Encyclopedia of Coastal Science

132 Pages·12.664 MB·English

by  Charles W. Finkl, Christopher Makowski (eds.)

A
Artificial Islands The history ofislandandland reclamationinto the seais
some2,000yearsold,startingwithdwellingmoundsinflood-
MarcelJ.F.Stive prone areas (cf. Kraus 1996; this reference provides historic
DepartmentofHydraulicEngineering,FacultyCivil context of works in Canada, Germany, Japan, the Nether-
EngineeringandGeosciences,DelftUniversityof lands, and Taiwan, described below). In the sixteenth and
Technology,Delft,TheNetherlands seventeenth centuries, land reclamations were becoming
commonpracticeinWesternEurope.Inthetwentiethcentury,
thispracticehasevolvedworldwide.Whilethiscontinuesto
Definition bethecase,theconstructionofislandsorreclamationsfurther
offshoreisonlyofrecenttimes.Islandsinsupportofalarger
Islands are defined as a relatively small land surface, infrastructureortemporaryislandsforpetroleumexploitation
surrounded by water. The largest island, Greenland, has a are of the last decades. Many feasibility studies on artificial
surface, which is still four times smaller than that of the islandswithanintrinsicpurpose(suchasindustry,urbaniza-
smallestcontinent,Australia.Thetotalsurfaceoftheearth’s tion, and airports) have been undertaken all over the world
islandsapproximates10millionkm2,whichiscomparableto sincethe1970s.However,itwasnotuntil1994thatthefirst
Europe’stotalsurfacearea. offshore-located island was completed for the realization of
Itiscommontodistinguishbetweencontinentalandoce- Kansai International Airport in the Bay of Kobe of Japan.
anic islands. Continental islands are considered part of a Mostrecently,strategictensionsintheSouthChinaSeaalso
continentwhentheyarelocatedontheassociatedcontinental knownastheEastSeahasledtonourishmentsincreasingthe
shelf. Oceanic islands, in contrast, do not belong to a conti- surface areas of very small islands that are not necessarily
nental shelf. The majorityofoceanic islands are ofvolcanic shorefaceconnected.
origin. Some oceanic islands (e.g., Madagascar, Greenland,
Zealandia)couldbeconsideredassubcontinents,whichhave
been separated from larger continents through tectonic ConceptsandApplications
processes.
All realizations of artificial or man-made islands as DwellingMounds
constructed so far are close to shores on relatively shallow Historically,artificialislandsandreclamationsgobackalong
water eitherinintertidal zones, inbays, ontheshoreface,or way(cf.VanVeen1962).Thefirstknownhistoricrecordings
onthenearbyshallowcontinentalshelf,andmostarelocated of artificial islands are by the Romans. Plinius in 47 AD
in a sheltered environment. Based on the above definition, describes how the Friesians along the northern boundaries
artificial islands belong to the class of continental islands. of the Roman Empire lived on artificial mounds (called
Becauseoftheirgeneralclosevicinitytotheshore,artificial “terpen” in Dutch) in order to keep “their heads above the
islands are very similar to land reclamations into the sea, water”duringspringtidesandstormsurges.Inalltheybuilt
certainly when such reclamation is separated from the 1,260ofthesemoundsinthenortheasternpartoftheNether-
existing land by a waterway or channel, which often has a lands, which still exist today, although by now situated in
watermanagementpurpose. reclaimedland.Theareasofthemoundsvaryfrom2to16ha,
andtheirsurfacelevelmayreachashighas10mabovemean
#SpringerInternationalPublishingAG2017
C.W.Finkl,C.Makowski(eds.),EncyclopediaofCoastalScience,
DOI10.1007/978-3-319-48657-4_14-2
2 ArtificialIslands
sealevel.Thevolumecontentofasinglemoundmaybeupto sacrificialbeachtypeimpliedthattherelativelysteepslopeof
onemillioncubicmeters(Mm3). the core was protected with a gently sloping lower beach of
less dense sediment, which would be able to withstand ero-
PoldertypeReclamations siveforcesbywater(insummer)andbyice(inwinter).The
This period of family-based shelter against high waters sandbag-retained type resolved the issue of required resis-
reverted into a more collective form of shelter by seawalls tancebyprotectingtheslopesofthecore throughgeotextile
andassociatedreclamations.Thestartoftheseconstructions sandbags (with volumes of 1.5–3 m3). The issue of subsi-
is expected to have been shortly after the declaration of the denceinthisareaisvirtuallyabsentbecauseofthepermafrost
LexFrisonianin802.Inthesixteenthandseventeenthcentu- conditions.
