc., says his company has gone through many iterations of the product, based on field experience, installing more than 50,000 linear feet of coir envelopes in more than 100 coastal locations.
The envelopes have been used successfully throughout southern New England. In one case, they were deployed to protect an eroding beachfront on Plum Island, a beach community near Newburyport, MA, where a Thanksgiving 2008 storm at the site had caused the complete loss of a beachfront home. Once installed, the mattresses were covered with sand and planted with native beach grasses.
Coir logs and mats have gained strong traction as coastal erosion control tools, particularly in the northeastern United States. In particular, this approach is very popular in the Cape Cod Region of Massachusetts. Coir logs share many of the flexible structural characteristics of the practices the Dutch have employed for centuries in the dike construction described earlier.
Anchoring Systems
A growing number of anchoring devices have also been developed. Large screw- or auger-type metal products, known as helical anchors, provide deep penetration belowground. Likewise, another set of products, known as duckbill anchors, work similarly to drywall toggle bolts. These anchors, which have a swivel head attached to a stainless steel cable, are driven deeply into the ground and then pulled upward, setting the anchoring toggle deep below the surface.
Drift Fence
Drift fence has been used for years to capture windborne sand, and this practice continues to be employed quite commonly. Many who employ this practice recommend deploying the fencing in a zigzag configuration for maximum performance. The wavelike zigzag pattern creates more overall length and greater capacity for sand capture. Depending on the site requirements, drift fence can be installed in multiple tiers along the beachfront.
Some users manufacture their own drift fence; others use prefabricated material. Still others have used drift fence to gradually repair breaches in dune structures or even to build new dune structures in successive lifts.
Beach Nourishment
Beach nourishment has been practiced in the United States for approximately 100 years. The beach nourishment process, simply stated, is the replacement of eroded beach sand. By adding sand to beaches, the buffer zone between tidal forces and coastal structures is extended.
Often used in conjunction with other coastal erosion control measures, beach nourishment is almost always a repetitive process. By nature it lessens the impact of coastal erosion, but cannot mitigate its root causes.
Beach nourishment projects are at once complex and costly. Many factors can influence the effectiveness of these projects. First of all, the characteristics of the fill sand must match up as closely as possible with those of the existing sand. Fine sand, for example, when placed over course sand, will erode at an accelerated rate. Additionally, extensive geological research is essential before embarking on such projects. It is critical to understand the site-specific ocean currents and normal sand transport patterns. Normally, beaches hold much more sand underwater than above. The volume of sand, its location, and its relationship to water movement patterns can help coastal geologists predict the likely effectiveness of beach nourishment programs.
Popham Beach is located at the mouth of the Kennebec River in Phippsburg, ME. It is one of Maine’s most popular beaches, and it is also extremely fragile and unpredictable.
Emptying in the Gulf of Maine at this point, the Kennebec is approximately 170 miles long and drains an area of nearly 6,000 square miles. Erosive forces at Popham Beach are very complex. The river mouth is populated by a series of peninsulas and islands, and the smaller Morse River enters the beach area just west of the main beach.
The sands at the beach shift continuously, but up until a few years ago, the beach was left to nature’s forces. That changed after Hurricane Irene in 2011. Unprecedented erosion and a suddenly menacing change of direction by the main current of the Morse River threatened a nearly new bathhouse/restroom structure at the beach. The response was rapid, and by early December a very aggressive beach nourishment program blocked this new eastward surge by the river. As of late 2013, this solution had held up.
Geosynthetic Tubes
Geosynthetic tubes are produced when high-strength geotextile fabric is sewn and fabricated into tubelike structures. For beach applications, the tubes are normally filled with beach sand and deployed as barriers or seawalls.
The tubes can be used as a standalone revetment structure, but can also be effectively used as a submerged foundation for sand dune creation. From an aesthetic point of view, they are certainly not attractive. Worldwide, however, geosynthetic tubes have gained some traction as a structural best management practice.
Sea Walls, Jetties, Groins, and Breakwaters
Hard-armor structures have been used for centuries to slow down or mitigate coastal erosion. More recently, other materials have been used to construct hard coastal structures, with metal sheet piling walls serving as one example.
