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INTRODUCTION

Coastal engineering has a long history, as land/body of water barriers have been a global phenomenon. In the Mediterranean, harbour jetties/breakwaters were constructed by Egyptians, Phoenicians, Greeks, Etruscans, and Romans (Vitruvio, 30 BC). Petty inverse until Napoleonic times, when "mod coastal engineering" can be said to have begun (Franco and Verdesi, 1999). Just after this era, Sir John Rennie (1845, p. 24) wrote, "I may confidently ask, where can we find nobler or more than elevated pursuits than our own; whether it be to interpose a bulwark against the raging ocean." The barrier referred to was a seawall/breakwater, as "soft applied science", eastward.g., nourishment was not considered. Emphasising the seawall point, Bascom (1964, p. 243) in his archetype volume wrote, "If wave motility is arrested past any imposing barrier, a part at least of the free energy of the wave will be exerted confronting the barrier itself, and unless the latter is strong enough to resist the successive attacks of the waves, its destruction will ensure."

For centuries, littoral protection every bit a barrier (normally seawalls/groynes) against the sea has been necessary to counter erosional trends. A rising sea level is expected in the future, possibly upwardly to 0.98 m by the end of the 21st century (IPCC, 2014), which could result in more than frequent/severe weather condition events in some regions furthering a consistent increment in erosion/flooding (Church et al., 2013). Protection structures come at a loftier price, but generally the price paid for hard/soft technology usually balances out through time, although great variability can occur due to factors, e.one thousand., location, labour costs, electric current erosion rate. For example, construction + maintenance (€/chiliad coastline/twelvemonth) costs over 50 years: for direct rock groynes is €50–100; seawalls €fifty–300; shoreface nourishments (every five years) of €100–200 (with readily available sand); rock revetments €100–200; (Marchment, 2010).

Udovyk (2003, p. 377) made an apt comment to the concepts expressed in this paper:

Assessments of adaptation strategies for coastal zones take shifted emphasis away from difficult protection structures of shorelines (eastward.yard., seawalls, groynes) towards soft protection measures (e.g., beach nourishment), managed retreat, and enhanced resilience of biophysical and socio-economic systems in coastal regions.

Currently, three alternatives exist for stabilizing an eroding shoreline with sand/gravel beaches. Interventions stabilizing mud, stone cliffs, and rock platform coasts are not considered here.

• Difficult: stock-still location emplacement of a permanent/hard structure, e.1000., a seawall, groyne, which tends to preserve upland property and infrastructures.

• Soft: beach replenishment and/or dune reinforcement, used more and more in littoral management.

• Managed retreat: moving structures backwards along with body of water-level rise.

Notwithstanding, many organisations, e.grand., National Trust, U.K., take a philosophy of, "letting nature take its course," unless strategic structures/settlements are threatened. A combination of hard plus soft engineering science is too becoming increasingly popular, the erstwhile used to lessen engineering maintenance costs; the latter—visual impact reduction. As sand is a possible finite entity, "in the future, in lodge to have sustainable beaches and coasts, nosotros may need to optimize our coastal embankment fills with appropriate structures to reduce annual losses of sand and maintenance costs" (Magoon, Border, and Ewing, 2001, p. 34). Nevertheless, dredgers can now accomplish sand reserves previously unavailable, and information technology could be expected that even more sand volition become available, just this tin have negative impacts on the marine ecology (Erftemeijer and Lewis, 2006; Newel, Seiderer, and Hitchcock, 1998).

In this newspaper, advances and new developments in the design of coastal protection structures such as seawalls and groynes accept shown what has been learned since Rennie's (1845) comment together with tenets given in the early years of the concluding century, when a report past the Imperial Committee on Coast Erosion and Afforestation (RCCEA, 1911) was published on the state of U.Yard. coastal erosion/protection. In Table 1, quotes ane through four are central remarks from the study; quotes 5 through 16 are supplementary ones. The RCCEA (1911) report was written when U.Grand. was a world power. Since then and especially after Earth State of war II, coastal protection has go a global entity, and ideas no longer are the prerogative of any one nation. Hence, this newspaper gives examples exterior the realm of the U.Chiliad., as the authors of the 1911 study would today be well aware of the global nature of current research in this field.

Table ane.

Selected primal quotes from the RCCEA Report (1911).

BACKGROUND TO THE RCCEA (1911) REPORT

The attention of many early U.K. coastal practitioners was geared to what Bascom (1964, p. 1) one time asked, "is there anyone who can sentinel without fascination the struggle for supremacy between state and ocean?" Prior to 1911, published Ordnance Survey (OS) coastal surveys, e.g., 1870 and 1899, were just estimates at all-time, and there should be no reliance placed on coastal erosion figures given. Erosion figures recorded were patchy apart from areas where large swathes of country had been removed by storms (RCCEA, 1911, betoken 7).

Table 2 shows some estimates given by the RCCEA (1911) report—compare these with Table 3, which emphasises this comment. No similar early on measurements to that shown in Table 3 could exist found even after an exhaustive literature search. Notwithstanding, it was emphasized that, "the corporeality and rate of erosion . . . must be governed to a big extent by the nature and arrangement of the geological formations on the coast line" (RCCEA, 1911, point 132, p. twoscore), which is certainly valid today. Furthermore, "erosion at many places is aggravated by the erection of defences of the incorrect type. . . . And small isolated attempts at protection fail where larger schemes embracing a longer stretch of the coast would testify more effectual" (RCCEA, 1911, point 146, p. 141), again a valid electric current viewpoint.

Table 2.

Coastal gain/loss (ha) of the high/low water lines, mainly from ii.v cm to the one.6 km (6 inches to the mile) Os maps based on the RCCAE (1911) written report.

Tabular array 3.

Electric current coastal erosion and protection in the U.K. islands with a surface expanse smaller than 1 km² and inland shores (estuaries, fjords, trophy, lagoons), after Masselink and Russell (2008).

