Regional Report ShorelineChangesintheWestern IndianOceanRegion 1. INTRODUCTION Theissueofshorelinechangeshasincreasinglybecomeamajorsocial,economicandenvironmental concerntoalargenumberofcountriesinthewesternIndianOcean(WIO)region,whereitposesaserious problemtotheenvironmentandhumansettlements.Anumberofinitiativesaimedatassessingthestateof erosionhavebeenimplementedbydifferentorganizations,butthedevelopmentoflong-termcoastal erosionmonitoringprogrammeshasnottakenplaceanywhereintheregiondespitetheavailabilityof differenttools,suchasmanuals,preparedspecificallyforthatpurpose Variouspreventionandmitigationmeasureshavebeenusedtoaddresstheproblemsofcoastal erosion,butmostofthemhavefailedtobringaboutanyreduction,andsomehaveactuallyexacerbatedthe problem.Oneofthemainreasonsfortheirfailureisthatmostofthemhavebeenappliedwithoutthe supportoflong-terminformationonerosionprocessesandrates,oradequatetechnicalsupport. ThedevelopmentofamanualonmonitoringofshorelinechangeintheWesternIndianOceanregion byIOC-UNESCO(KairuandNyandwi,2000)wasamongthefirstinitiativestoaddresstheproblem.In furtheranceofthevariousinitiativesbystakeholderstoaddresstheproblemanditsimpactsonthecoastal environment,thereisanurgentneedtodevelopmanagementtools,strategiesandmethodsand environmentallyfriendlystructurestoreduceandmitigatetheimpactofshorelinechange. TheThirdMeetingoftheContractingParties(ConferenceofParties,COP)totheNairobi Convention—ConventionfortheProtection,Management,andDevelopmentoftheMarineandCoastal EnvironmentoftheEasternAfricanRegion—heldinMaputo,inDecember2001discussedandapproveda biennial(2002–2003)workprogramme. TheworkprogrammeaimsatprovidingUNEP,astheSecretariatoftheNairobiConvention,the PartiestotheConventionandpartnerswithaframeworkforcoordinatingandimplementingpriority activitiesidentified.Theworkprogrammeistheproductofacollaborative,participatoryandconsultative processbetweenUNEP,GovernmentsofStatesPartiestotheConvention,andpartners. Theworkprogrammeidentifiedpriorityactivitiesthatfocusonfivemainthemes–assessment, management,co-ordination,andlegalaspects,andcrosscuttingissuese.g.informationdisseminationand exchangeaswellasemergingissues. Inthebiennialworkprogramme,underthethemesofassessmentandmanagementofthecoastaland marineenvironment,Ê(a)coralreefsandtheirassociatedecosystems,(b)shorelinechangesand(c)land- basedsourcesofpollution,haveallbeendefinedaspriorityissues. InfulfillmentoftherecommendationsofthethirdCOP,aRegionalCoastalErosionWorkshopwas heldinNovember2002,inNairobi,Kenya.Themainobjectivesoftheworkshopweretoreview,evaluate anddiscuss: Successfulapproachesintheimplementationofappropriatemitigationmethods,includingeffective enforcementofenvironmentalimpactassessmentrequirementsandregulationofcoastalconstruction anddevelopmentwheretheyexist; Reportsonactualdemonstrationprojectstorestorehabitatsaffectedbycoastalerosionusing acceptablemitigationmeasuresandlessonslearned,and 1 Shoreline changes in the western indian Ocean region Successfulplanningandapprovalprocessforspecialareamanagementplansforerosion-proneareas wheretheyexist. Theparticipantstotheworkshoppresentedseveralcasestudiesthataredemonstratingsuccessesand failuresofdifferentapproachesundertakentoaddressshorelinechangesindifferentcountriesinthe