Clyde River and Jervis Bay
River Flow Objectives explained
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At a Glance |
This section explains each of the River Flow Objectives (RFOs). See the RFOs for each part of the Clyde River and Jervis Bay catchments.
In total, there are twelve coastal River Flow Objectives, each dealing with a critical element of natural river flows and estuarine processes.
Flow patterns in many rivers have been significantly altered and will not return to natural flow regimes. The NSW Government is not attempting to restore completely natural flow patterns where the community benefits significantly from altered flow patterns. Communities and the Government have identified important areas where we can make adjustments to maintain or improve river health while continuing to benefit from water use.
Water sharing plans (WSPs), where developed, will contain integrated actions and timeframes to achieve objectives and implement identified actions in consultation with the community. Different approaches and outcomes will apply across different parts of the catchment.
Recommending variations to objectives
The Natural Resources Commission (NRC) will review the role of WSPs in achieving state-wide natural resource management standards and targets after 5 years of the plan being made. As part of this review the NRC will call for public submissions and consider other state-wide policies or agreements that are relevant to the catchment management area. The Minister for Natural Resources will consider the review undertaken by the NRC when deciding whether to extend the duration of the current water sharing plan or to make a replacement plan.
The Minister may also amend plan actions at any time if the plan so allows or if it is deemed to be in the public interest to do so.
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Protect pools in dry times
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Protect natural water levels in pools of creeks and rivers and wetlands during periods of no flows
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During dry times, some streams stop flowing and form pools. Pools and wetlands are refuges for aquatic plants and animals. Pumping water from these areas can make it more difficult for many species to recover after a drought.
Measures to achieve objective
- There should be no water extraction from streams or wetlands in periods of no flow.
- If conditions on water licences do not provide for meeting this objective, priority goes to implementing it by actions appropriate to local circumstances.
Supporting information
- Along with social and economic considerations, WSPs should define when and how to protect specific pools:
- in natural wetlands with licensed pumps
- in streams where water flows under the sediment surface
- where these pools have become deeper or shallower.
- Where water extraction for stock and domestic use is high (e.g. in rural subdivisions surrounding large urban centres), the NSW Government may recommend actions to protect the environment in periods of no flow.
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Protect natural low flows
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Protect natural low flows
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Water extraction and storage are high in dry times and impose long artificial droughts that increase the stress on aquatic plants and animals.
Measures to achieve objective
- Share low flows between the environment and water users and fully protect all very low natural flows.
- Very low flows: defined as flows below the level naturally exceeded on 95% of all days with flow.
- Low flows: defined as flows below the level naturally exceeded on 80% of all days with flow.
- Unless environmental, social and economic evaluations give an appropriate alternative, the following limits on water extraction apply:
- Environmental share in high-conservation-value streams: to be all very low flows and most of the low flows. There should be no increase in extraction of low flows.
- Environmental share in other streams: to be all of very low flows; and 50%-70% of daily low flows.
- New or transferred licences should not allow extraction during low flows below the 80th percentile.
- In streams with little water use, or with important conservation values, minimise risks to ecosystems during low flows.
- Review management of town water supplies to assess whether changes may help achieve the objective without significantly affecting reliability.
Supporting information
- Water sharing plans (WSPs) need to identify actions to achieve targets for each stream that will balance local environmental, social and economic considerations.
- In streams where extraction currently exceeds 50% of low flow, WSPs may include provisions to achieve targets. Where extraction is currently less than 30% of low flow, it should not be allowed to exceed 30%.
- Town water supplies will not need to be augmented to meet this objective. If augmentation is proposed for other reasons, appropriate levels of protection of low flows should be determined on a case-by-case basis.
- In urban streams, the changes made to the natural low-flow regime are generally unknown. Streams may be wetter than natural because of garden watering in the catchment. Alternatively, if inputs to groundwater are reduced, streams could be drier than natural during dry times. Site-specific studies and comparison with undeveloped streams would be needed to determine the amount of change.
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Protect important rises in water levels
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Protect or restore a proportion of moderate flows ('freshes') and high flows
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Rain causes peaks in river flows. This 'pulsing' of flows, and their duration, may trigger migration of animals and reproduction of plants and animals; provide over-bank flows to wetlands and floodplains; shape the river channel; and control water quality and nutrients. Water storage and extraction can alter or remove freshes, inhibiting these vital processes. The height, duration, season and frequency of higher flows are all important.
Measures to achieve objective
- Unless local information suggests appropriate alternative targets, use the following limits on extraction:
- No extraction of more than 30-50% of moderate to high flows on a daily basis. (This means that, for each stream, the WSP may recommend an appropriate limit on the proportion of flows that may be extracted whenever flows are greater than the level that would naturally be exceeded on 80% of all days with flow. For some streams this limit may be 30%; for other streams it may be as high as 50%.)
- No increase in extractions from high-conservation streams.
- Where use exceeds the above limit, develop appropriate ways of limiting the volume or controlling the timing of extraction.
