marine sand resources off kerala coast visàvis acute shortage of construction sand in the state of...
DESCRIPTION
The availability of good quality offshore sand in the state of Kerala is increasingly becoming a rarity and the construction industry has been facing serious challenges due to the paucity of sand. The river sand mining has become unsustainable from the ecological point of view. The systematic surveys by the Marine & Coastal Survey Division of the Geological Survey of India for construction grade sand have delineated five promising areas in the offshore waters of Kerala; viz. Ponnani sector, Chavakkad sector, Alleppey sector, Kollam North sector and Kollam South sector, with an estimated resource of 2030 million tons of marine sand suitable for use in construction industry. This resource can support the requirement of sand in Kerala for the next 50 years. The widespread societal concerns about the suitability of marine sand for construction are also addressed.TRANSCRIPT
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DineshACetalMineralsandresourcesofKeralacoast
MarineSandResourcesoffKeralaCoastvisvisAcuteShortageofConstructionSandintheStateofKerala
ACDinesh1,PPraveenKumar2,NMShareef2&CJayaprakash3
Marine&CoastalSurveyDivision,GeologicalSurveyofIndia1Kolkata,2Mangalore,3BhubaneshwarEmail:[email protected]
Abstract. TheavailabilityofgoodqualityoffshoresandinthestateofKeralaisincreasinglybecominga rarityandtheconstructionindustryhasbeenfacingseriouschallengesduetothepaucityofsand.Theriver sandmininghas becomeunsustainable fromtheecological point of view. Thesystematic surveys by the Marine & Coastal Survey Division of the Geological Survey of India for construction grade sand have delineated five promisingareas in the offshore waters of Kerala; viz. Ponnani sector, Chavakkadsector, Alleppeysector,KollamNorthsectorandKollamSouthsector,withanestimatedresourceof 2030million tonsofmarinesandsuitableforuseinconstructionindustry.Thisresourcecansupporttherequirementof sandinKeralaforthenext50years.Thewidespreadsocietalconcernsaboutthesuitabilityofmarinesandfor constructionarealsoaddressed.
Introduction
ThoughseveraloffshoremineraldepositshavebeenidentifiedduringthecourseofsystematicoffshoresurveysbyGeologicalSurveyofIndia(GSI),utilizationoftheseresourcesisyettobeinitiatedinIndia.Reasonsforthisaremanifoldincludingthequestionofcommercialviability; but themost important reasonprobably is that therewasnopressingneedtoutilize theseresourcesuntilrecently.Inthecaseofconstructionsand,riversanddepositswhichareeasilyrecoverableandavailableonshorearebeingminedinstateslikeKerala.Theeaseofextraction, proximitytotheresourceandunprecedentedpaceofconstructionactivityinthestateofKeralaarethemajorfactorswhichresultedinoverexploitationoflandbasedsandresourceswithfarreachingenvironmental consequences. This has forced the Government of Kerala to imposerestrictionsonriversandminingandthatinturnhasresultedinacuteshortageofconstructiongradesandinthestate.Withafuturisticview,GSIhastakenupinvestigationforconstruction gradesandintheoffshoredomainsinasystematicmanner.TheGovernmentofKeralahasalsoevinced keen interest in finding alternate sand resources such as the ones in the outercontinentalshelfofftheStateshores.EconomicfeasibilityofoffshoresandmininghasalreadybeenprovedbymanycountrieslikeJapan,NewZealand,Netherlands,SriLankaetc.Dolageetal(2013).
Availabilityofconstructiongradesandintheterritorialwaters(TW)andbeyondoftheKeralaCoast
OccurrenceofrelictsandwithinandbeyondtheTW(TW:22.2km/12nauticalmilesfromtheshoreline)offtheWestCoastwasidentifiedbyGSIduringthecourseofroutineseabedmappingsurveys. These sand formations represent, in most cases, palaeostrandlines or buried riverchannels/estuaries formed during the past marine transgressionregression cycles, of lateQuaternary period. Preliminary investigation of sand resources by systematic widespacedsampling(5x5,5x4and4x4kmgrids)usinggrabsamplerandvibrocoreronboardRVSamudra Shaudikama at selected locations carried out by the Marine and Coastal SurveyDivision(M&CSD)ofGSIduringthelastfewyearshashelpedforfurtherdelineationofthesand
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bodies.Thetargetareasfordetailedexplorationweredemarcatedbymoderatelyclosespacedvibrocoringon1x1and2x2kmgrids(Fig.1).
