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Title:
Assessment of environmental water requirements for the proposed Basin Plan:
Lower Balonne Floodplain
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Condamine-Balonne Region
Assessment of the Lower Balonne River Floodplain System
environmental water requirements
1. Introduction
The Water Act 2007 (Cwlth) established the Murray‐Darling Basin Authority (MDBA) and tasked it
with the preparation of a Basin Plan to provide for the integrated management of the Basin’s water
resources. One of the key requirements of the Basin Plan is to establish environmentally sustainable
limits on the quantities of surface water that may be taken for consumptive use, termed Sustainable
Diversion Limits (SDLs). SDLs are the maximum long‐term annual average volumes of water that can
be taken from the Basin and they must represent an Environmentally Sustainable Level of Take
(ESLT).
The method used to determine the ESLT is described in detail within ‘The proposed
“environmentally sustainable level of take” for surface water of the Murray-Darling Basin: Method
and Outcomes,’ (MDBA 2011). A summary of the main steps undertaken to determine the ESLT is
presented in Figure 1. The assessment of environmental water requirements including specification
of site-specific flow indicators at a subset of hydrologic indicator sites (Step 3 of the overall ESLT
method) is the focus of this document.
The work described herein is the MDBA’s current understanding of the environmental water
requirements of the Lower Balonne Floodplain. It is not expected that the assessed environmental
water requirements assessments will remain static, rather it is intended that they will evolve over
time in response to new knowledge gained through additional scientific research or implementation
of environmental watering actions. Within this context, feedback is sought on the material
presented within this document whether that be as part of the formal draft Basin Plan consultation
phase or during the environmental watering implementation phase within the framework of the
Environmental Watering Plan.
1.1. Method to determine site-specific flow indicators
Assessment of environmental water requirements for different elements of the flow regime using
the hydrologic indicator site approach is one of the key lines of evidence that has informed the
proposed SDLs. Effort focussed on regions and parts of the flow regime with greatest sensitivity to
the scale of reduction in diversions necessary to achieve environmental objectives, an ESLT and a
healthy working Basin.
Within the overall framework of the ESLT method (Figure 1) the MDBA used an iterative process to
assess environmental water requirements and develop site-specific flow indicators.
The hydrologic indicator site approach uses detailed eco-hydrological assessment of environmental
water requirements for a subset of the key environmental assets and key ecosystem functions
across the Basin. The Lower Balonne Floodplain is one of the key environmental assets where a
detailed assessment of environmental water requirements was undertaken.
1
Figure 1: Outline of method used to determine an Environmentally Sustainable Level of Take.
(Source: MDBA 2011).
Detailed environmental water requirement assessments lead to the specification of site-specific
flow indicators to achieve site-specific ecological targets. Flow indicators were expressed at a
hydrologic indicator site or sites. Environmental water requirements specified at hydrologic
indicator sites are intended to represent the broader environmental flow needs of river valleys or
reaches and thus the needs of a broader suite of assets and functions.
This report provides a description of the detailed eco-hydrological assessment of environmental
water requirements for the Lower Balonne Floodplain including information supporting the
development of site-specific flow indicators for the site (with reference to flows gauged on the
Culgoa River). More information on how the site-specific flow indicators for Lower Balonne
Floodplain were used within the Basin-wide modelling process to inform the ESLT (i.e. Step 5 and 6
2
in Figure 1) can be found in the report ‘Hydrologic modelling to inform the proposed Basin Plan:
Methods and results’ (MDBA 2012).
A description of the detailed eco-hydrological assessments of environmental water requirements
for other indicator sites are described in other documents in the series ‘Assessment of
environmental water requirements for the proposed Basin Plan’.
1.2. Scope and purpose for setting site-specific flow indicators
The MDBA’s assessment of environmental water requirements and associated site-specific flow
indicators at hydrologic indicator sites has been used to inform the development of SDLs. This
enables the MDBA to estimate the amount of water that will be required by the environment over
the long-term to achieve a healthy working Basin through the use of hydrological models.
Accordingly, site-specific flow indicators are not intended to stipulate future use of environmental
water. MDBA expects that the body of work undertaken to establish these site-specific flow
indicators will provide valuable input to environmental watering but this watering will be a flexible
and adaptive process guided by the framework of the Environmental Watering Plan. It will be up to
the managers of environmental water, such as the Commonwealth Environmental Water Holder,
State Government agencies, and local communities to decide how best to use the available
environmental water during any one year to achieve environmental outcomes.