ries all over Western Europe, including Russia, polder-type
reclamationshavebeenrealizedbothonseashores,estuaries ElevatedReclamations
andrivers,andlakes.Apolderthatisusedtoreclaimpartof The strong economic development of Asian countries over
the sea bottom consists of an endiked continental shelf or the last decades where the availability of land is scarce, for
intertidal basin area, with its surface, being the original sea example, Japan, Singapore, Taiwan, and South Korea, has
bottom,belowmeansealevelwhichismaintaineddrybythe alsoresultedthereinaseriesofreclamations.Withtheexcep-
useofpumpingstations(seeentryon“▶Polders”). tionofSouthKorea,theacceptationofthepolder-typerecla-
Oneoftheworld’slargestpolderreclamations(VandeVen mationinAsiahasshowntobelow.Althoughtheexecution
1993) concerns that of the Zuiderzee in the Netherlands, method initially is similar, viz., endiking the area first and
which started in 1918 (with the main damming realized in thendryingbypumping,thereappearstoexistapreferencein
1932 and the principle of constructing small polders first to Asia for elevating the reclamation to above mean sea level
learnbydoing)andwasfinalizedintheearly1970swhenit (seeentryon“▶Reclamation”).
was decided to not reclaim the last planned polder Examplesofthispracticearetherecentrealizations(mid-
(Markermeer Polder). The closing off and the partial recla- 1990s) of the industrial reclamation estates Chang Hua and
mation of the Zuiderzee have resulted in the gain of Yun-Lin on the west coast of Taiwan, comprising 3,000 ha
166,000 ha of new land distributed over four polders. This and 10,000 ha, respectively. The fill of these reclamations
newlandisusedforagriculture,urbandevelopment,recrea- amountedto800mm3ofsand,whichwasdredgedbytrailing
tion,andnatureconservation. suction hopper dredgers in the nearby offshore area. The
Although the polders in the Bay of San Francisco are – reclamation locations were primarily on diluvial substrates
intriguingly–called“islands,”thesearebasicallyrealpolders formedbypre-Holoceneebb-tidaldeltas,whichimpliesthat
with their ground elevation below mean sea level. These subsidenceproblemswerevirtuallyabsent.
solutions are also introduced in Saemangeum, South Korea; A recent (2017) mind changer in Singapore is the Pulau
inthePoDelta,Italy;andveryrecentlyinJiangsuProvince, Tekongreclamationwith810hawhichisbeingexecutedasa
China. polder, whereas all earlier reclamations were executed with
the ground level above mean sea level. The main reason
PetroleumExplorationandExploitationIslands behindthisisthedifficultytoarrangeaccesstosandresources
Inthepetroleumexplorationandexploitationindustry,there oftheneighboringcountries.
exist several examples of island reclamations. One such
example concerns Rincon Island off California (U.S. Army InfrastructureSupportingIslands
Corps of Engineers 1984). Another important example con- Over the last decades, a number of islands have been
cerns a series of artificial exploration drilling rig islands of reclaimed to support the construction of a larger infrastruc-
temporary nature in the Beaufort Sea – McKenzie Delta ture.AnearlyexampleistheislandNeeltjeJansinthemouth
region, Canada. Through the construction of a number of oftheEasternScheldtestuary.Thiswascreatedonasubtidal
such islands in the period 1973–1986, the presence of oil flat, separating the main estuarine channels, with a twofold
and gas reserves was confirmed, but exploitation in this purpose. The island served both as a working area for con-
remote,arcticenvironmentwascostly.Thedeclineoftheoil structionoftheelementsthatweretoformtheEasternScheldt
prices had hampered exploitation. The islands, with an StormSurgeBarrier(completedin1988)andtoformpartof
expectedlifetimeof3years,wereconstructedinwaterdepths thebarrieritself.
varying between 3 and 21 m, just before the frost and ice Other examples concern the construction of islands in
formationwouldsetin.Atotalofeightexplorationislandsof caseswherethetwobanksofawaterwayareconnectedbya
thesacrificialbeachtype andnine explorationislands ofthe combined bridge-tunnel connection. At the transition of the
sandbag-retained type were constructed. In both cases, a bridge to tunnel and vice versa, the island serves as the
dense sediment core was placed, which provided the explo- connectionarea.OneNorth-AmericanexampleistheChesa-
rationspaceneeded(surfaceareasoftheorderof1ha).The peakeBaybridge-tunnelconnection; aEuropeanexampleis
ArtificialIslands 3
theØresundbridge-tunnelconnectionbetweenDenmarkand the crest. The reclamation of the 4,700 ha required approxi-
Sweden. mately180Mm3offill.Around80%ofthefillwasdredged
from the sea, and the remaining 20% was quarried from
AirportIslands mountainsandhillsinthearea.Thetoplayerofthereclama-
It might be stated that the introduction of offshore artificial tionsite,whichislargelyanintertidalarea,iscomposedofa
islands in larger depths with a ground level above mean sea soft alluvial layer of 5 m average thickness. A sand drain
level was benchmarked by the construction of Kansai Inter- techniquewasappliedtoachievehighersoil-carryingcapac-
national Airport, Japan (1994). Chek Lap Kok International ity.Verticalsandpipesof400mmdiameterweredriveninto
Airport, Hong Kong (1998), and Inchon International Air- thesoftsoilevery2.8–3.8mtodrainporewater.Theexpected
port, South Korea (2001), followed up soon. A common additionalsettlementislessthan0.5m.