Fig.1StatusofsandinvestigationoffKeralaCoast
Based on the results, a fewpromising areas have been identified for detailed exploration.Resource estimation of sand is made for five sector viz., Ponnani sector (SD214&SD239cruises), Chavakkad Sector (SD214 & SD224 Cruises), Alleppey Sector (SD233 Cruise),KollamNorthsector(SD187&SD196Cruises)andKollamSouthsector(SD222Cruise).
ThispaperisaimedatprovidingconciseinformationontheexplorationforsandsofarcarriedoutinfivepromisingsectorsofftheKeralacoast.Thedatawillbeperiodicallyupdatedasandwhennewinformationcomesupwithfurtherdetailedexplorations,sothatthelatestdatawill bereadily available to all the concerned authorities as well as the stakeholders.Further, thesocietal concerns about usability of marine sandfor constructionpurposes andminingofoffshoresandresourcesisalsodealtinthepaper.
Sampling. Insandyareas,twotypesofsamplersarecommonlyused:thegrabandthevibrocorer.Thesamplescollectedusinggrabsamplergiveanideaaboutthesurfacedistributionofsandysedimentsbasedonwhichlocationsforvibrocoringaredecided.Vibrocoring(Fig.2)isthemostsuitablemethodemployedtoretrievecoresamplesfromsandyformations.BoththecoastalvesselsofGSIRVSamudraKaustubhandRVSamudraShaudikamahavethiscoring
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facility,whereinelectricallyinducedvibrationbythevibratorymotor,(Fig.3)causesthebarrelwiththePVClinertoslowlypenetrateintosandysediments.Afterthevibrocorerunitishauledup,thePVClinercontainingthesampleisremovedandtheopenendsaresealedafterrecordingthenatureofthebottomandtopsediments.
Fig.2:Vibrocorerbeingloweredfrom Fig.3:electricalmotorof VibrocorertheaftdeckofRVSamudra
Shaudhikama
Thecoresamples are later split; (Fig.4) loggedandsubsampledat 50cmor 1mintervals dependingonthenatureofthesampleandobjectiveoftheproject.Thesubsamplesaresundriedandrepresentativesedimentsamplesweighingabout80100gmarecollectedbyconingandquarteringmethod.Thissampleisweighedandthenwashedafewtimestoremovesaltandmud(silt+clay).Thesampleisdriedandweighedagaintogettheweightofmud.Thesample, freeofmudandsalt,issubjectedtosievingat1phiinterval(using5,10,18,35,60,120and230ASTMsieves)(Table1).Theweightsofsamplesheldindifferentfractionsaredetermined.ThesievedfractionsarethentreatedwithdiluteHCltoremoveshellsandweighedagaintogettheweightofcarbonatefreefractions.Thepercentagesofgranule,carbonatesand,mudandcarbonatefreesandfractionsarethusdetermined.Drybulkdensityiscalculatedfollowingthenormalprocedure
Fig.4:Asplitcore(PVCliner)containingsandysediments
Asperthedefinitionoffineaggregate;itistheinertorchemicallyinactivematerial,mostofwhichpassesthrougha4.75mmISsieveandretainsat0.075mmsieveandcontainsnotmorethan5percentcoarsermaterial.AsperthebureauofIndianstandards(BIS)ofBritishStandard(BS),thecarbonatefraction(shells)lessthan5mmdoesnotaffect thestabilityofconcrete.Hence,thetermSANDisusedheretoincludeallfractions(carbonateandcarbonatefree)lessthanorequalto4mm(5ASTMsieve)andmorethan0.0625mm(230ASTMsieve).
