The International Conference on Urban Drainage 2021

What’s going down the drain? Lockdowns, Bushfires and Run-off. (#57)

Emma Johnston 1
  1. University of New South Wales, Maroubra, NSW, Australia

When images of clear skies and deserted cities flashed around the world in 2020, the unprecedented restrictions on human activities due to COVID-19 appeared to be relieving pressures on the environment. The extended lockdown in Melbourne, Australia, last year provided a unique opportunity to identify changes in the volume and type of macro and micro debris flowing into the city’s stormwater drains and waterways. In the first comprehensive study to test the ‘lockdown effect’ on waterborne debris, we studied pre- and post-lockdown debris patterns across four land use types (central business district, shopping centre, transport hub and industrial precinct), confirming a significant overall reduction in debris flowing into drains. The benefits, however, were not uniform, enabling us to identify the sources and types of persistent debris based on land use, as well as new opportunities to target debris reduction programs post-pandemic.

Less than a year earlier, another national disaster, Australia’s 2019-2020 Black Summer bushfires provided unequivocal new evidence to support the protection and/or regeneration of riparian vegetation around the edges of waterways. We studied the impacts of these extensive and destructive bushfires on the receiving aquatic habitats of six urban/regional waterways along the NSW east coast. When drought-breaking rains began to fall after months of blazes, huge volumes of ash and sludge moved rapidly into waterways, with flow on effects evident as chemical and biological changes right down to the estuary basin. Where riparian vegetation buffer zones had been burned or previously cleared, the contamination (N, P, TOC, ROC and metals) of receiving sediments was sufficient to alter microbial communities (as assessed using eDNA approaches). However, where substantial riparian buffer zones remained intact, there was little evidence of impact on the lower estuarine habitat quality or biological structure.

Our studies of these two recent crises generated valuable new knowledge at a time when urbanised estuarine and marine ecosystems in Australia and worldwide are under extraordinary stress - as warming waters coincide with increasing inflows of contaminants such as microplastics and nutrients and the toxic legacy of early industrial contamination. This keynote will detail the findings from our lockdown effect, mega bushfires and other recent stormwater studies. By drawing on this new knowledge - and over 20 years of research in Sydney Harbour - this presentation will provide insights into the impacts of debris, stormwater and urban runoff on estuarine and marine ecosystems, and potential opportunities for upstream mitigation.