Natural flood management: Lessons and opportunities from the catastrophic 2021–2022 floods in eastern Australia

Abstract

Natural flood management (NFM), a nature‐based solution to flood mitigation where hydrological and biophysical processes are harnessed to reduce flow velocity, erosive energy and flood risk, is an emerging global theme of water and river management. The catastrophic 2021 and 2022 floods in eastern Australia are used to assess the hydrological properties of discrete events and to start an investigation of whether widespread changes in flood hydrology are occurring. We find that most coastal rivers in New South Wales (NSW) had a noticeable decrease in flood wave celerity (increase in flood travel time) when the 2021 and 2022 floods are contrasted with equivalent floods since the 1970s and that several also exhibit increases in flood peak attenuation. For some rivers, there is a coincident trend between these changing flood properties, riparian vegetation regrowth (regreening) and geomorphic recovery over the last +30 years. These may be the first signals that passive riparian management is counteracting some of the more severe hydrological effects of floods on these rivers and that some degree of NFM is possible. Lessons from this work are that there is an immediate opportunity to implement large‐scale NFM in coastal catchments of NSW, but this will only occur if we re‐examine current flood mitigation and adaption strategies and recognise and prioritise nature‐based solutions that include space‐to‐flood and corridors of river recovery, as essential parts of the modern flood mitigation toolkit.

Detection of decadal time‐series changes in flow hydrology in eastern Australia: Considerations for river recovery and flood management

“…Hunter River at Singleton goes back to 1913; Appendix 1). The end date of the analysis is March 2022, to capture the most recent set of floods in the study catchments (Fryirs et al, 2023).…”

“…This evidence could potentially help the public and decision-makers to justify the up-scaling of nature-based techniques in practice (i.e. riparian revegetation) and realise the potential for natural flood management (NFM) at the regional scale (Black et al, 2021;Fryirs et al, 2018;Fryirs et al, 2023;Grant, 2008;Guan et al, 2016;Howgate & Kenyon, 2009;Lane, 2017). The database produced here could be used to determine where signals of NFM are occurring and where to focus efforts (e.g.…”

“…The data could also be used to better calibrate and validate flood models for monitoring, risk assessment and prediction (Arash & Yasi, 2022;Merwade et al, 2008). However, the challenge is significant, particularly given that most coastal catchments of NSW are already experiencing the effects of climate change with changes in the intensity of flooding, the recurrence of catastrophic floods and the severity of droughts that occur between them (CSIRO and BoM, 2022;Fryirs et al, 2023).…”

“…Similar to in-channel fresh and high flows, the distance between gauges and drainage area is dominant for overbank floods with weightings of 0.68 and 0.69, whereas peak-to-peak travel time has a lower weighting of 0.07.Hence, both peak-to-peak travel time and flood peak attenuation are positively correlated with drainage area and distance between gauges and negatively correlated with peak arrival time.To assess changes in peak-to-peak travel time and flood peak attenuation over time, peak-to-peak travel time was normalised by dividing it by distance between gauges to generate flood wave celerity, and flood peak attenuation was normalised by dividing it by drainage area to generate the FWAI. A decrease of 1 m s À1 in flood wave celerity can be considered significant (e.g Fryirs et al, 2023)…”

A Systematic Literature Review on Transit-Based Evacuation Planning in Emergency Logistics Management: Optimisation and Modelling Approaches

“…There has been an increase during recent years in the impact of natural hazards and extreme weather, such as flooding, hurricanes, tsunamis, heatwaves, fires, and earthquakes all around the world, while their intensity has also intensified resulting in significant losses for humans and societies [1]. There are many examples, including the 2008 Sichuan earthquake in China [2], the 2011 Tohoku Earthquake and Tsunami in Japan [3], the 2012 Sandy Hurricane of the USA [4], the 2019-2020 Australian bushfire season [5], and the devastating floods in eastern Australia during 2021-2022 [6]. Furthermore, newly emerging hazards have also resulted in significant property losses and human casualties, including hazardous chemical releases, massive crowds, and terror attacks [7][8][9][10].…”