Preventing reservoir evaporation during droughts with floating balls may not help conserve water overall, due to the water needed to make the balls.
During droughts, communities may rely on water stored in reservoirs. However, significant amounts of water can evaporate from the surface of the reservoir.
Amid California’s latest drought, which lasted from 2011-2017, 96 million ‘shade balls’ were deployed into the 175-acre Los Angeles Reservoir in Sylmar, California. These floating, black plastic balls cover the water surface to prevent evaporation.
Also known as bird balls, they were developed initially to prevent birds from landing on toxic tailing ponds produced by mining operations.They have been used by airports to prevent birds from being attracted to drainage ponds and thus risking collisions with planes.
The shade balls used in the Los Angeles project are made of high-density polyethylene (HDPE) with carbon black additive to protect the plastic from UV radiation. Adding carbon black also prevents the formation of bromate, which causes stomach problems when water contaminated with it is consumed.
They are about 10 cm in diameter, and partially filled with water to avoid being blown by wind. HDPE plastic is commonly used for food and beverage containers as well as water distribution pipes.
The balls were estimated to have cut the amount of water lost to evaporation by about 300 million gallons annually.
However, a new study published today in Nature Sustainability shows that producing the balls probably used more water elsewhere than was saved during their deployment – which could have knock-on environmental impacts.
The balls were deployed on the reservoir for one and half years during the latter part of the drought. For each drop of water saved by the balls, however, the study estimates that more than one drop would have been used up in another part of the country or the world.
Co-author Dr Kaveh Madani, from the Centre for Environmental Policy at Imperial College London, said: “We are very good at quick technological fixes, but we often overlook the long-term and secondary impacts of our solutions. This is how the engineering community has been solving problems; solving one problem somewhere and creating a new problem elsewhere.”
The shade balls are made of a kind of plastic that requires oil, natural gas and electricity to produce, all of which require large quantities of water. Producing 96 million balls of standard 5mm thickness would use up to an estimated 2.9 million cubic metres of water. During their time on the reservoir, the balls are estimated to have saved 1.7 million cubic metres of water.
The study team from Imperial, M.I.T. and the University of Twente predict the balls would have to be deployed for two and half years before the water they saved matched the water they used.
However, this is only if they were preventing evaporation at the same rate even outside the dry period; when not in drought conditions, the balls are expected to be less efficient at preventing evaporation, meaning they would have to be deployed for longer to save as much water as they used.
This is alongside other potentially negative effects on the water, such as affecting life in the reservoir or promoting bacterial growth. In addition, the balls’ production could have negative effects on the environment associated with water pollution or carbon emissions.
As more extreme temperatures and more frequent droughts are predicted to occur due to climate change, water management will become an important topic in the coming decades. Dr Madani said: “We are not suggesting that shade balls are bad and must not be used. We are just highlighting the fact that the environmental cost of shade balls must be considered together with their benefits.”
Australia has a better idea
Australia is building a floating solar power plant that will generate 3.5 MW of electricity to not only supply a water treatment plant, and likely generate more electricity than this facility needs, but also keep the water free from algae formation while maintaining water quality and keeping up with utility demand. The company in charge of project development, Infratech Industries, alleges that because the surface is water, solar panels operate at top temperatures.
The power generation sector is one of the most polluting for the environment and is a major contributor of greenhouse gases (GHGs). Among the least polluting energy is hydropower which is classified as a renewable energy source. However, it has been found that this method of generating electricity is a large emitter of methane. And, according to the Intergovernmental Panel on Climate Change (IPCC), methane (CH4) has the potential to contribute to global warming 21 times more than carbon dioxide (CO2).
Further Reading: Shade balls or floating solar panels?
Source: Nature Sustainability ‘The water footprint of water conservation using shade balls in California’