Sea walls and other coastal structures have been constructed along coastlines everywhere in the world. While effective in many cases, these practices have been called more and more into question.
We now understand that solving a problem in one location can simply transfer the problem elsewhere. A pair of jetties at a river mouth, for example, can cause disruption of normal seaborne sand flows. The jetty facing the normal flow will predictably intercept a large volume of sand. Whole beaches have been built that way. The negative side, or course, is that sand will become depleted on the down-flow side of such structures.
Many states have outlawed new hard structures of any kind. In almost all cases, existing structures have been grandfathered. Others allow such structures only under the most extreme of conditions.
The city of Saco, ME, has been battling severe erosion at Camp Ellis Beach for years. A proposal has been made to extend an existing sea wall and to embark on a beach nourishment program. The project comes with a very expensive price tag. The extended sea wall alone will cost tens of millions of dollars. Of even greater concern is that not everyone agrees this solution will produce positive long-term results. In many ways, the situation at this site underscores the heart of the problem: While erosion prevention itself is a most complex topic, coastal erosion protection takes that complexity to a much higher level.
Drainage and Soil Stabilization
Coastal erosion can be worsened by erosion control practices adjacent to the shoreline. In one example, Maine State Geologist Stephen Dickson described how a septic system installed on a coastal bluff actually “lubricated the bluff” and undoubtedly accelerated its eventual failure.
In general terms, drainage and soil stabilization are two very important issues that must be addressed before any erosion control system is installed. If problems caused poorly drained or unstable soils are not addressed correctly, failure is very predictable. In coastal applications, such considerations are that much more critical.
Hybrid Solutions
Hybrid solutions involve the use of multiple practices and technologies in combination. In many cases, hard armor can be used in combination with degradable materials. For example, in a coastal wetland restoration, degradable coir logs could be used alongside an artificial reef.
In a project completed last spring in Madison, CT, an existing sea wall along Long Island Sound was performing well, but the unreinforced vegetation above it had been ravaged by a series of coastal storms. An installation of turf reinforcement mats above the hard-armor wall solved the problem. The turf reinforcement mats allowed for the establishment of a strong stand or vegetation, while at the same time reinforcing the root-and-stem structure. This created a hybrid system far more resistant to wave impact and runoff from the property above.
Hybrid solutions offer project owners and designers the option to match site needs with a growing toolbox of both methods and materials. To use an old adage, “When the only tool you have is a hammer, everything starts to look like a nail after a while.”
Legal Implications
With expensive coastal properties at high risk in many areas, legal questions abound. Here are a just a few questions that are raised over and over again.
- When abandonment of coastal properties is mandated, who is responsible, and how are the owners compensated?
- If a manmade structure such as a groin or jetty causes damage to adjacent property, how is this issue fairly resolved?
- When a severe storm destroys access to coastal homes, who pays for new road construction or emergency access?
- Many homes have literally fallen into the sea. Do the owners have the right to seek compensation?
- When homes are allowed to be built in highly vulnerable areas, can public officials find a way to justify their actions?
These are all troublesome questions; they are only a brief sampling of issues that have already been litigated, and there is no end in sight.
Moving Forward
As we look to the future, it is important to be proactive. We must pay close attention the scientific facts, and we must react accordingly.
Hard decisions loom ahead, including abandonment of existing coastal properties and even the abandonment of whole coastal communities. These are difficult issues to face. We must embrace and examine all the technology and best management practices that have been developed, and innovation in these areas must continue.
Regulations are already toughening, and that has to continue. Many states have already made provisions for sea level rise with regard to new construction. Other unresolved issues will continue to be discussed, such as who should pay the cost of retreat and risk assessment. The risks to our environment and our infrastructure are high; the risks to human life are even higher.
Our government bodies and our regulators have an obligation to take a leading role in this area. They must communicate with each other and share their successes and their failures. Of paramount importance is that our government leaders must keep an open mind and resist “digging their feet into the sand” that is literally eroding around them.
Most of all, all groups and individuals concerned with coastal erosion should work together toward making the best possible decisions.
As Ian McHarg states brilliantly as he wraps up his “Sea and Survival” chapter in Design With Nature, “May it be that these simple ecological lessons will become known and incorporated into ordinance so that people can continue to enjoy the special delights of life by the sea.”
