Recently climate change has challenged Australia, inflicting climate extremes of increasing severity, with droughts, bushfires, and floods breaking historical records. Events such as the 2017–2020 drought, the 2019–2020 Black Summer bushfires, and the 2021–2022 East Australian Floods have adversely affected water quality and supply in many regional New South Wales centres. Future events are predicted to increase in severity, and vulnerable Local Government Areas (LGAs) need to prepare to ensure water quality for their residents. Currently, there are limited information and case studies documenting the ongoing effects of climate change on water management for regional NSW centres. This research addresses the existing knowledge gap by providing insight into regional NSW LGAs affected by droughts, bushfires and floods, the challenges faced, the capacity to maintain water quality to Australian Drinking Water Guidelines (ADWG) and the ability to ensure sufficient storage supply. DAC (drought), BAC (bushfire) and FAC (flood) LGAs supported the case studies produced to target councils’ management during these periods, highlighting the success of the strategies and treatments implemented. The performance of the LGAs proved their existing systems could maintain water quality and supply throughout the differing climate extremes. Practices within the catchment management and treatment procedures require continual improvement to meet the increasingly volatile climate effects and heightened system demand of increased populations. This study provides recommendations to help address the impacts of future climate extreme events on the specified LGAs and other LGAs across regional NSW.
Research Article
Performance of regional water purification plants during extreme weather events – three case studies from New South Wales, Australia
https://doi.org/10.21203/rs.3.rs-2618694/v1
This work is licensed under a CC BY 4.0 License
Journal Publication
published 15 Jun, 2023
Read the published version in Environmental Science and Pollution Research →
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bushfire
climate change
climate extremes
drought
flooding
water management
water quality
water supply
Since the beginning of the new millennium, Australia has suffered climate extremes of increasing severity, withstanding catastrophic droughts, floods, and bushfires (Colvin et al., 2020). Recent climate extremes in Australia include ‘The Millennial Drought’ and the 2017–2020 drought, the historic ‘East Australian Floods’ across Queensland and NSW, and the ‘Black Summer’ bushfires, the most destructive series of bushfires in Australian history. The effects of these climate extremes compound the severity of successive disasters (Hoffmann et al., 2019; Kemter et al., 2021), and the impacts across environmental, economic, and social sectors have caused great concern for Australia’s future.
The hot and dry conditions across Australia’s landscape between 2017 and 2020 resulted in abundant fuel in bush and grasslands. As a result, from the beginning of July 2019, bushfires raged across all parts of the country, with New South Wales (NSW) and the Australian Capital Territory (ACT) the worst affected. In NSW alone, the Black Summer bushfires resulted in 5.4 million hectares being burned, an estimated 800 million animals killed, 2,439 homes destroyed, and 25 deaths (Hughes et al., 2020). The economic, social, and environmental effects of the Black Summer bushfires will be felt for many years. Additionally, the effects of the bushfires caused adverse conditions that were exposed following the heavy rains that extinguished the fires in February 2020, then peaked in March 2021.
Drought is also associated with high temperatures, particularly in the summer months. The effects of drought within NSW have been catastrophic, with average record temperatures continually being broken in recent years. For example, 2019 was the hottest year recorded in Australian history, with mean temperatures 1.52°C above average (Hughes et al., 2020; Losso et al., 2022). In addition to record temperatures, rainfall levels were measured at all-time lows throughout 2018–2019, which were southeast Australia’s driest years on record (Bureau of Meteorology, 2021). According to new studies from the NSW/ACT Regional Climate Modelling (NARClim) project, the trend for drought and its related effects is expected to intensify continually. The NARClim model forecasts regional climate scenarios, making its outcomes relevant to this research conducted in regional NSW. NARClim simulations project, depending on location and season, that between 2060–2079 day time maximum temperatures may increase by 3.5°C, areas may see a threefold increase in heatwave days, and an Australian wide increase on average of more than a week of days over 30°C (Herold et al., 2018). Figure 1 displays the NARClim predicted monthly future temperature change projections.
