Heavy rains are great news for Sydney's dams, but they come with a big caveat 13 February 2020, by Ian Wright and Jason Reynolds Warragamba supplies more than 80% of Sydney's water. Other Sydney water storages, including Nepean and Tallowa dams, are now at 100%.WaterNSW report that 865,078 megaliters of extra water has been captured this week across all Greater Sydney's dams. This dwarfs the volume of water produced by Sydney's desalination plant, which produces 250 megaliters a day when operating at full capacity. Even at this rate, it would take more than 3,400 days (or nine years) to match the volume of water to added to Sydney's supply this week. But then comes the pollution The authors crossing the Coxs River during very low flow last September. Author provided Thankfully, the rain appears to have extinguished bushfires burning in the Warragamba catchment for months. Throughout summer, Sydney's water storage level But the water will also pick up bushfire debris and fell alarmingly. Level 2 water restrictions were wash it into dams. imposed and the New South Wales government prepared to double the capacity of its desalination Over the summer, bushfires burnt about 30% of plant. Warragamba Dam's massive 905,000 hectare water catchment, reducing protective ground cover But then it began to rain, and rain. Sydney water vegetation. This increases the risk of soil erosion. storages jumped from 41% in early February to Rain will wash ash and sediment loads into 75% now – the highest of any capital city in waterways—adding more nitrogen, phosphorous Australia. and organic carbon into water storages. This is great news for the city, but it comes with a Waterways and ecosystems require nutrients like big caveat. Floodwaters will undoubtedly wash phosphorous and nitrogen, but excess nutrients bushfire debris into reservoirs—possibly aren't a good thing. They bring contamination risks, overwhelming water treatment systems. We must such as the rapid growth of toxic blue-green algae. prepare now for that worst-case pollution scenario. Drinking water catchments will always have some Reservoirs filled with rain degree of contamination and water treatment consistently provides high quality drinking water. The water level of Sydney's massive Lake But poor water quality after catchment floods is not Burragorang—the reservoir behind Warragamba without precedent. Dam—rose by more than 11 meters this week. 1 / 3 We've seen this before However at the time, bushfire ash had already reportedly entered the Warragamba system. In August 1998, extreme wet weather and flooding rivers filled the drought-affected Warragamba Dam Look to recycled water in just a few days. Sydney's water storages may have filled, but This triggered the Cryptosporidium crisis, when the residents should not stop saving water. We protozoan parasite and the pathogen Giardia were recommend Level 2 water restrictions, which ban detected in Sydney's water supplies. It triggered the use of garden hoses, be relaxed to Level 1 health warnings, and Sydneysiders were instructed restrictions which ban most sprinklers and watering to boil water before drinking it. This event did not systems, and the hosing of hard surfaces. involve a bushfire. While this measure is in place, longer term The Canberra bushfires in January 2003 triggered solutions can be explored. Expanding desalination multiple water quality problems. Most of the is a popular but expensive option, however greater region's Cotter River catchments, which hold three use of recycled wastewater is also needed. dams, were burned. Intense thunderstorms in the months after the bushfire washed enormous loads Highly treated recycled water including urban of ash, soil and debris into catchment rivers and stormwater and even treated sewage should be water reservoirs. purified and incorporated into the water supply. Singapore is a world leader and has proven the This led to turbidity (murkiness), as well as iron, measure can gain community acceptance. manganese, nitrogen, phosphorus and carbon in reservoir waters. The inflow of organic material also It's too early to tell what impact the combination of depleted dissolved oxygen which triggered the bushfires and floods will have on water storages. release of metals from reservoir sediment. At times, But as extreme weather events increase in water quality was so poor it couldn't be treated and frequency and severity, all options should be on the supplied to consumers. table to shore up drinking water supplies. The ACT Government was forced to impose water This article is republished from The Conversation restrictions, and built a A$38 million water under a Creative Commons license. Read the treatment plant. original article. Have we come far enough? Provided by The Conversation Technology in water treatment plants has developed over the past 20 years, and water supply systems operates according to Australian drinking water guidelines. Unlike the 1998 Sydney water crisis, WaterNSW, Sydney Water and NSW Health now have advanced tests and procedures to detect and manage water quality problems. In December last year, WaterNSW said it was aware of the risk bushfires posed to water supplies, and it had a number of measures at its disposal, including using booms and curtains to isolate affected flows. 2 / 3 APA citation: Heavy rains are great news for Sydney's dams, but they come with a big caveat (2020, February 13) retrieved 28 September 2021 from https://phys.org/news/2020-02-heavy-great-news- sydney-big.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. 3 / 3 Powered by TCPDF (www.tcpdf.org).