Coasts & Estuaries - City of Port Adelaide Enfield - SA.Gov.au

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Coast & EstuariesOne of the major issues associated with increasing coastal development is erosion of the foreshoreand a change in the rate of sand movement along the coast.North Haven, 1949 North Haven, 1999(Source: http://www.environment.sa.gov.au/coasts/adelaide_background.html#factors)Sand Movement - beachesThe sandy beaches of Adelaide are highly modified environments that require significantmanagement to maintain. The manual management of sand has occurred over the last 30 years.The sand along the coast moves in a northerly direction, resulting in less sand on the southernbeaches and large amounts of sand along the northern beaches such as Semaphore. It is estimatedthat between 40,000 and 70,000 cubic metres of sand are moved north each year along the erodingcoastline between Brighton and Semaphore.There is currently major sand accumulation at Largs Bay, while sand has been depleted atSemaphore Park. Sand is carted from Semaphore to maintain this beach and protect coastalproperties.The manual sand management to date has been carried out by the Coast Protection Board andCouncils, and has involved beach replenishment by carting sand from the northern to southernbeaches, sand trapping and sand bypassing at Patawalonga, West Beach, and Torrens River outlet.The Department for Environment and Heritage have recently released ‘Adelaide’s Living Beaches, AStrategy for 2005 – 2025’. The current system of sand management has been reviewed, and the newplan focuses around building a series of pipelines to pump sand slurry from north to south. This sandwill also be supplemented by sand from external sources, most likely from Mount Compass.Investigations also continue into coastal structures that will capture sand at a few critical locations.An example is the breakwater installed at Semaphore South constructed to trap sand to be used forbeach replenishment.The type of pipeline system to move the sand slurry is still being explored by the State Government.A pipeline system will mean that trucks should no longer be used. The trucks can damage the sanddunes and beaches, and often need to move through residential streets.Sand DunesThe Semaphore dunes have developed over the last 30 years. The pre-European settlement dunesno longer exist due to housing development fronting the esplanade. Adjacent to the Semaphore jetty,158
Coast & Estuariesthere were no dunes in the 1970s, and by 2001 the dune width at the jetty was approximately 100m.This occurred due to the accumulation of sand on the beach as a result of changes in wavepropagation influencing the movement and deposition of sand and further exacerbated by the loss inoffshore seagrasses (Townsend, 2005).Accumulation of sand remains significant despite at least 700,000 cubic meters of sand having beenremoved to replenish southern beaches.As a result of the young age of the dunes colonising vegetation is also recent. The dunes aredominated by introduced species such as Thynopyrum juncieform (se wheat grass) and Euphorbiaparalias (sea spurge) (Townsend, 2005).Off shore impact of Port Adelaide River DredgingAs part of the Flinders Ports development, dredging of the Port Adelaide River has been completed,resulting in the deepening of the channel by 2 metres to accommodate large ships.Land based disposal was not undertaken - the dredged soil was deposited off shore in the Gulf StVincent. It was suggested that this activity may threaten off-shore marine ecosystems by potentiallyspreading Caulerpa racemosa and Caulerpa taxifolia. The wider spread of this invisible alga issignificantly detrimental to seagrasses already under threat in this area. A point worthy ofconsideration and follow up is that the impacts of an influx of soil into the Gulf may lead to thesmothering of benthic (living on or in sediments of the sea floor) flora and fauna and increasedturbidity.Stormwater and waste water discharge to the seaLocally stormwater is discharged to the coast through the Port Adelaide River systems, as well asseveral smaller outfalls that discharge stormwater within the dunes or directly onto the beach. Thetotal estimated annual flows from the Barker Inlet system to the sea is 10.3GL (Wilkinson et al 2005 –ACWS Technical Report No.3).The Bolivar and Port Adelaide wastewater treatment plants have discharged treated effluent into GulfSt Vincent. Effluent from the Port Adelaide plant is now diverted to the Bolivar plant for treatmentrather than being discharged into the Port Adelaide River. Up until 1993, sludge from the sewagetreatment process was also discharged offshore from the Port Adelaide plant. These dischargesincrease nutrient and sediment levels in near shore waters.In 2001/02 around 85% (or 77,329 mega litres) of this treated wastewater was discharged to the sea.Despite improvements to wastewater management and a reduction in the volume of treatedwastewater discharged in recent years, nutrient enrichment and eutrophication of marine waterscontinues. Table 31 provides more detail on the volume of treated wastewater discharged to Gulf StVincent in 2001/02.(Source: http://www.environment.sa.gov.au/coasts/adelaide_background.html#factors).159
Page 1 and 2: City of Port Adelaide EnfieldState
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Coasts & Estuaries - City of Port Adelaide Enfield - SA.Gov.au

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