The most recent climate extreme has been extensive flooding across NSW and Queensland following the drought and bushfires. In March 2021, the East Australian floods broke many records; this month included the wettest week for coastal NSW since records began (Han et al., 2021; Kelly & Kuleshov, 2022). Aside from the benefits of replenishing catchments and providing long-needed recharge to rivers and reservoirs, the floods caused damage to infrastructure and eroded soil left vulnerable by the drought and bushfires. A flood following a drought or bushfire significantly affects water quality as it provides a mode of eroded material and pollutant transport and yields higher runoff rates due to increased precipitation rates (Alexandra & Finlayson, 2020; Dahm et al., 2015; Delpla et al., 2009).
The extent of the drought and subsequent conditions of a water body can impact the severity of the effects on water quality (Mishra et al., 2021; Mosley, 2015). Reduced rainfall can affect a body of water as both water volume and flow decrease. Reduced volume or flow may cause the inability of a system to flush via outflow, raising levels of nutrients, turbidity, and algal blooms (Mosley, 2015). Drought causes water bodies to turn from lotic to lentic as a system customarily associated with flow becomes stagnant, altering how an ecosystem operates. This provides a mode for increasing microorganism production and changing physical and chemical characteristics (Vazquez et al., 2011). This change can be attributed to the reduced dilution of properties within the water, creating higher concentrations. Thermal stratification is also a common result of increased ambient temperature and often leads to lowered dissolved oxygen, causing eutrophication (Mosley, 2015). The smaller the water volume, the greater the change in water temperature can occur due to higher ambient temperatures. The correlation between the effects of volume, flow, and high ambient temperatures within drought and the rising likelihood of adverse effects are directly associated (Greenough et al., 2001).
Extreme climate events provide challenges for LGAs to meet the Australian drinking water quality guidelines (ADWG). As the ADWG provide a holistic management approach for water quality management, NSW Health’s public health regulator has endorsed the requirements for use by water utilities, private suppliers, and water carters (Byleveld et al., 2016). Each of the LGAs nominated in this research has faced different challenges during droughts, bushfires, and floods. Following an intense drought between 2017–2020, which included record-breaking dry spells (Bureau of Meteorology, 2021) and all-time high yearly average temperatures (Hughes et al., 2020), regional areas in NSW faced difficult water supply and management conditions. The unprecedented drought highlighted the challenges for water security in larger settlements within central NSW.
As extreme weather events are expected to continue and, in many cases, increase in severity, the changing context requires research into how regional NSW centres can adapt and accommodate a water quality and supply system already facing significant challenges. This research examines the effects of climate extremes on water quality and supply management for NSW regional centres through several case studies. It provides water management and future planning recommendations for the specified LGAs, documenting the different scenarios that will assist in targeted responses for future inevitable climate extremes and LGAs facing similar challenges.
Data and information sourced to produce case studies conducted on the LGAs were collected through correspondence between council water resource managers and engineers. Raw and treated water quality parameters during the specified climate extreme were extracted from the council database to show the effectiveness of strategies and treatment methods. In addition, dam storage data were provided to determine supply and its effect on water quality. The data date ranges were 10-day periods selected to follow the climate extreme event’s timeline, in which water quality parameters would be affected.
Case studies
The climate extremes of drought, bushfire, and flood were the focus of water management for this study, with three LGAs selected for case studies targeting one climate extreme for each council.
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Drought affected council (DAC).
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Bushfire affected council (BAC).
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Flood affected council (FAC).
The selection criteria used to determine the suitability of LGAs to be examined were as follows.
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The main town of the LGA must be a centre located within regional NSW.
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Climate extreme events of significance occurred within the last five years.
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Council was willing to support research and provide data and non-sensitive information.
Table 1 summarises the catchment and water quality characteristics of each study area.
