Environmental floods for Victorian regulated rivers

Dams, whilst critical to society for water supply, impact on the environment and alter flooding patterns downstream of a dam. Floods perform an important role in sustaining many abiotic and biotic components of an ecosystem, such as channel maintenance and triggers for fish spawning. Environmental floods are a promising management technique but their release has only been reported from 16 of more than 45,000 large dams worldwide. This thesis is the first review of issues surrounding the implementation of environmental floods from large Victorian dams. The study identifies the large dams in Victoria that (a) have the most altered flood hydrology downstream of the dam, and (b) have the least physical constraints on releasing floods. The extent of flood regime change from 21 dams is quantified using flood statistics. All of the 21 dams reduced the magnitude of natural 1 to 10-year recurrence interval floods and extended the recurrence interval of natural floods. A worldwide review of environmental floods reveals six major limitations to environmental floods and five factors common to all successful environmental flood releases. One of these limitations - capacity of the dam to release an environmental flood is examined in more detail. Twelve Victorian dams have the physical capacity to release a natural one-year recurrence interval flood. Foremost among these are Thomson, Rocklands, Eildon and Upper Yarra dams which have a high impact on floods and potential to release a flood without requiring infrastructure modifications. Implementing an environmental flood in Victoria is a long term process taking up to ten years. Environmental flood design requires that a link between flood change and ecological condition be established. This requires substantial data to be available. Coordination among stakeholders involved in environmental flood planning, particularly optimising the operation of a dam to maximise environmental benefits of a flood release while minimising impacts on other water users, is a key aspect of environmental flood implementation