- In areas of new development, ensure that stormwater is managed in such a way that there is no increase in the height or flow rate of high flows.
- In areas of existing development, explore opportunities for improving stormwater management to mitigate flooding.
Supporting information
- These targets are currently being met in many streams, particularly those with low water extraction.
- Management plans need to include appropriate actions to achieve this objective that will balance environmental, economic and social considerations.
- High flows may cause flooding, which is a significant community concern. Mitigation requires both better stormwater management (increased detention and infiltration) and planning to avoid the problem (relocating houses and infrastructure from flood prone areas and preventing new development in these areas).
- Adequate management of stormwater is easier in new developments. It may be costly and more difficult to retrofit in existing developed areas.
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Maintain wetland and floodplain inundation
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Maintain or restore the natural inundation patterns and distribution of floodwaters supporting natural wetland and floodplain ecosystems
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Floodplain and wetland ecosystems develop in response to flow patterns and the nature of the landscape between the river and the wetlands or floodplains. Floodplain works can change the flooding patterns, which will then lead to changes in habitat and vegetation. These changes can be expected to reduce or change the diversity and abundance (or both) of species in the ecosystem. In particular, they can lead to reduced numbers of native fish and to water quality problems.
Measures to achieve objective
- In management plans and actions for waterways, include strategies to:
- maintain, restore or mimic natural inundation and drying patterns in natural and semi-natural wetlands and remaining native floodplain ecosystems
- ensure adequate access for native fish to and from floodplain wetlands.
- Flooding patterns should not be altered without proper environment assessment.
Supporting information
- This objective needs to be implemented in only a few locations.
- Maintaining wetlands and floodplains will improve water quality and reduce downstream flooding.
- Property protection issues need to be taken into account.
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Mimic natural drying in temporary waterways
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Mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary waterways
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In urban areas, the preponderance of hard-surfacing (e.g. paved or concreted areas) and garden-watering can cause streams and wetlands to be 'wetter' than natural. In streams and wetlands that would dry out naturally if these impacts were absent, this can create problems in maintaining habitat and vegetation, nutrient cycling, and signals for breeding. It can also lead to a high watertable and associated salinity problems. Natural wetting and drying cycles produce diversity of habitat and, therefore, high species diversity.
Measures to achieve objective
- Identify any streams where unnatural flows have greatly reduced drying-out periods. Assess the potential short- and long-term environmental, economic and social effects of this change, and of possible management alternatives.
- Decide what (if any) action is appropriate to implement this objective in streams and wetlands on a case-by-case basis, after giving due consideration to local views.
Supporting information
- This objective is being met in most or all the streams.
- There are few streams where drying periods differ significantly from natural conditions. In urban streams, the change to the natural low-flow regime is generally unknown. Streams may be wetter than natural because of watering in the catchment; alternatively, if inputs to groundwater are reduced, streams could be drier than natural during drying times. Site-specific studies and comparison with undeveloped streams would be needed to determine the change.
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Maintain natural flow variability
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Maintain or mimic natural flow variability in all streams
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Australia's rainfall and river flows are naturally variable. The way we currently store and divert river water can reduce natural pulsing of water down rivers and maintain artificially high or stable river heights. In urban areas and other places where the ability of the land to absorb or detain rainfall is reduced, more water runs off rapidly, so water levels will rise higher. These changes often create problems with streambank stability, biodiversity and signals for breeding and migration.
Measures to achieve objective
- Identify streams with unnatural flow variability and develop actions to mimic natural variability.
- Identify streams or development proposals with potential to have or cause flow variability problems, and take early action.
Supporting information
- Changes in variability occur mainly in controlled rivers, but may occur in certain locations or situations in other streams, such as in urban streams. In these areas, the objective should be addressed through stormwater management plans.
- This objective may also affect the achievement of Water Quality Objectives.
- This objective is being met in most or all streams in this catchment.
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Maintain natural rates of change in water levels
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Maintain rates of rise and fall of river heights within natural bounds
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Unnaturally fast changes in water level can occur in creeks with hard-surfaced catchments (such as in urban areas) or in streams that receive large releases from dams too quickly. If water levels fall too fast, water does not drain properly from riverbanks and they may collapse. Migration of aquatic animals may also be restricted by such sudden falls in river height. Very fast increases in flow and stream height can endanger people or aquatic organisms and contribute to bank erosion.
Measures to achieve objective
- Identify locations where water levels often rise or fall faster than they would naturally. Identify the reasons (in urban areas, usually the result of increases in hard-surfacing) and impacts. Remedial action requires case-by-case assessment.
- Identify potential problems and take early action.
Supporting information
- Local observations, such as bank erosion, may indicate a need for action.
- In urban streams, solutions may require increasing on-site detention or infiltration.
