How does the Trust manage stormwater in the Parklands?
A six-year Parklands Pond Restoration Program - aimed at minimising the impact of stormwater pollution, upgrading several of the ponds and improving water quality – was completed in 2006.
During this period a major storm event caused a partial collapse of the Kensington Pond embankment, necessitating substantial repairs and a reassessment of the suitability of the dam for a 1 in 100 year event. The embankment was subsequently raised by 1.5 metres in height and the culvert redesigned.
Gross Pollutant Traps have been installed at most stormwater entry points. Aquatic plantings have helped to improve the aquatic habitat by filtering out some dissolved pollutants such as phosphorus.
A multi-pronged European carp removal program has been implemented and native Australian bass introduced. New islands and underwater berms were constructed to prevent areas becoming stagnant.
Regular water quality analysis is undertaken to monitor the health of the ponds. Since the restoration program, testing indicates that water quality has improved.
However as a major stormwater retention basin, the ponds will always potentially be subject to environmental factors beyond the Parklands’ control. Continuing issues are turbidity, high nutrient levels, suspended silt and other solids, and warm temperatures – a response to the shallow depth. These conditions sometimes favour the development of ephemeral algal blooms.
The ponds provide a home for large numbers of aquatic birds, and the large amount of bird faeces deposited in the water contributes to the high nitrogen and phosphorous levels that favour algal blooms.
In dry weather water flows between the ponds cease and the temporary lack of flushing of the system can lead to nutrient imbalances, de-oxygenation and sometimes sudden eutrophication.
Aquatic weed species are sometimes present. Previous severe infestations of Water Hyacinth (Eichornia crassipes) have been removed, but Mexican Water Lily (Nymphaea mexicana) originally introduced as an ornamental continues to be problematic.
The ponds in the Parklands form the largest freshwater wetland system in inner-metropolitan Sydney. Although an artificially constructed system the ponds nonetheless provide a refuge for indigenous fauna and water birds, migratory waders, fish, turtles and frogs.
An ongoing challenge
There is an ongoing need to minimise the impact of pollution from stormwater runoff into the Parklands, and to work closely with the Catchment Management Authority, Sydney Water and local councils to continue to address these issues.