Mathews (1918) showed that the 56 km (35 miles) long Holderness coastline had exhibited serious erosion problems, some 1,900,000 tons of cliff cloth being eroded annually, and since 55 BC the amount lost related to ca. v.vi km (three.five miles) of coastal retreat. Equally an example, the Bridlington–Spurn Head section had the virtually serious erosion issues in Britain—2.7 g (3 yards) per annum from 1848 to 1893. Canton examples of loss were

• Yorkshire from 1858 to 1906: 313,000 ha (774,000 acres)

• Lancashire from 1842 to 1893: 221,000 ha (545,000 acres)

• Kent from 1858 to 1906: 213,000 ha (526,000 acres)

• Suffolk from 1879 to 1904: 210,000 ha (518,000 acres)

• Lincolnshire from 1833 to1905: 162,000 ha (400,000 acres)

• Very serious erosion existed at Cromer, Southwold, Lowestoft, Flamborough Head, Herne Bay, Beachy Head, Selsey Bill and the Dee Estuary (England and Wales), Solway Firth, Irvine, Croman (Scotland) and Kilmichael Bespeak, Wexford, Tralee, and Cork (Ireland).

The RCCEA (1911) report concluded that options for a sea defence appear to autumn conveniently into two distinct parts—either a hard (inflexible) seawall, or a soft (flexible) defence, both either with or without groynes. Seawall failure was deemed to be caused by a loss of mass in the section, deficient foundation depth, and want of efficient surface protection against the force of the falling water. Comments on the remarkable diversity of views held on the subject of erosion and its remedies were catholic in scope (RCCEA, 1911, p. 117). One such was that of an almost vertical seawall with a prominent molar, which, "at Hastings the class sent the majority of rising water outwards, a design feature being the weight higher up the projection" (RCCEA, 1911, p. 133; Effigy 1a).

Figure 1.

Erstwhile and new shore protection structures in U.K. (a) The Hastings seawall in the 1960s (East Sussex Library). (b) Seawall and groynes at Dimchurch, circa 1940s. (East Sussex Library). (c) Towyn, 1960s. (d) Towyn, 2015. (e) Groynes at Seaford, 1912 (East Sussex Library). (f) Seaford, electric current atmospheric condition (E Sussex Library).

Many examples were given of the fact that seawalls and groynes were interlinked, i.e. "In all works of bounding main defence, groyning is of the kickoff importance, and is necessary in nearly cases where a bounding main-wall or any kind of breastwork is built so that seawalls take little value unless accompanied past groynes" (RCCEA, 1911, p. 43; Effigy 1b). Grantham (RCCEA, 1911, p. 43) farther commented on this theme stating that seawall scour was recognised, in that "to build seawalls offset, and thus set up scour, and and then to protect them by groynes, was putting the cart before the horse."

RESULTS

Many examples of littoral protection can exist given, but the main thrust of the RCCEA (1911) report was on groynes and seawalls. Consequently this review newspaper has concentrated upon these two types of structures.

Bounding main Walls (RCCEA quotes 1 through 9, particularly 1 and 3)

These are built not only to protect settlements, industrial plants, roads, railways, and promenades from moving ridge attack and storm surge, just also to preclude low lying lands flooding. The classic Mathews (1918) book showed how well seawalls protected a coastline; nonetheless, the report (RCCEA, 1911, p. 136) commented that, "jetties were cheaper and preferable to seawalls." I century after, Kim (2015) wrote that seawalls and revetments create a hard engineered shoreline that can resist wave forces/storm surge action and provide hinterland evolution protection (Effigy 2a). It should be noted that erosion processes developing downdrift are ofttimes countered (especially in Mediterranean areas) by adding further engineering structures—the and so called "domino" effect (Anfuso, Martínez-del-Pozo, and Rangel-Buitrago, 2012).

Effigy 2.

Shore protection structures in use in RCCEA times. (a) 3 km long rubble-mound rock armour revetment, Buddon Ness, Scotland. Built 1992/3 by Ministry of Defence force to protect a war machine training expanse. Sand/beach interchange is now inhibited causing degraded dunes. Photo past Robert Westward. Duck. (b) Vertical masonry walls dating back to the 1800s at Pittenweem, Scotland. It has been repaired many times. Photo by Robert Due west. Duck. (c) Rock groynes (Rosslare, Ireland). (d) Wood permeable groyne (Kołobrzeg, Poland).

It is generally accepted that beaches experiencing erosion, e.yard., because of relative sea-level rise (or reduced sediment budget) and fronting a seawall, will eventually disappear, since they cannot adapt to the new ocean level. Coastline landward migration becomes impossible because of homo-made structures, and erosion processes related to sea-level rise together with increasing storminess can deepen nearshore areas fronting the structures causing complete disappearance of the beach/salt marsh, i.e. the littoral squeeze (Doody, 2004). The furnishings on beaches tend to be most sensitive to its surf zone position, embankment slope, and the reflection coefficient (Ruggero, 2009) which tin can be reduced with dissipative rubble-mound seawalls (Effigy 2a) or with complex structured profiles. If seawalls are built they should have the lowest possible reflectivity and highest possible permeability to drain groundwater from the landward side (Toyoshima, 1985).

More controversy exists on the seawall effect on beaches experiencing active erosion during episodic events, and each seawall construction produces an ongoing contend over its long/brusk-term effects. Van Rijn (1998) has given an overview of the physical processes and the seawall outcome on nearby hydrodynamics and morphology distinguishing betwixt two scouring types caused by a sea wall: toe and dune/beach scour at seawall ends. Several empirical formulas were presented to quantify these types of erosion mechanisms.

Seawalls do change onshore-offshore/longshore sediment movement. Allsop (2005) raised the following questions. "How and how much" exercise they impact transport processes? Are "effects beneficial/detrimental"? Do they "best serve public interest"? Dean (1987a) evaluated common assumptions in the calorie-free of engineering concepts, whilst a state of the art paper by Kraus and McDougal (1996) summarised findings of many workers concluding that the seawall/beach interaction is very complex, and seawall effects on beaches accept not been well documented, many statements beingness mere conjecture based on limited observations and quantitative information. Even up to the mid 1980s, viewpoints on seawalls were all the same unclear, i.e. "the effect of seawalls on beaches and on coastal processes has not been well documented" (Weggel, 1986, p. 29).