| Drought affected council (DAC) | Bushfire affected council (BAC) | Flood affected council (FAC) | |
|---|---|---|---|
| Drinking Water Supply Catchment Characteristics | The DAC comprises six major creek catchments with a dedicated drinking water reservoir with a storage capacity of over 17,000 ML. It also gains additional inflows from a secondary water supply reservoir. The town’s water treatment plant (WTP) uses the conventional water treatment process, ozone treatment, and biological activated carbon (BAC) filtration to produce a potable supply for the township. The major catchments of the DAC are mainly used for agricultural purposes, including stock grazing and fruit-producing farmland. | The BAC catchment is situated among steep gradient sandstone and ironstone rock formations, covered with natural bushland. Water entering the dam occurs through sheet flow and filtering through rock, making soil addition through erosion generally minor. Water quality effects following a rain event generally occur within three days, with quality stabilisation occurring quickly due to the catchment’s nature and largely rock composition. Rainfall occurring months and years after a major bushfire continues to wash bushfire affected material into waterways and causes ongoing water quality issues. | The FAC catchment area has both a high potential for salinity and erosion. It is estimated that 118,000 tonnes of sediment would be washed into the catchment each year due to gully, sheet, and rill erosion. Willow trees have spread throughout the catchment after their introduction to stabilise riverbanks. Excessive willow debris resulting from high rain events has contributed to increased flood inundation and infrastructure damage. Due to the nature of a large catchment feeding the FAC’s town supply, the most change to water quality will occur within three days after a downpour. The FAC consists largely of an agricultural catchment contributing animal by-products, trees and fertilisers to runoff entering the water supply system. |
| Water Supply Microbial Issues | During the summer months of the recent droughts, the DAC reservoirs developed algal blooms due to rising water temperatures and higher nutrient levels. Reservoir circulators are positioned to address water stratification, aiming to prevent favourable conditions required for algae reproduction. Variable offtake trunnions enable water piped to the WTP to be sourced from advantageous depths, reducing the extent and need for treatment. To combat algal effects entering the WTP, such as taste and odour, the DAC uses ozone treatment to destroy pathogens present in the water. | Microbial activity affecting water quality is insignificant to the BAC catchments. They consist mainly of natural bushland and lack agricultural farmland, which contributes to faecal matter and excessive nutrients. Any microbial effects occurring within the BAC catchments are not considered related to bushfire events. The BAC monitors microbial levels within raw water and treats it with chlorination doses to control rare microbial occurrences. However, following bushfires the BAC water managers use higher doses of chlorine to ensure water left stagnant in supply mains is not a source of microbial activity. | Of the microbial effects, E.coli has the greatest effect during flooding within the FAC catchment, largely due to stock defecating within watercourses giving the microorganisms conditions suitable to thrive. In catchment areas, the FAC restricts access to stock through fencing. A destratification system which uses reservoir circulators prevents stratification and conditions suitable for microbial growth. In addition, the FAC pumps the water of the best quality out of reservoir by having variable offtake trunnions to select water at the most advantageous depths. |
| Water Supply Physical and Chemical Issues | In drought, physical and chemical issues arise after rain transports matter built up in watersheds into storage. The DAC did not experience excessive effects in recent droughts, partly due to its location in a closed catchment with watersheds having an adequate ground cover that limited the amount of eroded material entering the system. The physical and chemical effects that occur are managed through conventional treatment. | Rains following bushfire events contribute greatly to both turbidity and colour change and changing pH levels for the raw water supply. Additional erosion can arise due to trees being uprooted and plant matter that binds soils being destroyed, exposing soils to concentrated runoff occurring on steep gradients. Due to limited access to the catchment, very little to no erosion and sediment strategies are used to reduce ash, soil and other pollutants entering the system. The BAC used a larger quantity of chemical dosing during the Black Summer bushfires to account for the increased effects on water quality. | Turbidity and colour are two characteristics that are highly changeable within the FAC catchment. The FAC catchment soils are rich in manganese, which high rainfall events wash into the reservoir catchment and the rivers feeding the WTP. Manganese present in the water supply may result in a colour change to residents’ water treated before use. The FAC uses the conventional water treatment process, which involves three main stages –flocculation, filtration, and chlorination. The first two of these processes remove physical properties. A new filtration system was established to oxidise manganese further by using additional chemicals, including caustic soda and polymer, to initiate sedimentation. |
| Water Supply Infrastructure Damage | Although the recent droughts did not cause infrastructure damage, the DAC invested in identifying and rectifying leaks within the water reticulation network and implementing additional water-saving systems on both residential and industrial levels. | Following the bushfire, debris mainly from trees, shrubs and other flora entered the water system. High rainfall events months and years after a major bushfire can continue to dislodge remnants, enabling larger debris to impact structures over a long period. | Over the years, flooding has caused damage through increased debris and erosion. The FAC implements flotation boom deflectors and trash racks to deflect debris during flooding from infrastructure such as the weir pool offtake at the WTP. Areas are patrolled to move unwanted accumulated debris and assess the need to increase erosion measures. |
Drought affected council (DAC)
During the 2017–2020 drought, the DAC airport weather station data showed that temperatures were well above average each year, with an annual average increase of 1.5°C. In 2019, there was an annual increase of 1.9°C, and the summer months increased by 3.5°C, with January and December approaching 5°C above average (Bureau of Meteorology, 2022). Due to evaporation and higher water consumption, the summer months featured the greatest loss in the water supply. Figure 2 demonstrates monthly temperature comparisons for the 2017–2020 drought and the average monthly temperatures since the DAC airport weather station records began (Bureau of Meteorology, 2022).
