State of the Environment

2006

Indicator: IW-11 Number of licenced dams, weirs, regulators and levees

Data

There are estimated to be over 3 000 weirs on rivers in New South Wales. In some rivers significant lengths of stream are impounded behind weirs. For example 40% of the Barwon-Darling River is in weir pools.

What the data mean

There are a significant numbers of structures on rivers that alter habitats and obstruct fish passage. There are programs in place to remove some weirs or build fishways.

Data Limitations

Continent-wide data are not available. There are also no data on trends in this indicator. The indicator, even if fully populated, does not distinguish in terms of size or likely impacts of waterways dammed. Data on unlicensed constructions are also available.

Issues for which this is an indicator and why

Inland Waters - Catchment scale influences - Hydrological condition - Connectivity - dams, weirs, regulators and levees 

Dams and weirs reduce the connectivity of rivers and streams, which interfere with the movement of sediment and nutrients and the dispersal of the biota. Number of weirs and dam is a crude but direct measure of this interference.

Inland Waters - Catchment scale influences - Hydrological condition - Ecological aspects of river flow regimes 

A significant pressure on aquatic ecosystems has been artificial flow regimes as a result of diversion of water, channelisation of rivers, weirs and dams, construction of levee banks to reduce the land areas affected by low to moderate flooding, modification of natural drainage patterns, and vegetation clearing and grazing. Number of weirs and dam is a crude but direct measure of this pressure.

Other indicators for this issue:

Inland Waters - Habitat scale influences - Fish passage 

Dams and weirs reduce the connectivity of rivers and streams, which interfere with the dispersal and movement of fish species. Number of weirs and dam is a crude but direct measure of this interference.

Other indicators for this issue:

Inland Waters - Response of biota - Fish 

Dams and weirs reduce the connectivity of rivers and streams, which interfere with the dispersal and movement of fish species. Number of weirs and dam is a crude but direct measure of this interference.

Other indicators for this issue:

Inland Waters - Human response - policy and management - Environmental flows allocation and management 

Dams and weirs reduce the connectivity of rivers and streams and can reduce environmental flows. This can have consequences for aquatic ecosystems. Number of weirs and dam is a crude but direct measure of this pressure.

Other indicators for this issue:

Biodiversity - Species, habitats and ecological communities - Condition of freshwater biodiversity 

As barriers to movement both upstream and downstream, dams and weirs can have a significant impact on the condition of freshwater flora and fauna. Individuals may migrate for several reasons, including seasonal changes, for dispersing populations and to food, shelter and mates. Number of weirs and dam is a crude but direct measure of this pressure.

Other indicators for this issue:

Human Settlements - Pressures created by human settlements on the environment - Water use 

Dams and weirs have been designed to increase the security and productivity of human activities and to ensure constancy of supply. In many cases they have highly modified the natural conditions. They have changed the connectivity of the aquatic and disrupted the life cycle of many aquatic species. Number of weirs and dam is a crude but direct measure of one of the pressures resulting from human use of water.

Other indicators for this issue:

Further Information

NSW weirs:

Key

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