Basco (1999) and in particular Basco (2004), emphasised that there are many misconceptions behind the perception that seawalls increase erosion and destroy beaches. The latter argued that about negative effects attributed to seawalls take been proved wrong. Basco et al. (1997, p. 208) commented that:

…volume erosion rates are not higher in forepart of seawalls but seasonal sand volume variability in front end of walls is more often than not greater than at non-walled locations. Wintertime season waves elevate more sand offshore but summer swell waves pile more sand up against walls in beach rebuilding.

Colina et al. (2004) also showed that beaches with seawalls recover after storms, but later than natural beaches. Similarly Gabriel and Terich (2005) plant few differences between seawall backed and non–seawall backed beaches.

A completely different opinion was expressed past Bernatchez and Fraser (2012, p. 1559–1560) who, in two coastal sectors located in the Gulf of St. Lawrence, found that "hard cogitating defence structures built parallel to the declension contribute to the sediment deficit of beaches formerly backed by sandy coast" and that, "the rates of shoreline retreat were establish to be 3 to 5 times higher around the structures after they were implanted." Similarly, Romine and Fletcher (2012) plant that armouring on eroding coasts can atomic number 82 to embankment destruction.

So how much progress has been made since the statement of Mathews (1918), that seawalls neither promote accretion nor reduce any regional erosional trend of generally stabilising a contained area but non protecting the fronting/adjoining beaches? Embankment width reduction, and later disappearance, is due to the resilience reduction of the littoral system, which cannot accommodate to the new body of water level (or reduced sediment upkeep) with inland profile migration. In essence seawalls stand for shore protection structures and not beach protection structures—a very important distinction on an eroding coast.

Allsop et al. (1999) showed that seawall associated processes all relate to wall base of operations scour depth. All the same scour does not always take place (Kraus and McDougal, 1996), beingness a function of location and construction type. Carter, Monroe, and Guy (1986) also emphasised location, final that increased protection leads to narrower beaches. Runyon and Griggs (2003) showed that Californian armoured structures (18% of the total Californian beach area) reduce the sediment almanac supply by some 20%, simply stressed the uncertainties, every bit natural processes vary spatially and temporally. In a afterwards paper, Kinsman and Griggs (2010, p. 73) argued that, "shoreline orientation and blocking distance are the nigh of import factors contributing to sand retentivity success based on the impermeable structures nowadays along California'south coastline today." Their findings suggested that seawall removal to increase sediment supply did non have significant impacts on the normal coastal budget.

Toe scouring is the major concern with vertical structures, so much then that in 1906 the Porthcawl seawall, U.K., had eroded to its toe; in 1982 a tar macadam ramp was superimposed on fronting cobbles (Figure 3a) and has been a resounding success, equally waves now break some thirty m from the seawall (Blott et al., 2013). Today, there exists a variety of blueprint shapes for these walls, all designed to excerpt wave energy and protect the toe, which in plough protects landward infrastructures. Blueprint is oftentimes focused on certain parameter values, due east.g., p _max for touch pressure and V _max every bit maximum overtopping wave volume. A structure tin can so be designed using the proper fractional safety factors, or with a full probabilistic arroyo (van der Meer, 2015), e.k., slope breaks in the physical seawall profile, inserting prominent elements to increment roughness, and using perforated elements discharging water in an underlying permeable core.

Figure iii.

Shore protection projects in use today. (a) Seawall and tar macadam ramp (Porthcawl, Wales). (b) Groyne with a crest walkway (Cecina, Italy). (c) Low-crested breakwaters (Emilia-Romagna declension, Italy). (d) Beach nourishment with "rainbowing" (Tuscany declension, Italy).

In 2010, a serial of papers appeared in Shore and Beach, giving examples of the structural response to erosion, and a salutary idea is that:

…many of u.s.a. have recognised for many decades that both natural and engineered structures play a crucial function in maintaining embankment width where there would exist less or no beach without them, . . . to say that all structures on the coast are "bad" is, well structurally deficient, and downright wrong (Picture show, 2010, p. ii).

This echoes the codification elements of coastal hazards, seawalls, and coastline natural character adopted by New Zealand, where they are function of a "package" of responses focused on a long-term sustainable event, where policies allow seawalls merely where they are the all-time (as compared with nourishment) time to come practicable option (Jacobson, 2004).

Groynes (RCCEA quotes i through 4, particularly 2 and 4, and quotes x through 16)

Quotes two–four relate to techniques that are "an erstwhile and intuitive ways of reducing embankment erosion and are establish forth the coast worldwide as both engineered and nonengineered, ad hoc structures" (Kraus and Kelly, 2004, p. i). The possibility of using whatsoever kind of cloth, wood, rock (Figure 2c), bricks, steel sheet pile, geocontainers, precast elements, etc. and apparent ease of pattern make them one of the most widespread and oldest shore protection structures (Traynum, Kana, and Simms, 2010). The RCCEA (1911) documents groynes at Spur Head (Yorkshire, U.K.) in 1850, but European groynes are very one-time, i.e. at Texel, the Netherlands, "beginning in the early 17th century, the kickoff defensive works such every bit wooden groynes and underwater willow mattresses were placed on the southern embankment to retard the erosion and to protect the toe of the dikes" (Elias and van der Spek, 2006, p. 12). Mathews (1918) showed how many different groyne types were in existence, e.grand., loftier/low timber, concrete block, Owens-Example reinforced concrete, adaptable/flexible, the RCCEA (1911, p. 136) adding "that low groynes gave meliorate results than high groynes." Today, groynes extend laterally for kilometres in many countries, e.one thousand., Italy, where more than 200 elements "should" defend twenty km of Puglian declension.

