Oaklands Wetland Background and Functionality

Project background

A wetland on the existing Driver Training Centre at Oaklands Park has been under consideration since the mid 1990s. There are numerous social, environmental and cultural benefits.

The wetland will treat stormwater harvested from the Sturt Drain. The wetland will remove contaminants from the catchment runoff which would otherwise discharge into the Sturt River and ultimately into the Gulf St Vincent.

Council and the Adelaide and Mount Lofty Ranges Natural Resources Management Board (NRM Board) have been collaborating on the proposed scheme for 12 years.

The project will be delivered jointly by council and the NRM Board.

The Oaklands Wetland Project is being co-funded by the City of Marion, the Adelaide and Mt Lofty Ranges Natural Resources Management Board and the Australian Government's Water for the Future initiative through the National Urban Water and Desalination Plan.

To confirm the aquifer's capacity to store the treated stormwater, a new investigation bore was drilled and tested in May 2011.


Past project updates

Wetland landscaping

The project site has two distinct sides – the eastern side being more urban and formal and the western side being more natural and informal – refer to Figure 1. The western side is dominated by large trees, some of which are Kaurna heritage scar trees. The community supported this concept of the two (formal and informal) sides throughout the feedback period.

Figure 1 – Oaklands Precinct
Oaklands Precinct
 
Figure 2 – Oaklands Wetland Concept Plan
   Oaklands Wetland Concept Plan
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Oaklands Wetland Plan with Legend(672 kb)

The wetland’s concept plan responds to these site conditions by being shaped more formally with a concrete path along it at its eastern boundary. The wetland’s western side blends in with its natural environment through informal walking trails. The final and most northern wetland cell, which forms an entry statement off Oaklands Road has a stronger urban design with hard edges. The inlet pond is also designed in the urban context although at the start of the wetland (southern end).

The wetland shape is guided as much as possible by the existing vegetation on site, that is wherever possible significant trees will be retained. Close communication has been maintained throughout the wetland design with City of Marion’s coordinators of arboriculture and biodiversity.

Wetland and ASR functionality

The wetlands at Oaklands Park are designed to receive stormwater flows from the adjacent Sturt River channel. Flow will be collected in a sump beneath the existing concrete channel. SA Water have provided in-principle support for this concept. From this sump a pipe will deliver flows to a new pump station and rising main to deliver flows into the inlet pond of the wetlands at a maximum pumping rate of 50 L/s.

A gross pollutant trap (GPT) will be installed just upstream of the inlet pond to remove the majority of debris carried in the stormwater. This will then deliver flows (by gravity) to the inlet pond of the wetlands. The wetland area has a natural fall of approximately 1.5 metres from south to north.

The inlet pond of the wetland is set at the highest levels of the wetland and is used to collect coarse sediments (any passing through the GPT). It will be predominately open water with edge vegetation. The inlet pond will also serve to regulate flows into the macrophyte area of the wetland with two equal length weirs dividing the flows into two ‘arms’ of the wetlands evenly. It is proposed to connect the two wetland boundaries to the ‘tree island’ between the two ‘arms’ via a boardwalk with a kicker and a stepping stone walk just south of the cascade.

The main macrophyte areas of the wetlands are divided into two levels to work with the site topography and also to reduce earthworks around existing trees. Two cascades (or weirs) are incorporated into the design, one at the inlet pond and one between the two macrophyte cells.

The wetland is designed to have a 2-3 day detention time. This is used to provide sufficient treatment for inflows to be suitable for ASR injection. The wetland has a series of connected deeper pools. These allow the system to be drained for maintenance purposes. Experiences on other harvesting wetlands in Adelaide suggest the ingress of pest fish species represents a significant risk to wetland function.

Outflows from the wetland are collected in an underground pump pit (wetland outlet pit) at the northern end of the wetland. The pumps will deliver treated water via a dedicated injection ring main to six ASR wells at suitable flows and pressure to enable sufficient injection. There will be 5 new bores required as one bore was drilled in April 2011.

The ASR wells are spaced approximately 150m apart (refer to Figure 3) and will be drilled to 120m targeting the Tertiary limestone aquifer. The wells are located at the perimeter of the site to avoid the wetland area in the middle and to manage the pressure in the aquifer due to water injection.

Extraction pumps in each well will enable injected water to be recovered and transferred (via a dedicated extraction ring main) to a buffer tank located at the north west of the site.

The buffer tank will be connected to a distribution pump station within the existing work shed also in the north-western corner of the site. The distribution pump station will supply water through a network of reticulation pipes to nominated council reserves. The distribution pump station will be configured to have outflows at two pressures, a lower pressure to supply reserves to the north (i.e. downhill) and a higher pressure output to supply reserves to the south (i.e. uphill).

Wetland Integration with Open Space Master Plan

The wetland footprint has been developed to ensure that it integrates with options canvassed with the community regarding the future development of the overall precinct.

The wetland footprint will enable the future development of all of the open space/recreation facilities and components whilst ensuring that council has flexibility in determining their final location on the site.

Stage 1 will incorporate the wetland design and construction taking place from June 2012 (design) and construction of the wetland to be completed by December 2013.

Stage 2 incorporates the open space and recreation components with timing for implementation to be staged and dependent upon funding availability. A funding application for $800,000 has been lodged with the Department of Planning, Transport and Infrastructure to contribute towards this stage.

Figure 3 - Layout of the main components of the Oaklands Park
stormwater harvesting system
Oaklands Wetland Stormwater system
Download the: Oaklands Park Stormwater Harvesting System(214 kb) 
Managed Aquifer Recharge Scheme

Managed aquifer recharge (MAR) is the purposeful recharge of water to aquifers through mechanisms such as injection wells, infiltration basins and galleries for rainwater, stormwater, reclaimed water, mains water and water from other aquifers for subsequent recovery for a variety of uses or environmental benefit (Dillon et al. 2009).

The type of MAR scheme to be adopted is governed by the local situation, that is, type of aquifer, topography, land use, source water and intended uses of the recovered water. The National Water Commission’s Waterlines Report No 13 on Managed Aquifer Recharge (2009) identifies 14 different methods of MAR.

It is considered that aquifer storage and recovery (ASR) is the most suitable method to support the storage and recovery of water under the Oaklands Park Stormwater Reuse Scheme. ASR entails the injection of water into a well for storage and recovery from the same well. This method is useful in brackish aquifers, where storage is the primary goal and water treatment is a smaller consideration e.g. Grange Golf Course, South Australia (Dillon et al. 2009).

In the Adelaide Metropolitan area under the Environment Protection Act 1993 ASR is a prescribed activity of environmental significance and requires licensing by the South Australian Environment Protection Authority (SA EPA).