I keep hearing talk about a water shortage, or an impending water shortage, or that the world is running out of water. This gets me scratching my head a bit because when I went to school, many many many years ago, we were taught about the hydrologic cycle and how there is pretty much the same amount of water on this blue/green planet as there has always been, give or take a small (tiny) amount. It's just the amount of fresh water that we have available for human use in some areas that is really the problem.
I mean, some 70% of the earth's surface is covered in water, along with large quantities of water in polar ice and glaciers, water in the ground and water in plants and animals. About 3% of our atmosphere, on average is water as well. The hydrologic cycle will keep replenishing the relatively low percentage of fresh water in the total amount and as long as we are aware of that and work with that, there are many ways we can ensure our water supply into the future.
In fact, we can even prosper and grow without having to resort to energy expensive solutions such as desalination plants or iceberg mining. I mean, rain falls from the sky and runs down the gutter. Where does that water go? Usually it goes out to sea, carrying a lot of other rubbish along with it. Coastal city and urban areas are particularly bad for this as urban managers need to get the storm water away as fast as they can to avoid flash flooding and all the problems that can cause. To me, this is a big waste of what is essentially fresh and delivered by nature to the very places that require large amounts of that very substance.
How can we harvest that water, clean it of pollutants and store it for our use? Here is an example on an urban scale that has been developed in the City of Salisbury in South Australia, the driest state on the driest continent on the planet.
In the 1990's the City of Salisbury defined a vision that it would seek to eliminate the flow of polluted water into the marine environment of the Barker Inlet of the Gulf of Saint Vincent. The Barker Inlet is a delicate marine environment of mangroves and sea grass meadows serving as a nursery for a majority of the State's fishing industry. However, years of neglect and polluted inflows have reduced the Barker Inlet to a delicate state. The creation of wetlands to cleanse stormwater was Salisbury's key strategy to help the ecological rehabilitation of the Barker Inlet while providing cheaper water to local industry and other users.
Stormwater is treated and harnessed in a series of more than 30 wetlands along urban stormwater paths to slow the flow and allow pollution to settle out. The wetlands cover an area of 260 hectares enhancing the landscape and creating habitat diversity. All the wetland plants are propagated at the Council's nursery and they play an important role in the treatment of polluted stormwater. The nursery has developed a high level of expertise in propagating various wetland species, and it sells wetland plants to users all around Australia.
Parafield Stormwater Harvesting Facility
The Parafield Stormwater Harvesting Facility originated from a discussion in 1999 between City executives and the management of G. H. Michell & Sons, Australia's largest wool processing company.
The company's processing involves the use of 1100 million litres (~ 300 million gallons) per year of mains water to wash the wool, which in turn produces large quantities of effluent and sludge. The costs of fresh water and sewerage disposal were high enough to force the company to consider alternative, cheaper locations elsewhere, potentially resulting in the loss of around 700 local jobs.
The Parafield stormwater project involves diversion of stormwater via a weir in the main Parafield drain to a 50 million litres capacity capture basin. From there, it is pumped to a similar capacity holding basin, from where it gravitates to a two hectare cleansing reed bed.
Nutrient and pollutant loads are typically reduced by up to 90 per cent and the treated water salinity is less than 250 mg/L. The system is designed to hold stormwater for around 10 days to ensure optimal treatment efficiency. The current supply capacity of the scheme is 1100 million litres per year. The second stage would add other catchments and boost the supply to 2100 million litres per year.
Continuity of supply is gained through the creation of large underground storage of treated stormwater. This is achieved by the development of an Aquifer Storage and Recovery (ASR) system. Two ASR bores have been installed allowing supply when the system has no flow. The recharge water quality has to meet the Environment Protection Authority (EPA) requirements.
Through the project, G.H. Michell & Sons receives water with a salinity (TDS) of 250mg/L, which is significantly lower than the average salinity of water from the River Murray (> 400 mg/L). The ASR project helps foster the growth of new and established industries, especially those with high water quality requirements. Prospective employment opportunities in the region are subsequently increased.
The City of Salisbury's investment in a unique and diverse series of wetlands has significantly enhanced the amenity and environment, and contributed to the social well being of the community. Projects such as the Parafield Stormwater Harvesting Facility are a great way to deliver on the triple bottom line of sustainable environment, economy and community.