Environmentally Friendly Stormwater Works

Stormwater Excellence Award

Stormwater Excellence Award August 2018 Mayor Glenn Spear and General Manager Dan BakerOur community and Elected Members have recently been awarded a Stormwater Excellence Award from Stormwater SA to acknowledge our support for water sensitive urban design and green infrastructure projects.

The award recognises the City of Mitcham’s involvement in progressing stormwater management and research and innovation. Council has initiated and supported research into water sensitive urban design by installing monitoring devices in streets, reserves and kerbing as well as working closely with universities and research organisations, research scientists and postgraduate students. Together we have collected, analysed and interpreted data to improve the health of our environment.

As a result our our involvement in this research we have introduced permeable paved road sections in Wheaton and Brookside Roads, large-scale soakage trenches in Thurles Reserve in St Marys and The Strand in Colonel Light Garden.

The City of Mitcham acknowledges the support from the State Government, AMLR NRM Board, universities, students, research organisations and the private sector.

Collecting stormwater to keep Mitcham green is another way Council is building a better City now and for the future.

Council, with support from the Adelaide and Mount Lofty Ranges Natural Resources Management Board, the Environment Protection Agency and Water Sensitive SA, is building water-sensitive infrastructure across Mitcham.

With a $270,000 grant from the Adelaide and Mount Lofty Ranges Natural Resources Management Board and $67,500 provided under the EPA’s Rain Garden 500 Program, Council built new rain gardens, self watering reserve soakage trenches and permeable pavements to harvest stormwater. By using stormwater locally we can keep our trees healthy, reduce downstream pollution as well as solve flooding issues.

Rain gardens have been built in Barretts Road, Clapham; Lochness Avenue, Torrens Park; Aldershot and Neville Avenues, Clarence Gardens and in Springfield. The gardens filter stormwater runoff to remove pollutants and sediment before soaking into the soil to water trees, with excess clean water discharged into the stormwater network.

In Netherby, a flood issue has been solved by upgrading drainage and soaking water into trenches on the reserve at the corner of Netherby and Bartley Avenues. Stormwater collected will help the established trees and the new Oaks and Callery Pears to flourish.

Soakage trenches totalling 180 metres in length have been installed in Thurles Avenue Reserve in St Marys. These trenches harvest stormwater from three of the surrounding streets and hold it while it soaks into the soil to water the trees. Council has also planted new trees on the reserve to help to soak up even more stormwater.

Permeable paving was included in a new footpath in Watt Street in Hawthorn and has been used in the road on parts of Norseman Avenue and Garden Road in Westbourne Park and Wheaton and Kegworth Roads in Melrose Park. Permeable paving allows water to soak through into the soil below, so it reduces flood risk and stormwater runoff while removing pollutants and helping to keep our City cool and green.

Soakage trenches and permeable paving at Kegworth Reserve in Melrose Park will help to maintain the health of the trees, including some large and significant River Red Gums.

These environmentally friendly stormwater works reduce the strain on traditional stormwater drainage, reduce flooding issues and save Council and ratepayers millions of dollars.

Harvey Hayes Reserve Rain Garden

The new rain garden constructed last year in Harvey Hayes Reserve, between Wilmott and Day Avenues in Daw Park receives stormwater from as far as Goodwood Road, soaking it into the reserve’s soil to reduce the potential for flooding downstream, while any overflow is filtered through the pond’s sedges and rushes. Indigenous plants surrounding the pond will continue to grow over the next year or two and more species will be added in the future to increase biodiversity, add colour, attract butterflies and provide improved cover for birds.

Harvey Hayes Reserve in Daw Park BeforeHarvey Hayes Reserve in Daw Park After

Treenet Inlets

Council is keeping our city greener and cooler as well as reducing flooding and pollution issues downstream by collecting rain where it falls and using it in the local environment.

In streets where much of our urban heat is generated we have been introducing Treenet Inlets.

Treenet Inlets collect stormwater from streets when it rains, the water then soaks into the verge though a ‘leaky well’, where it can be used by trees or can soak into the groundwater.

Council with assistance from the Goyder Institute for Water Research and UniSA’s School of Natural and Built Environments is monitoring stormwater flows in Hawthorn to measure the benefits of Treenet Inlets.