Groynes should generally not be considered the most advisable shore protection method along low/moderate erosion charge per unit beaches (Traynum, Kana, and Simms, 2010)—the dictum followed in 1911. The basic groyne introduction effect is nearshore longshore sediment ship (LST) reduction, triggering upcoast expansion with a consistent limited feeding effect on downdrift sectors. Walter and Douglass (2011, iii) argued that downdrift effects may be minimal or naught where, "net littoral migrate is small and littoral drift is not dominant in 1 management or the shoreline is dominated past adjacent headlands or other construction." Groynes are seemingly most successful where internet LST is substantial (Everts and Eldon, 2011). In mixed sediment beaches, groynes trap coarse material in updrift cells, allowing effectively grains to overpass groyne tips so feeding downdrift segments (Cipriani and Pranzini, 1990).

A dictum is that upcoast filled beach size is a function of effective groyne length, spacing, tip alignment, sediment size, and relative angle betwixt incoming waves and coastal orientation determining the net/gross send rates, with fillet gradient increasing with the sediment size independent within embankment (Everts and Eldon, 2011). French (2001, p. 76) suggested extending groynes for, "40–60% of the width of the surf zone in order to interrupt enough sediment for beach accumulation, but permit sufficient to keep downdrift to minimize the impact of sediment starvation." Design criteria more often than not differ betwixt permeable/nonpermeable groynes. Suggested groyne spacing/groyne length values have varied from 1:one.5 to one:5 (Silvester and Hsu, 1993). Permeable groynes (Figure 2d) should have a length slightly larger than surf zone width, and spacing should be equal to their length (Trampenau, Oumeraci, and Dette, 2004). Impermeable groynes generally have a groyne spacing (Due south) betwixt one.5 and 3 times the groyne length (Van Rijn, 2011), and the effectiveness of these dimensions has been confirmed by wave bowl experimental research (Özölçer et al., 2006). To promote sufficient sand bypassing, groyne length should exist smaller than storm surf zone width. These studies were non exactly conflicting in 1911, but the prevailing viewpoint was width equal to length, and extent from shore to depression water spring tide position.

Groyne lengths have been classified as long (overpassing the breaker line) and brusk (staying within), and equally the bulk of LST occurs between the shoreline and breaker line, long groynes trap about all the sediment flux and are effective simply trigger stronger erosion on the downcoast beach segment. This was known in 1911, but perhaps not on a theoretical level. In the U.K., many such examples of long groyne fields exist, e.thousand., Lancing, where in 2006 an £18 million scheme for iv.3 km of coast constructed 44 rock groynes (160,000 tonnes) to replace 34 original timber ones with additional wooden ones in betwixt. A more recent example is the $xi million coastal protection structures at Towyn, Wales, U.One thousand., involving a seawall and extensive groyne series, advisedly chosen with respect to length, spacing etc., every bit over the last 100 years, the beach width had decreased and its level dropped by up to 3 m (Effigy 3d; Atkins, 2009).

At nowadays, T, Γ (gamma), Y groynes, or fishtail groynes, oft with a submerged appendix, are common, simply they were essentially unknown in 1911. For example, as role of a £36 million coastal defence force scheme funded by the U.Chiliad. Surround Agency and Essex County Council, 23 new fishtail rock armour groynes, 90 g in the length and with a 220 m altitude between groynes, are currently being installed. These groyne types tin be designed forth very exposed, eroding coasts to reduce wave energy into the compartments preventing/diminishing rip current generation nearly groyne heads (Van Rijn, 2011). For T-groynes to farther accrete, caput length should be equally long every bit possible, resulting in more expensive construction; therefore, cost–benefit analyses is required, but, "in order to reach more than reliable conclusions, more field information are necessary!" (Özölçer et al., 2006, p. 402).

Other configurations have been developed to increase containment efficiency, with structures curving more or less sharply to the updrift direction, eastward.g., bayonet groynes whose construction started at Marina di Pisa in 1913. Groyne orientation research, mentioned in the 1911 report, is an area that has been studied intensively in the past century. In 1911 groynes were substantially normal to the embankment, and it was far sighted of the 1911 report authors to claiming this viewpoint. Currently, oblique groynes have been used to reduce scouring at their heel (root), with an bending suggested to be equal to that of the strongest wave's crests, which, when combined with nourishment, reduces down coast erosion (Donohue, Bocamazo, and Dvorak, 2004). Reflection on oblique groins tin be used to reshape a embankment following specific needs, e.1000., an oblique (20°) steel sheet pile constructed at Elba Island (Italian republic) pocket beach prevented longshore sediment transport silting a marina (Farrell, Pranzini, and Steinhardt, 2003).

Groynes have fallen out of favour, since they do not always attain their objectives and may exacerbate erosion issues (Short, 1991), and in this context an interesting ascertainment was that of Bruun (1953, p. 68), "in many cases it would probably have been improve if groynes had never been constructed, because they have done more harm than practiced," and a sound example of this comment is the Seaford groyne system (Figure 1e). In 1987, groynes were eliminated and a major beach recharge project was formulated using seabed shingle. Apart from the final groyne at Splash Bespeak (foreground of Figure 1f) no groynes terminate longshore drift, and each year lorries take accumulated shingle from the groyne westwards to replenish the beach.

The long groyne northern Tuscany coast sequence, built to counteract erosion in the 1970s–1980s, triggering or increasing erosion exemplifies this point. Shabica et al. (2004) gave an opposite viewpoint of a groyne field located well inside a Lake Michigan surf zone, finding no long-term downdrift effects. Positive results were attained at isolated groynes at East Hampton, New York, U.s.A., where the gross longshore send was far larger than the cyberspace one: aggregating on both groyne sides made the structures behave like headlands creating crenulated shorelines on both sides (Bokuniewicz, 2004). Some U.S. coastal states have even enacted stringent coastal zone management guidelines that severely restrict, or prohibit, groyne construction, e.g., South Carolina. Groyne fields take even been removed—virtually unheard of in 1911, e.g., at Sandy Hook, New Jersey, U.S.A., due to its dandy affect on downdrift coastal sectors (Nordstrom and Allen, 1980).