problemtothesethreeairportislandsisformedbythefoun-
dation. Being international airports demands that important
loading forces (400 metric tons for future intercontinental Conclusions
aircraft) need to be sustained. Since all of these islands are
constructedinrelativelyshelteredareas,thelocalseabottom Although the history of artificial islands or island reclama-
commonly consists of alluvial clay, which calls for special tionsislong,itmaybeexpectedthattheincreasingpressure
measures. of urbanization, industry, and tourism in the densely popu-
KansaiInternationalAirport,Japan:Themainconcernin lated coastal regions is yet to result in a further boom of
creating the artificial island has been the foundation of the constructionofislandsandislandreclamations,eventhough
island.Notonlywasthelocalwaterdepthsome18mbutalso the constructed Palm Islands (Dubai) and the World Islands
an alluvial clay layer of more than 20 m covered the (Dubai) are still struggling to turn into a success. The three
geotechnically stable diluvial (Pleistocene) clay substrate. main technical problems that one will generally face in the
The alluvial clay layer was artificially compacted by about designandexecutionarethoseofgeotechnicalfoundation,of
one million piles that were driven into the layer to drain the connectiontothemainland,andofavailabilityoffillmaterial.
water out. Subsequently, a sea defense was constructed of Besides this,onefaces theimportantissueofenvironmental
some11kmcircumference,withinwhich178mm3ofmate- impact, where the aspects of impact minimization, nature
rialwasdumped.Becauseofthescarceavailabilityofsuitable substitution, and working in harmony with natural system
sanddredgematerial,themajorityofthefillwastakenfrom forcesarethekeywords.
quarriesnearOsaka.Thus,anislandwascreatedwhichhasan
elevation of33mabovetheseabottom. Sincetheconstruc-
tion,thesubsidencehascontinuedandisexpectedtocontinue Cross-References
another30–50years.Inthenextphase,thesurfaceareaofthe
islandwillbeextended. ▶DredgingofCoastalEnvironments
ChekLapKokInternationalAirport,HongKong:Aquar- ▶GeotextileApplications
ter of the artificial island consists of the island of Chek Lap ▶Polders
Kok(350ha);threequartersconsistofseareclamation. The ▶Reclamation
average local depth was some 6 m. In contrast with the ▶SmallIslands
solutions for Kansai and Inchon, the alluvial clay layer of ▶StormSurge
10–15mwasremoved.Thereclamationconsistedofalower
layerofrubblemoundmaterialquarriedfromChekLapKok
and supplemented with sand dredged in the nearby area. To Bibliography
avoidexpensivelayergradation,transitionsbetweentherub-
ble mound material and the sand geotextiles were applied. KrausNC(1996)Historyandheritageofcoastalengineering:acollec-
Thefillquantitiesamountedto350Mm3,ofwhichtwo-third tion of papers on the history of coastal engineering. International
conferenceoncoastalengineering1950–1996.AmericanSocietyof
wasdredgedsand.
CivilEngineers,p601
Inchon International Airport, South Korea: This airport USArmyCorpsofEngineers(1984)Shoreprotectionmanual.Coastal
site covers 5,600 ha in total, of which 4,700 ha consists of EngineeringResearchCenter,Vicksburg
Van de Ven GP (ed) (1993) Man made lowlands: history and water
reclaimedlandbetweentheislandsofYeongjongandYongyu
managementandlandreclamationintheNetherlands.MatrijsPub-
alongwith900haofexistingland.Toendiketheareabetween
lishers,Utrecht
the islands, three dams of a total length of 17 km were VanVeenJ(1962)Dredge,drain,reclaim:theartofanation.Nijhoff
constructed, varying in crest height between 7.5 and 9.4 m. Publishers,TheHague
Their widths attheirfoundations are90–120mand 20mat
B
Bay Beaches wave-energy continuum, other terms, such as stream bank,
intertidalmarshmargin,orbaybottom,maybemoreappro-
KarlF.Nordstrom1andNancyL.Jackson2 priatethanbeach.
1DepartmentofMarineandCoastalSciences,Rutgers
University,NewBrunswick,NJ,USA
2DepartmentofChemistryandEnvironmentalScience,New ShoreProcesses
JerseyInstituteofTechnology,UniversityHeights,Newark,
NJ,USA Waves generated by local winds in bays have low heights
(usually mean heights <0.2 m and storm wave heights
<1.0 m) and short periods (2.0–4.5 s) (Nordstrom 1992).
Definition Ocean waves entering bays play a limited role in beach
change where shores do not face ocean entrances. Tidal
Beaches in mostly enclosed bays subject to reworking by range affects the vertical distribution of wave energy over
locallygeneratedfetch-limitedwaves. the profile, determining the width of the foreshore and the
Beachesarefoundinbays,sounds,lagoons,andestuaries duration that waves break at any elevation. Bay beaches are
(herealltermedbays)andcancomprisealargeproportionof usuallycharacterizedbyasteepupperforeshorefrontedbya
theshoreline.ExamplesincludebeachesinChesapeakeBay, broad,relativelyflatbottom,oftencalledalow-tideterraceor
PugetSound,theTagusRiver,andarmsoftheBalticSea.The subtidal terrace. Spilling waves break in a broad surf zone
termbayinrelationtotheopencoastissomewhatsubjective, across thegentlysloping terrace atlow water levels,butthe
andbayssuchasMontereyBay,California,maybeexposed energyinthewavesislow.Duringhighwaterlevels,waves
tooceanwaveswithenergylevelsthatareamongthehighest reachtheupperforeshorewithlittlelossofenergyandusually
in the world. This discussion is confined to low-energy break as plunging waves. Waves frequently break on the
beaches that occur in mostly enclosed bays where fetch dis- upper foreshore and convert directly to swash without an
tances for local wave generation are generally less than interveningsurfzone.Thus,swashprocessesplayarelatively
50 km. Bay beaches are a subset of low-energy beaches greatroleinsedimenttransport.