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Table1:SizesandterminologyoffractionsofSand
ASTM(meshsize)
Phi( ) mmTerminology(Udden,1914&Wentworth,1922)
510 2to1 42 Granule1018 1to0 21 Verycoarsesand1835 0to1 10.5 Coarsesand3560 1to2 0.50.25 Mediumsand60120 2to3 0.250.125 Finesand120230 3to4 0.1250.063 Veryfinesand
SandResources. Sandresourcesinthebelowmentionedfivesectorswereestimatedfortheavailable core length bycreating sand tonnageraster using sediment thickness raster, sandpercentraster,drybulkdensityandpixelareainArcGIS.TheresourcesestimatedforthefivesectorsaregiveninTable2inweightaswellasinvolume(Table1.2).Thesamplingintervalfor Ponnani,Chavakkad,AlleppeyandKollamSouthSectorsare2Kmx2KmwhereasforKollamNorthSector it is 1Kmx1Km.Theresourcesestimationcanbefurther refinedbydetailedexplorationbysamplingin250mx250mor500mx500mgrids.
Fig.5:Pointshapefileforsamplepoints
SandResourceestimation. Forsandresourceestimation, PointshapefileswerepreparedinArcGIS9.3.andprojectedtoUTM(Fig.5).Asedimentthicknessrastersurfaceiscreatedusingthecorelengthandshowninfig.6.Interpolationrasterswerecreatedforsedimentthickness,sandpercentageandsandtonnagefollowingIDW(InverseDistanceWeighted)method.Sandpercentageraster(Fig.7)wascreatedusingthesandpercentagewhichincludesallcarbonateandnoncarbonatefractionshavingthesizebetween4mmand0.0625mm.Rastersurfaceforsandtonnage(Fig.8)iscreatedusingtheformula:thicknessraster*sandpercentageraster/100*bulkdensity*cellsize.ThemapAlgebrawindowwiththeformulaforcreatingsandtonnagerasterisgiveninFig.8.Foruniformityandconsideringthesamplinginterval,acellsizeof50mx50mwasselectedforallthefivesectors.Hencetheareaofeachcellis2500sq.m.
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Fig.6:Sedimentthicknessraster Fig.7:Sandpercentageraster
Fig.8:MapAlgebraexpressiontocreatesandtonnageraster Fig.9:SandtonnagerasterPonnaniSector.Sandtonnagevariesinaverywiderangefrom0to15600duetothepresenceofmuddominatedsedimentsalongtheperipheryofthesector.Thesandtonnageisobservedmaximumatthecentreofthesector(Fig.10).Astudyofthespatialdistributionofdifferenttypesofsediments inthesurfaceandbeyondandthedatainterpolatedaswell suggests thatthePonnani Sector could be a part of a palaeoestuary into which the palaeochannel ofBharathapuzhaRiverdebouchedandoccupiedthecentral part of thesector.ThetotalsandresourceestimatedinPonnaniSectoris597milliontons.
ChavakkadSector. Thesandpercentageismaximumintheeasternandwesternpartofthesector(Fig.11).Sandtonnagevariesinaverywiderangefrom0.1to12450duetothepresenceofmuddominatedsedimentsatthetopandbottomofthesector.Thespatialdistributionofthedifferent typesofsedimentsinthesurfaceandsubsurface,aswell astheinterpolateddatasuggeststhattheChavakkadSectorcouldbeapartofapalaeoestuaryintowhichthepalaeochannelofChetwaiRiverdebouchedandoccupiedthecentralpartoftheestuary.ThetotalsandresourceestimatedinChavakkadSectoris202milliontons.