According to DAC airport weather station data, during the 2017–2020 drought, the DAC averaged 512mm of annual rainfall, with a low in 2019 of 425mm. The DAC’s yearly average between 1996–2021 is 924mm, equating to 412mm above the recent three-year drought period. Figure 3 shows monthly rainfall average comparisons for the 2017–2020 drought and the average monthly rainfall between 1996–2021 at the DAC airport weather station.
The DAC’s water supply design has resulted in several different water-saving and recycling schemes. In addition to existing dam supplies, the DAC has added additional sources to supplement the potable supply and reduce potable water use by operating other systems. The 2017–2020 drought saw the DAC’s residents reduce their average water consumption by 70 L/per day. That equates to an average yearly saving per person of 25,550 litres.
Drought water quality and supply management
March 2016 was the beginning of a good year of rain where the DAC reservoir was above 60% capacity. During such times, there is significant dilution, reducing the concentrations of impurities compared to severe drought. The 10-day period in this month had two small rain events of between 10mm and 15mm, and provided a basis for measuring water quality. September 2018, April 2019, and December 2019 were key milestones of the drought period as the DAC’s primary water source continually declined. The events were similar, which indicated potential declining water quality as the dilution of the serovar decreased. When the first rain was observed toward the end of the drought (75mm of rain over three days), the reservoir storage levels were at their lowest. At this time, the DAC was operating under Level-5 water restrictions as residents faced the potential “day zero” scenario of having the town’s water supply run dry. It was observed that a large portion of sheet flow was captured by farm dams, dry earth, and water networks upstream of the storage. However, flow entering the catchment brought eroded material, agricultural-related pollutants, and the general build-up of material left on the land during the drought when there were no rainfall cleansing events.
Without new or regular inflows to the main raw water reservoir, the DAC was confronted with water quality issues and algal production that occurred during the summer months, in addition to thermal stratification, causing temperature differentials and varying depths of water quality. To improve the raw water directed to the WTP, the DAC conducted vertical mixing with reservoir circulators and piped water from advantageous depths with variable offtake trunnions. This ensured that the raw water supplied and tested to the treatment plant was of higher quality and required less treatment. During the 2017–2020 drought, the DAC maintained all treated water to the ADWG standards. The DAC’s water treatment processes have ensured stability within water quality parameters to enable ADWG standards to be achieved. However, the supply caused concern for the DAC, with the primary potable water source reaching a low of 19.2% capacity in February 2020. The infrastructure built over the last ten years and the implementation of a demand management strategy and water restrictions allowed the main township in the DAC to successfully manage its way through the millennium and 2017–2020 droughts.
Drought Lessons Learned
The 2017–2020 drought resulted in the DAC facing a day zero scenario that highlighted the WTP’s effectiveness in maintaining high water quality throughout undiluted storages and reinforced the need to explore other options to increase the township’s supply. Water security has been at the forefront of the DAC’s planning to account for future growth and sustainability. The DAC and its residents’ cooperative action to reduce water usage through audits, network improvements, and conscious water use ensured an adequate supply throughout the recent drought. Droughts will further educate the DRC as they have highlighted the effectiveness of the town’s water supply management. The benefits of the planning and implementation of the infrastructure proved capable of navigating the 2017–2020 drought; however, the reduction of the town’s storage capacity also displays the need to search for additional town water sources to provide further security.
