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"Faced with continuing dry conditions over many years and the uncertainty of future rainfalls, Orange City Council has broken new ground in the harvesting of stormwater for urban use...
...The Council’s stormwater harvesting scheme, which kicked off in 2008, is already giving residents access to significantly more water every year and giving the Council new confidence in its ability to secure urban water supplies.
The first large scale, indirect-to-potable stormwater harvesting project in New South Wales – the Blackmans Swamp Creek Stormwater Harvesting Scheme – got underway in 2008. The scheme is ultimately capable of providing up to 2000 megalitres (ML) of additional water into Orange’s raw water supply each year. That represents up to 35 per cent of the city’s 5700ML normal annual water usage.
The scheme has been so successful that the Council has since expanded the project to include Ploughmans Creek, starting in 2010. The final part of Council’s stormwater harvesting strategy is a proposed extension of the Blackmans Swamp Creek scheme.
Developed with the aid of eWater CRC’s powerful modelling tool music (model for urban stormwater improvement conceptualisation), the Blackmans Swamp Creek harvesting scheme evolved from concept to operational reality within 18 months at a cost of $5 million. It involved extensive consultation with the community and government authorities and a thorough analysis to satisfy concerns about the safety, reliability and capacity of the scheme.
“The concept of the Blackmans Swamp Creek Stormwater Harvesting Scheme involves capturing a portion of the high flows in Blackmans Swamp Creek during storm events, and transferring these into the nearby Suma Park Dam to augment the city’s bulk water supply,” says Martin Haege, Environmental Engineer at Geolyse Pty Ltd, who played a major part in the development.
“A key tool to assist in the consultation process has been the development of the Review of Environmental Factors (REF), including a series of operating rules to provide a clear outline of environmental impact and how the scheme will work. A critical issue throughout the development of the scheme has been the need to ensure the harvested stormwater meets the appropriate standards of the Australian Drinking Water Guidelines.”
Haege used music for the catchment hydrology component of the Blackmans Swamp Creek Harvesting Scheme to generate daily water flow series and runoff from catchments, because it was important to evaluate how much water the catchments generated to Blackmans Swamp Creek.
“music enabled me to generate a synthetic stormwater stream flow data set. I put 118 years of daily rainfall data into music which generated the creek flow data,” he says.
After the simulation in music, Haege exported the data into an Excel Water Balance Model to get a full water cycle for Orange. He then sized and optimised the stormwater harvesting scheme for Orange City Council.
Now the harvesting scheme has expanded to include Ploughmans Creek, where construction started in May 2010. Haege applied music in a more comprehensive way in this part of the scheme, simulating a synthetic stormwater stream flow data set under natural conditions. He says “With music, I estimated what the water stream flow of Ploughmans Creek catchment would be like before development: the natural flow series. Regulators set a limit of how much water can be harvested and music helped me estimate the stream flow series under natural and developed conditions. music is an excellent tool when sizing harvesting schemes, and working out natural water stream flow including base flow elements.”
The Ploughmans Creek Harvesting Scheme also incorporated four constructed wetlands for harvesting water. Haege says “With music I could estimate the pollutant loadings from the four wetlands, and assess the improvements in the water quality in Ploughmans Creek. It was important to demonstrate that the Review of Environmental Factors and operating rules could be met”.
The stormwater harvesting from Blackmans Swamp Creek and Ploughmans Creek makes up about 1600 ML of water or 28 per cent of Orange’s annual water usage. The water from the creeks is slowly pumped to a holding pond and pumped to Suma Park Dam where the Council takes its water.
To reach the stormwater harvesting scheme objectives of delivering 35 per cent of Orange’s annual water supply, the Council plans to extend the stormwater harvesting scheme to include a constructed wetland adjacent to Blackmans Swamp Creek. The wetland will make up the last seven per cent.
“In time the stormwater harvesting scheme will supply 35 per cent of the council’s annual water usage. It is seen as a good way to diversify water sources and at the same time a good local solution.”
Haege sees many benefits of using music which he says is simple to use.
“It is easy to set up and export data,” he says. “It is a very good tool for the simulation of wetlands. music has excellent data calibration and a great rainfall library and it has saved me significant time when developing the stormwater harvesting scheme for Orange City Council.”
Without the tool Haege says run off calculations would only be poor estimates and his designs and models would not have worked as well, nor would any natural flow estimates be available.
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