Practical guide to reservoir management

Abstract

This report summarises a range of studies and consolidated practical knowledge related to reservoir management in the Australian context, which also have wider international application. The guide provides an overview of processes that impact upon drinking water quality in reservoirs and also a range of selected procedures and tools for reservoir management. This is supported by a series of case study investigations that were largely carried out within the Source Water Program of the CRC for Water Quality & Treatment. The first section of this guide deals with reservoir monitoring and modeling with discussion about the application of hydrodynamic models in reservoir management. It is followed by sections on catchmentderived contaminants, including description and case studies of the use of a simple model to assess contaminant transport, such as pathogens in reservoir inflows. The guide outlines the importance of natural organic matter dynamics and transformations in reservoirs. Subsequent sections address reservoir-derived contaminants such as cyanobacteria and iron and manganese and provide a case study of the use and importance of variable depth reservoir offtakes to optimise withdrawal of the best quality water. The guide includes discussion of managing the impacts of wildfire on water quality and has an overview of the emerging area of climate change and reservoir management. Reservoir management should be considered in the context of the Framework for Management of Drinking Water Quality contained in Chapter 2 of the Australian Drinking Water Guidelines (ADWG), (http://www.nhmrc.gov.au/publications/synopses/_files/adwg_11_06_chapter_2.pdf). This Framework offers effective means of assuring drinking water quality and the protection of public health through adoption of a preventive management approach that encompasses all steps in water production from catchment to consumer. When using the Framework there are a number of elements that need to be considered in relation to reservoir management including: assessment of the role and importance of the reservoir in the context of the overall supply system; identification of preventive measures available for water quality management in the reservoir; and the identification of operational and process controls available. It is important to note that reservoirs can form one of the important barriers to contamination in this preventive strategy from ‘catchment to tap’, however they can also be a source of water quality deterioration. The first step in the development of a reservoir management plan using this key element approach should be to consider the potential hazards from catchment activities and the circumstances under which these will develop as risks to water quality. This risk assessment not only informs the reservoir management plan but may also reveal opportunities for managing contaminants at the source. The most common contaminants of concern generated from catchments are pathogens, particulates and natural organic matter but in some cases industrial and agricultural chemicals may also be important. High rainfall and associated inflows represent the major risk period to deliver these contaminants. During storage of water in the reservoir a number of beneficial water quality changes can occur. Reduced water movement increases the rate of sedimentation of particulates. This reduces turbidity and may also result in the sequestering of the contaminants associated with the particles. Many of the pathogens of concern are attenuated by environmental conditions with temperature and UV being the most critical factors. They may also be consumed by grazers. Chemical contaminants may be subject to beneficial transformations that can de-toxify them. Understanding these mechanisms is criti cal to the understanding of the effectiveness of reservoirs as barriers to contamination. Of particular importance is a good knowledge of the hydrodynamic processes that control water movement in the...