Bushfire affected council (BAC)
The BAC experiences an average of 128 bushfires and grassfires annually, with approximately three burning more than 20 ha and considered major fires. However, over 512,000 hectares were burned in the bushfire in 2019–2020. The BAC’s Bushfire Management Risk Plan identifies Drinking Water Catchments as an economic asset at risk of future bushfires. The result of the bushfire was that 121,300 hectares, or 46% of the council’s tree canopy, was lost in addition to grassed and open areas. Figure 4 displays the extent of tree cover lost within the BAC due to fires between 2001 and 2020.
Following the driest year on record (2019), with 466.2mm falling across the year, there were minor rain events in January, followed by drought-breaking rains throughout February, which helped extinguish bushfires across the region. August 2019 was at the end of the drought; however, the BAC’s reservoir was still above 80% capacity. In this period, there was significant dilution, reducing the concentration of impurities compared to lower dam levels. The 10-day period has very little rain and provides a basis for water quality where water is not mixed. January 2020 had 40.6mm of rain falling across five days during the bushfire. At this point, the BAC’s reservoir has fallen to below 35%. This event allowed a review of a burning bushfire's effect on water quality. A bushfire extinguishing high rainfall event occurred in February 2020, when 111.0mm of rain fell across four days, including a high of 51mm in a day. The heavy rains transported burnt matter and debris into the storage and increased the dam’s storage from 45.3–100%. Another rainfall event three weeks after the bushfire, in March 2020, produced 35.8mm falling over three days. The heavy rains continued transporting bushfire affected matter into the water storage system. In January 2022, following another bushfire, 153.5mm of rain fell across nine days, including 75.0mm in one day.
Bushfire water quality and supply management
The results show that during the 2019–2020 Black Summer bushfires, the BAC maintained all treated water to the ADWG standards. The BAC’s water treatment processes have ensured stability within water quality parameters to achieve ADWG standards. The data shows the BAC’s effectiveness in managing water quality throughout a bushfire – the treatment processes and raw water were at manageable levels and effectively treated for each parameter. It is noted that the BAC raw water was typically acidic, reaching pH levels as low as 5.56. For the treated water, the pH ranged between 6.95–8.40 within the tested ranges. The apparent colour for raw water was typically not below 100 HU. Aside from 469 HU following the extinguishing rains in February 2020, the worst period occurred more recently in January 2022, when HU values within the 10-day period were all above 260. The colour ranged between 0–10 HU within the tested ranges for the treated water. This range meets the requirements set within the ADWG. Tested raw water turbidity levels generally didn’t see a direct correlation with heavy rainfall. The highest reading for the data shown was 41.90 NTU in February 2020. The BAC treatment processes successfully maintained the treated water within the ADWG throughout the identified period. However, these readings have extended above 0.5 NTU, with a maximum reading of 0.85 NTU, nearing the ADWG standard of less than 1 NTU. The supply within the BAC reservoir dropped significantly in the lead-up and during the bushfire. In August 2019, the reservoir was at over 80.0% capacity. Five months later, in January 2020, the capacity was less than 35%. The rains that extinguished the bushfire just two weeks later replenished the catchment to 100% capacity. This shows the catchment’s ability to recharge following significant rainfall.
The BAC’s key challenges for water management following a bushfire are catchment management and pre-WTP treatment or filtration. The BAC reservoir and surrounding catchment area are within steeply sloped rock formations and dense bushland. This creates access issues and is unfavourable to the initial and continual response to a bushfire where treatments cannot be implemented, and debris removed from the site. As the BAC does not undertake pre-WTP water treatment or filtration, the raw water entering the WTP is unregulated. Therefore, the raw water requires additional chemical dosing and treatment to meet ADWG standards. Although the BAC maintained supply throughout the period, the extent of additional supply changed quickly with residents’ early preparation to wet down areas to green landscaped areas and pre-empt ember attacks. The event proved that the supply change timeframe occurs over far longer periods than previously expected by the BAC water managers, as residents act and prepare following events elsewhere in the country. The historic event will enable a greater understanding and reference for regional water managers to future events. The BAC has concerns about future bushfire events and associated water management issues due to the inaccessible nature of the catchment. The dense, steep terrain will make it difficult for operators, rangers, and water managers to maintain and manage events following a bushfire. The lack of accessibility also negates the ability to implement pre-storage water quality treatments and catchment recovery and monitoring procedures.