A further consideration concerns stakeholders' acceptance, not taken into account past the RCCEA (1911), merely pertinent for the 21st century. Gòmez-Pina (2004) argued that their unattractive aspect makes them unpopular, and special care must be paid to their aesthetics, merely Williams et al. (2005) showed that beach users really liked them. Today, modern groynes are frequently built with a crest walkway to allow piece of cake, nondangerous access, transforming defence structures into promenades (Figure 3b); that was unheard of in 1911 when they were simply coastal protection structures. Additionally, the RCCEA (1911) report was a study of the U.K. coast's geomorphology and protection measures in place, so no consideration was given to groyne rip electric current formation (Short and Masselink, 1999). Rips are of not bad concern today, not only for the sediment loss (Silvester and Hsu, 1993), but likewise for beach safety bug (Leatherman, 2013).

For centuries, in parallel with traditional rock groynes, wood permeable groynes were used (Figure 2nd), but now are considered a "soft" groyne version. They slow down longshore currents, favouring sediment deposition without offshore deflection. Updrift top occurs at all groynes, and scouring, indicating a current velocity increase, is invariably present at the tip (Trampenau, Oumeraci, and Dette, 2004). Nevertheless, permeable groyne adoption remains express to its origin area, with few Mediterranean but many U.M. applications, e.g., 89 permeable between Trimingham and Happisburgh (13.six km).

Discussion

The above has given a spine to the findings relating to seawalls/groynes. Within the past 100 years, there has been a mushrooming of innovative techniques relating to coastal protection that was unheard of in 1911. Stepped seawalls had been introduced, only physical/numerical modelling, all-encompassing monitoring, reefballs, geotextiles, etc. now appear to be mandatory considerations for many coastal protection projects. Similarly, the basis of 1911 littoral protection was the safety of coastal settlements and roads, now aesthetics too plays an important function.

The Main Differences

If RCCEA members could visit the coast today, they could encounter many differences regarding coastal structures; the most evident being the textile used: once natural rocks were prevalent (except in seawalls where concrete was increasingly used, although often covered by rocks), at present concrete precast elements of unlike shape are frequent (dolos, tetrapods, accropods, etc.), but behind this sounder differences be. 2 of the main differences between groyne and seawall research within the last century have undoubtedly been laboratory testing and explicit field studies. A third, based on new concepts and techniques, is dealt with later in this newspaper. Today, engineers, developers, and littoral planners need qualitative/quantitative descriptions and models of seawall effects on coastal environments in order to brand intelligent decisions about when/where protection structures are appropriate.

Early laboratory seawall testing studies were conducted during World War Ii, e.1000., Dorland (1940), concluding that the main wave activity force did not necessarily crusade seawall base of operations scour but placed material in suspension and removal by currents. This is as true today as when first written, but a scaling problem existed in these early experiments. Sawaragi and Kawasaki (1960) found the maximum scour depth is approximately equal to the incident (deep water) moving ridge height. Xie (1985) showed that for fine sediments, maximum scour was at standing wave system nodes in front of the seawall, where velocities are highest. For coarse sediments, maximum scour was between node and antinode, but different scouring patterns were found for regular and irregular waves. Sato et al. (2014) from physical and numerical studies showed that some deposition tin can occur in front of a seawall.

A deficiency in nigh field studies was an absence of description of concurrent changes in waves, currents, etc. through storms, which obscures relationships between crusade and event on embankment changes and equilibrium profile development. If a beach profile is close to equilibrium, storm inflow may result in no change or erosion—Dean's (1991) approximate principle. Nonetheless, most profiling depths are not unremarkably taken to the depth of closure (Phillips and Williams, 2007), so erosion/deposition refers mainly to the visible embankment and not to the total active profile. Found and Griggs (1992, p. 183) showed that in mild conditions, pocket-sized furnishings occurred simply concluded "that increasing wave energy would increase the differences in responses between natural beaches and those protected by seawalls."

Protection emphasis was put on groynes in the RCCEA (1911) report, but since then a lot of water has passed nether the span, only basic questions remain. The deviation today is that based on many built and monitored structures and the availability of sophisticated physical/numerical models, answers are no longer based only on experience but also on a audio theoretical basis. Notwithstanding, the coastal organisation variables and the structures themselves are so big that, like to other defence devices, a comprehensive solution of all aspects is still not possible, e.g., "Few quantitative studies of groyne performance accept been conducted. . . . little field monitoring has been done. Nearly moveable concrete models were performed at pocket-sized scale and may not exist reliable in all aspects" (Wang and Kraus, 2004, p. 342). By century studies on permeable groyne efficiency, wave tank experiments, and numerical models take resulted in "design criteria and guidance for groyne length and permeability, pile depth and spacing, and groyne field characteristics such equally multiple groynes and spacing versus double width groynes" (Poff et al., 2001, p. 238). In this fashion an onetime intuitive structure has been elevated to the condition of a scientifically based device after one century.

What definitely has changed from 1911 to the present is seawall design. Their evolution was driven past the need to reduce seawall height, e.g., from a cost or landscape impact viewpoint, but maintaining efficiency in shore protection, prevention overtopping, and reduction of backwash toe velocity to limit scouring. This is the rationale for the different seawall profiles resulting from numerical equations and physical studies that continue today (Anand, Sundar, and Sannasiraj, 2011). All the same, "Results from the use of these equations are very approximate at best. If determination of overtopping rates is important in coastal projection design, considerations should exist given to the deport of model studies" (Sorensen, 2010, p. 237). Enquiry (both laboratory and field) in the area of wave run upwardly and overtopping has been exhaustively documented by, amongst others, van der Meer et al. (2006), Hoffmans et al. (2008), van der Meer (2011, 2015), and Le Hai Trung et al. (2010).

The Societal Debate

Whether hard stabilisation is worth the price is still an ongoing contend. Price and technological solution sustainability are critical factors, as seawall toll effectiveness in social club to protect coastlines is at present being questioned (Cipriani, Pelliccia, and Pranzini, 1999; Wiegel, 2002). In that location is also an issue of toll/benefit timeframes—the immediate problem of private property falling into the bounding main is easily seen, but the long-term effects of seawalls on public property are less tangible. In communities facing imminent littoral run a risk threats that directly affect beachfront residents, local councils tend to focus on the false economy of an immediate "quick prepare" (commonly a seawall) that looks reassuringly solid and is idea to protect threatened individual property, remove liability claims, etc. (Jacobson, 2004). For example, over the past 25 years erosion has claimed some 405 ha (1,000 acres) of barrier isle in Due south Carolina, UsaA. In 2014, the Due south Carolina Firm Natural Resources and Agriculture commission voted 17:1 to accelerate a bill allowing Debordieu Beach, Pawleys Island community to reconstruct the one-time relict seawall despite a 26-yr-old statewide ban on seawall building (Fretwell, 2014).

