Lo­cals start to get the drift

Port Douglas & Mossman Gazette - - NEWS - Shane Ni­chols

THE angst over the pos­si­bil­ity of huge amounts of silt be­ing dumped at an en­larged ver­sion of the cur­rent Cairns port dump site – which is slightly north of Cairns and about 15 km out to sea – has been height­ened by a re­port by Sin­clair Knight Merz, com­mis­sioned by GBRMPA and filed last June.

It is sig­nif­i­cant be­cause, as Dr Eric Wolan­ski, in­de­pen­dent re­viewer to the GBRMPA stated, ‘‘for prob­a­bly the first time in the his­tory of modelling the fate of dredged sed­i­ment in the GBR, the au­thors did model the long-term fate of fine sed­i­ment af­ter ini­tial set­tling near the dump sites, ie, they at­tempted to an­swer the ques­tion where does the sed­i­ment ul­ti­mately go?’’

The dif­fer­ence is that the cur­rents have been called into the modelling. The SKM pa­pers say that ‘‘the use of large-scale cur­rents has high­lighted that dredge ma­te­rial may travel longer dis­tances, through con­stant re­sus­pen­sion from the ma­te­rial place­ment site than pre­vi­ously ap­pre­ci­ated’’.

The modelling shows wind and cur­rent pat­terns could help dredge ma­te­rial ‘‘drift’’ to the north-north west from where it is dumped.

Their modelling looked at var­i­ous sce­nar­ios us­ing the cur­rent dump site off Cairns and two more the­o­ret­i­cal ones – Model Case 1, 20 km north-north-east of Cairns port in 18m deep wa­ter; and Model Case 2, 32 km north-north­east of the port in 18 me­tres (lat­er­ally, out to sea off Rex Look­out).

In the var­i­ous sce­nar­ios sed­i­ment was ex­pected to have been found in wa­ters around Low Isles and all the way to Point Kim­ber­ley, to some de­gree or other.

Dis­cus­sion of this at the Dou­glas LMAC meet­ing last Thurs­day was ‘‘ro­bust’’, ac­cord­ing to chair­per­son Robert Hanan.

GBRMPA di­rec­tor Dr Adam Smith at­tended the meet­ing. He ex­plained the Ab­bot Pt de­ci­sion by GBRMPA, and sub­se­quently the is­sue of the Trin­ity Inlet dredg­ing came up. Lo­cal tourism oper­a­tors who are on the Dou­glas LMAC ex­pressed con­ster­na­tion at the lat­est stud­ies on pos­si­ble sed­i­ment drift from the Cairns project. Oth­ers re­marked that a goa­head with more mar­itime dump­ing ‘‘makes a mock­ery’’ of all the pol­lu­tion mit­i­ga­tion work that lo­cal farm­ers have done, and the work of the school reef guardians.

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