2. Site location and extent
The Lower Balonne Floodplain hydrologic indicator site covers approximately 1,988,000 ha (Sims
and Thoms 2002). The Lower Balonne system is a distributary river network that extends from St
George in Queensland to the Barwon River in northern New South Wales (Figure 2). The Balonne
River divides into five separate channels. The Culgoa and Narran Rivers are the main channels,
conveying 35% and 28% of the long-term mean annual flow at St George respectively; while the
Ballandool and Bokhara Rivers and Birrie Creek flow only during higher discharge periods (Thoms et
al. 2002) (Figure 2). Approximately 30% of the system is in Queensland and 70% in New South Wales
(McCosker 1996).
The MDBA has used the wetlands geographic information systems of the Murray-Darling Basin
series 2.0 (Kingsford, Thomas and Knowles 1999) to define the lateral and downstream extents of
the asset. Data from A directory of important wetlands in Australia (Department of the
Environment, Water, Heritage and the Arts 2001) was used to determine the upstream extent of the
asset at Jack Taylor Weir.
The Narran Lakes is the terminal wetland system at the end of the Narran River, which is located on
the eastern extent of the Lower Balonne Floodplain. The floodplain immediately surrounding the
Narran Lakes system was not included in the extent of this asset and is considered a hydrologic
indicator site in its own right (see separate environmental water requirements report for Narran
Lakes).
3
Figure 2 Location and extent of Lower Balonne River Floodplain System hydrologic indicator site
4
3. Ecological Values
Land use on the Lower Balonne Floodplain is predominantly grazing and dryland and irrigated
cropping. There are two national parks on the Lower Balonne floodplain: the 22,430 ha Culgoa
National Park, managed by NSW National Parks and Wildlife Service, and the adjoining 42,800 ha
Culgoa Floodplain National Park, managed by Queensland National Parks and Wildlife Service
(CSIRO 2008).
The vegetation community composition of the Lower Balonne Floodplain varies across the
floodplain according to flood frequency (Sims and Thoms 2002). High flood frequency areas are
dominated by river red gum (Eucalyptus camaldulensis), coolibah (E. coolabah) and lignum
(Muehlenbeckia florulenta), and open grasslands dominate less frequently flooded areas (Sims and
Thoms 2002; Sims 2004). The extents of major vegetation communities found in the section of the
Lower Balonne Floodplain between Hebel on the state border and St. George approximately 110 km
to the north-east are shown in Table 1.
Table 1 Key Vegetation Communities of the Queensland Section of the Lower Balonne
Floodplain (adapted from Sims 2004)
Vegetation
Community
Functional
Group
Extent
(ha)
Riparian
Forest
11,588
Key Species
Trees/Overstorey
(cover %)
Shrub Layer
(cover %)
Ground Layer
(cover %)
E. camaldulensis, E.coolabah,
Acacia spp,
E. populnea,
M. florulenta
Sporobolus mitchelli, Cyperus bifax,
Eragrostis setifolia,
Casuarina cristata, Melaleuca
spp.
(15%)
Ptilotus exaltatus
(15%)
(70%)
Lignum
shrubland
45,234
E. coolabah,
M. florulenta
S. mitchelli, C. bifax
Acacia cambagei
(70%)
(15%)
E. coolabah,
M. florulenta
C. bifax, Eliocharis spp., Eragrostis spp.
E. populnea, A. cambagei
(20%)
(20%)
E. populnea
M. florulenta
C. bifax, Eliocharis spp., Aristida spp.
(10%)
(20%)
(65%)
-
M. florulenta
Astrebla lappacea, Bassia spp,
(10%)
Cenchrus ciliaris, Marsilea drummondii,
(15%)
Coolibah
Woodland
52,087
(40%)
Nutgrass
Open
Grassland
33,526
101,882
E. setifolia, Paspalidium
jubiflorum, C. bifax, Plantago
spp, Medicago spp, P. jubiflorum
(70% - seasonal)
In order to inform Park management activities, floristic surveys and associated vegetation mapping
was undertaken across the Culgoa National Park. Surveys undertaken in February 1999 identified six
5
distinct communities with coolibah (Eucalyptus coolabah)/river cooba (Acacia stenophylla) and
coolibah/weeping myall (Acacia pendula) woodlands covering over 70% of the park (Hunter 2005).
Hunter also notes that the Park includes expanses of lignum (Muehlenbeckia florulenta).
