Coast & Estuaries
Page 231
shore marine ecosystems by potentially spreading
Caulerpa
species
.
The wider
spread of this alga is significantly detrimental to seagrasses already under
threat in this area. A point worthy of consideration and follow up is that the
impacts of an influx of soil into the Gulf may lead to the smothering of benthic
(living on or in sediments of the sea floor) flora and fauna and increased
turbidity.
In mid 2008 the initial Penrice dredging campaign of solids recovery from the
Port River began. Approximately 50,000m
3
of sediment was removed during the
campaign. Further removal was undertaken in late 2010 (Penrice, 2010).
Stormwater and waste water discharge to the sea
Locally stormwater is discharged to the coast through the Port Adelaide River
drainage systems, as well as several smaller outfalls that discharge stormwater
within the dunes or directly onto the beach. The total estimated annual flows
from the Barker Inlet system to the sea is 10.3GL (Wilkinson et al 2005 – ACWS
Technical Report No.3). Council is developing Stormwater Management Plans
(SMPs) for its key catchments, all of which discharge collected stormwater to
the sea. SMPs are required to be developed in accordance with the State’s
Guidelines, and a key objective of an SMP is to include an assessment of the
water quality in the catchment and recommendations to improve water quality
via a range of practical strategies.
The Bolivar and now defunct Port Adelaide wastewater treatment plants have
discharged treated effluent into Gulf St Vincent in the past. Effluent that used to
be treated at the Port Adelaide plant is now diverted to the Bolivar plant for
treatment rather than being discharged into the Port Adelaide River. Up until
1993, sludge from the sewage treatment process was also discharged offshore
from the Port Adelaide plant. These discharges increased nutrient and sediment
levels in near shore waters.
In 2009/10 around 70% (or 59,612 mega litres) of Adelaide treated wastewater
was discharged to the sea. Improvements to wastewater management and a
reduction in the volume of treated wastewater discharged in recent years, has
lead in many cases to reductions in nitrogen, phosphorous, suspended solids
and soluble 'biochemical oxygen demand' (BOD) discharge to the sea. Tables
37 and 38 provide more detail on the volume of treated wastewater discharged
to Gulf St Vincent from 2002/03 onwards.
