Theme 3: Human Impacts on Catchments

Topic: Water Flows

What are environmental flows?

Environmental flows are natural flows or releases of water intended to supply the environment's needs. They are critical for maintaining the health of the waters and rivers upon which ecosystems and industries depend. The timing, quantity and duration of flows and the quality of our waters are inextricably linked and depend upon interactions between the catchment, floodplain, wetland, groundwater and stream. For more information on water flows please click here www.rivermurray.sa.gov.au/major/water_flow.html

Floods and High Flows

Floods and high flows are an important part of the natural flow patterns and overall ecology of rivers. For example, River Red Gums in the Murray River require floods and high flows to initiate germination of young trees across the floodplain. Without the high flows the trees would not be able to regenerate.

Droughts and Low Flows

In Australian waterways and wetlands, the lifecycles of plants and animals are adapted to droughts and low flows. For example, there are some species of plants that require drying of the wetland to set seed ready for germination in a flood event. Without the drought or low flow the seeds would not be able to develop.

Flow Management

Flow management traditionally involves structures such as weirs and locks to hold back floodwaters and maintain water levels during drought conditions (primarily for irrigation purposes and continued water supply).

Prior to flow management techniques being developed, the natural flow of water involved cycles of flooding, drought, high flow and low flow. Now, natural extremes of high flow and low flow have been reduced with the introduction of flow management techniques. For example, weirs create deep-water immediately upstream and shallow water immediately downstream. This alters the natural flow patterns of a waterway and, depending on the flows, can impact on the ecosystems and biodiversity.

Impact of flow management

Impact on biodiversity
Altered water flows can result in native fish being unable to move upstream or downstream for breeding, sensitive aquatic invertebrates are no longer present immediately downstream from weirs and tadpoles are only able to disperse in a flood event. You can see that changing the natural water-flow patterns impacts on the diversity and population of fish, aquatic invertebrates, frogs and birds.

Impact on water quality
Water flow management can positively or negatively impact on water quality. The reservoirs of the River Torrens are a positive impact. Flow management through these reservoirs reduces the impact of highly turbid River Murray water on water quality in the downstream area of the river. The reservoir allows the turbid water to settle, thus improving water quality.

A negative impact of flow management is changes in water temperature. For example, in the River Murray, immediately upstream from the locks, the water temperature is lower as the water is deeper. Immediately downstream, the water is shallower and is subject to much warmer temperatures. Aquatic plants and animals can be sensitive to temperature changes throughout their lifecycles. Altered flow patterns means there are constant temperatures in one location, resulting in less species diversity. With natural flow patterns there is greater variability of water temperature, resulting a greater spread of species diversity.

Student Activity Ideas

• How have changes to water flows in urban and rural catchments impacted on water quality and biodiversity in our waterways and marine environments? (Consider issues such as stormwater infrastructure, channel development, irrigation, building of weirs and dams, removal of native vegetation, compaction of soils and removal of woody debris.)
• Take a trip around your local area to view water flow management techniques (e.g. locks, weirs, wetlands, channels etc.)
• Research water flow management techniques in a particular area. What is the history of the water flow? Why was flow management introduced? How have things changed the environment?

Enquiry Learning

• What is an environmental flow?
• Why are floods and high water flows, as well as droughts and low flows, important parts of the natural flow patterns and overall ecology of rivers?
• How has water flow management changed the natural flow of water, and impacted on biodiversity and water quality?

Internet Resources

Type	Description	Resources Covering the Topic
Easy	Comprehensive look at flows in the Murray.	River Murray Urban Users www.murrayusers.sa.gov.au/ river_flows.htm
	Is flooding good or bad? All about floodplains and why they are important.	River Murray Urban Users www.murrayusers.sa.gov.au/ floodplains.htm
More Comprehensive	Flows maintain natural services and benefits of rivers.	The Nature Conservancy www.freshwaters.org/docs/ natflow.pdf
	Natural Advantage: A Blueprint for Sustainable Australia. Comprehensive overview of sustainable development, including flow issues.	Australian Conservation Foundation www.acfonline.org.au/asp/pages/ publicationtyp.asp?IdPublicationTyp=7
	Dams and weirs. The environmental issues.	Australian Conservation Foundation www.acfonline.org.au/asp/pages/ document.asp?IdDoc=384
	River flows. The environmental issues.	Australian Conservation Foundation www.acfonline.org.au/asp/pages/ document.asp?IdDoc=383
	Environmental flows in the Murray River.	Murray-Darling Basin Commission www.mdbc.gov.au/naturalresources/ flow/flowproject.htm
	Why flows are important. Covers the main issues in NSW.	NSW EPA www.epa.nsw.gov.au/soe/soe2000/ cw/cw_flows.htm
More Complex	A comprehensive look at the issue of environmental flows.	Inland Rivers Network www.nccnsw.org.au/member/ wetlands/news/media/ 19991118_EFpaper.html

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