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Fig.10.EstimatedsandresourceinPonnaniSectorFig.11.EstimatedsandresourceinChavakkadSector
Fig.12.EstimatedsandresourceinAlleppeySector
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AlleppeySector.Sandpercentageismorethan82%inmostoftheareaexceptafewpatches.Sandtonnagevariesinawiderangefrom557to12670(Fig.12).Maximumtonnageisobservedwherethesedimentthicknessismore.Thespatialdistributionofthesedimentsinthesurfaceandsubsurfaceinconjunctionwiththeinterpolateddata,theorientationanddispositionofthesand body suggests that Alleppey Sector could be a part of a palaeostrand body whichsubmerged under sea during the Holocene transgression. The sand resource estimated inAlleppeySectoris742milliontons.KollamNorthSector. Sandtonnagevaries inawiderangefrom1097to12886.Maximumtonnageisobservedwherethesedimentthicknessismore(Fig.13).Thespatialdistributionof thesediments in thesurfaceandsubsurface inconjunctionwiththe interpolateddata, theorientationanddispositionofthesandbodysuggeststhatKollamNorthSectorcouldbeapartofapalaeostrandbodylikeAlleppeySectorwhichsubmergedunderseaduringtheHolocenetransgression.ThesandresourceestimatedinKollamNorthSectoris343milliontons.
Fig.13.EstimatedsandresourceinKollamNorthSectorFig.14.EstimatedsandresourceinKollamSouthSector
KollamSouthSector.Sandpercentageismorethan92%inthecentralpartofthesector.Sandtonnagewasinterpolatedusingtheformulagiveninthe initialchapterandwasreclassified(Fig.14).Sandtonnagevariesinawiderangefrom550to5600.Maximumtonnageisobservedinthecentralpartofthesector.Thespatialdistributionofthesedimentsinthesurfaceandsubsurfaceinconjunctionwiththeinterpolateddata,theorientationanddispositionofthesandbodysuggeststhatKollamSouthSectorcouldbeapartofapalaeostrandbodylikethatof KollamNorthSectorwhichsubmergedunderseaduringtheHolocenetransgression.ThesandresourceestimatedinKollamNorthSectoris146milliontons.
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Table2:SandResourcesEstimatedforFiveSectors
P.V.Sukumaranetal(2010)hasgivenapreliminaryassessmentofsandresourcesintheKeralaoffshore,viz.probablesandreservesof184milliontonnesoveranareaof180sqkmtoadepthof1.5mdownfromtheseafloorandlocated2540kmawayfromthecoastoffKollamand267milliontonnesoveranareaof500sqkmoffKannur1336milliontonnesoveranareaof543sqkmoffChavakkad.
SocioeconomicSignificanceofMarineSand.Sandandconstructionaggregates,whichincludecrushedrock,areclassifiedasminormineralandaresubjectedtoverylittle,miningregulationsbytheregulatoryauthoritiescomparedtootherminerals.Butthesandandaggregatesconstitutethelargestcommodityinminingindustryintheworldbyvolumeaswellasbyvalueamongthenonfuelminerals.So,forallpracticalpurposes,sandisthemajormineralamongthenonfuelmineralsintheworld.Inrecenttimes,constructionindustryhasbeenfacingseriouschallengesduetothepaucityofsand.Theunprecedentedboominconstructionindustryhasmaderiver sandminingunsustainable fromtheecological point of view. Unregulatedsandmininghasadverselyaffectedtheriversnotonlyfromanenvironmentalperspective,butaestheticallytoo.RivershavebeenthecradleofcivilisationssincetimeimmemorialandIndiahasaculturalandemotionalbondingwithmostofitsrivers. Theenvironmentalimpactcausedbytheunregulatedriversandmining,scarcityofsandandtheresultantpriceescalationetc.,areadverselyaffectingthesensitivesocioeconomicandenvironmental fabric and is increasingly felt bymanystates in India, especially Kerala. Theerosion of river banks leads to loss of valuable agricultural and commercial land, weakensstructureslikebridges,roads,buildingsetc.,posesseriouschallengetohumanlifeaswellastheeconomy.Groundwaterlevelsgetdrasticallyloweredandwaterqualitygetsaffectedduetosalt