These ecosystems support important species that are listed in international agreements such as the
Ramsar Convention, and include vulnerable and endangered species. Appendix B provides a
summary of the conservationally significant species recorded at the site.
The ecological values of the floodplain are reflected in MDBA’s assessment against the criteria used
to identify key environmental assets within the Basin. The MDBA established five criteria to identify
important environmental assets in the Basin. The criteria broadly align with the National Framework
and Guidance for Describing the Ecological Character of Australian Ramsar Wetlands (Department
of the Environment, Water, Heritage and the Arts 2008) and the draft criteria for identifying High
Conservation Value Aquatic Ecosystems (SKM 2007).
Based on the ecological values identified on the Lower Balonne Floodplain, the site meets at least
three of the five criteria (see Table 2).
6
Table 2 Assessment of the Lower Balonne River Floodplain System against MDBA key
environmental asset criteria.
Criterion
Ecological values that support the criterion
2. The water-dependent
The Lower Balonne Floodplain is a unique water-dependent ecosystem, as the floodplains of
ecosystem is natural or
the Culgoa, Birrie, Bokhara and Narran Rivers support the largest area of native grasslands in
near-natural, rare or unique
New South Wales (Dick 1993). It is also unique as the coolibah (Eucalyptus coolabah)
woodlands in the Lower Balonne are some of the most extensive and contiguous communities
remaining (Whittington et al. 2002).
Various types of Coolibah Woodlands are commonly found throughout the Culgoa National
Park (Hunter 2005) with areas of Coolibah – Black Box (Eucalyptus largiflorens) woodland
being particularly significant (NSW Scientific Committee 2011).
The floodplains can be considered near-natural as they have only 8.5% exotic vegetation, one
of the lowest records of introduced species in the Murray–Darling Basin (Dick 1993).
The Lower Balonne Floodplain wetland complex is a unique water-dependent ecosystem as
the region supports the second largest number of wetlands greater than 5 ha in size within the
Murray–Darling Basin. More than 3,400 wetlands have been identified within this complex, the
majority of which are freshwater wetlands (25.8%) and floodplain areas (24.2%) (Thoms et al.
2002). This floodplain ecosystem is sustained by water, sediments and nutrients from the
upstream Condamine–Balonne catchment, which comprises 14% of the Murray–Darling Basin
(Rayburg and Thoms 2008).
3. The water-dependent
The natural drainage system of the Lower Balonne provides diverse habitat for fauna. Fauna
ecosystem provides vital
present in the Lower Balonne Floodplain are included within the Lowland Darling River
habitat
aquatic ecological community, which is considered threatened under the Fisheries
Management Act 1994 (NSW), as listed in Appendix B. The habitat preferences of the
endangered aquatic species found within the Lower Balonne Floodplain have been
summarised by Smith et al. (2006).
4. Water-dependent
The Lower Balonne Floodplain meets this criterion because it supports species listed as
ecosystems that support
threatened under state or federal legislation. Of particular note is the Coolibah-Black Box of
Commonwealth, State or
the northern riverine plains in the Darling Riverine Plains and Brigalow Belt South bioregions.
Territory listed threatened
As part of its assessment of the significance of Coolibah-Black Box of the northern riverine
species or communities
plains in the Darling Riverine Plains and Brigalow Belt South bioregions, the NSW Scientific
Committee found that the distribution of the community had been reduced by 61% (NSW
Scientific Committee 2011). As noted by the Committee, the structure of this community may
vary from tall riparian woodlands to very open grassy woodlands and consist of a wide variety
of species. Based on 19 separate findings, the NSW Scientific Committee (2011) recognised
the value of the community and maintained its listing as an endangered ecological community
under the Threatened Species Conservation Act 1995.
Species and communities listed as threatened under both Commonwealth and state legislation
that have been recorded at the site are in Appendix B.
7
4. Hydrology
The Lower Balonne is a complex floodplain channel system that is heavily dissected by well-defined
channels of various sizes. During flood events these channels carry a significant proportion of the
‘overland’ flow (Thoms et al. 2002). The Balonne River enters the floodplain downstream of
Beardmore Dam, flowing through St George and over Jack Taylor Weir. It then travels more than
70 km before splitting into the Culgoa and Balonne Minor Rivers at the so-called ‘first bifurcation’.
Downstream, the Balonne Minor River subdivides further to form four identifiable streams — the
Narran, Bokhara, Ballandool and Birrie Rivers.
