Weir Pool Manipulation
Frequently Asked Questions
2014 Spring Raising Events at Locks 1 and 2
A weir pool water level raising trial at Locks 1 and 2 is planned for this spring 2014. The aim of this trial is to raise the
water level by up to 20 centimetres above the normal operating range. The exact timing and extent of water level
variations above the normal operating range will be dependent on factors such as water availability and weather
conditions. Weir pool water level manipulations are a common component of normal River Murray operations from the
headwater storages to the barrages.
What are weirs, and how are they operated?
Weirs are structures built across rivers that are used to control water levels. Weirs are often accompanied by locks which
allow river vessels to travel through a weir. There are six weirs and locks on the main channel of the River Murray in
South Australia. The weirs are currently operated to keep the water levels relatively stable and within the normal
operating range. This is done to allow for navigation and provide a reliable level of water for supplying critical human
water needs, irrigation, recreation, stock and domestic purposes.
Why do we need weir pool manipulation?
Prior to river regulation, water levels in the River Murray varied in response to changes in flow conditions driven by
seasonal inflow conditions. The weirs and locks can significantly influence the water levels and are operated as a series of
relatively stable pools. This highly modified environment has dramatically reduced water regimes, resulting in reduced
connectivity to floodplains and wetlands. Floodplains and wetlands can also be permanently connected to the main
channel and therefore do not get the chance to partially or completely dry out. Weir pool water level manipulation
involves use of the weirs to raise and lower water levels in a weir pool to connect these floodplains and wetlands and
mimic some of the natural variation in water levels in order to improve the health of the river.
Why are we undertaking weir pool raising at Locks 1 and 2?
River Murray flows were restored with the long awaited high flows during late 2010 and early 2011 after years of drought,
providing significant benefits to the environment and communities. Recovery of the system has begun with these recent
high flows and it is important that we make the most of every opportunity to further enhance the natural flows to assist
in the ongoing recovery. Locks 1 and 2 provide us with the opportunity to test the flexibility of weir pool manipulation
within a reach of the river that is relatively uniform in width and depth.
What is the normal operating range?
The normal operating range is defined as the expected water level variations under routine River Murray operations
above full supply level. The full supply level at Lock 1 is 3.2 meters AHD and the operating range is from 3.2 to 3.5
meters AHD and Lock 2 from 6.1 to 6.4 meters AHD. Water levels within these weir pools are routinely monitored by the
Department of Environment, Water and Natural Resources and SA Water. The operating range may be changed over
time as a result of undertaking water level manipulation trials. Conducting operations within the normal operating range
will not affect the entire length of the weir pools and the extent of water level rise is limited due to the pre-existing
gradient along the River Murray. Please refer to the diagram on the final page.
What benefits are expected from weir pool raising?
Through manipulation of water levels by using the weirs, it is possible to return some aspects of the natural (preregulation) hydrological regime including natural variations in water level. Weir pool raising is expected to provide
benefits to in-channel and low-level wetland and floodplain areas. Ecological and environmental benefits from weir pool
raising include:
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Improved vegetation and macro invertebrate communities by improving seed bank viability;
Reduced water stress in floodplain vegetation;
Improved biofilm community diversity, thereby increasing their value as a food source for fish; and
Improved vegetation coverage and recruitment.
The proposed spring 2014 weir pool raising at Locks 1 and 2 would bring beneficial ecological outcomes for the major
biological components inhabiting the littoral (fringing) margins of the River, with a focus on food web pathways leading
from biofilms (algae and nutrients) through to primary grazer and consumers (fish and birds). We will be monitoring the
ecological response resulted from the weir pool raising.
Will the change in weir pool levels affect my road access?
Modelling and mapping indicates that there will be minimal impact to infrastructure. Monitoring will be undertaken by
the Department for Environment, Water and Natural Resources. We would also like any information from you on any
roads you think might be impacted or are being impacted, please refer to the contact officer at the end of the document.
Will I have access to water for irrigation?
Raising weir pool water levels is not likely to affect irrigation practices; conditions will be just like a normal high river but
without proportionally increased flow. However you may need to raise your pump and other infrastructure if the weir
pool water levels are raised above the normal operating range. This situation will arise whenever South Australia receives
flow above its normal daily entitlement, particularly under unregulated flow conditions. See below to find out how best to
find out to keep up-to-date with the project.
Will the change in pool levels affect boat access?
The weir pool raising is unlikely to lead to any major navigational problems. Boat operators should always use caution
when navigating near the river banks as elevated water levels may increase the width of shallows near the banks in some
places. Water levels will also be elevated at some boat ramps and jetties and boat users should always use caution.
How long will the weir pool raising last?
The water manipulation is planned to last approximately 8 to 12 weeks during spring 2014.
Will changing water levels influence the fish populations?
Introducing greater variations in water levels are likely to improve habitat and food availability and there will be a greater
chance of spawning and recruitment to improve populations in the river system. This is one of the longer-term benefits
of undertaking weir pool manipulations.
What will we see after the weir pool raising event?
After raising water levels at Locks 1 and 2 you may observe a change in the extent and condition (health) of vegetation
along the river channel and in the adjoining wetlands. Some vegetation will respond quickly to the conditions, but
greater and more valuable vegetation response will result from longer term improvements to river management,
including repeated weir pool manipulations over many years.
Will there be any other weir pool manipulation events be planned for the future?
Further weir pool manipulation events will be planned for several other weir pools over the next two years. Where
possible, attempts will be made to maximise the height of water levels in a weir manipulation trial.
It is also planned to trial a regime in the future that involves both weir pool raising and lowering to mimic a degree of the
variability of water levels that occurred under natural conditions in order to drive the ecological benefits. The extent of
weir manipulation (raising or lowering) at any weir will depend on:
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the operational constraints of the weir;
consideration of impacts on water quality and river users;
requirements under the Basin Plan;
the flows in the river at the time; and
potential impacts on infrastructure in the chosen river reach.
How can I keep updated on the weir pool manipulation project?
The easiest way is to either email RiverineRecovery@sa.gov.au your name, address and email address or fill out the
enclosed postcard. An email address will allow us to quickly inform you of how the project is tracking and let you know
when a date is confirmed for raising the water and when the water begins to be lowered. We will also keep the media
and our website updated. www.naturalresources.sa.gov.au/weirpools. Alternatively the contact officer is Wendy
Georganas on (08) 8463 3918.
Normal River Operation and Weir Pool Raising Trial – Conceptual Diagram