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South East Drainage Network

The South East drainage and floodway network has a range of functions:

Remove floodwaters caused by significant annual rainfall events and mitigate the impact of broad-scale and prolonged inundation of production land and groundwater recharge - requiring surface water drainage;
Drain saline groundwater from the upper soil profile in the ‘at risk’ parts of the landscape and thereby mitigate the effect of salinity in the root zone of pasture and native plant species – requiring deeper drainage
Provide for appropriate environmental flows to key wetland systems of regional, national and international significance - requiring flood-ways and regulators for manipulation of fresh surface water resources.

Types of drains

There are three major types of drains in the region:

Surface water drains

Surface water drains aim to drain surface water from the landscape, generally without the requirement to intercept groundwater (i.e. relevant in the lower South East and parts of the upper South East).

Flood mitigation drains

Floodwater drainage serves to alleviate the broad-scale and prolonged inundation of the landscape, associated with significant seasonal rainfall events. Such inundation has been known to put large areas modified for production under water for many months.

Groundwater drains

Groundwater drainage provides for drawdown of saline groundwater away from the surface root zone of plants. Most significantly this drawdown of the groundwater table during the summer months can impede the wicking (drawing up) of salts into the root zone by lowering the water-table beyond the effective zone of influence of evaporation.

Assets

There are a number of elements and considerations involved in managing the drainage network. The four main areas are:

Built assets
Plant and equipment
Drain maintenance
Flow management.

Fact sheet: Structure and function of the South East Drainage Network.

Upper South East

In the Upper South East, the drainage network gives us the ability to separate saline groundwater from fresh water. Saline groundwater is transferred through the network to the Coorong. Fresh water is used as environmental flows, including diversions to the REFLOWS Floodway which recreates the natural historic south to north flowpaths across the region.

A combination of drains and floodways, physical infrastructure like weirs and surface water crossovers, fauna crossings, and proactive protection of natural habitats is delivering regional economic prosperity without compromising the environment.

A strategy to manage the drainage network

The Drainage Network Management Strategy outlines the core policy principles for the management of the Upper South East Drainage Network (USE Network). The principles help us to:

meet the needs of key environmental features and habitats of biodiversity significance, such as wetlands linked to the USE Network
address agricultural issues relating mainly to flood mitigation, groundwater and salinity management.

This is in the context of:

managing water resources that are or may be manipulated by the USE Network, for purposes including environmental flows, flood mitigation and groundwater/salinity management
supporting both environmental and agricultural production values that are affected by the manipulation of water resources within the USE Network
managing discharges from the USE Network, including those to the south lagoon of the Coorong
further developing and managing infrastructure within and/or relating to the functions of the USE Network.

The strategy provides a high-level policy document to guide the future management of the USE Network. It is not an operational business plan but is supported by an implementation plan.

Download our fact sheet on the long-term management of the South East drains and wetlands.

South Eastern Water Conservation and Drainage Board

The SEWCD Board has a long history of local and regional management of flooding, surface water and drainage in the South East.

Under the SEWCD Act, the board has the following functions and obligations:

To provide an effective and efficient system for managing the surface water of the non-urban lands in the South East, by conserving, draining, altering the flow of or utilising that water in any manner
To carry out works for the purpose of lowering the level of the water table of lands in the South East
To undertake, assist or promote research in the fields of water conservation, drainage and management
To give advice and assistance to others in the fields of water conservation, drainage and management
The enhancement or development of natural wetlands and the natural environment generally in the South East.

Water from the South East is important to the restoration of the Lower Lakes and Coorong. See the Murray Futures South East Flows Restoration project plan for more.

South East Drainage Network — An environmental watering event in the Upper South East in September 2011

Adaptive management

Operating decisions are made according to the principles of adaptive management, which simply means ‘learning by doing’ and ensures continuous improvement. It includes a rigorous program of planning, operating, monitoring and improvement.

Each year pre-winter, objectives are set for the annual management of the system. Examples include delivering environmental flows to priority wetlands and ensuring the operation of a key regulator to minimise inundation of an at-risk agricultural area. The system’s winter/spring operations are run to achieve the management objectives and each operation (e.g. the lifting of a regulator) is recorded for subsequent review.

A hydrological monitoring network allows operators to manage the drainage system in response to catchment conditions and rainfall. Ecological monitoring captures the response of wetland ecosystems using the numbers and variety of vegetation, waterbirds, fish and frogs as key indicators.

Operating the system

The SEWCD Board operates the South East’s drains and floodways.

The drainage system is operated to:

protect infrastructure, land, soils and ecosystems from flooding and dryland salinity
provide water for environmental purposes to enhance the natural environment
protect and enhance South East agricultural lands for primary production
assist in the proper conservation and management of water in the South East.

Prolific growth of rushes and other vegetation in drainage channels encourages silt deposits. The SEWCD Board maintains 2589 kilometres of drains and associated structures through a comprehensive annual maintenance program. This program includes machine cleaning of silt deposits, control of vegetation obstructing flows and regular attention to road bridges and other structures.

See our fact sheet on operating the South East drains and floodways.