waterintrusionparticularlyincoastalareas.Italsoadverselyimpactstheriparianhabitat.Anoffshootofthehighdemandandconsequenthighcostofsandhasalreadybeenrecognisedasanissueleadingtoalawandorderprobleminmanypartsofthecountry. Many countries like England, France, Germany, Netherlands, and Switzerland havealreadybannedriversandminingandmanyothernationsoftheworldareimposingsevereregulations.InIndiatoo,theMinistryofEnvironment&ForestandNationalGreenTribunalhaveinitiatedplacingsevererestrictionsonsandmining.Recently,Msand,ormanufacturedsand produced by crushing of rocks has entered the market and is being considered as areplacementfornaturalsand.However,all thecrushedrockmaterialcannotbeusedintheconstructionindustry.Besides,largescalerockminingalsowillhaveaseriousimpactontheenvironmentapartfromtheairpollutionitcancreate.Fromanengineeringperspectivealso,theMsandisnotasensustrictoalternativetonaturalsandastheflakydustinthemcouldaffectthesuitabilityofmortarandthepresenceofchemicallyactivemineralscouldaffectthestrengthofconcrete. Hence, only those particles that meet the specifications will qualify as a fairreplacement for natural sand. But what is available in the market today, hardly meets thespecified standards. Natural sand is predominantly composed of quartz, which is inert orchemicallyinactiveandsoisamoststablemineral,whereasMsandcomprisesdifferentfelsicandmaficmineralsinvaryingproportionsandmanyarechemicallyactivetoo.Theirefficacyor
ShajiE&PradeepkumarAP(Eds)2014MineralResourcesofKeralaTrivandrum:DeptofGeologyUnivofKeralaISBN9788192344904100
Sector EstimatedSandResources(inmilliontons) (inmillioncubicmeter)
Ponnani 597 346Chavakad 202 150Alleppey 742 431KollamNorth 343 250KollamSouth 146 116Total 2030 1293
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otherwiseonstructuresinthelongrunisyettobeproven.Addedtothisistheveryhighcostof Msand which has multiplied the construction cost. This has its own ramifications ininfrastructureindustryandeconomyofthestateofKerala.ItisundersuchascenariothattheMarineSandDeposits withintheTerritorial Waters(TW)andtheExclusiveEconomicZone(EEZ) off Kerala coast needs to be considered for its availability and suitability in theconstructionindustry.Thereisawidespreadapprehensioninthesocietyabouttheusefulnessofmarinesandforconstructionpurposes.Anattempthasbeenmadeheretoallayallsuchfearswithscientificexplanation.
ConcernNo.1:EffectofsaltcontentinMarinesandanditssuitabilityforuseinconcrete.Chloridecontentinthetotalcementmixdeterminestheextentofcorrosioninconcrete.AspertheBritishStandard(BS882:1992),thechlorideioncontentpermissibleforreinforcedconcreteis0.05weight%,prestressedconcreteis0.01weight%(Table3).AconservativeestimateofthechloridecontentpermissibleinOrdinaryPortlandCement(OPC)foruseinconcreteis0.075weight%.
Table3.BritishStandardonChlorideionContent(wt%).
Permissiblechlorideinconcreteis0.3percentbyweightofcement.Cementtoohaschlorideupto0.05percent.So,offshoresandcanaffordtohavechlorideupto0.25percentwithoutanydeleteriousinfluence.EachcubicmetreofGrade25concretemixturecontains339kgofcementand837kgofsand. Hence, sandcanaffordtohavechlorideupto0.101percent(0.25x 339/837).ThechlorideinfreshoffshoresanddredgedfromcertainpartsofSriLankanoffshoreis0.04percentwhichisfarbelowtheacceptablelevelof0.101percent.Evenarainfallaslowas9.9mmcanreducethechloridecontent(rangefrom0.01to0.05)tolevelsfarbelowtheadmissiblelimit(0.101)whenexposedtorains.Rainfallsashighas581mmcouldwashawaychlorides almost completely(Dolageet al., 2013). Inastate likeKeralawhere theaverageannualrainfall ismorethan3000mm,dredgedmarinesandcanbestockpiledasshowninFig.15andwashthechloridesawaybyexposingtorain.
