Living with the Puerto Rico Shore

Bush, Webb, Gonzalez Liboy, Hyman, Neal

The material presented in this section is taken from the book, but local photographs have been added from my files

Shoreline Stabilization: Trying to Stabilize the Unstable

The fundamental problem with constructing buildings, roads, utility supply lines, and supporting structures along the shoreline is that rigid, immobile structures are placed in a highly mobile environment. When the shoreline begins to change, as it is certain to do, we try to hold it in place through coastal engineering or shoreline "stabilization." Methods of stabilizing beaches and coasts range from planting dune grass and placing sand-trapping fences to constructing huge, costly, and complex seawalls and groins. Navigation safety, port development, and storm protection of urban areas are good reasons for trying to stabilize the coast; however, structures such as jetties may have negative impacts beyond the project area. Puerto Rico has only a few large coastal navigation projects (i.e., the ports of San Juan, Ponce, Arecibo, and Mayagüez ). On the other hand, shoreline stabilization has been undertaken at hundreds of sites in order to protect buildings. Some of these projects are temporarily successful; others are not. All are costly and require frequent maintenance.

The alarming truth is that a stiff price is paid for most types of shoreline stabilization. Adjacent recreational beaches are almost always lost or damaged when seawalls or other structures are built - The people of Puerto Rico must decide whether the protection of the private property of a few is worth the loss of their beaches. Consider the following examples.

The same pattern of accelerated beach erosion associated with engineering structures is repeated around the island. In the examples cited above, the first structure generated a need for additional structures. Many small structures around the island have had the same effect (i.e., seawalls in Puerto de Cerro Gordo, Joyuda , Punta Las Mareas, and countless other locations).

The Choices: Balancing Social, Economic, and Environmental Needs

A society living along an eroding shoreline has three basic management alternatives: Hard stabilization is the construction of "permanent" structures, such as seawalls, to hold the shore in place and protect upland property. Soft stabilization refers to shoreline maintenance by adding new sand to replace the eroding beach or planting vegetation to hold sediment in place. The goal is to protect property and maintain the economic and environmental value of the beach by working with natural processes rather than by confronting nature. Relocation, as the name implies, includes moving buildings back from their endangered locations when the time comes. Relocation may include a passive "do-nothing" alternative if the management strategy is to let buildings fall when their time comes or to demolish them before the sea takes them. A "before the fact" approach to shoreline construction requires all new structures to be set back from the shore. In the end, shoreline retreat dictates that one of the three choices noted above must be made.

Setback regulations are interim or temporary solutions to the erosion problem. Such laws require buildings to be set back a certain "safe" distance from the shoreline. That distance is usually determined by the natural rate of erosion. In North Carolina, oceanfront houses must be set back from the shore a distance that is 30 times the annual erosion rate, while larger multifamily buildings must be set back a distance 6o times the erosion rate. In Puerto Rico, this interim approach is based not on measured erosion rates but rather on the type of shoreline. In areas of sandy beaches, for example, buildings must be set back 20 meters.

Which Way to Go? Which Alternative to Choose?

All coastal states and communities face a shoreline management dilemma. The need for a wise and scientifically sound approach to management is magnified by the current accelerated rise in sea level just at a time when coastal development is intensifying at a record-breaking rate. Any management decision should take into account the needs and rights of future generations. Our grandchildren and great-grandchildren should have a beautiful Puerto Rico shoreline too! And, more practically speaking, the beaches are essential to today's economy.

Some states (i.e., Maine, North Carolina, and South Carolina) have declared an official policy of retreat that forbids hard walls. An erosion-threatened community must either move back or pump up (replenish) a new beach. Future generations will enjoy the beaches of these states. In contrast, areas that have opted for seawalls, such as northern New Jersey, have already lost a significant portion of their recreational beaches.

Hard Stabilization

Although numerous types and designs of hard stabilization structures exist, they can be grouped into two major categories: Detailed descriptions, line drawings, and photographs of the various types of hard stabilization structures can be found in the Shore Protection Manual

Shore-Parallel Structures

The seawall family. A wide variety of structures are referred to as seawalls, but a true seawall is a wood, steel, rock, or concrete structure separating land and water areas, designed to protect the land and buildings behind it from the impact of waves. Puerto Rico's shores are literally rimmed with sea-walls , as documented in recent studies.

Sandbags are often used as a temporary protective measure, but sandbag walls rarely have a foundation and are swept away by the first big storm.