(Jackson et al. 2002) and share many characteristics with Longshore currents are predominantly generated by the
beachesinsmalllakesandreservoirs(NordstromandJackson breaking of local wind waves, but refracted ocean waves,
2012). tidalflows,andwinddriftarelocallyimportantandmayresult
The length of bays greatly exceeds the length of ocean in flows bayward of the breaking waves that are opposite
shoreinmanycountries.Beachesarecommoninthesebays, flows generated by local wind waves. Tidal currents are
but they are often so small and isolated that they escape importantnearchannels,projectingheadlands, andconstric-
attention,exceptinpopulatedlocations.Theprincipalfactors tions in the bay, and they may be the dominant agent of
affecting the morphodynamics of these beaches are locally sediment transport on the terrace bayward of the foreshore.
generated waves and wave-induced currents, but Ice forms faster and has a greater influence on mid- and
wind-induced and tidal currents play a role in morphologic high-latitude bay beaches than on nearby ocean beaches
change. Fluvial processes may be dominant at estuarine because bay waters are colder in winter, shallower, and less
shores in narrow basins or tributaries. At the low end of the saline;icelastslongerbecauselowwaveenergiesareslowto
#SpringerInternationalPublishingAG2017
C.W.Finkl,C.Makowski(eds.),EncyclopediaofCoastalScience,
DOI10.1007/978-3-319-48657-4_29-2
2 BayBeaches
remove it. Ship and boat wakes are higher on bay beaches vegetationinbaysandthereducedabilityofthelow-energy
than onoceanbeaches because vessels canpass close tothe wavestomoveit.Vegetationhelpsbindbottomsedimentand
shore, but the average energyin thewakes is usually only a attenuatewaveenergies;vegetationflotsaminthebreakerand
smallpercentageoftheaverageenergyofwindwavesinall surfzonesaltersthewaveandcurrentcharacteristicsandthe
butthesmallestbays. likelihoodofentrainmentofbeachsediment;vegetationlitter
Water level changes can be locally induced by winds inthewracklineformsbarrierstowaves,currents,andswash
blowing across the bay or they can be induced by flow of uprush.
waterthroughinletsfromsurgesgeneratedontheopencoast. Bay shorelines are often composed of numerous isolated
Windscanincreasewaterlevelsonthedownwindsideofthe beaches with different orientations. The beaches have high
bay while lowering water levels on the upwind side, but a variabilityinmorphologyandrateoferosionoversmallareas
largeopeningtotheseaonthedownwindsideofthebaycan resultingfromlocaldifferencesinfetch,winddirection,stra-
resultinlowerwaterlevelsdownwind. tigraphy,inheritedtopography,resistantoutcropsonthefore-
shore, variations in submergence rates, and amounts of
sediment in eroding formations (Phillips 1986; Rosen
BeachandShoreCharacteristics 1980).Beachcompartmentsareisolated intolongshoredrift
cellsdefinedbydeepcovesorheadlandsformedbyresistant
The best development of beaches occurs where relatively rock,marsh,orhumanstructures.
highwaveenergiesexposeabundantunconsolidatedsandor The net rate of longshore transport on estuarine beaches
gravel in the eroding formations, such as moraines, glacial varies with orientation, fetch distance, and size of each drift
outwash, fluvial deposits, and landward portions of barrier cellandrangesfromtensofcubicmeterstotensofthousands
islands and spits (Nordstrom 1992; Freire et al. 2007). of cubic meters (Wallace 1988). Although rates of transport
Beaches in small bays, with limited availability of sand and are low, the magnitude of erosion can be high because the
gravel, may be highly localized or confined to ocean quantitiesofsedimentintransportrepresentasizablefraction
entrances.Manybeacheshavebeencreatedbyhumanefforts of the total unconsolidated sediment in the active beach
in urbanized estuaries at locations where no beach would (Jacksonetal.2017).Manybayshoresareerodingatgreater
occurnaturallybecausewaveenergiesaretoolow.Artificial ratesthannearbyoceanshores.