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BRITISH STANDARD Chloride ion Content
(expressed as Mass % Aggregate)Pre stressed concrete / Heat cured ConcreteContaining embedded metal : 0.01
Concrete Containing embedded metal made with cement complying BS 4027 :0.03
Concrete Containing embedded metal made with cement complying BS 12BS 146, BS1370, BS 4246, BS6588, BS6610:0.05(Reinforced concrete)
Other Concrete : No Limit
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Diasetal.,(2008)carriedoutacomprehensivestudybyusingoffshoresandsamplesobtainedfromastockpile,dredgedintheyear2002,justnorthofColombo,SriLanka,andconcludedthatoffshore sand is suitable for reinforced concreting work. Studies of Limeira and Etxeberria(2010)andLimeiraetal.,(2011)alsoshowthatdredgedmarinesedimentcanbesuccessfullyusedasafineaggregateforconcreteproduction.
Fig.15.EstuarineSandpileatPonnani(Kerala)harbournearBharathapuzharivermouth
ConcernNo.2:presenceofshellsfragmentsinmarinesandThe presence of shells and shell fragments is viewed by many as a deleterious factor inconstructionsand.Offshoresandmaycontainalargeamountofshellsandshellfragments.Butshellhasnoadverseeffectonstrengthbuttheworkabilityisreducediftheconcreteismadewithaggregatehavinglargeshellcontent,ChapmenandRoeder(1969). Withrespecttotheeffectofshellandotherimpurities,Limeiraeta.l(2011) statesthatthepresenceofsmall,normallyacceptablepercentagesofcoal,chalkorclayisunlikelytoaffectworkability.AspertheBritish Standard(BSEN1971:2011) specification for aggregates fromnatural resources inconcrete,publishedinSept.2011,sandasaggregateforuseinconcreteisthatforallwhosesizeiscoarserthan10mm,theshellcontentallowedismaximumof8%,forallaggregatesfinerthan10mmandcoarserthan5mm,theshellcontentpermissibleis20%andforaggregatesfinerthan5mm,thepresenceof shell fragments is immaterial (Table4). Theaverageshell content inKeralaoffshoresandis 510percent. As perBureauof Indianstandards(IS:2386(Part II)1963), the amount of deleterious substance in the form of soft/shell fragments in fineaggregates, is immaterial. This implies that thepresenceof shell fragments matters only inaggregatescoarserthan5mm,andforsandoffinersizewhichismainlyusedinconstructionindustry,theshellisconsideredaspartofthemineralgrainsinceitdoesnotaffectthestrengthordurabilityofthestructure. Themajortakeawayisthat,thelimitsonshell contentisnotapplicable to fine aggregate below 4.5mm i.e. for grains classified as SAND as per thespecificationgivenbyeitherBISorBS.
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Table4.BritishStandardonLimitsonShellContent(wt%)
ConcernNo.3:StrengthofconcretemadeofmarinesandDolageetal.,(2013)presentedtheconcretemixdesignresults,togetherwithstrengthresults,forconcretesmadewithoffshoresandforgrade25concrete,thatbeingthemostwidelyusedstructuralconcrete.Thefreshoffshoresand,withoutbeingwashedandcleaned,wasusedfortheconcretemixdesignspecifiedinthepaper.Intheirstudy,freshlydredgedoffshoresandbroughttothesitewasusedwithaviewtocheckthestrengthofconcrete.Fromtheresultsobtainedforgrade25concreteitcanbeseenthatthestrengthofconcreteiswithinthespecifiedlimits.SimilarstudyonoffshoresandstockpiledatMuthurajawela(SriLanka)showsthatthecompressivestrengthiswithintherequiredlevel(Diasetal.,2008).
ConcernNo.4:EnvironmentalissuesofOffshoreSandMiningThemajorconcernsregardingtheeffectsofmarinesandminingonenvironmentare:
1. CoastalerosionandSlopeerosion2. Effectonmarinefloraandfauna
CoastalerosionandSlopestability.Thedistributionofmarinesand,identifiedintheoffshoreofKerala,iswidelyvaryingandisinfluencedbymanyfactors.TheminimumwaterdepthanddistancefromtheshoreineachsectorisgivenintheTable5.