Sometimes, a seawall is an accented necessity, especially in coastal urban centres, e.g., the stepped seawalls of Rhyl, Wales, and the recent aforementioned $11 million seawall and groyne construction, Towyn, Wales (Figure 1d). These are practiced examples of modern littoral protection. When RCCEA (1911) was written, well-nigh seawalls were simply an most vertical wall or stepped, although some more sophisticated structures did be in U.Yard., such as the Hastings seawall (Effigy 1a).

In his 1987 paper, Dean (1987b) commented on the fact that whilst "passive" erosion—erosion which would occur without the seawall—can occur; "agile" erosion—associated with erosion acquired by the seawall—does not, and is widely quoted to favour hard structures in recreational areas. A key point is whether any seawall is partially or fully exposed to waves, and it is prudent to remember that "the best gauge of the probable success or environmental impact of coastal engineering . . . is the historical experience on that beach" (Cooper and Pilkey, 2004, p. 642). On this score, it is a salutary thought that at i of the nigh iconic and historic places in the U.South.A.—Jamestown, Virginia—"if it hadn't been for Colonel Yonge's sturdy rock and concrete bulwark that has withstood the erosive waters of the James for a century, there would be no reason to visit Jamestown at all" (Tucker, 2002, p. B3). The Association for the Preservation of Virginia Antiquities has a plaque there that reads:

Col. Samuel H. Yonge (1843–1935) designed and built, during the early years of the 20th century, the stone and physical seawall at Jamestown that successfully stopped the erosion of the celebrated island, thereby preserving it for posterity.

Some Innovative Concepts and Schemes for Littoral Protection, mail service 1911

Several new concepts and schemes have been developed since RCCEA (1911), and some older concepts have been adjusted/improved to address new societal and environmental requirements not considered 100 years ago, e.g., a larger attention to aesthetics and its impact on the surrounding landscape; reduction of possible impact on water quality and local hydrodynamic atmospheric condition (e.chiliad., for swimmer safety); and attending to long-term and large-scale issues (east.g., ocean-level rise). There is now a deeper ecological sensation that motivates coastal engineers to blueprint coastal structures following a "Edifice with Nature" principle. Other examples are oyster reefs or the employ of plants as nearshore wave reductors (Cheong et al., 2013). These concepts are nothing else than a newer version of the old sea-wall and breakwater schemes in that the principles of wave energy dissipation are substantially the same despite reefs/vegetation being used rather than concrete. The premise of using engineering structures to raise biological/ecological multifariousness is very unlike from traditional Victorian approaches to coastal protection.

Firth et al. (2014) reported on work carried out on the design of coastal defense force structures in the THESEUS project (2009–2014), which aimed to conserve/restore native species diversity. They manipulated biodiversity on defence structures through various interventions, eastward.one thousand., bogus rock pools, pits and crevices on breakwaters; tested the utilize of various rock sizes in gabions; used a precast habitat enhancement unit of measurement; gardened native habitat-forming species, e.thou., threatened canopy-forming algae on littoral defence structures. Strong evidence exists that physical structures are poor surrogates for natural rocky shores, often supporting assemblages with lower species affluence and diversity (Coombes et al., 2015). Their findings indicated that texture had a significant effect on colonisation. Smoothed tiles supported significantly fewer numbers of barnacles; intermediate roughness (grooved concrete) supported significantly greater numbers. Early on colonists, e.m., barnacles on marine physical, are helped by manipulating surface heterogeneity at a millimetre scale.

Submerged breakwaters, which reduce a structure's visual touch, are at present often used instead of standard breakwater schemes. Recirculation and water quality tin can also improve when these structures are replaced. These come in many formats interim as sills to retain sand and take had mixed reactions, due east.k., Beachsaver reef^TM, Double T-sill (Basco, 2008; Morang, Waters, and Stauble, 2014). In Tuscany and Emilia-Romagna (Italia) a number of quondam high-crested breakwaters have been lowered and combined with nourishments and monitored for a 10-year time window (Preti et al., 2011; Figure 3c). The experiment was successful (i.e. lower visual impact, improvement of water and seabed quality, beach widening), although costs increased due to nourishment maintenance. Yet, design of submerged structures is a more circuitous task than for standard structures. Therefore, numerical (and mayhap physical) modelling usage is really required (run across next section). An experimental submerged breakwater project at Palm Beach (Florida, United states of americaA.) showed that when no proper preconstruction particular studies were carried out, then structures tin can lead to increased erosion due to longshore current formation—developed because lesser currents cannot overpass the reef—behind the structure. Here volumetric erosion rates doubled after construction, and the experiment was concluded with the structure's terminal removal (Dean, Chen, and Browder, 1997).

Macro tides have significant impacts on sediment ship processes, especially on high-crested breakwaters producing larger yearly changes, whilst low crested ones form salients and embayments at a much reduced rate (Pan et al., 2010). Wave overtopping has a pregnant touch on on waves and currents in these embayments (van der Meer, 2011). The near successful sustainable beaches on sediment starved coasts can exist associated with nearshore attached breakwaters, where the beaches are filled with sand before mitigation (Pan et al., 2010).

Submerged groynes not mentioned in the 1911 report are recent and present only in the Mediterranean. Those rooted to the dry embankment, frequently with a buried segment, enter the sea at the swash zone and run offshore with a one–2 k high crest (Berriolo and Sirito, 1973). built with rocks, concrete precast elements, sand bags or geocontainers filled with sand or physical, they trap sediments moving longshore, triggering updrift side ramp formation. Sediments are deposited downdrift due to electric current velocity reduction after passing the groyne crest. Postconstruction beach monitoring and numerical model runs showed tip structure scouring equally in permeable groins (Aminti et al., 2004).