Bulkheads are generally indistinguishable from seawalls to the eyes of the general public. Their primary stated purpose is to prevent the land from slumping or eroding into the sea. Bulkheads are commonly used in quiet-water areas such as lagoons, although they are also often located on the upper part of beaches (e.g., Ocean Park and Isla Verde). In storms, bulkheads and seawalls both reflect wave energy and cause increased wave turbulence and scour.

gabons are also used to construct seawalls and bulkheads in Puerto Rico; for example, in La Perla and Punta Las Marias in San Juan; in Aguada; and in Playa de Humacao on the east coast. A gabon seawall consists of rectangular rock-filled steel-wire mesh cages , or "blocks," piled one on top of another to form a wall. Although the wire is coated with plastic, the mesh inevitably rusts, the rocks spill out, and the wall disappears. The rocks strewn over the beach are a nuisance to beach strollers.

Revetments, perhaps the most common hard shoreline structures in Puerto Rico, consist of an armor facing of rocks or construction debris. Their role is to act as a buffer to the waves, like a seawall does. As a wave breaks on a revetment, much of the water contained in the wave is absorbed in the openings between the rocks, reducing erosion-causing backwash. On open-ocean, high-wave coasts, revetments are among the least expensive type of erosion protection; however, their design and construction require care. Revetments are often ugly structures because some people throw cans and kitchen sinks, among other things, along with rocks onto the beach. Proper revetment design requires carefully placed, heavy, resistant material that is properly angled and backed by filter cloth. Examples include much of the shore along Route 65--the coast from Punta Corozo to Punta Boca Juana. Storm waves can toss boulders about like toy blocks, and as far as most storms are concerned, the difference between a revetment and a seawall is negligible.

Seawalls are subject to tremendous hydraulic forces, which must be considered when designing a wall and choosing the construction materials. Walls should be constructed high enough to prevent storm-wave overtopping, but this requirement is usually not realistic economically. Walls also must be implanted deep enough in the beach to prevent scour (the removal of underwater material by waves and currents) and eventual undermining. In general, the maximum depth of expected scour is roughly equal to the highest-breaking wave at the site. Thus, maximum storm waves of meter require a footing depth of greater than meter in order to maintain support after scour has occurred. Some scour will still take place, but large rocks placed at the foot of the structure will help reduce it. Hurricane Hugo overtopped walls, destroyed property behind walls, and caused several walls to topple - The bottom line with seawalls is, "you get what you pay for." Puerto Rico's shoreline is littered with "low-cost" hard stabilization structures that do nothing more than give property owners a false sense of security. Gabon walls are cheaper than rock or concrete seawalls, but they are totally inappropriate for marine shorelines. A seawall needs to be tall enough to defeat wave overtopping and deep enough to be protected from piping, scour, and collapse. Piping is erosion caused by percolating water behind an engineering structure such as a seawall, bulkhead, or revetment. The water may be from groundwater, breaking and overtopping waves, rainfall runoff, or even water from lawn sprinklers. A well-designed seawall is likely to cost far more than the structures it is meant to protect.

A seawall or bulkhead protects only the land and buildings directly behind it. Thus, the ends of the wall should be joined to neighboring structures. If none exists, wing walls or tie-ins to the adjacent land must be built to prevent wave erosion on the flanks. Wing walls, also known as return walls, only delay the inevitable, however. In time, end effects will work on the flanks of the wall. That is, as the seawall sticks out along the eroding shore, the flanks will begin to concentrate wave energy and will experience erosion. This problem will continue to propagate along the shore over the course of many years. Flank erosion is particularly evident around the Empress Hotel in Isla Verde, where erosion around the seawall built on Punta el Medio resulted in beach erosion and property damage to the Playamar Condominium to the west and to the Hotel La Playa to the east.

Water and soil accumulate behind bulkheads and seawalls, and drainage must be provided to allow the water to escape from the landward side of the wall without carrying the backfill material with it. Backfilling with gravel and frequent openings (weep holes) along the lower part of the wall allow the water to escape. Walls also should be backed by filter cloth, a resistant mesh fabric that allows water to escape but prevents soil loss. Tie-backs, steel cables or rods that anchor the upper part of the wall to logs or other anchors embedded deep in the beach or bluff, add additional strength.

This very brief discussion of seawalls is intended only to illustrate some of the considerations of construction and to indicate why walls fail. A professional engineer should be consulted about design before any construction is started. Remember to ask the engineer bow much the wall maintenance will cost, how long the wall is guaranteed to last, how the wall will perform under typical hurricane conditions (to be expected during the wall's life), and what impact the wall will have on the adjacent property and beaches.

