Hunter River
River Flow Objectives explained

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This section explains each of the River Flow Objectives (RFOs). See the RFOs for each part of the Hunter River catchment, except regulated streams.

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 significantly benefits 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.

Top of PageEnvironmental flow rules for regulated rivers

River Flow Objectives were not recommended for the regulated parts of the Murray, Murrumbidgee, Lachlan, Macquarie, Namoi, Gwydir and Hunter Rivers, as well as for the Barwon-Darling River. This is because as part of water reforms, in 1998 the Government established Environmental Flow Rules for these rivers, after consideration by River Management Committees. These flow rules considered the principles of the River Flow Objectives and generally applied from 1998 until 2004. River Management Committees developed Water Sharing Plans for these rivers, which commenced in July 2004. These Plans contain updated environmental flow rules, which are generally based on the principles of the River Flow Objectives, consistent with the State Water Management Outcomes Plan.

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.

Protect pools in dry times

Protect natural water levels in pools of creeks and rivers and wetlands during periods of no flows

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

Supporting information

Protect natural low flows

Protect natural low flows

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

Supporting information

Protect important rises in water levels

Protect or restore a proportion of moderate flows ('freshes') and high flows

Rain causes peaks in river flows. This 'pulsing' of flows may trigger migration of animals and reproduction of plants and animals; provide over-bank flows to wetlands and floodplains; shape the river channel; control water quality and nutrients; and provide necessary freshwater inputs to estuaries. 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

Supporting information

Maintain wetland and floodplain inundation

Maintain or restore the natural inundation patterns and distribution of floodwaters supporting natural wetland and floodplain ecosystems

Floodplain and wetland ecosystems develop in response to flow patterns and the nature of the landscape between the river and wetlands or floodplains. Floodplain works can change the flooding patterns, which will 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

Supporting information

Mimic natural drying in temporary waterways

Mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary waterways

Water releases from storages or, in urban areas, the preponderance of hard surfaces and garden-watering can mean streams and wetlands can sometimes be 'wetter' than natural. In streams and wetlands that naturally dry out, this can create problems in maintaining habitat, 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

Supporting information

Maintain natural flow variability

Maintain or mimic natural flow variability in all streams

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. Hydro-electric releases can vary unnaturally between day and night. 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

Supporting information

Maintain natural rates of change in water levels

Maintain rates of rise and fall of river heights within natural bounds

Shutting off dam releases, starting many pumps together or extensive hard-surfacing in urban areas can cause river levels to change too quickly. If water levels rise too fast, there may be human risk from flooding. 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.

Measures to achieve objective

Supporting information

Manage groundwater for ecosystems

Maintain groundwater within natural levels and variability, critical to surface flows and ecosystems

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. Seriously depleting groundwater in dry times may lead to unnatural recharge of groundwater from surface waters during the next flow. Lowering groundwater in many coastal areas may expose acid sulfate soils.

Measures to achieve objective

Supporting Information

Minimise effects of weirs and other structures

Minimise the impact of instream structures

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

Supporting information

Minimise effects of dams on water quality

Minimise downstream water quality impacts of storage releases

Many dams release water from the bottom of reservoirs where temperatures and dissolved oxygen are low and nutrient concentrations are high. These changed water quality conditions can affect the river downstream for hundreds of kilometres. For instance, many native fish will not breed in colder water.

Measures to achieve objective

Supporting information

Make water available for unforeseen events

Ensure river flow management provides for contingencies

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

Supporting information

Maintain or rehabilitate estuarine processes and habitats

Maintain or rehabilitate estuarine processes and habitats

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 the decline in the number and abundance of species that use estuaries as habitat, nursery grounds or both.

Measures to achieve objective

Supporting information

This page was published 1 May 2006

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