A littoral applied science exercise little known in Britain at the fourth dimension of RCCEA (1911) was large-scale nourishments (Figure 3d), and a sound account of the European experience is given past Hanson, Brampton, and Capobianco (2002). Increasing ecology awareness together with contempo predicted body of water-level rising scenarios has also led to upscaling of standard nourishment volumes, an farthermost example being the "Sand Engine," in southern Holland (Stive et al., 2013). This mega-nourishment has a sand book of approximately 21.5 one thousand thousand m³, and avant-garde monitoring and modelling techniques were crucial for its design. Figure 4 shows how much soft engineering has largely replaced hard engineering, and this is also exemplified in the literature (Figure 5).

Effigy 4.

Shift from hard to soft engineering science alternatives past the U.Due south. Army Corps of Engineers (from Hillyer, 1996).

Effigy 5.

Difficult engineering vs. embankment nourishment: the contribution by published books from 1800–2010 (www.googlengrams).

Increasing environmental attention is besides driving designers to use multifunctional structures, e.g., those favouring line-fishing via bogus reefs (Lokesha and Sannasiraj, 2011; Miles, Russell, and Huntley, 2001; Morang, Waters, and Stauble, 2014) composed of precast elements acting as wave attenuators (e.g., Tecnoreef ^® modules, Reef Assurance, Wave Attenuation Devices).

Beach dewatering has been practical in many places, east.yard., Sweden, Kingdom of denmark, Great Britain, French republic, only independent comprehensive monitoring has been performed only at Alassio, Italy, and showed inconclusive results (Bowman, Ferri, and Pranzini, 2007). Ciavola, Vicinanza, and Fontana (2008) analysed beach response at several Italian installations and was critical of its efficiency in limiting erosion. The Force per unit area Equalization Module©, i.e. vertical drains connecting upper sand layers with deeper ones, appears to be even more ineffective (Walstra, Brière, and Vonhögen-Peeters, 2014).

Therefore, although many new technologies have occurred, seawalls, groynes nonetheless grade the majority of nonharbour defence force projects present along nearly of the world coasts. Currently, along with the question of negative fallouts on adjoining littoral sectors of traditional hard projects, there exists a growing environmental concern plus sensation of the natural landscape's economical value, which has moved designers toward softer shore protection strategies. Protection of natural landforms, including cliffs, beaches, and spits, should non "freeze" their morphologies but permit process reshaping, peradventure reducing erosion rates.

The Part of Monitoring and Physical/Numerical Modelling later 1911

Advances in coastal engineering practices would have never been possible without development of monitoring, concrete modelling, and numerical modelling techniques (Figure six), e.g., Ozasa and Brampton (1981). Monitoring has a long history, only near measurements carried out in the past mainly focused on development of the coastal profile'southward dry portion. In the netherlands, for example, yearly data of dune human foot position, mean depression- and loftier-water line existed for every alongshore kilometre of the entire coastline from the eye of the 19th century. Although very valuable to study long-term morphological trends, these information did not provide information about nearshore zone morphological changes, e.k., due to interaction with coastal engineering structures. Moreover, shoreface interventions, e.g., nourishments, submerged breakwaters, could not exist implemented because there was no means of measuring their efficiency. Consequently, shoreface breakwaters were difficult to implement as long equally there were merely limited means of measuring efficiency. A combination of long-term data from the dry beach (since 1900) with comparatively curt-term (50 years) profile information of the shore face tin can provide useful results on the morphological development of the coast itself and related morphological processes (Kunz, 1997; Ladage and Kunz, 2002).

Figure 6.

Examples of numerical and physical models used today to blueprint and validate shore protection projects. (a) Mean velocity field in forepart of a dune–dike system for obliquely incident waves from the right (Van Geer, et al., 2012). (b) Modelled wave-induced currents within a groyne field at Deltares. (c) Testing submerged breakwater efficiency in a moving ridge aqueduct (DICEA, UNIFI). (d) Concrete modelling of erosion at a dune–dike connection (Boers, Van Geer, and Marcel, 2011).

Much business concern relates to single events or experiments, which might have no bearing over periods of 1 or 2 years to even decades (Pilkey et al., 1980), e.k., projects developed using concrete models, but interlaboratory calibration projects tend to demonstrate the inaccuracy of small-scale experiments (De Rouck et al., 2007). McDougal, Kraus, and Ajwibowo (1996) using a numerical model and rewriting the standard SBEACH model, compared results with those obtained from SUPERTANK experiments and found that the influence of reflection on a seawall profile was minor. Seawall inclination was of import, with erosion existence roughly proportional to the reflection coefficient, vertical walls giving the largest scouring values (Schiereck, 2001). Laboratory tests proved that the transition between hard structures/soft defences is besides a very critical betoken, equally downdrift of seawall increased embankment erosion may occur (Komar and McDougal, 1988).

Morphological modelling (Brøker et al., 2007) and concrete modelling of erosion processes in a seawall breach and the junction between dike (Netherlands proper noun for littoral seawalls) and unprotected dune have been extensively carried out at Deltares (Boers, Van Geer, and Marcel, 2011; Figure 6d). Experiments showed that these structures can promote a significant dune erosion increase of between 27% for a connection between dune and dike and 88% for a dike breach. Van Geer et al. (2012) used the aforementioned dataset to validate the 10-Embankment numerical model, showing that mostly the primary dune set back processes are well captured past numerical model results. Many laboratory experiments chronicle to breakwater pattern, e.g., Kramer et al. (2005), and for moving ridge flumes and basins, "the waves and the wave processes during wave-construction interaction are simulated correctly using a Froude scale" (van der Meer, 2015, p. two).

