Background
Beating drought: Environmental flows
Building drought into river operational plans
For freshwater ecosystems, river operational plans already exist which take into account the balance of water allocation for extraction (such as for urban use or irrigation) and water for the environment, and the rules for managing this balance. During drought, managers often find themselves adjusting the rules and changing the balance, to support human activities.
Since we cannot predict the intensity, duration and geographical extent of drought, how do managers decide whether, when and where in the catchment to provide environmental flows to relieve stress in the river ecology?
It could be helpful to review and revise water management plans on a case-by-case basis, within relevant legislative and policy frameworks, to determine priorities for environmental flows under drought in each catchment. Knowing the locations of tributaries, reaches and refuges of high conservation value would underpin this. For example, assessment of conservation issues and priorities in catchments is embedded in Queensland's water resource planning processes.
Eking out environmental flows
Environmental water is not necessarily flowing, some being static, but the term 'environmental flow' is commonplace.
Where freshwater ecosystems are stressed even at the onset of drought, there could be complete collapse of valued aquatic ecosystems and the plant and animal species that comprise them - unless rivers are allowed some flow during drought, or unless particular water levels or volumes are somehow maintained in standing water bodies.
If there is simply not enough water to make continuous releases for environmental purposes, it may be possible (as at least one valley management group of a dammed river in Victoria has done) to introduce periods of zero flow interspersed with pulses of flow to maintain water quality in refuge pools. This could save enough water, over a six-month summer period (October-March), to maintain the cycle for an additional 13 weeks (well into the winter) without additional rainfall.
Some other mechanisms being applied to share environmental water are:
- limiting the volume of water pumped during flow releases, or
- limiting the time of day of pumping, or
- setting 'cease to pump' levels.
It may be possible to call upon a 'contingency flow' held in storage, and release a fresh or two at times when even a small pulsed flow would be beneficial. For example, a modest volume of flow at the right time of year, coming after a large antecedent flow some years prior, might tip the scales in favour of beneficial ecological outcomes in the shape of, say, seedling recruitment or fish spawning events. This could be sufficient to sustain individual species or assemblages of species until the drought breaks.
Best use of 'contingency' environmental water will require knowledge of the life-history patterns and recruitment strategies of important species that need protection, as well as weeds and alien fauna that could be eliminated by strategically managed dry spells. Water also has a valuable role in ecological functions such as nutrient spiralling, processing of organic matter, food web dynamics, predator-prey dynamics and interactions between native and alien species. Priority habitats - possibly tributaries, reaches, waterholes, or runs - need to be identified.
Can the pattern of abstracting water be modified so that particular streams or rivers of high conservation value continue to receive flows during drought? Such opportunities could arise by taking a more flexible approach to the approval, uptake and use of water licences. It may be feasible to not use particular water licences, or to trade licences among properties, so allowing some streams respite during drought or even in the long term.
Prescriptive environmental flow rules are probably not going to work as a means of guiding water management during drought, because each drought - and its effects on rivers in particular catchments - is likely to be different.
In some systems, isolated pools of water (refuges) in otherwise dry stream beds may be sustained by groundwater. Here the ideal management approach is to:
- prevent stock access,
- cease all groundwater pumping near such pools, and
- prohibit water extraction from them.
The objectives here are to identify:
- the critical water levels or volumes that must be maintained in each pool or waterhole to enable it to function adequately as a refuge; and
- which species or assemblages are likely to survive, and for how long, if the critical water volume can be ensured.
If a particular refuge of great conservation significance passes this critical volume threshold, it is time to consider transferring in water from elsewhere or perhaps even moving species of high conservation and ecological value to another location. Such intervention would be a last resort as it carries potential hazards (see Beating drought: species conservation). It also would involve knowing which species are at risk and where they could be moved to for temporary protection.
Dry habitats
It is well worthwhile to protect dry stream beds and their riparian zones from damage, even if it is impossible to provide environmental water to them. When flows resume, eventually these habitats will be recolonised by the organisms able to disperse into them. See Sustaining aquatic ecosystems through drought for more about their management.
Learning from the drought
To understand the impacts of drought and recovery from it, we should try to monitor ecological responses to managed environmental flows and their benefits. This should lead to a better understanding of drought consequences under natural or managed flows in different ecosystems, and how different types of river cope and recover from drought. The information will be useful in future efforts to manage environmental flows and river restoration during droughts.
When the drought breaks, the refuges can be assessed and plans developed to restore their quality, character and functional roles for the longer term … that is, for the next drought or other disturbance. This recovery phase may require extra environmental flows to restore water quality and habitat characteristics, or restoration works such as strategic addition of logs.
River red gums
River red gum (Eucalyptus camaldulensis) is a tree species of high ecological significance to floodplain rivers but already under enormous stress in places. The poor condition of river red gums reflects long periods of alteration to natural river flows as well as the effects of salinity (George 2005). At least salinity can be partially mitigated by the transfer of fresh water from the river into the superficial groundwater.
Failure to continue to deliver environmental flows to forests of river red gum, such as the Barmah-Millewa on the Murray River, will cause irreversible loss of whole stands, as well as having major impacts on many other plants and riverine animals, including water birds. Red gums forests and other wetlands rely on just that - 'wet land' - terrain that must be inundated periodically to sustain biodiversity and associated values.
Useful references:
- Arthington A.H., Bunn S.E., Poff N.L. and Naiman R.J. (2006) The challenge of providing environmental flow rules to sustain river ecosystems. Ecological Applications 16(4): 1311-1318.
- Bunn S.E. and Arthington A.H. (2002) Basic principles and consequences of altered hydrological regimes for aquatic biodiversity. Environmental Management 30: 492-507.
- Poff N.L., Allan J.D., Palmer M.A., Hart D.D., Richter B.D., Arthington A.H., Rogers K.H., Meyer J.L. and Stanford J.A. (2003) River flows and water wars: emerging science for environmental decision-making. Frontiers in Ecology and the Environment 1: 298-306.
- Tharme R.E. (2003) A global perspective on environmental flow assessment: emerging trends in the development and application of environmental flow methodologies for rivers. River Research and Applications 19:397-441.
See downloads:
- Watering patterns for floodplain eucalypts. Watershed August 2005, p.16. Author: A. George.
- Environmental flows monitoring and assessment framework. (2005) Technical report , CRC for Freshwater Ecology. Authors: P. Cottingham, G. Quinn, A. King, R. Norris, B. Chessman and C. Marshall.
- A framework for monitoring and assessing the effects of environmental flows. Watershed April 2005, pp. 6-7.
- Case study: Monitoring the effects of Wimmera-Glenelg environmental flows. Watershed April 2005, pp. 8-10.
Keywords:
Topics:
| Water supply | View Frequently Asked Questions | View Bibliography |
| Principels for protecting aquatic biodiversity | View Frequently Asked Questions | View Bibliography |
| Refuge habitats | View Frequently Asked Questions | View Bibliography |
| Drought impacts | View Frequently Asked Questions | View Bibliography |
| Ecological responses | View Frequently Asked Questions | View Bibliography |
| Recovery from drought | View Frequently Asked Questions | View Bibliography |
