The influence of recent bushfires on water quality and the operation of water purification systems in regional NSW

Abstract

The occurrence of extreme weather events aggravated by global warming has increased exponentially in the past decade. In recent years, New South Wales (NSW) has experienced catastrophic, unprecedented drought followed by extreme fire conditions and widespread, record-breaking floods. However, the impact of the drought and bushfires on regional water quality is poorly investigated. This study investigates immediate changes in regional environmental water quality and specific issues reported from water purification unit operations after the 2019 bushfires in NSW. Water samples were collected from the waterways in bushfire affected catchments, water intakes, unit operations of water purification systems, and treated water reservoirs. The performance of water purification processes and operational issues of regional water purification plants were extracted from daily maintenance records. Elevated levels of suspended sediment and algae blooms were of most concern in terms of aesthetic and recreation aspects of environmental water use after the drought and bushfires. Compared to the control samples, extremely high turbidity and low dissolved oxygen concentrations were reported in bushfire affected water samples. Shock loads of sediment and ash detected in waterways posed the greatest threat to aquatic ecosystems following fires. Elevated turbidity levels, suspended sediments, pH, and alkalinity were the parameters of most concern for water purification. The maximum turbidity level in raw water was reported as more than 195 NTU. Flocculation and sedimentation were the most affected unit operations in the water purification process. Immediate measures to handle shock loads due to bushfires included sediment traps, aeration on the intake lines, pre-chlorination, and inline monitoring for pH and turbidity. These results can be used to develop management strategies to minimise the impacts of bushfires on water quality and modify and operate water purification plants within bushfire prone catchments.