Table5.MinimumwaterdepthanddistancefromshoreSector WaterDepth(m) Distance(Km)Ponnani 20 10Chavakad 25 13Alleppey 20 11KollamNorth 50 29KollamSouth 40 12
Sandminingisproposedtobecarriedoutbeyond20mwaterdepth.Sincethesedepthsaremuchbeyondthedepthofclosure,thereislittlechanceofminingaffectingthelittoralzoneor
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theshoreline. Moreover, theseabedslopebeyondtheterritorial wateris negligiblylowlikeabout20mper10000m,i.e.theslopeangleis0.1.Therefore,thechanceofslopefailureduetominingattheminingsitesoratthedistantslopedoesnotexist.Sincetheproposedsandminingisbeyond20mwaterdepth,whichis,onanaverage,atleast10kmawayfromthepresentdayshoreline,anyminingactivityatsuchafaroffdistancefromtheshorewillhaveextremelylessimpactontheshorelinetotriggererosion.ThestudybyHobbs(2007)hasprovedthat changes in wave transformation resulting from modifying the bottom topography arerelativelysmalland,asthesandminingsitestendtobeinwatersgreaterthan10mdeepthe impactwillbeminimal.
Effect onmarine floraand fauna. Another apprehension amongthepublic, especially thefishermencommunity,relatestotheimpactofsandminingonthemarinefaunaincludingthefishes. They fear that marine sandmining candisrupt habitat anddisturb fishes andothermarineanimals.Themarineanimalslikelytoliveonsandybottomaredemersalfishes,starfish, seaurchin,crabs,shrimps,gastropods,squillaetc.StudiesbyCMFRI(CentralMarineFisheriesResearchInstitute)incollaborationwithM&CSD,MangaloreduringtheSD229cruiseshowthatthesandysedimentscollectedoffAlleppeyareoflowtomediumfertilityandwaterisofnormal quality. Further, copepod is dominant among zooplanktons. Field study testing the draftmonitoringprotocolwasconductedintheactive,sandminingregionofSandbridgeShoal,offVirginiaBeach,Virginia,USAbyHobbs(2007).Resultsindicatethatrepopulationofdredgedareas is enhancedby leavingpatchesof undisturbedbottomwithinthedredgedregion. Nonegativeimpactsonmacrobenthosordemersalfisheswerenoted. Whileallayingthefearsofgeneralpublicaswellaspolicymakersregardingthelikelyimpactofoffshoresandminingonthe marine habitat, it will be prudent to understand the impact monsoonwaves anddailytrawlingcreateontheseabottombychurningmudintosuspension.However,theadverseeffectofsandminingifany,onmarinefloraandfaunahastobestudiedindetail.
Conclusion
TheestimatedmarinesandresourcewithinthefivesectorsoffKeralacoastisabout2030milliontonnes.Thiswillbesufficienttomeetthesandrequirementofconstructionindustryinthestateforabout50years@40milliontonnesperyear.CentralWaterResourceDevelopmentandManagement(CWRDM)(1999)hasestimatedthat32milliontonnesperyearistheaverageconsumptionofsandinthefieldofconstruction.Studieshaveprovedbeyonddoubtthatmarinesandissuitableforconstructionpurposes.Theimpactofmarinesandminingontheseafloorcanbe controlled if it is exploited scientifically. A proper monitoring mechanism and strictcomplianceofmininglawswillenableustoutilizethishugenaturalresourceforthebenefitofsocietywithoutdegradingtheenvironment.Aresponsibleapproachwillensurethatresourcesareutilizedscientificallyandsustainably.
Acknowledgements
TheauthorswishtoexpresstheirsincerethankstoDr.S.K.Wadhawan,DirectorGeneral,GSIforpermittingtopublishthispaperaswellasforhisconstantencouragementforpublication.OursincethankstoDr.S.Kannan,DeputyDirectorGeneral,marineandCoastalSurveyDivision,GSIforscrutinyofthepaper, valuablecommentsandhelpprovided. TheauthorsexpresstheiroverwhelminggratitudetotheparticipantsofmarinescientificcruisesSD214,SD239,SD214,SD224,SD233Cruise,SD196andSD222whohavepainstakinglycollectedthesamplesandcarriedoutthelaboratoryanalysis.
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ShajiE&PradeepkumarAP(Eds)2014MineralResourcesofKeralaTrivandrum:DeptofGeologyUnivofKeralaISBN9788192344904105