The BAC has an opportunity to adopt pre-storage water quality treatments to improve water quality before pumping to the WTP. Additionally, there is no treatment or filtration between the storage and WTP other than drawing water from advantageous depths with variable offtake trunnions. Therefore, an overall opportunity to implement strategies to improve raw water quality is available. This would improve the health of the catchment and the BAC’s storage dams and reduce the extent of chemical dosing required to meet the ADWG standards. Increased accessibility to the site and its surroundings would improve catchment management following a bushfire and benefit the monitoring and maintenance of the water supply infrastructure.
Floodwater affected council (FAC)
In 2021, the FAC endured its third wettest year since records began in 1908, with 977.2mm compared to FAC’s annual average rainfall of 639.7mm. In addition, November 2021 was the wettest month in the FAC’s history, with 142.4mm, far greater than the November average of 65.6mm. Figure 5 shows monthly rainfall comparisons for 2020–2022 and the average monthly rainfall between 1908–2022 at the FAC Weather Station. Except for December, between 2020–2022, all monthly rainfalls exceeded the long-term average monthly rainfalls, with both March and November recording more than double the long-term averages.
Flood water quality and supply management
In March 2020, the FAC recorded its first rainfall event greater than 60mm in 14 months. This followed three consecutive years where only 75% of the average annual rainfall was reached. At this stage, the FAC’s reservoir was at about 30% capacity. High rainfall events were reported in March 2021 (135mm) and January 2022 (80mm), when reservoir capacity exceeded 100%. November 2021 was the wettest month in the FAC’s history. The FAC’s catchment was saturated before the rainfall occurred, and the reservoir exceeded full capacity. To provide context for the 10-day data period for water quality following rainfall events, Table 2 shows the average daily raw and treated water quality and ADWG maximum values for the selected water quality parameters.
Table 2: Maximum and minimum values for raw and treated parameters
From the floods following the drought-breaking rains in 2020 to the present day, the FAC has maintained all treated water to the ADWG standards. Following the treatment processes, the data shows the FAC’s effectiveness in managing water quality throughout high rainfall. The E.coli during flooding often rose significantly above the normal range expected. For example, E.coli level was reported as > 16000 CFUs/100ml in a day in November 2021. However, the following day the value was 790 CFUs/100ml. For the treated water, the pH ranged from 6.8–8.37. This range approaches the outer bounds accepted by the ADWG standards making it acceptable. The average colour of the raw water was 68 HU. Following flooding events in data captured, colour typically increased, with a high of 553 HU in November 2021. The colour ranged between 0–5 HU within the tested ranges for the treated water. This range meets the requirements set within the ADWG. Raw water turbidity levels generally showed a significant spike immediately following a high rainfall event. The highest reading for the data shown was 298.00 NTU in March 2021.
The recent historic flooding events have proven that the dam’s storage capacity is sufficient to stop major flooding, as the systems in place can release water in a controlled manner to reduce the risk to downstream properties. In addition, the flooding has proven that there is currently sufficient potable storage to enable the WTP to cease treatment during flooding periods where water quality is at its worst. This has enabled less processing and treatment, allowing raw water to stabilise before the WTP continues operation. With extensive population growth projected in the area, the FAC will need a significant increase in water filtration infrastructure to manage the increased system loading. Currently, the network is serviced by one WTP, and residential areas are spreading, likely requiring further infrastructure to accommodate the growth.
A series of levee banks in the FAC are designed for a 1/1000-year flood event. Climate change and the increase of record-breaking events leave uncertainty in the operation of flood mitigation infrastructure for councils across the country, including the FAC. Over time, managing the treatment process of raw water has required further advanced technology and stringent treatment processes to keep up with the ADWG and reduce raw water quality. The mark left on raw water quality by human actions has continued to reduce the quality of water entering the WTP. The FAC is on a flood plain, with large areas of floodwaters inundating the landscape in periods of high rainfall. Water harvesting could be implemented during flooding to redirect floodwaters to storage reservoirs or catchments to boost storage in dry spells. In addition, looking at alternative storage could provide a location to capture water harvested during floods, which would require further studies.