beaches are often wider than natural beaches would be in a Thenarrowbeachwidths,wrackdeposits,laggravels,and
similar wave climate. Some new beaches are accidental by- beach slopes may restrict sand transport by wind, but dunes
productsoflandfilloperations;somearecreatedintentionally and deposits of wind-borne sediment covering preexisting
asrecreationareas(Nordstrom1992). topography are more common than perceived. Relatively
Bay beaches may be unvegetated or partially vegetated largedunescanoccurasinheritedformswheretheymigrated
and composed of sand, gravel, or shell. Surface sediments from ocean beaches or they formed in the bay during more
areoftencoarseronbaybeachesthanonoceanbeacheswitha optimumclimaticconditionsinthedistantpastorwherethey
similar source. Lag gravel is common on the beach surface, have been artificially constructed by human action
formed from particles exhumed by swash or by preferential (NordstromandJackson2012).
eliminationoffinesbylow-energywaves.Individualpebbles
move readily over the sand surface, and swash excursions
createbandsofgravelontheupperforeshore. BeachChange
The depth of mobilization of sediments on the upper
foreshore is shallow (e.g., <0.2 m under storm conditions), Theupperforeshoresofmostbaybeachesaremodallyreflec-
andtheactivebeachmaybeonlyathinveneerofunconsol- tive. Conspicuous cyclic morphologic change is confined to
idated material overlying an immobile layer of coarse sedi- the immediate vicinity of the foreshore. Sediment removed
ments, clay, peat, or a shore platform. Mobilization of fromtheupperforeshoreduringhigh-wave-energyeventsis
sediments on the low-tide terrace by waves may occur only depositedonthelowerforeshorewithachangetoaconcave
to depths of 10–30 mm. Biologic processes can have an upwardprofileshape.Sedimentsmovedfartheroffshoreonto
influenceonsedimentmobilizationandtransportofamagni- theterraceformonlyathinveneeroverthesurfaceinsteadof
tudecomparabletothatofwavesandtidalcurrentsaloneand formingthebreakpointbarthatisprominentonmanyocean
play a greater role than wave processes in altering the char- beaches. Landward and bayward displacement of the entire
acteristicsofthesurfaceandsubsurfaceofthelow-tideterrace foreshore profile may also occur, while the profile slope is
(Nordstrom1992). maintained. This parallel-slope retreat and advance is com-
Vegetationplaysagreaterroleininfluencingmorphologic mon when sediment exchange is due primarily to longshore
change on bay beaches than on ocean beaches (Nordstrom transportandismostpronouncedneartheendsofdriftcom-
1992; Pilkey et al. 2009) because of greater abundance of partments(Nordstrom1992).
BayBeaches 3
ResourceValuesofBayBeaches structuresdeepenoughtopreventtoescourorhighenoughto
preventovertopping,weakfastenings,failuretouseadequate
The fronting terrace of a low-energy bay beach has a rela- sized armor stones, or failure to perform maintenance. As a
tively stable substrate that allows macroscopic plants and result,thereismuchevidenceofstructuralfailure.Beachfill
fauna to thrive. The upper foreshore is more energetic and is increasingly used for protection or recreation, but fill can
mayhavelessspeciesdiversityandabundancebutneverthe- cover benthic habitat and eliminate shallow-water areas for
less high ecological value (Dethieret al.2016). Infauna and aquatic plants. Bayside beach nourishment projects can be
macroalgae provide prey to juveniles of commercially valu- inexpensivebecauseonlysmallquantitiesoffillarerequired.
able fish, and the intertidal area provides habitat for Fill materials brought in from outside the region may retain
recreationallyimportantclamsandnumerousspeciesofepi- their exotic appearance because of limited mixing by low-
faunaandinfauna.Fishandinvertebratesarepreyforforag- energywaves.
ingbirds,especiallyintheregularlyexposedintertidalzone. Beaches in short-fetch environments comprise just one
Wrackfromplantlitterisinhabitedbynumerousamphipods type of shoreline, and vegetated reaches may have greater
andinsects.Theswashzoneanddryupperforeshorearealso managementinterest(NordstromandJackson2012).Living
foragingareasforbirds,includinguplandspecies. shoreline projects often eliminate beach environments in
Baybeachesarenotasintensivelyusedasoceanbeaches favor of marsh habitat. Alternatively, managed realignment
for recreation, but they have important complementary projects that involve removing or abandoning shore protec-
values. They provide convenient surfaces for launching and tionstructurescancreateconditionsfornewbeachestoform.
landingboatsandboardsforwindsurfing.Theyarefavored Lack of sediment is an issue facing ocean beaches and bay
by parents with small children because they provide a safer beaches alike, and sediment resources are likely to be even
environment than on the ocean. Many bay beaches are morerestrictedinthefuture(OrfordandPethick2006).There
underutilized for beach recreation because of the unclean has been considerable government intervention in decisions
appearance of the beaches or lack of awareness of their ondevelopingbayshores,especiallyinproductiveestuaries,
existence orunique attributes, butease ofaccess causes bay but this intervention is rarely conducted to maintain beach
beaches close to urban areas to have relatively high rates of resources. Alternative human uses such as transportation,
use(Nordstrom1992). industrialdevelopments,residences,boating,andmarshres-
toration are compatible with a coastal location according to
most policies, and actions to enhance these uses may elimi-
ShoreProtectionandManagement nate beaches. The number and value of bay beaches can be
enhancedbyimplementingbeachnourishmentprojects,alter-
Erosion control strategies for bay beaches may differ from ingvegetation,constructingappropriateprotectionstructures,
strategies for ocean beaches because of differences in the acquiringkeysitesforpublicuse,andenhancingaccess.The
scale of erosional forces and in the value of resources. Pro- ease of constructing and maintaining bay beaches and the
tection programs are facilitated because beach segments are paucity of quality recreation space in many urban areas
small,isolateddriftcells,oftenunderjurisdictionofonlyone makecreationofnewbeachesassurrogatesforoceanbeaches
management agency and because small-scale, low-cost pro- anattractiveoption.
