Pitfalls of Shoreline Stabilization

The Tweed River mouth on the Gold Coast of Queensland, Australia, has undergone extensive modification. Initial operations involved the construction of rock training walls to stabilise the river mouth and to maintain a deep navigation channel. These modifications interrupted the natural longshore transport and ebb tidal delta processes causing accretion on Letitia Spit and contributing to the erosion of southern Gold Coast beaches. In 2001 a sand bypassing system was built to mimic the natural longshore transport, pumping sand from Letitia Spit to southern Gold Coast beaches. Initial operations brought public concern over wide beach widths, however, the sand bypassing system has been highly successful in maintaining a deep navigation channel in the Tweed River entrance and delivering sand to southern Gold Coast beaches.

Ebb-tidal deltas or ebb shoals in moderate to high-energy environments often contain well-washed sandy sediments. These clean sands attract the attention of coastal engineers because they are commonly suitable for shore protection efforts such as beach renourishment (replenishment), dune restoration, and marsh remediation. Ebb-tidal deltas are sediment sinks where sandy materials are sequestered in deposits that can build up to such significant proportions that they form large coastal salients. In addition to sediments debouching from the inlet, longshore sediments are either trapped in the shoal or are bypassed in swash bars. Accumulation of sediments in these depocenters at the mouths of inlets often appear as a ready-made point borrow source that can be accessed for shore protection by dredging and placement on adjacent eroded shores. Ebb-tidal deltas are, however, in delicate balance with inlets, longshore drift, beach-dune systems and overall coastal stability. Removal of sediment volume by dredging from deltas interrupts the sand-sharing balance between inlets, ebb-tidal shoals, coupled beach-dune systems, wetlands, and shoreline stability.

The island of Puerto Rico is densely populated and heavily developed in some places, particularly along the shore and in coastal lowlands. Hard shoreline engineering is commonplace, even in low development density portions of the island. There are many examples of small trash revetments or cemented rock seawalls in front of individual buildings. In some cases, buildings themselves located within reach of waves and tides at the shoreline are behaving as seawalls too. Gabions have proliferated, even though they are decidedly not designed for either high-wave energy or salt-water usage.

Along the island’s approximately 500-km long shoreline, and not counting major port city developments, 48 shoreline stretches were identified where segments of the shore contained a seawall and an immediately adjacent sandy stretch. A comparison between beach width in front of the walls and beach width of the adjacent sandy stretch showed that the ratios of natural (unstabilized) dry beach widths to those of beaches in front of seawalls is between 2:1 and over 4:1, respectively. These data corroborate findings of Wright (The effect of hard stabilization on the sediment transport system along the shoreline of Puerto Rico. Unpublished Master's thesis, Duke University, Durham, NC, 200 p, 1989) and lend credence to the claim that seawalls actively influence narrowing of beaches. The fate of beaches along developed stretches of the shoreline is grim if efforts continue to concentrate on hard structures to armor the coast.

Mitigating, or adapting to, the impacts of environmental change on coastal landscapes, from both social and engineering perspectives, requires accurate baseline data that must be related to geomorphic processes. However, the inherent social and environmental dynamics of the coastal zone set up a contentious situation for decision makers and researchers because of the real, perceived, and stochastic nature of catastrophic threats to human life and property loss. Anecdotal accounts and first person observations generally propel the media and influence governmental policy far more effectively than scientific data. However, claims of extreme erosion rates are more adequately addressed through photogrammetric studies of erosion. Contrary to anecdotal accounts from Shishmaref, Alaska, sequential aerial photographs from 1950 to 2007 reveal that erosion has increased on the south-facing shores of the Chukchi Sea, while prior to 1977, erosion was higher on the north-facing shores such as Shishmaref. In addition, comparisons of property records indicate that high rates of erosion prevailed prior to 1950. Several engineering solutions were attempted in Shishmaref between 1983 and 2003, including gabions and cinder block/boulder/cobble revetments, leading to increased end-around erosion downdrift and an erosion rate twice that of undeveloped, unarmored shorelines. To adapt to heightened erosion rates, societies should either retreat from the shore or confront ever-increasing engineering costs.