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Manage groundwater for ecosystems
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Maintain groundwater within natural levels and variability, critical to surface flows and ecosystems
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Some shallow groundwaters are directly linked to flows in streams and wetlands. They may provide base flows in rivers during dry periods and may be primary sources of water for wetland, floodplain and riparian vegetation. Also, serious depletion of grounwater in dry times may lead to unnatural recharge of groundwater from surface waters during the next flow event. Lowering groundwater in many coastal areas may expose acid sulfate soils, which-in many coastal areas-may contribute to soild and water quality problems. Lowering groundwater levels may cause seawater to intrude into aquifers and wetland soils that previously held fresh water.
Measures to achieve objective
- Implement the State Groundwater Policy (DLWC 1997a, 1998b).
- Identify any streams or ecosystems that may depend on high groundwater levels, and assess whether impacts on these may be caused by changed recharge rates or excessive pumping.
- Identify areas where groundwater may be rising and likely to threaten ecosystems or surface water quality.
- Identify long-term trends or changes in groundwater levels that are likely to threaten ecosystems or the quality of ground- or surface-water.
- Determine appropriate action to keep changes in groundwater level within acceptable bounds.
Supporting information
- WSPs should identify areas and actions needed, particularly where there are threatened ecosystems.
- This objective also covers areas of acid sulfate soils, where draining can mobilise acid and toxic metals, affecting surface ecosystems.
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Minimise effects of weirs and other structures
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Minimise the impact of instream structures
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Most instream structures (e.g. weirs) convert flowing water to still water, thus altering habitat and increasing the risk of algal blooms or other water quality problems. Barriers restrict the passage of plant propagules (e.g. seeds) and animals.
Measures to achieve objective
- Implement the NSW Weirs Policy (DLWC 1997b).
- Identify and take action to reduce the impact on native fauna of other structures that impede movement of water-e.g. floodgates, tidal barriers.
Supporting information
- The NSW Weirs Policy (DLWC 1997b) and weir review process helps set priorities and assess management options.
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Minimise effects of dams on water quality
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Minimise downstream water quality impacts of storage releases
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Many dams release water from the bottom of reservoirs where temperatures and dissolved oxygen are low and nutrient concentrations are high. These differences in water quality can affect the river downstream for hundreds of kilometres. For instance, many native fish will not breed in colder water.
Measures to achieve objective
- Determine whether water quality from dam releases limits achieving WQOs in unregulated streams and develop appropriate actions.
Supporting information
- WSPs need consider this objective only in relation to those streams with dams or large weirs.
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Make water available for unforeseen events
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Ensure river flow management provides for contingencies
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River systems can sometimes be affected by unforeseen or irregular events-such as algal blooms or the start of bird-breeding seasons. As river flows are a major determinant of many of these processes, we can sometimes alleviate a water-quality or environmental problem by better managing river flows.
Measures to achieve objective
- Current water licence conditions enable pumping to be suspended in the rare event that this may be necessary. WSPs should identify potential situations when such action may be warranted, as well as the steps to be taken to manage flows at these times.
Supporting information
- Protecting or mimicking elements of a natural flow regime is preferable to making water available for unforeseen events.
- WSPs need consider this objective only in relation to streams with significant water extraction or dams from which releases can be made.
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Maintain or rehabilitate estuarine processes and habitats
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Maintain or rehabilitate estaurine processes and habitats
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Coastal lagoons, estuaries and river mouths often change naturally in response to storms or tides. Flood-mitigation structures, weirs and other works also affect estuaries by limiting tidal flow, changing salinity conditions or altering water levels. Development of estuarine areas can also disturb acid sulfate soil deposits, which may release large amounts of sulfuric acid and toxic metals into the estuarine environment.
Upstream management of rivers also affects estuaries and lagoons. Stormwater carries nutrients, organic matter and sediments. Scouring as a result of flooding can affect the opening and closing of river mouths. Reduced freshes and flooding in estuaries severely depletes food sources for estuarine species. These effects can contribute to a decline in the number and abundance of species that use estuaries as habitat, nursery grounds or both.
Measures to achieve objective
- Adequate environmental assessment is necessary to determine the optimal opening regime of coastal lagoons and lakes. Management in the longer term should require planning to reduce the risk of flooding, and management of catchment activities to improve water quality.
- Dredging beyond the minimum needed to maintain navigation channels should be subject to environmental assessment before being allowed to proceed.
- Minimise draining or disturbance of areas of potential acid sulfate soils.
- Protect fish habitats-such as protected areas, seagrass beds and mangroves-from pollution and increased sedimentation or erosion. Polluted sites should be rehabilitated.
- Ensure that water-based activities have minimal impact on fish habitat.
- Deal with other processes affecting (or potentially affecting) estuary health-e.g. where increased urbanisation is proposed, ensure that impacts are avoided or minimised.
Supporting information
- Dredging or drainage could expose acid sulfate soils. As treatment of acid sulfate soils is expensive and relatively untested, the priority is to minimise exposure of these soils.
- Marinas and extensive moorings may affect water circulation patterns or aquatic habitats. This may expose acid sulfate soils and contaminated sediments, and affect the water quality and tidal flows generally.
This page was published 1 May 2006
About the Objectives