tection may be utilized. Low wave energies and gentle off-
shore gradients make construction of fixed offshore
engineering works more practical than on high-energy Summary
beaches.Shore-parallelwallsareoftenconsideredsuccessful
becausetheycanwithstanddirectattackoflocalwaves,they Bay beaches are characterized by short-fetch distances that
takeupminimalspaceonthebeachandadjacentupland,and resultinlowwaveheightsandshortwaveperiods,although
they limit the loss of biological resources on the fronting erosion rates can be high because of limited sediment avail-
terrace or bay bottom. Detrimental effects of walls include ability.Biologicprocessesplayagreaterroleinbeachchange
reductions in beach width, riparian vegetation, amount of than on exposed coasts, and the ecological value of bay
woodydebris,andtypesofbeachwrackandassociatedinver- beaches is considerable. These beaches provide human-use
tebrates(Dethieretal.2016). values alternative to those provided by beaches on exposed
Protection projects funded by national or state/provincial coasts, but human alterations can come at the expense of
governmentsareoftennotconsideredcost-effective,resulting naturalvalues.
inafragmentedapproachtoprotectionbyindividualproperty
owners. Simple engineering principles are often ignored in
constructingsmall-scaleprotectionstructures,includinglack
of filter cloth or weep holes in bulkheads, failure to build
4 BayBeaches
Cross-References Jackson NL, Nordstrom KF, Eliot I, Masselink G (2002) Lowenergy
marineandestuarinebeaches:areview.Geomorphology48:147–162
▶BeachErosion Jackson NL, Nordstrom KF, Farrell EJ (2017) Longshore sediment
transport and foreshore change in the swash zone of an estuarine
▶BeachNourishment beach.MarGeol386:88–97
▶BeachProcesses Nordstrom KF (1992) Estuarine beaches. Elsevier Applied Science,
▶DissipativeBeaches London
▶Estuaries NordstromKF,JacksonNL(2012)Physicalprocessesandlandformson
beaches in short fetch environments in estuaries, small lakes and
▶HumanImpactsonCoasts reservoirs:areview.EarthSciRev111:232–247
▶ReflectiveBeaches OrfordJD,PethickJ(2006)Challengingassumptionsoffuturecoastal
▶SedimentTransport habitat development around the UK. Earth Surf Process Landf
▶ShoreProtectionStructures 31:1625–1642
PhillipsJD(1986)Spatialanalysisofshorelineerosion:DelawareBay,
NJ.AnnAssocAmGeogr76:50–62
Pilkey OH, Cooper JAG, Lewis DA (2009) Global distribution and
Bibliography geomorphology of fetch-limited barrier islands. J Coast Res
25:819–837
RosenPS(1980)ErosionsusceptibilityoftheVirginiaChesapeakeBay
DethierMN,RaymondWW,McBrideAN,ToftHD,CordellJR,Ogston shoreline.MarGeol34:45–59
AS,HeerhartzSM,BerryHD(2016)Multiscaleimpactsofarmoring WallaceRS(1988)Quantificationofnetshore-driftratesinPugetSound
on Salish Sea shorelines: evidence for cumulative and threshold andtheStraitofJuandeFuca,Washington.JCoastRes4:395–403
effects.EstuarCoastShelfSci175:106–117
FreireP,TabordaR,SilvaAM(2007)Sedimentarycharacterizationof
TagusEstuarinebeaches(Portugal).JSoilsSediments7:296–302
C
Changing Sea Levels Our only true benchmarks are the former sea-level posi-
tionsinthefield.Thepresentlevelofthosedatapointsarethe
Nils-AxelMörner combinedfunctionbothofpastchangesinsealevelandpast
Paleogeophysics&Geodynamics,Stockholm,Sweden changes in crustal level. In opposite to all types of crustal
deformations,wetermalldifferenttypesofsea-levelchanges
“eustatic” (Mörner 1986). In the old concept of eustasy, all
Synonyms sea-level changes were parallel over the globe (e.g.,
Fairbridge1961).Thisisnolongertenable;sea-levelchanges
Eustaticchanges;Relativesea-levelchanges can never be fully parallel over the globe and are often of
compensational, even opposed, character (Mörner 1976).
Therefore, we nowadays talk about “regional eustasy” (not
Definition global eustasy). The old and new concepts of eustasy are
illustratedinFig.1.
Changing sea levels refer to variations in the level of the
ocean mean sea level regardless of causation mechanism.