Since 2016 the amount and quality of stormwater flowing from the catchment has been monitored. This coming winter further data will be collected to reveal the benefits of 180 Inlets that have recently been installed.

As part of these trials PhD candidate Hussain Shahzad will be analysing the data and reporting on the effectiveness of Treenet Inlets in moderating stormwater flow and improving water quality.

Council acknowledges the support of the Adelaide and Mt Lofty Ranges Natural Resources Management Board, the University of South Australia’s School of Natural and Built Environments, the Goyder Institute for Water Research, the Department of Environment, Water and Natural Resources, Water Sensitive SA and the Environment Protection Authority of SA for this ongoing research into sustainable urban water management.

Norman Reserve Award Winning Project

We have won a Public Works Engineering Australia Award for our Water Sensitive Urban Design Project on Norman Reserve, St Marys.

Council has constructed water sensitive urban design features in Norman Reserve to collect stormwater from neighbouring roads to improve the natural environment. Rain gardens linked by grassed swales and shallow pools have been constructed to collect stormwater to water the existing trees and improve the appearance of Norman Reserve. These rain gardens will keep the reserve greener for longer, improve the natural wildlife habitat and create an attractive place within the reserve that people want to use.

Norman Reserve St Marys residential catchment

Norman Reserve catchment area

This project has created some of the largest rain gardens extending over an area of 2,500m2 and using over 15,000 local native plants.

Norman Reserve St Marys rain garden installationNorman Reserve St Marys soakage trench installationNorman Reserve St Marys planting rain garden
Rain garden filter layers being installed

Soakage trench being installed

Rain garden planting

Stormwater from Auricchio Avenue and Norman Streets is collected in Norman Reserve using a combination of rain gardens, soakage trenches, swales and overflow paths. The water is filtered through rain gardens and then distributed to soakage trenches which allow the clean stormwater to irrigate the surrounding reserve and trees.

Very little water will leave the site as the rain gardens, built downstream on the reserve, clean and direct the stormwater to soakage trenches to water the reserve and surrounding trees.

The difference can be seen in a heat map modelling analysis, previously the existing hard, clay reserve surface was a major generator of heat build-up. The rain gardens are projected to reduce the heat build-up by over 25ºC providing a cooling effect for the surrounding community.

Norman Reserve Heat Map

Heat map before rain garden and after installation of rain garden

Norman Reserve Rain Gardens

Feature A

Rain Garden. Vegetated with local Indigenous sedges, rushes and reeds; Grassed open space to allow pooling to 100 mm depth; Series of gravel filled soakage trenches beneath pooling area; new compacted gravel footpath.

Feature B

Rain Garden; Vegetated with local Indigenous sedges, rushes and reeds; grass lined swale to allow seepage and overflow for uniform overland flow with gravel filled soakage trench under; gravel filled soakage trenches to maximise infiltration into soil; new compacted gravel footpath.

Feature C

Swale connection to new stormwater management in Dorene Street and Auricchio Avenue; gravel filled soakage trench under swale; formed localised long, grass lined swale to allow seepage and overflow for uniform overland flow; gravel filled soakage trenches to maximise infiltration into soil. Swale to intercept excess stormwater flows; discharge excess stormwater flow to street kerb and gutter.

Feature D

Widen out grassed swale from Feature A to enter into open space; gravel filled soakage bed beneath pooling area; discharge excess stormwater flow to street kerb and gutter.

The Rain Gardens will provide a focal point containing a mixed palette of drought tolerant indigenous plant species which co-habit successfully while providing a sustainable environment for local native wildlife.

What is Water Sensitive Urban Design (WSUD)?

Water Sensitive Urban Design uses natural elements to clean the stormwater and allow it to soak into the ground providing a source of water for trees and grass. This allows the traditional underground pipes that typically carried water from the streets to larger drains, to be made smaller or removed. They can include:

  • Rain gardens - use native vegetation to treat rainwater runoff before infiltration into the ground through material such as sand. Water is available within the sand bed for use by plants during dry periods.
  • Vegetated shallow pools – are usually about 100mm deep allowing rain water to sit for a few days before soaking into the ground.
  • Grass lined shallow swales – carry water between rain gardens and along the reserve to drainage systems outside the reserve. Water soaks into the ground along the length of the swale.