The Advantages and Disadvantages of Hard Stabilization Structures

A seawall doesn't absorb all of a wave's energy--some of that energy is reflected off the wall and scours and erodes the sediment in front of the wall. Some of the energy is refracted along the wall to adjacent unprotected property, where it is spent eroding the shore. Where wall-protected areas form mini-headlands, the waves may be refracted by the wall into the adjacent unwalled shore, where the erosive wave energy is concentrated. The reflection effect can be seen off beachless eolianite headlands. Climb to a safe and dry vantage point and watch a roller come in against the rock face. After the wave breaks with great force, a small wave will return seaward to trip the next incoming wave. You may also notice that the water moving seaward is brownish, laden with the sediment scoured from in front of the cliff. Seawalls work the same way, so it's no surprise that beaches narrow in front of walls and often disappear . A recent study of beach widths in front of seawalls in Puerto Rico clearly shows this relationship, and a study conducted along the eastern coast of the United States shows the same relationship along a much longer stretch of shoreline. Stroll along the shore of hotel-condominium row in San Juan and observe where the beach is narrow or missing--walls, bulkheads, or revetments will be obvious at the points of narrowing. Walk along the beach at Puerto Nuevo, a much smaller community but with similar walls and similar beach loss. Try to enjoy the beach at Aguada's Parque de Colon, but take care to step over the debris from the deteriorated gabon. The name of the community is of no consequence--the effects of seawalls are the same everywhere.

The immovable object has another significant consequence. Beaches often get part of their sediment from erosion of the land at the back of the beach. Walls cover up that source, starving the beach of its sediment supply either in the area of the wall or downdrift of the wall.

If beaches are the attraction, and if we build walls to protect property at the expense of the beaches, then we are killing the goose that lays the golden egg. Opting for seawalls sets in motion an economic commitment to maintain them. As such structures fail, bigger and "better" structures will be required as replacements.

Breakwaters

Breakwaters are structures specifically designed to block wave energy, thus sheltering a portion of the shoreline. They are usually, but not always, built parallel to the shore. Breaking the wave energy has the effect of interrupting or lessening the longshore transport of sand. The sand accumulates behind the structure, and the downdrift beaches starve.

Some major breakwaters in Puerto Rico include those at the La Concha Hotel in the Condado, Puerto Arecibo, Puerto del Rey Marina in Bahia Demajagua, and Playa El Tuque. The La Concha breakwater is significant in that the sand trapped behind it would have been lost from the beach system. Before the breakwater was built in 1970, La Concha was a site where the littoral transport of sand separated from the shore and continued moving northwestward into deeper water.

A unique breakwater was built for the Dorado Beach Hotel. The structure is a double overlapping breakwater that allows boats to enter and exit the harbor. The compartmentalized nature of the shoreline here prevents detrimental downdrift effects. Other novel breakwater designs are aesthetically more pleasing but function the same way.

Shore-Perpendicular Structures

Groins

Groins are low walls built perpendicular to the shoreline. They are designed to trap sediment flowing in the longshore current, and thus to rebuild an eroding beach. Made of rock, wood, concrete, or steel, groins are an attempt to retain sediment already on the beach or to retain the new sand placed there by nourishment projects. Groins are often, but not always, used in conjunction with seawalls. The problem with groins is that they trap sediment on one side but intensify erosion on the other, according to the net littoral drift direction. As is the case with breakwaters, groins also starve the downdrift beaches. In Puerto Rico, it is common to find piers and boat ramps blocking longshore drift. The construction of Mosquito Pier in Vieques resulted in several hundred meters of erosion on the downdrift side, and the boat ramp built on the public beach in Dorado has caused more than l0 meters of erosion on the western (down-drift) side. Many property owners have initiated lawsuits over increased erosion damage resulting from nearby groin construction.

Groins should be used only where there is a large supply of sand flowing along the beach and where no other "soft" or retreat alternatives exist. If no sand builds up, the groin is not doing its job. In big storms, waves can erode the sediment away from the landward end of groins, detaching them from the shore. Water and sediment can pass freely in back of the detached groins, rendering them ineffective. Beach replenishment sometimes is used in conjunction with groin construction to increase the life span of the beach.

Jetties

Strictly speaking, jetties are not designed to protect open-ocean shoreline property. Their purpose is to maintain harbor entrances and channel depth. Jetties confine flow within the channel and block sediment transport into the channel, thus minimizing the need for dredging. The sediment blockage also deprives downdrift beaches of needed sand while generating updrift shoreline accretion. Fortunately, Puerto Rico is blessed with natural harbors such as San Juan, Arecibo, Mayagüez , Boqueron, Guayanilla, and Ponce, and the need for jetties is small. The entrance to Boca de Cangrejos and Las Mareas has been stabilized with a small jetty that blocks the westward flow of sediment to Balneario Carolina, increasing the erosion problem there.