Portballintrae has had a protracted history of human interference ranging from small-scale sand removal to hard coastal engineering. A small, horse shoe embayment and a once popular seaside destination on the north coast of Northern Ireland, it has suffered from progressive sediment loss over the last 116 years. From a once sediment-rich system, with a wide sandy beach, it now contains only a limited amount of sand draped over bedrock and/or gravel substrate and a relatively narrow beach. Installation of a pier in its western section is thought to have interrupted the natural hydrodynamics and set in motion a progressive longshore transport and removal of sand into deeper water. Successive hard engineering ‘solutions’ prompted through public pressure and engineers keen to do business, have been largely ineffective as they failed to address the root causes of erosion in this sediment-starved beach system.

Beach nourishment is a “soft” coastal erosion control strategy that involves the importation and emplacement of sand along dynamic shorelines in an attempt to stabilize and artificially maintain a minimum subaerial beach width. In the United States beaches are typically nourished to protect human economic development vulnerable to shoreline erosion/migration and coastal storms. While preferable to hard erosion control structures such as seawalls and groins, fiscal and economic issues have cast doubt on the efficacy of beach nourishment as an affordable, equitable and sustainable erosion response measure. Of particular concern are the delineation of costs and benefits, how costs and benefits are distributed and the possibility that storm damage reduction benefits – the economic force that drives nearly all beach nourishment projects – may never materialize. An accurate accounting of potential future costs must be combined with a pragmatic expectation of potential benefits before beach nourishment can be compared, let alone considered preferable, to non-traditional coastal erosion response measures such as retreat.

Coastal stabilization, mostly involving coastal dune cordon destruction, has been practised on the KwaZulu-Natal coast for the last two decades. During this time no major swells occurred. The last Lunar Nodal Cycle (LNC) tidal peak was associated with a series of unusually high swells. The temporal coincidence of exceptionally high tide and large swell led to catastrophic coastal erosion and underlined the folly of coastal stabilization, especially at reversing erosion hotspots, many of which are urbanized and defended. These locations remain at risk and will experience future erosion.

Fifty-five breakwaters were constructed in 1992 along Presque Isle, a 7 mile-long spit extending into Lake Erie, Pennsylvania. A US Army Corps of Engineers Project, the breakwaters have halted the minor erosion along much of the peninsula and a good swimming beach has been retained. On the other hand, sand was predicted to continue to flow behind the breakwaters and it has not. This has required annual bulldozing of around 30,000 cubic yards per year to remove tombolos. Preservation of Gull Point, a critical natural area at the tip of the peninsula was also an important element of the original design and environmental impact statement but it has suffered severe erosion because the breakwaters blocked the point’s sand supply. Engineering groups have declared the project to be a great success in spite of breakwater impacts on sand flow and the preservation of Gull Point. The Presque Isle project emphasizes the need for monitoring of project success or failure by independent groups.

Coastal armoring (defined as any structure designed to prevent shoreline retreat that interacts with wave run-up at some point of the year) has, historically, been a typical response to managing the problem of beach erosion on the island of Oahu, Hawaii. By limiting the ability of an eroding shoreline to migrate landward, coastal armoring on Oahu has contributed to narrowing and complete loss of many kilometers of beach. In this paper, changes in beach width are analyzed along all armored and unarmored beaches on the island using historical shoreline positions mapped from orthorectified aerial photographs from as early as the late 1920s. Over the period of study, average beach width decreased by 11%±4% and nearly all (95%) documented beach loss was fronting armored coasts. Among armored beach sections, 72% of beaches are degraded, which includes 43% narrowed (28% significantly) and 29% (8.6km) completely lost to erosion. Beaches fronting coastal armoring narrowed by −36%±5% or −0.10±0.03m/year, on average. In comparison, beach widths along unarmored coasts were relatively stable with slightly more than half (53%) of beaches experiencing any form of degradation. East and south Oahu have the highest proportion of armored coast (35% and 39%, respectively) and experienced the greatest percent of complete beach loss (14% and 12%, respectively). West and north coasts, with relatively little armoring (10% and 12% armored, respectively), experienced little complete beach loss (2% and 6%, respectively). However, beaches are still significantly narrowed compared to historical patterns on west and north coasts (61% and 70%, respectively). We find at these sites that cultivation of coastal vegetation may be a factor in beach narrowing on Oahu, along with beach erosion. Increased ‘flanking’ erosion (accelerated shoreline retreat adjacent to armored sections) is documented at several beaches, often requiring extension of armoring structures to protect abutting coastal properties, a process that leads to alongshore seawall proliferation.