In NSW, 81% of the land is agricultural farmland, much of which overlaps water catchments, particularly in regional NSW (Department of Agriculture, 2021). The runoff from agriculture greatly pollutes water following flooding, as high concentrations of pollutants build-up on farms over long periods. Animal by-products, fertilisers, and pesticides are examples of pollutants attributed to farmland (Xia et al., 2020). The effects of these substances entering waterways include increased microorganism production and distortion in the water’s chemical and physical properties (Howe & White, 2003). The microbial effects of flooding are evident, as is the case for Escherichia coli (E.coli), where studies have shown that the highest values are driven by surface runoff. This is mainly due to faecal matter on watersheds being washed into waterways feeding town water supplies (Clarke et al., 2017). During flooding events, suspended sediment concentration in water is far greater than in times of drought or low flow. This occurs due to heightened soil erosion with water washing soil from cultivated lands, uncultivated pastoral lands, and channels and gullies (Wallbrink et al., 1998). The effect of rainfall on water quality and turbidity depends on various factors, including the state and size of the catchment and the intensity of the rainfall event (Fitzgerald et al., 2014). Sediment significantly raises turbidity levels and occurs at a higher rate when intense storms or rainfall events occur (Sun et al., 2001). In addition to the finer pollutants and particles that floods carry into rivers and water bodies, debris is carried into systems during flooding events. Debris can damage and create blockages to infrastructure, causing water management issues. A flood’s intensity contributes to the velocity of water within rivers and its capability to carry debris (Kalendher et al., 2016).
In addition to the benefits of replenishing catchments that provide long-awaited recharge to rivers and reservoirs, the floods caused significant damage to infrastructure and eroded soil left vulnerable by the drought and bushfires. Droughts leave behind residual effects, which become prevalent if followed by flooding. The water quality is affected significantly as concentrated sheet flow provides a mode of transport for eroded material and chemical and physical pollutants (Delpla et al., 2009). Increased precipitation in combination with baron landscapes meant the higher runoff rates provided little resistance to floodwaters as water sheeted across exposed catchments. As a result, heavy rainfall often compounds the effects of extreme weather events before impacting water quality to a greater extent (Fitzgerald et al., 2014). A flood following a drought makes water bodies susceptible to blackwater events as years of organic matter in leaf litter build-up. Blackwater events occur through floods washing the organic material into water bodies and allowing carbon to egress into the water, elevating dissolved organic carbon levels. The increased levels of carbon allow a means for increased microorganism growth, which uses up dissolved oxygen within the water body. Although blackwater events are part of natural ecology, the severity of events is increased due to a changing climate. Following extended periods of drought, floods make blackwater events detrimental to water quality and leave water bodies susceptible to further events such as fish kills (Howitt et al., 2007). Rainfall subsequently transports an abundance of matter into waterways and storage, reducing raw and final water quality (Fitzgerald et al., 2014).
Regional LGAs’ preparation and response to drought are essential to resilience following periods of drought. Improving an organisation’s technical knowledge, in-house expertise and capability, and learning from past events on local, national, and international levels can benefit outcomes following drought (Wright et al., 2014). Monitoring water quality levels within a system and implementing strategies to address common water quality themes associated with drought, including turbidity, taste and odour, higher chemical and physical concentrations, and pathogen concerns, will greatly assist in maintaining compliance with standard regulations. In drought, trace element concentrations are greater due to a lack of inflow and decreased dilution. Studies have shown that water stratification and settlement cause varying depths to contain higher levels of some water quality characteristics, such as trace elements. Supply intake levels that can operate at varying depths enable supply raw water with quality. Exploring improved intake structures may be beneficial to block or use shallow/deeper water depending on the water quality at various depths (Wright et al., 2014). Vertical mixing has proven to be an important control of the growth of microorganisms such as cyanobacteria or blue-green algae for several decades. The circulators disturb the conditions favourable to eutrophication. Artificial mixing disrupts stratification in reservoirs in drought by creating vertical diffusion (Han et al., 2020). As cyanobacteria thrive in slow-moving warm, nutrient water and can remain buoyant to use sunlight to create a food source, mixing the water disrupts these conditions (Funari et al., 2012).