Avoid the "hard" line. All things considered, hard stabilization is a very costly means of combating erosion. The long-term costs will exceed property values, beaches will be lost, and erosion of adjacent properties will be accelerated.

Soft Stabilization

Beach Replenishment (Nourishment)

Eroded beaches can be artificially rebuilt with new sand to maintain their recreational value and protective role against storm waves. Beach replenishment is the "wave of the future" in a number of states, including Florida, North Carolina, and New Jersey. More than 100 beaches have been replenished on the East Coast since 1960. Miami Beach, the largest and most successful of these projects, cost around $5 million per mile of replenishment for 10.5 miles (ca. 17 kilometers) of beach. Replenished beaches maintain the recreational economy, provide storm protection, and provide a sediment source for the adjacent shoreline. In most cases, replenished beaches erode much faster than the natural beaches that preceded them. Replenished beaches on the East Coast, for example, rarely last more than five years, and the standard design parameters used to predict the durability of artificial beaches, such as grain size and beach length, have proven to be poor predictors. Storms and storm frequency seem to be the most important factors controlling beach durability. Most likely these generalizations also hold true for Puerto Rico.

Beach replenishment has not been used to any large extent in Puerto Rico, probably because there has been no widespread public recognition of a need to maintain beaches. After a replenishment program at El Tuque , erosion of the finer grained replenishment sand was very rapid. The usual response to an eroding beach or threatened house is to build a seawall or revetment. The average minimum cost of replenishing open beaches in the United States by pumping in offshore sand is $1 million per mile of shoreline. Because Puerto Rico's beaches often tend to be short and separated by headlands, smaller and less expensive nourishment projects might be possible. Sand could be pumped in from just offshore. This would be "robbing Peter to pay Paul," but it is preferable to shoreline hardening. The Puerto Rico Department of Natural Resources and the U.S. Geological Survey have looked for and identified sand resources outside the beach system, both onshore and offshore.

Dredging or pumping sand from offshore seems like a quick and simple solution to replace lost beach sand; however, such operations must be considered with great care. The offshore dredge hole may allow larger waves to attack the adjacent beach. Offshore sand may be finer in grain size, or it may have a carbonate composition that breaks up quickly under wave abrasion. In any of these cases, the new beach will erode faster than the original beach. Dredging may also create turbidity that will kill bottom organisms and damage protective reefs offshore. Loss of reefs means faster beach erosion as well as the more obvious loss of fish habitat.

Sand can be trucked in from inland sites, but this may be very expensive and it causes excessive wear and tear on local roads. Sand is a scarce resource, and beaches and dunes have been more frequently regarded as a source to be mined rather than as areas that need artificial replenishment. In fact, past beach and dune mining may be a principal cause of the present beach erosion. In some cases, gravel may be better for beach nourishment than sand, but the recreational value of beaches declines when gravel is substituted for sand.

Puerto Rico still has much to learn about nourishment projects. In i986, over 40,000 cubic meters of sand were trucked to a location near Pinones to construct an artificial dune. The dune disappeared in the first storm! The replenished beach at Playa E1 Tuque near Ponce had better luck. This beach seems to have excellent durability. Unfortunately, the dredged material deposited there is dark, and it makes an unpleasant contrast to the original light color of the beach. A different problem arose at El Tuque, where the construction of a groin to keep the sand in place lowered the wave energy so that silt now settles in the nearshore areas. Even the waves generated by minor storms stir up the silt. Locals consider the beach "dirty," resulting in lower recreational use than predicted for the post-nourishment period.

The western 200 meters of Cana Gorda Balneario have eroded up to 5 meters in the last 20 years. Many of the dressing rooms and showers built in the 1960's were lost to the encroaching sea. More than 9,000 cubic meters of sand have now been deposited on the beach, restoring it to its previous dimensions. The facilities for the island's recreational beaches are usually built too close to the shoreline and are damaged whenever big storms pass.

In addition to the finite sand supply, cost, and environmental impact in the borrow area, beach nourishment often disrupts turtle nesting. Sea turtles, which include threatened species, come ashore to lay their eggs in beaches, and beach construction projects must be limited to times when the turtles are not nesting (December-February).