In the last few decades, monitoring techniques have received a large boost, east.m., Eu projects, remote sensing techniques to monitor morphological changes (e.1000., satellite imagery, Airborne LIDAR Bathymetry, ARGUS cameras), and techniques to measure out wave activeness and hydrodynamic weather, all frequently used in theoretical and applied studies (Pranzini and Wetzel, 2008). Those techniques set boundary conditions for evolution of innovative methods for coastal protection. In kingdom of the netherlands, for example, with the JARKUS monitoring program, yearly measurements from the first dune row to approximately the −8 thousand contour has go available with an alongshore resolution equal to 250 m (Giardino, Santinelli, and Vuik, 2014). This on-going programme was started in 1963 past Rijkswaterstaat (Ministry of Infrastructure and the Environment). The dataset derived by this plan was the footing for implementation of the large nourishment policy, which commenced in 1990, and the shift from the use of standard embankment nourishments towards shoreface nourishments.

Attributable to increasing ciphering power, numerical modelling techniques are at present widely used in dissimilar design phases of littoral applied science protection schemes (Chiranjeevi and Mani, 2005). One-dimensional coastal evolution models are generally used in feasibility studies to assess coastal development in the reference situation and after solutions are implemented. Two and 3-dimensional models are practical in the detail blueprint phase to optimize the pattern schemes and to assess their behaviour on the short and long term. A sound overview has been given past Van Rijn (2011). Some geologists/geomorphologists are partly still sceptical near the value and accuracy of numerical models (Cooper and Pilkey, 2004), but if correctly used and calibrated, they accept proved to be extremely powerful, flexible, and relatively cheap systems to assess design efficiency and to choose the one that is most constructive (Effigy 6b). However, difficulties be in using empirical relationships to predict embankment response in meso- and macro-tidal coasts (Shabica, Michael, and Nagelbach, 2010), but remote sensing monitoring and process algorithms are powerful tools for studying the morphology and hydrodynamics.

CONCLUSIONS

In this paper, progress in littoral protection measures during the last century has been discussed. The reference certificate (RCCEA, 1911) investigated the country of coastal erosion and resulting protection measures in the U.K. The present paper focuses on "traditional" littoral defence measures (i.e. seawalls and groynes), widely used at the time of RCCEA (1911), together with new concepts and schemes that were completely unknown when RCCEA (1911) was written.

What has actually changed in terms of coastal protection measures during the concluding century? Was this a "century of modify" as the paper title suggests?

The kickoff important departure relates to the "what" and "why" coastlines are being protected today, which is unlike than a century ago. Coastal protection measures are much more widespread considering of the larger human pressure level on coasts (eastward.thou., evolution of new settlements, infrastructures, harbours, tourism, etc.). Therefore, large coastal stretches, which were unprotected one century ago, now need protection, and the pros and cons of different solutions have been categorised and widely distributed internationally.

Much new knowledge and experience has go available, followed by blueprint and monitoring of these new coastal protection structures. The "why" question relates to the contempo coastal protection measures objectives. A century ago the main office was (brusque-term) safety of coastal settlements and roads; nowadays new objectives play an important role on optimal coastal erosion pattern measures, due east.thousand., an Italian 1907 police force was canonical with the aim of making big financial resource available for defending littoral towns. This objective was partly achieved, but the result was many urban beaches were lost. This, in principle, would non be admissible anymore in the present situation.

Besides, sensation for a landscape'southward aesthetic value has boosted development of designs that are non only "functional" simply besides "cute." Large coastal restoration projects are now the result of multidisciplinary studies involving mural architects, engineers, geologists, and ecologists, a collaboration almost unknown a century ago, so that groynes with very diverse shapes have been designed—and they even act as tourist pathways.

A gene that was completely disregarded a century ago is climatic change/sea-level rise. While discussions are ongoing on sea-level rise rate and change in storminess, it is widely accustomed that hateful sea level is on average increasing. Many studies and projects are being implemented to design structures that are more resilient to climatic change in coastal areas, which can be flexible to account for the uncertainties underlying predictions. Big sand nourishments, nearly unknown a century ago, are a very good example because they integrate well with the surrounding landscape and because they tin easily adapt by changing nourishment volumes.

As new technologies appear, unlike solutions and designs become possible. Shoreface nourishments are now implemented, and monitoring techniques extend to the underwater bathymetric profile. Likewise, the large increase in sand and gravel usage in combination with traditional "hard" structures is at present possible cheers to dredging sector improvements, which makes it possible to accomplish sediment resource at larger depths at competitive prices.

Finally, improvements in numerical modelling (next to the traditional concrete) have immune optimization of traditional schemes, unknown a century ago, just designed and based on experience (due east.chiliad., groyne fields). This is i reason that hard structures, so poorly evaluated by researchers, environmentalists, and stakeholders in the 2nd one-half of the 20th century, have been recently reconsidered, in combination with "soft" types of solutions, east.thou., groynes and revetments combined with nourishments, use of hard structure in combination with vegetation. Recently there has been a quantum shift towards environmental as a value and, associated with this, a judgement/assessment of coastal areas, seemingly without taking into business relationship natural forces. Retreat options have become feasible and, forth with the principal "safety" targets, an enhanced resilience (biophysical and socio-economy) in littoral regions is demanded for integrated littoral zone direction. Withal, there remain littoral sites where "hard" types of solutions are the merely alternatives.

Can all this be called a "century of change" in coastal engineering? Maybe it is more advisable to talk about a continuous and integral improvement in approach, methodology, and technology. Definitely, RCCEA (1911) members would be very positively surprised past modern littoral protection projects. Or would they? Whatever one'due south view is on coastal erosion and protection, the shoreline is an area where sometimes, "the rocky shore beats back the envious siege/Of watery Neptune" (Shakespeare, Richard Two), but sometimes anthropogenic help is needed. This paper started with a quote by Bascom (1964) then fittingly information technology ends with, "for the short span of human being involvement . . . the beginning and nearly valuable lesson ane can learn about the sea is to respect it" (Bascom, 1964, p. 256).

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Source: https://bioone.org/journals/Journal-of-Coastal-Research/volume-32/issue-5/JCOASTRES-D-15-00213.1/Canons-of-Coastal-Engineering-in-the-United-Kingdom--Seawalls/10.2112/JCOASTRES-D-15-00213.1.full

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