Relative sea-level changes denote the observed changes in WaterDistributionandSea-LevelChanges
sealevelascausedbythecombinationofoceanvariablesand
crustalcomponents.Eustaticchangesrefertochangesinthe Thedistributionovertheglobeoftheoceanwatermassesis
oceaniclevelitself(exclusiveofcrustalandcompactionfac- definedbytheEarth’srotationalellipsoid,thegeoidtopogra-
tors). Nowadays, we talk about regional eustasy, because of phy, and various dynamic forces (air pressure, current beat,
thespatialvariabilityof“eustasy.” coastalrunoff,etc.).Anychangesinanyofthoseparameters
willinducesea-levelchangesonthelocal,regional,orglobal
dimension.
Characteristics Sealevelcanonlychangewithinlimitsdeterminedbyits
physicalcauses(e.g.,Mörner2011).Themainsea-levelvari-
The geodetic sea level – better known as the geoid – is the ablesarelistedandquantifiedinTable1.
equipotential surface between the attraction and repelling The global water volumeiscontrolled by glacial eustasy,
forces. The actual sea level – known as the dynamic sea evaporation/precipitation, loss/gain of water, and steric
surface–closelyapproximatesthegeoidsurface.Thedevia- expansion/contraction due to changes in temperature and
tionsofthedynamicsurfacefromthegeoidsurfacearecaused salinity.
by different oceanographic, hydrographic, and meteorologi- The volume of the ocean basins is controlled by tectonic
cal forces acting upon the distribution of the water masses. deformation (ocean floor subsidence, mid-oceanic ridge
Neither the dynamic sea level nor the geoid remains growth,andcoastaltectonics).
undeformedwithtime.Sea-levelchangesrefertochangesin The distribution of the waterover the globe is controlled
mean sea level over time units larger than daily and annual by Earth’s rate of rotation, geoid deformation, and various
cyclic changes. Longer-term cycles, like the 18.6 and dynamicforces(airpressure,currentbeat,coastalrunoff).
60years’cycles,aremeasuredassea-levelchanges.
#SpringerInternationalPublishingAG2017
C.W.Finkl,C.Makowski(eds.),EncyclopediaofCoastalScience,
DOI10.1007/978-3-319-48657-4_66-2
2 ChangingSeaLevels
a: Old concept ChangingSeaLevels,Table1 Sea-levelvariablesandquantities(in
meters)fromMörner(2013)
T1 SEA LEVEL Presenttides
Geoidtides 0.78
T2 Oceantides Upto~18
Presentgeoidrelief
Maximumdifference 180
b: New concept Presentdynamicseasurface
GEODETIC SEA LEVEL (GEOID) LMoawjohracrumrroennitcss UUppttoommaaxx~~52
Earth’sradiusdifferences
T1
Equatorvspole 21,385
T2 Presentlystoredglacialvolume(cid:1)meterssealevel
Antarctica ~60
ChangingSeaLevels,Fig.1 Theoldandnewconceptof“eustasy” Greenland ~6
(afterMörner1987)illustratedbythechange(arrow)fromonesea-level Allmountainglaciers 0.5–0.4
position (black dot and T1) to a new, lower, position(T2). In the old
concept (a), any eustatic change in sea level was parallel all over the Glacialeustasy
globe.Inthenewconcept(b),therealsea-levelsurfaceisanirregular LastIceAgeamplitude 120–130
surfacethatneverremainsparallelatachangeinsealevel Geoiddeformation
Last150ka 30–90
Last20ka 30–60
Actualchangesinthesealevelrepresentanintricateinter- Last8ka 5–8
actionofmultiplefactorsrequiringunderstandingofvarious Tectono-eustasy(oceanbasinvolumechanges)
Maximumannualrate <~0.00006
subjects and processes. The dominant controlling factor dif-
Globalglacialisostasy ?
fersthroughtimeandwiththetimescaleconsidered.
Oceancirculationandrotationbeat
On the million-year timescale, sea level is mainly deter-
HoloceneGulfstreambeat 1.0–0.1
minedbyoceanbasinvolume,massdistribution,andrateof
High–lowlatitudechanges(grandsolarpulses) ~0.5
rotation.
HoloceneequatorialE–Wpulses ~1
On the thousand-year timescale, sea level varies mainly
SuperENSOevents ~1
duetoglacialeustasyandrelatedglacio-isostasy,Earthrota- ElNiño–ENSOevents 0.3
tion, and geoid shape as determined by lithospheric mass
Thermalexpansion
change. Openocean <1.0
Onthemulti-decadaltohundred-yeartimescale,sea-level At100mwaterdepth <0.035
changes seem primarily to reflect changes in water–mass At10mwaterdepth <0.0035
distribution related to changes in the oceanic circulation Attheshore always(cid:3)0.0
(superENSOevents,PDO,NAO,etc.)caused byvariations Coastalrunoff
inclimate,tidalforcesandEarth’srateofrotation, andther- Atriveroutlets 1–2
mal expansion, which differs significantly with water depth Evaporation/precipitation
(Fig.2). Indianoceanevaporationlow 0.3–0.4
On a yearly scale, sea level varies locally because of Airpressure
dynamic factors and El Niño–Southern Oscillation (ENSO) 1millibar 0.01
MonsoonalrangeatBangladesh 0.15
effects.
