Floods play a vital role in supporting ecosystems within floodplains, wetlands, billabongs, rivers and streams. How beneficial a flood is to the environment can depend on many factors, including the flood size, duration and time of year it occurs.
Many plants and animals rely on flooding for their species to prosper. For example, some birds breed as a response to flooding, and we often marvel at the hundreds and sometimes thousands of waterbirds that arrive to breed at flooded wetlands. Some fish species commence spawning as a result of a flood event, while flooding can also help fish move up or down a waterway.
Many plants rely on floods to survive also. For example, many of the River Red Gum forests along the Murray River in northern Victoria only exist because of flooding, caused by large rainfall that occur upstream and flow down the river. These forests could not survive on local rainfall alone. There are also many smaller plants that only germinate, grow and reproduce in a flooded environment like a wetland.
Sometimes floods create environmental problems, such as ‘Blackwater’ events. Blackwater events occur naturally and can result in very low oxygen levels in the water, as a result of organic matter from the forest floor breaking down, particularly in warmer weather. As fish and some other aquatic animals breathe the oxygen from the water, critically low oxygen levels can cause some fish to die. However, this process also reflects a major benefit of floods, the addition of organic matter into the water to stimulate the food chain.
With human development for towns, farming and other infrastructure such as roads and rail lines, the frequency and distribution of natural occurring floods has changed. Levees are built along riverbanks to protect our homes and crops, dams are built in the hills to catch water for people to drink and for irrigation, and much of our landscape has been cleared of vegetation. This makes our remaining wetlands and billabongs, as well as the river and creeks that provide them with water in times of flood, very important environments to protect.
Further reading can be found at the Department of Environment, Land, Water and Planning website wetland page