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More intense rainfall events caused by climate change—and the resulting pressure on urban stormwater systems—is raising questions around damage to fragile waterways and flooding in our cities.

The Stormwater NSW (franc.sydney) 2022 Conference on the 29th and 30th March will have experts from across the country to explore issues with current stormwater management systems and discuss solutions.

Michael Smit, the Technical and Sustainability Manager at Kingspan Water and Energy, will talk about rainwater as part of the solution.

But, before we share what makes rainwater harvesting a good solution, let’s discuss what the problem is in the first place.

In a forested landscape, water follows a cycle where only about 20 per cent of rainfall travels into waterways. About 40 per cent of rainfall is evaporated or transpired back into the atmosphere, and the other 40 per cent seeps into the water table through a permeable topsoil.

This system has developed over millions of years, and it has multiple benefits.

The transpiration and evaporation of the water back into the atmosphere has a significant cooling effect and ensures that there is enough moisture in the air to support future rainfall. A permeable topsoil allows the water table to act as a constant source of water that slowly trickles into waterways, so that even during a dry spell, rivers continue flowing with cool, clean water.

In urban areas, however, this system is essentially reversed with 80 per cent of rainfall rushing into the local creek Without as many plants to absorb the water, less of it gets returned to the atmosphere.

Moreover, impermeable infrastructure, like buildings and roads, stops rainfall from reaching the water table. Most of it has no other option than to flow directly into rivers and streams. Fast moving water damages stream ecologies adapted to groundwater flow.

Not only does this system cause more floods, but less transpiration also contributes to the heat island effect and increases the chances of future droughts.

“We’ve got this very unfortunate effect that when it does rain, there’s far too much water in our creeks, and when it’s not raining, the reduced base flow is causing a permanent drought”, Mr Smit says.

And it’s expected to get worse. Continual development in cities is increasing impervious surfaces from 65 per cent per block to 90 per cent, giving water even less opportunity to seep into the water table. This will exacerbate the impact of climate change, which is already causing drastic changes in our weather.

The franc.sydney conference intends to find solutions to this growing problem, and Mr Smit hopes that rainwater harvesting can be part of the solution.

“The way we manage stormwater should be ‘at the source’ and through volume reduction.  The Australian Rainfall and Runoff Guideliness 2019 recognise these as contributory roles of rainwater harvesting. Rainwater tanks won’t stop the riverine flooding we have recently experienced, but they reduce the impact of events up to the one in 10 year events which is where most of our infrastructure expenditure is focussed.

Rainwater harvesting is as simple as it sounds: catching rainwater in water tanks to stop it from flowing directly into waterways, creating opportunities to divert the volume as a utility water replacement and into evapotranspiration and groundwater replenishment. Rainwater can be used at the household level for irrigation, washing machines and flushing toilets.

Utilising rainwater on this level has added benefits in that it reduces the need for water to be stored in dams, which further damages river ecosystems, and pumped long distances, which uses a lot of energy.

Michael’s personal vision is that every building should have a small rainwater tank, for stormwater benefits, for the health of local waterways, to reduce the cost of water infrastructure and for water in a crisis.

Smart Tank sensor to keep you informed and engaged – and provide useful data for the environment

Kingspan has also developed an integrated sensor and software that tracks the amount of water flowing in and out of a water tank.

Not only does this allow households to track their individual water usage, but “we can identify at a network level how many rainwater tanks are working, how much water is used and what volume of stormwater is reduced. We can understand our cities in a different way”.

franc.sydney will provide an opportunity for Mr Smit and other experts to share their solutions and discuss how they might work in conjunction with each other to reduce floods and protect local environments.

Kingspan will expand on the benefits and challenges of rainwater harvesting, discuss how and why South Australia has made it a deemed-to-satisfy response and the cost of alternative solutions, such as the cost of upgrading our current stormwater infrastructure.

Lock in the conference dates of 29th and 30th of March, virtually via the OnAIR platform and in person at Dockside Darling Harbour in Sydney. Register to attend at https://www.franc.sydney/register-now.

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  1. It sure was nice when you said that rainwater could be harvested and used for irrigation and on washing machines. With this in mind, I will consider having a rainwater tank installed at home before this month ends. It is critical for us to ensure that we will always have accessible water during emergencies.