A variety of patented approaches have been devised in efforts to halt shoreline erosion. Commonly termed ‘alternative’ or ‘innovative’ technologies, these are typically variations on the traditional approaches. A categorization of these approaches is presented that identifies devices placed in the water and devices placed on the beach. These categories are further subdivided. Despite their innovative nature and the claims of their inventors and promoters, these devices suffer from a variety of weaknesses when deployed in the real world. We present a non-exhaustive list of 110 devices for which US patents were awarded since 1970.

The view of success of ‘alternative’ devices often differs between reports made by the developer and those of the end-user and only in a few cases have objective assessments been made. Using a variety of sources we review experiences with artificial surfing reefs and beach drainage systems. We conclude that ‘alternative’ devices offer the same range of shortcomings as traditional shoreline stabilization approaches because of the inherent inability to control such a dynamic sedimentary environment and the failure to address the underlying causes of shoreline recession (sea level rise, sediment supply, other engineering structures, and the presence of infrastructure in the active coastal zone).

This case study from Sicily illustrates a common sequence of events where one unwise action was countered with another, which in turn created additional problems. The situation arose through strong political interference and ignorance (or lack of concern) regarding the environmental impacts of human interventions on the shoreline and by the public perception that government has a duty to protect private property. The poor design and location of ports and harbours produced infilling problems and huge updrift accretion with concomitant downdrift erosion. The human-induced coastal retreat was counteracted by the progressive emplacement of breakwaters creating a “domino” effect. On many occasions these were constructed to protect unplanned and illegal (in the sense that they do not conform to planning regulations) beachfront summer houses. Without the presence of these structures, there would have been no need for publicly funded intervention.

Furthermore, only a narrow coastal belt close to the shoreline is used by bathers on the wide beaches formed updrift of ports and harbours and in the lee of breakwaters, most of the accreted beach being unused or partially occupied by tourist developments. Thus beach users and municipalities acquired some benefits from beach accretion at specific sites, the opposite being true in eroding areas.

The assessment of failure or success in coastal stabilization depends on various factors. Most of the arguments for the implementation of coastal protection and/or stabilization rest on the need perceived by the local population, users and managers of a coastal stretch to stop shoreline recession or modify beach behaviour in some way. However, it is critical to establish at the onset of a process of beach stabilization what is the long-term trend of the beach system and, consider the long-term implications of maintaining any intervention in the coastal behaviour.

Costa del Sol in southern Spain is one of the most heavily developed coastal stretches in Europe (and the World) and is internationally renowned for attracting both mass- and high-income tourism. Annually more than nine million tourists visit the 100 km steep coastal segment, which supports a permanent population of over 1.2 million people. A significant proportion of the national economy is based (directly or indirectly) on tourism. Faced with threats to infrastructure from shoreline mobility, investing in coastal stabilization is the obvious response from the Public Administration, which is, by Law, responsible for the safe keeping of the shoreline and the Public maritime-terrestrial land around it.

The question considered here is: how healthy was the morphosedimentary system at the onset of mass tourism and how healthy is it now that up to 96% of some coastal council areas comprise consolidated urban land? When beaches began to suffer severe erosion in the 1970s, the question arose of whether to develop an alternative tourism economy based on golf courses and marinas or whether to try to stabilize and maintain a recreational beach system?

This paper provides an analysis of the environmental and socio-economic context and the sequence of shoreline stabilization approaches that have been applied but failed. Coastal stabilization techniques essentially attempt to stop nature from finding its equilibrium, but in Costa del Sol despite several major changes in strategy no approach has been successful.

Coastal defense in Portugal has a long history. The first attempts to resist coastal change date from early in the twentieth century, when the town of Espinho saw its most seaward streets damaged by wave impact. A coastal defense work (a “muralha”, or wall) was built. The 1980s saw the building of several groins at different locations in Portugal. The fight against the sea continued during subsequent years in a tentative effort to achieve an “artificially stable” coastal zone. Coastal retreat and thinning of beaches continued, especially downdrift of structures. The pattern has progressively revealed the inefficiency of efforts to stabilize the coastline. The underlying causes have not been addressed and indeed are poorly understood. Coastal defense is simply a temporary and palliative means of addressing the impacts of coastal erosion and, sometimes gives a false sense of security to coastal populations. In this chapter an overview of the NW Portuguese coastal defense structures is presented, their efficiency is discussed and some representative examples are described. Some recommendations are presented to create a more efficient coastal zone management policy.