region.Itwasagreedthatareportdescribingthesecasestudiesandtheirresourcesneedsindetailshould beprepared,highlightingpriorityactivitiesthatneedtobeundertaken.Thisreporthasbeenpreparedto fulfillthatpurpose. Thisreportisstructuredasfollows: SectionTwointroducestheregionintermsofitsclimaticconditions,hydrodynamicprocessesandthemain geomorphologicalfeaturesandrelatingthemtothevulnerabilitytoshorelinechangesofdifferentareas. SectionThreedescribestheshorelinechangeproblem.SectionFourdiscussessomeofthenaturalcauses aswellashumanactivities,thatthroughacomplexinteraction,arecontributingtotheshorelinechange experiencedindifferentareasoftheregion.Themainsocial,economicandenvironmentalimpactsof shorelinechangearehighlightedinSectionFive,whileSectionSixfocusesonvariousmeasures,strategies andmethodsthathavebeenundertakentoaddressshorelinechangeproblemsintheregion.SectionSeven discussesanumberoflessonsidentifiedfromtheanalysisoftheinformationprovidedinthecasestudiesas wellasothersourcesofinformation.SectionEightproposesmorespecificrecommendationstodealwith theissuesandproblemsidentifiedinthereport. 2. GENERAL OVERVIEW OF PHYSICAL AND GEOLOGICAL PROCESSES IN THE WIO REGION ThewesternIndianOceanregionencompassesawiderangeofenvironmentalsettingsasitextendsfrom thewatersofSomaliainthenorth,tothesubtropicalwatersoffthecoastofnorthernSouthAfrica.The regionincludesthewatersandcoastalzonesofthefivemainlandStatesofSomalia,Kenya,Tanzania, MozambiqueandSouthAfrica;aswellastheislandStatesofMauritius,Comoros,Seychelles,Reunion (France)andMadagascar.Theregionextendsfromlatitude0oto30oSandlongitude30oto65oE(Figure1). 40° SOMALIA50° 60° ETHIOPIA 5° 5° INDIAN OCEAN UGANDA 0° KENYA 5° 5° TANZANIA SEYCHELLES I COMOROS W A L A 15° M 15° UE IQ B R M A ZA O SC M A MAURITIUS G A D A RÉUNION M 25° SOUTH AFRICA 40° 50° 60° Figure 1. Map of the western Indian Ocean(WIO) region 2 Regional Report 2.1 Climate,hydrologyandoceanography TheclimateofmostoftheWIOregionistropicalhumidanddominatedbyseasonalmovementsofthe IntertropicalConvergenceZoneandthemonsoons. ThenorthernpartoftheWesternIndianOceanregionisdominatedbythemonsoons,whichhavea dominantinfluenceonwinddirectionandstrength,oceancurrents,temperature,andrainfall,amongothers. Oceancurrentsareimportantfeaturesthatstronglyinfluencethedistributionofmarineorganismsandthe availabilityofnutrients.Themajorcurrentsintheregionarestronglyinfluencedbythemonsoonwindsandshift, reversingdirection,accordingtotheseason. Therearetwomonsoonseasons,namelytheNortheastmonsoon,whichprevailsNovembertoFebruaryand ischaracterizedbyhigherairtemperaturesandweakerwindsandtheSouthwestmonsoonwhichlastsfromApril toSeptemberandismarkedbylowertemperaturesaswellasstrongerwinds. TheSouthEquatorialCurrentandtheEastAfricanCoastalCurrentarestrongestduringtheSouthwest monsoon;theEastMadagascarandtheMozambiquecurrentsystemsarestrongestduringtheNorth-east Monsoon.TheSomaliCurrentshowsreversalsindirectionreflectingthealternatingmonsoons. ThesouthernpartoftheWIOregion,includingsouthernMozambique,Madagascar,Comoros,Reunion, andMauritius,lieswithinabeltaffectedbytropicalcyclones.CyclonesoccurduringDecemberandMarch. MostoftheWesternOceantidesaresemidiurnalormixed,mainlysemidiurnal.Tidalrangesverygreatly withintheregion(AlusaandOgallo,1992).Basedonthespringtidalrange,thetidesarecharacterisedasfollows: Micro-tidal(0.3-1m)foundmainlyintheMauritiusandtheReunion; Mesotidal(1-2m)foundmainlyintheSeychelles,theeasterncoastofMadagascarandtheRodriguez Macrotidal(above3m)foundmainlyinthemainlandcoasts,theComorosandthewesterncoastof Madagascar. 