Construction Setback

The most obvious way to avoid any hazard is to stay away from it. So it is with an eroding or shifting shoreline. The prudent planner will build well back from the shoreline or shore bluff, recognizing that some erosion is likely to occur over the years. Probably the best example of prudent construction setback in Puerto Rico is the community of Villa Palmira near Humacao on the east coast. The houses are set on the landward side of the road, which is behind a zone of vegetation, well back from the wide beach. The homeowners thus have the best of both worlds: a beautiful beach to enjoy and the security that it will be there for years to come.

How far back is a "safe" building setback? That question is difficult to answer and will vary from place to place. On the eastern coast of the United States, erosion rates are likely to be relatively uniform for long distances. Not so in Puerto Rico, whose irregular coastline results in irregularly distributed erosion rates. Thus, appropriate setbacks for buildings might vary significantly from place to place. A 1983 report suggests that a 60-meter setback will be a sufficient distance to protect structures on the northwest coast of Puerto Rico from wave attack during a great hurricane.

Setback of construction is also important along bluffed shorelines and sea cliffs. Average erosion rates or recession rates are somewhat meaningless in this case because large blocks of bluff may fall in a single event. Living near the edge of a sea cliff requires special precautions.

The builders of El Morro Fort at the entrance to San Juan Harbor didn't use--or need--much of a setback. They built a very sturdy structure on a high-elevation, rocky shoreline with an almost imperceptible erosion rate. Although a protective breakwater was recently added, the fort's 400-year history indicates that the Spanish knew what they were doing!

Relocation

When a building is threatened by erosion, the costs and benefits of moving the structure back from the shore must be weighed when considering the alternatives. Depending on the nature of the problem, relocation may prove to be economically and aesthetically better than the alternatives. Moving San Juan's oceanfront hotels out of harm's way may not be economically or geographically feasible, but relocation is a viable option for smaller buildings on much of the Puerto Rico shore.

The 1987 Upton-Jones Amendment to the National Flood Insurance Program (NFIP) provides owners of threatened buildings insured under the NFIP with up to 40 percent of the insured value of the building for relocation costs, if the building is moved before flooding. Basically, the law is saying that relocation is a more economical, more permanent, and more realistic way of dealing with long-term erosion problems. The federal government is willing to pay a little to help you move your house, instead of paying a lot to help you rebuild it. In the past, the rebuilt houses were destroyed in subsequent storms, and the insurance payment was used to rebuild in the same spot again... and again!

Advantages and Disadvantages of Relocating Beachfront Structures

Remember that the cost of moving back from the shore, although high, is likely to be a onetime expense, whereas hard and soft stabilization approaches will require repeated expenditures. When combined with the cost of ongoing maintenance, these latter "solutions" are generally more costly than relocation. In some cases, letting the sea claim a building when its time comes may be the most realistic solution, both economically and environmentally.

Summary

Many hotels and condominiums in Puerto Rico have concrete walls or piles of rock to "protect" them. The beaches in front of these walls are narrowing, and lack of a high-tide beach is a common phenomenon. Sometimes the beaches have retreated so far, or the walls were built out so far, that there is no longer a beach even at low tide.

So why don't we hear more people complaining about the loss of the beaches? After all, the millions of people who visit Puerto Rico don't plan to spend all their time in the casinos--they want to "hit the beach." But every year there is less and less beach to hit, particularly in the urban tourist hangouts. When beaches disappear or become polluted, tourists complain only once--and then go somewhere else (as the hotels fronting Rio de Janeiro's polluted beach have discovered).

Part of the answer lies in the fact that much of the construction on the shoreline in Puerto Rico was completed before we really understood what was happening--and before we really started to care. That is an unsatisfactory alibi, however, because beach-endangering construction at the shoreline continues. Rock revetments are built or added to every year in the San Juan area. If the construction-associated beach loss were restricted only to the areas of tourist hotels, it would not be so alarming. The problem, however, is associated with all shoreline construction, and all Puerto Ricans lose when their beaches disappear. So Puerto Rico's beaches, one of the island's most valuable natural resources, are disappearing. They are being degraded in many areas by unrestricted construction of shore-protection structures, and in other areas by sand mining, past and present. The beaches need help--from the public and from farsighted planners and developers--if they are to be available both today and tomorrow.

Truths of the Shoreline

Certain generalizations or "truths" about the shoreline can be drawn from events and experiences elsewhere in the world. These truths are equally evident to scientists who have studied the shoreline and to longtime coastal residents. As aids to safe and aesthetically pleasing shoreline development, they should be the fundamental basis of planning and development along the shoreline.