The western shore of the Delaware Bay estuary is lined with low-profile fetch-limited barrier beaches. Prime Hook National Wildlife Refuge was established in 1963 to provide habitat to migratory waterfowl. Two study sites are adjacent to the refuge, Prime Hook Beach with a community of houses along the water and Fowler Beach, which is undeveloped. Construction in the region has impacted coastal hydrology and longshore sediment transport throughout the last century. After the 1962 nor’easter, soft stabilization and beach scraping became common. Scraping artificial dunes has also become a method of choice to isolate freshwater marshes from the bay. Both methods require frequent repetition as well as permits and lengthy planning processes. Benefits from this type of stabilization include an increase in recreational appeal, preservation of freshwater habitat and sustained property values for private landholders. Negative impacts of stabilization include overhead costs to taxpayers, degradation of natural habitat, loss of aesthetics of natural beaches, and continued public expectation of government intervention. As the threats of rising sea level and more frequent storms increase, beach overtopping and marsh inundation will become more frequent. Coastal development and infrastructure is at continued risk of flooding. Future management must take a long-term perspective on these realities and plan for the changing coastline.

Shoreline stabilisation in South Wales was driven by historical industrial development. Coal from the hinterland was brought to the shore, especially during the nineteenth century for use in metal industries that were located on the coast, and for export. At that time coastline impacts were not understood and development legacies have proven to be environmentally and financially expensive. Even when early in the twentieth century seawall and groyne impacts were recognised, coastal defence strategies still followed previous patterns. With industrial decline, economic regeneration has been supported by coastal location but unfortunately, lessons from the past have not been learned. Case studies show damage to new developments resulted from inappropriate infrastructure location, while undermined seawalls are now being protected by rock armour. This is becoming increasingly serious as there is little available funding to undertake effective remedial measures. It is concluded that new strategies which consider prevailing coastal processes are needed for long-term management; otherwise paving the shoreline may become more common on the Welsh coastline.

The expansion of coastal urban fronts, leisure ports and tourism in the course of the twentieth century has been the main driver of large-scale modification of the coastal zone in France. The development pressures generated by mass tourism and the economic boom of the 1960s have had their strongest effects in the Mediterranean, but pressures have also been important on the coast of Normandy and Picardy. In the Mediterranean, where large-scale planned development involving joint state and private capital ventures was implemented, this situation has, in many cases, exacerbated coastal instability, while endangering coastal ecosystems, and the growth of urban fronts has commonly led to a drastic reduction in beach width and to dune degradation. Coastal sediment budgets have also been seriously affected by updrift stabilization of cliffs and beaches, especially in Normandy and Picardy. In France, some of the causes of, and the responses to, shoreline destabilization have been essentially a matter of ‘hard’ engineering, for both historical and cultural reasons, although the situation has been changing over the past decade. A brief overview of shoreline stabilization procedures and structures highlights the overwhelming predominance of seawalls and groynes. Recent practices have tended to move closer to beach nourishment, which is gaining ground in France.

Four case studies briefly highlight the benefits and disbenefits of shoreline stabilization in France. These are: (1) a sandy city-front beach protected by breakwaters on the macrotidal southern North Sea coast downdrift of the large industrial port of Dunkirk, (2) the regularly renourished and heavily groyned gravel barrier of Cayeux in Picardy, the largest coastal gravel barrier in France, (3) a strongly eroding sector of the Rhône delta shoreline where various combinations of coastal stabilization projects have succeeded each other for over a century and a half, and (4) the regularly renourished gravel beach of Nice, on the French Riviera. These examples show that the emphasis on coastal stabilization at whatever cost that has underpinned coastal management practice needs to be reconsidered, as stabilization will become costlier in the future, as pressures from coastal development increase, as sea level rises and as sediment stocks diminish. Openings in this regard are coming from larger environmental awareness, the recognition of the failure or poor performance of many coastal stabilization projects, and the diversification of the actors involved in coastal management and planning. These developments are progressively generating a new logic of wider concert, on the basis of a more prospective, upfront and long-term approach to coastal management, instead of the logic of a ‘stabilization-only’ and a commonly one-shot immediate response to storm erosion problems that had tended to prevail in the past.