Rotationrateandsealevel
~15msrotation(LOD) 1
TheSea-LevelDebate
In the 1960s the debate was intensive whether sea level,
Sea-level changes wererecorded and debatedfrom the early after the last glaciation maximum, rose with oscillations in
eighteenth century(Mörner 1987). The effectsof changesin mid-Holocene time reaching even above the present level
rotation,inoceanbasinsubsidence,indeflectionoftheplumb (Fairbridge 1961) or as a smooth line continually rising to
line,andinglaciationwereadvocated.Withtherecordingof its present level (Shepard 1963). The curves of Jelgersma
multipleIceAges,itbecamenaturaltoconsidercyclicchanges (1961), Scholl (1964), Mörner (1969), and Tooley (1974)
inglacialeustaticvolumeoftheoceans(e.g.,Daly1934). added detailed records from single regions backed up by
numerous dates ruling out the occurrence of high-amplitude
ChangingSeaLevels 3
ChangingSeaLevels,Fig.
2 Variationsofmainfactors
affectingrelativesea-level
changesinaprofilefromlandto
theabyssaloftheoceans.Atpoint
2,theshoreorland/seainteraction,
thereisacomplicatedinterplay
betweencrustalmovements,
sedimentcompaction,and
differentoceanicvariables.The
thermalexpansionfactoriszeroat
theshore,however.Intheopen
oceans,allthemainoceanic
variablesareactivelyinoperation
sea-leveloscillations.Assumingthateustaticsealevelcould themainoceaniccurrentsystemsinresponsetotheinterchange
be expressed in one globally valid eustatic curve, all differ- of angular momentum between the “solid” Earth and the
ences in observed levels had to be explained in terms of hydrosphere(e.g.,Mörner1995).Thisincludesamulti-decadal
changes in the crustal or sedimentary level. In 1971 Mörner E–W swash of oceanic water masses in the Equatorial plane
calledattentiontothefactthatmostsea-levelcurves,despite andaN–Sinterchangeofwatermassesbetweenhighandlow
very large differences in level in mid-Holocene time, con- latitudesduringsolarmaximaandminima(Mörner2017).
vergedfairlycloselyatabout8000radiocarbonyearsBP.This ThisimpliesthattheEarthwasinatotallydifferentmode
seemedtoindicateamajorcyclicredistributionoftheocean in the last 5000 years as compared with the previous
masses in Holocene time. Later, the explanation became 15,000 years with different dominant driving forces for the
obvious;thegeoidreliefissubjectedtodeformation(Mörner changesinsealevel.
1976). Consequently, each region has to define its own
regionaleustaticcurve(aglobalcurvebecameanillusion).
Clark (1980) and Peltier (1998) presented their global ToReconstructPastSea-LevelChanges
glacial isostatic loadingmodels,which calledfor major sea-
levelirregularitiesovertheglobe. Field observations of past sea-level positions are the only
The “World Atlas of Holocene Sea-Level Changes” meansofreconstructingsea-levelchangesinpre-instrumental
(Pirazzoli 1991) gives a good and comprehensive view of time.Theobservationalobjectmaybeastratigraphiclayer,a
thechangesinsealevel.Besidesglobaldifferentiationinthe morphologic feature, or single objects referring to sea-level
eustatic ocean components, the recorded relative sea-level changes.Thisobjectmustbefixedinaltitudewithrespectto
changes are strongly affected by differential tectonics and presentsealevel(thismayrangefromanabsoluteleveltoa
sedimentary compaction. Despite this complexity, one may relativelevel).Thenextstepistointerprettheobservedfield
distinguishsomegeneralregularities:allcurvesshowagen- object with respect to the sea level at the time offormation.
eral rise up to about 5000–6000 radiocarbon years BP Thisimpliesthestudyofsea-levelrelation,sedimentarychar-
followedbyanoutofphasetoopposedoscillatorytrendfor acteristics, paleoecological inference, paleoenvironmental
the last 5000–6000 years around the present zero level interpretation, and coastal dynamics. Finally, the object
(Mörner1995).Thefirstpartrecordsageneralglacialeustatic needs proper dating. After all these steps, we have a past
riseinsealevelpriorto5000–6000BPplusalocaltoregional sea-level datum or a paleo-sea-level indicator, which can be
differentiationduetotectonics,geoiddeformation,andglobal used in sea-level curves and sea-level reconstructions. The
isostatic compensation. The second part (the last qualityofthisdatumpointdependsuponthequalityofeach
5000–6000years)lacksanysignificantglacialeustaticcom- individualstepinitsestablishment.Thedatingofacontinu-
ponentandisinsteaddominatedbytheredistributionofwater ouscatching-upcoralreefgrowthmayprovideanexception-
massesaroundthepresentmeansealevel. allycontinuousrecord(e.g.,Fairbanks1989).
The redistribution of water masses during the last Wehavetounderstandthatthereisalongchainofuncer-
5000 years seems primarily to be the function of changes in tainties concerning sea-level changes as they are interpreted