Dredging at Outer Harbor

January 25, 2018 | Posted in: Coastal activities, Conservation, Education, intertidal zone, Marine Protected Areas, Pollution, Stormwater

Dredging will again be carried out in the Outer Harbor shipping channel and the swing basin next winter. The EPA has recommended that Flinders Ports use a smaller dredging vessel than what was used 13 years ago. In 2005, dredge spoil spread down Gulf St Vincent, reducing visibility and smothering seagrass. Environmental groups have called for all dredged silt to be disposed of on land this time. The EPA, however, says that “the level of contamination of sea matter …. was below national guidelines”. It says that by dredging in winter, and using “a smaller “no side-casting” dredging vessel,….would reduce the amount of excavated “fine sediment” spilling back into the (Port) river and smothering seagrass during the dredging by 39%”. 2000ha of seagrass loss occurred in 2005. A 39% reduction would still lead to the loss of some 1229ha of seagrass, but the EPA says that dredging in winter will result in only 1000ha of seagrass loss. So, if everything goes to plan, only half as much of the seagrass lost in 2005 will be lost in 2018. 2000ha in 2005 and 1000ha in 2018, however, means a total loss of 3000ha!

This photo from the Friends of Gulf St Vincent shows the sediment plume following dredging of the Port River at Outer Harbor in 2005: –

Speaking of dredging, all of our metropolitan marinas require dredging sometime or other. Recall the West Beach boat ramp getting clogged up with seaweed or seagrass late last year? It seems that the Wirrina Cove marina has not been maintained as necessary and dredging of the marina and its entrance channel could take a year to complete. One can only wonder just what effect the dredging will have on nearby dive sites.

Former Onkaparinga Councillor, Rex Manson believes that the government should give the Outer Harbor dredging Major Project status so that a full EIS would be required. Rex points out that the proposed dredging would result in over 1m cubic metres of dredge spoil being dumped into the middle of Gulf St Vincent. He feels that there is a strong possibility that the resulting plume will be pushed down to Port Noarlunga reef by the predominantly northerly winds in winter. Rex was involved in having $15m spent on stormwater harvesting and sediment reduction in the Christie Creek catchment north of Port Noarlunga reef in 2006. The whole expense and effort could be ruined by the proposed dredging at Outer Harbor.

Container shipping at Outer Harbor

(Taken by Steve Reynolds)

Once the seagrass is gone, it’s gone for good, destabilizing sand drift even further along our metropolitan beaches. Commercial fishers have indicated they will picket the Port River to stop the spoil being dropped in the gulf. It has been suggested that divers and recreational fishers join in this protest.

 Our Society has sent a message to the Planning Minister, John Rau saying that the planned dredging of Outer Harbor requires that the spoil be used as landfill, not left in Gulf St Vincent to shift about and silting everything up.

 

Steve Reynolds is the current President of MLSSA and is a long-standing member of the Society. Steve is a keen diver, underwater explorer, photographer and is chief author of the Society's extensive back catalogue of newsletters and journals.

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