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Managing future low reservoir levels

Project Number # 1133

Understanding water quality risks under low and variable water level conditions

Project Leader:  David Hamilton, Michele Burford

Water levels in dams and reservoirs are likely to be consistently lower and more variable in a future climate where rainfall-runoff will decrease and become more sporadic in many areas of Australia. Demand for water supply and recreation may also intensify in some areas with changing demographics and demand for recreational water use, as well as having to maintain water levels to provide for ecosystem life-supporting capacity in some cases. These changes are likely to present major challenges for the water industry to manage water quality and quantity.
Dams and reservoirs are now recognised as an important barrier to reduce water supply contamination hazards. They are a low-cost preventative measure that can give multiple log reductions in contaminant and pathogen concentrations, and therefore provide an important ecosystem service in the water supply cycle. Water levels have been demonstrated to play a key role in the efficiency of the dam barrier, with potential to affect water treatment processes and costs, as well as human health.

There is potential for water quality to be impacted by lower and more variable water levels in dams and reservoirs. Importantly, there is some evidence that recovery of water quality from extremely low water levels may not occur or may at least be delayed. Symptoms of poor water quality relate to increased occurrence of cyanobacteria (=blue-green algae) blooms, elevated iron and manganese, and particulate (e.g., inorganic sediment) and dissolved organic matter, including taste and odour producing compounds, as well as increased potential for short-circuiting of pathogens and other contaminants from inflows to dam and reservoir offtakes.

There is potential for water quality to be impacted by lower and more variable water levels in dams and reservoirs. Importantly, there is some evidence that recovery of water quality from extremely low water levels may not occur or may at least be delayed. Symptoms of poor water quality relate to increased occurrence of cyanobacteria (=blue-green algae) blooms, elevated iron and manganese, and particulate (e.g., inorganic sediment) and dissolved organic matter, including taste and odour producing compounds, as well as increased potential for short-circuiting of pathogens and other contaminants from inflows to dam and reservoir offtakes.