FAQ

The proposed basin will capture and remove litter, suspended solids and nutrients generated by runoff from the upstream urban catchments prior to discharge into the conservation park. Having the basin online maximises the volume of water that will be treated.

Based on a qualitative assessment of the potential water quality benefits of both options, it is considered that Option A would likely provide a greater level of treatment due to the greater area of macrophytes (dense vegetation) that will filter the water. 

The clearer water (during low flow events/no flows) would provide a suitable habitat for introducing native fish with a high level of diversity and abundance. 

Macroinvertebrates are also likely to thrive in the dense wetland environment offered by Option A, providing further water quality improvements Option B would not achieve the same level of water quality improvement, and it is possible that pest fish species may thrive. Water birds may prefer to land and take off within the larger open water environment, however bird numbers and diversity are likely to be greater with Option A, given the additional vegetation and habitat area.

A formalised operations and maintenance strategy will mean that captured sediments are removed from the basin, minimising the risk of resuspension during flood events. The basin (both options) will also result in:

• Improved biodiversity through diversification of plant species.

• Enhanced natural environment through removal of exotic vegetation. • Creating amenity for users of the reserve.

• Education opportunities and improved recreation (should this be desirable).

The basin will look similar to the ponds in upstream Glade Crescent wetland (refer photos in gallery). There will be visible areas of open water with dense fringing vegetation. Option A will have more vegetation than Option B.

An impervious liner will be constructed to minimise the losses from the basin, thereby maximising the duration during which there will be water in the deeper pools. The shallow pools will still dry out during summer. Water balance modelling shows that water will be retained within the deeper pools during most years. 

The basin may still empty during extended dry periods, but this will be infrequent. The proposed plantings and a formalised maintenance strategy will mean that the amenity impacts of the basin drying out will be less than compared to the current basin.

Council did not construct the pond, it was built by private developers in the early 70’s during the construction of Hallett Cove housing estate. Although no design drawings or specifications exist, its role is to prevent sediment entering the high value conservation park and to manage peak flows to minimise downstream erosion. The pond also provides some amenity and recreational value.

Q. Why did the pond dry last year?

A. The pond emptied due to several reasons. Council engaged an independent consultancy and Flinders University to fully understand the reasons and develop longer term sustainable solutions. The reports provided concluded that the recently constructed wetlands upstream, have no material effect on downstream flows. Evaporation exceeded inflows and inflows were low due to very low annual rainfall and due to a recent change in the way water was leaking through the creek floor into the underlying bedrock.

Q. What are the three options being considered for the longer term management of water?

A. The three options presented are as follows;

·  Retain the existing basin/pond with ongoing dredging (circa every 20-25 years)

·  Re-engineer the basin to create an offline wetland (as recommended in the Stormwater Management Plan, which assessed the holistic management of the entire catchment).

·  Reinstate Waterfall Creek to its natural condition

Q. How are the three options, currently under consideration being assessed?

A. A multiple criteria analysis was undertaken by an independent consultancy, with consideration to social, environmental and economic factors.

Q. Which option is recommended and why?

A. The wetland option has been recommended because of the high score for visual amenity, semi-permanent waterbody, educational and recreational opportunities. The wetland scores highest for ecological benefits, providing the greatest water quality improvement, increases in biodiversity and the potential for stormwater harvesting. From an economic perspective, the wetland had the highest whole of life costs.

The pond emptied due to several reasons. Council engaged an independent consultancy and Flinders University to fully understand the reasons and develop longer term sustainable solutions. The reports provided concluded that the recently constructed wetlands upstream, have no material effect on downstream flows. Evaporation exceeded inflows and inflows were low due to very low annual rainfall and due to a recent change in the way water was leaking through the creek floor into the underlying bedrock.

Q. What are the three options being considered for the longer term management of water?

A. The three options presented are as follows;

· Retain the existing basin/pond with ongoing dredging (circa every 20-25 years)

· Re-engineer the basin to create an offline wetland (as recommended in the Stormwater Management Plan, which assessed the holistic management of the entire catchment).

· Reinstate Waterfall Creek to its natural condition

Q. How are the three options, currently under consideration being assessed?

A. A multiple criteria analysis was undertaken by an independent consultancy, with consideration to social, environmental and economic factors.

Q. Which option is recommended and why?

A. The wetland option has been recommended because of the high score for visual amenity, semi-permanent waterbody, educational and recreational opportunities. The wetland scores highest for ecological benefits, providing the greatest water quality improvement, increases in biodiversity and the potential for stormwater harvesting. From an economic perspective, the wetland had the highest whole of life costs.

The three options presented are as follows;

· Retain the existing basin/pond with ongoing dredging (circa every 20-25 years)

· Re-engineer the basin to create an offline wetland (as recommended in the Stormwater Management Plan, which assessed the holistic management of the entire catchment).

· Reinstate Waterfall Creek to its natural condition

A multiple criteria analysis was undertaken by an independent consultancy, with consideration to social, environmental and economic factors.

The wetland option has been recommended because of the high score for visual amenity, semi-permanent waterbody, educational and recreational opportunities. The wetland scores highest for ecological benefits, providing the greatest water quality improvement, increases in biodiversity and the potential for stormwater harvesting. From an economic perspective, the wetland had the highest whole of life costs.