Organic matter is a forerunner to increased levels of disinfection by-products (DBP) and Total Organic Carbon (TOC), which are increased following rainfall proceeding a drought (Yang et al., 2008). Raised DBP and TOC occur due to increased organic matter washed into the network interacting with the disinfectants used in the water treatment. Spikes in organic matter can be avoided with vegetation control on reservoir embankments, limiting the amount of organic matter built up over extended periods of drought (Wright et al., 2014). To manage water quality during drought, water quality monitoring is essential to enable quick adjustments (Wright et al., 2014) to comply with regulatory standards. Monitoring and documenting for historical and reflective purposes provide lessons learned and opportunities for improvements during future events.
Effective treatment processes such as ozone treatment and adsorption, in addition to conventional treatment processes, have enabled drinking water quality standards to be maintained in extreme weather events. Detailed audits of critical water reticulation networks help to identify leaks and provide water-efficient substitutes for common items to lower system demand. Sufficient infrastructure and the implementation of a demand management strategy and water restrictions allowed the township to successfully manage its way through the millennium and 2017–2020 weather extremes. To further droughtproof regions across NSW, LGAs must increase collaboration and share resources to ensure towns can sustain enough supply to handle future droughts of equivalent or greater magnitude. This should be paramount for organisations such as CENTROC.
A systematic study is required to understand systems capacity considering each LGA’s water storage capacity and system demand and capabilities to withstand the recent drought. This could enable the identification of surplus resources to be shared where areas cannot meet demand across regional NSW.
Research into regional NSW consumers’ perceptions of treating the untapped resource of effluent would provide insight into fast tracking the acceptance of treated effluent as a potential drinking water source.
Additional case studies are required to provide a more generalised picture of the current situation for drought affected areas in regional NSW. This would include areas where water quality may be more greatly affected due to different catchment characteristics and the impact of localities with different agricultural uses, particularly where intensive irrigation is used. These case studies would likely present different challenges to water quality and supply management where different social, economic, and environmental factors are present.
The water quality effects of the bushfires were largely physical and chemical, with the microbial effects considered negligible. The BAC’s water treatment processes relied predominately on increasing chemical dosing following the effects of the bushfires to stabilise turbidity, colour, and pH levels in addition to conventional treatment. The results following the bushfires indicated that turbidity and colour were higher than pre-bushfire levels. In contrast to droughts and floods, a bushfire event of the magnitude of the Black Summer bushfires was not something water managers in the past could have envisaged. As future extreme bushfire events must now be considered plausible, improving dam and catchment accessibility would be essential for targeted action in the bushfire affected areas. This would enable the implementation of pre-treatment strategies such as land and channel treatments.
The case studies reviewed have proven the capability of the regional NSW councils observed to manage water quality and supply during the various climate extremes of the past five years. The changing context of regional areas will provide further challenges in addition to a more volatile climate. Further research, continual review, the development of new innovative strategies, and regional and state collaboration must be undertaken to ensure the future of residents in regional NSW.
Recommendations
Due to the volatile nature of regional NSW and the occurrence and resounding effects of drought, there is an opportunity to water harvest from floods to further droughtproof the region. To redirect floodwaters, local councils could use a series of levee banks located around town as a capture point to pump to storage. Further studies should be undertaken into securing this resource to supplement storage, particularly when storage levels are low, or whether another storage could be established to serve this event. With extensive population growth projected in the area, regional NSW councils will need a significant increase in water filtration infrastructure to manage the increased system loading. Currently, most regional councils depend on single water treatment facilities and the reach of residential areas is spreading, which will likely require further infrastructure to accommodate the growth. As many regional towns may suffer both flood and drought over extended periods, pooling resources could benefit the LGA of concern and neighbouring LGAs, where a town may not have the resources to manage an event. Different locations using alternate strategies and treatments would provide insight into what has been done successfully elsewhere and other councils’ issues. Council collaboration and further research into water management during extreme weather events are key to future practices.
Ethical Approval
Not applicable
Consent to Participate
Not applicable
Consent to Publish
All authors agreed with the content and that all gave explicit consent to submit and that they obtained consent from the university.
Authors Contributions
Both authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Adrian Hickey with the supervision of STMLD Senevirathna. The first draft of the manuscript was written by STMLD Senevirathna, and Adrian Hickey commented on previous versions of the manuscript. Both authors read and approved the final manuscript.
Funding
The authors declare that no funds, grants, or other support were received during the preparation of this manuscript
Competing Interests
The authors have no relevant financial or non-financial interests to disclose.
Availability of data and materials
Not applicable
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