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Managing Stormwater

Centennial Park’s ponds are physically linked to each other via a series of sluices and pipes, and also to the outside world via a number of major stormwater inlets. But most park users and neighbours are probably not aware of this interrelationship.

Read our Fact Sheet on Centennial Parklands' Ponds

The catchment for stormwater runoff covers about 600 hectares of which the Parklands themselves make up about 45%. A further 45% is developed land and includes the suburbs of Bondi Junction, Waverley, Paddington and Randwick. Stormwater run-off from this urban catchment flows via drains and channels controlled by Sydney Water and local councils into Centennial Park’s ponds.

Model Yacht Pond is the primary entry point for water flowing from eastern suburbs stormwater drains (see diagram below). From there water flows via underwater channels into Fly Casting Pond which in turn feeds Willow Pond, Duck Pond, Randwick Pond and finally Kensington Ponds. A gross pollutant trap and silt arrestors at the entry to Model Yacht Pond capture most of the rubbish that comes through the drain, but sometimes heavy rainfall may cause rubbish to overflow into the pond.

Musgrave Pond is fed by another stormwater inlet that also feeds One More Shot Pond before flowing into Willow Pond to join the primary system outlined above ending in Kensington Ponds. A gross pollutant trap and silt arrestors also trap a large proportion of rubbish arriving in stormwater at this point.

Busbys Pond is fed by two stormwater inlets, which in turn feeds Randwick Pond before flowing into Kensington Ponds.
Lily Pond is the only pond not fed by stormwater. Its source is a fresh water spring located in the remnant Lachlan Swamp, joining the larger system via Busbys Pond.

In heavy rainfall, water leaves the Park system from an overflow point in the Kensington Ponds – via a culvert in the Alison Road embankment. From there water flows almost three kilometres via underground pipe and formed channel to the Botany Wetlands.

The ponds were created by constructing a series of earth dams to impound water in the former Lachlan Water Reserve during the 1870s.

Surprisingly this was done in response to heavy rainfall that had caused local flooding in Alexandria and Kensington. When Centennial Park was being constructed in the 1880s the dams were incorporated into the overall design to form a series of permanent ornamental ponds.

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 Local Land Services, Sydney Water and local councils to continue to address these issues.