2.2 GeologyandGeomorphology Manytypesofgeologicalformationarefoundintheregion,withagesrangingfrom200millionyearsto Recent.Forinstance,theformationsofTanzaniavaryinagefromJurassicthroughCretaceoustoTertiary andQuaternary,andarecomposedofbothmarineandterrestrialsedimentaryrocks(Kentetal.,1971).The islandsofReunion,ComorosandMauritiusareessentiallyvolcanicwhilethoseoftheSeychellesare granitic. Intermsofitsgeologicalstructure,thecoastlineofEasternAfricarepresentsapassivecontinental margin,fromwhichthroughgeologicaltimecontinentalfragments,largeandsmall,haveseparatedand migratedacrosstheadjoiningoceaniccrust.Someofthesedetachedcontinentalfragmentsremainwithin theregion,notablytheSeychellesBankandMadagascar.Thisstructuralhistoryhasleftthemainlandstates withgenerallynarrowcontinentalshelves.ExceptionsincludethecoastsofsouthernMozambiqueand centralTanzania(inthevicinityofUngujaandMafiaislands)andintheIslandstatesofMadagascar(western coast)andtheSeychelles,whicharecharacterizedbyrelativelywidershelvesfeatures.Theregionhasan extensivecoastlineandanexpansivecoastalzone(Table1). ComorosandMauritiusaresurroundedbydeepwatersfromafewhundredmeterstoseveral kilometresoffshore.ThereareshallowbanksaroundRodriguezandotherMauritiandependencies.The mainislandsoftheSeychellescanbecharacterisedassteepgraniticoutcropsrisingfromabroad ‘continental’platform;whiletheAlmirantesArchipelagoisbasicallyashelfarea.Thereisanextensiveshelf- Table 1. Coastal Plains and Continental and Island Shelf Areas of the Western Indian Ocean Land area Coastal land % Coastal Shelf Coastline Country (km2) area (km2) land area area (km2) length (km) Comores 2,236 2,030 100 900 350 Kenya 582,650 32,447 6 655 500 Madagascar 595,790 242,745 41 135,000 4,000 Mauritius 1,865 1,328 100 1,600 200 Mozambique 738,030 162,938 21 120,000 2,500 Seychelles 443 455 100 48,000 600 Somalia 637,657 n/a n/a 32,500 3,000 Tanzania 939,703 6 6 30,000 800 3 Shoreline changes in the western indian Ocean region platformontheaxisbetweentheSeychellesandMauritius. TheprimarycoastaltypesoftheWIOregioninclude:Exposedlow-lyingsandycoasts;Exposedrocky coasts;Fringingreefcoasts;Patchreefcoasts;andinlets,estuariesandcreeksassociatedwiththeprimary coastaltypes(R.S.ArthurtoninKairuandNyandwi,2000).Thecomponentfaciesforeachofthecoastal type,theirmaincharacteristicsaswellassomeoftheareaswheretheyfoundareindicatedinTables2and 3. AroundMauritiusduneandridgecomplexescharacterisemostofthebeachesandthebeachwidthvaries fromafewmetresintheEasternandSouthernregionstoabout25minthenorth.Ingeneralthesediments arecorallineexceptatthemouthsofriverswheretheyaremuddywithalargecomponentofsiltandclay.In manyplacesandinparticularinthesouthernregionstherearescatteredlow-lyingbasalticrocksonthe shoreline. ThecoastlineofMozambiqueischaracterisedbyastripofbeaches,recentdunesandinlandlagoonsin