The hydraulics of the Lower Balonne resembles that of a delta, with flows of up to 30,000 ML/d at
St. George dispersing into many small flood channels (Thoms et al. 2002). At higher flows, water
spreads out over the floodplain, and a significant portion does not return to the river as a result of
evaporation and infiltration into the soil. Consequently, under without-development conditions, the
flow crossing the Queensland – New South Wales border is lower than the flow recorded at
St George. The median annual flow at St George is 1,300 GL, but flows are highly variable. The
maximum annual recorded flow of 8,000 GL occurred in 1954–55, but extended periods of no-flow
occur during droughts. Based on recorded flows, the record period of no-flow exceeds 600
consecutive days (NSW Western Catchment Authority 2006).
Floodwaters received in the Balonne River result from rainfall in the northern part of the
Condamine–Balonne catchment and occur mainly in summer and autumn (NSW National Parks and
Wildlife Service 2003). Flood frequency is highly variable, occurring anywhere between several
times a year to once every five years (Sheldon et al. 2000). The depth of the floodwater varies from
a few centimetres to 10 metres and inundation of the floodplain can last for up to four months
(Smith et al. 2006). During floods, large amounts of sediment are trapped or deposited onto the
floodplain (Smith et al. 2006). The main river channels in the Lower Balonne system are very
unstable and small changes to the flow can result in significant changes in channel morphology
(Smith et al. 2006). Sediment movement has increased with the increase in management
infrastructure in the upper catchment (Cullen, Marchant and Mein 2003).
The historical flow record suggests that multiple flood events have been common over a yearly
timeframe (see for example Figure 3). The occurrence of multiple events of a similar threshold in
close proximity are important in this system for extending the duration of floodplain inundation,
something to which the flora and fauna of these systems has become adapted (Roberts and
Marston 2000).
8
50,000
45,000
River flow (ML/d)
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
1/05/1940
1/04/1940
1/03/1940
1/02/1940
1/01/1940
1/12/1939
1/11/1939
1/10/1939
1/09/1939
1/08/1939
1/07/1939
1/06/1939
1/05/1939
1/04/1939
1/03/1939
1/02/1939
1/01/1939
1/12/1938
1/11/1938
0
Date
Figure 3 Highly variable flows past St George gauge, Balonne River
The Lower Balonne Floodplain has been grazed since the 1840s (Sims et al. 1999), predominantly by
cattle and sheep. The change to irrigated agriculture since the 1990s represents a significant shift in
land-use practice and use of water resources (Thoms et al. 2002). The major irrigated crop is cotton,
with cropped area increasing significantly since 1988. Associated with this expansion in the cotton
industry has been the expansion of private water storages on the floodplain over the same period.
The construction of public storages in the mid and upper sections of the system has resulted in a
degree of regulation, particularly of the Balonne River downstream of the Beardmore Dam.
However the systems major public storages and weirs have a combined capacity of 234 GL (CSIRO
2008) and when compared to average surface water availability (1305 GL/year) (CSIRO 2008), their
capacity to regulate flows is relatively low compared to other parts of the Basin. It is important to
note that within the Condamine-Balonne system irrigation water is primarily retained in on-farm
private storages; with these storages holding approximately seven times the total volume of public
storages.
5. Determining the site-specific flow indicators for the Lower
Balonne River Floodplain System
5.1. Setting site-specific ecological targets
The objective setting framework used to determine the ESLT is outlined in the report ‘The proposed
“environmentally sustainable level of take” for surface water of the Murray-Darling Basin: Method
and Outcomes’ (MDBA 2011). In summary, the MDBA developed a set of Basin-wide environmental
objectives and ecological targets, which were then applied at a finer scale to develop site-specific
objectives for individual key environmental assets. Using these site-specific objectives, ecological
targets that relate specifically to the Lower Balonne Floodplain were developed (Table 3).
Information underpinning site-specific ecological targets is shown in Table 3.
9
Site-specific ecological targets formed the basis of an assessment of environmental water
requirements and the subsequent determination of site-specific flow indicators for the Lower
Balonne Floodplain, as described below.
5.2. Information used to determine site-specific flow indicators
The site-specific flow indicators have been determined through a synthesis of current literature
(including studies cited in Table 3) and MDBA’s analysis of modelled flow data, in addition to
consultation with state government staff and research providers. The following sections provide a
summary of the knowledge used to develop the flow indicators.
5.2.1. Vegetation
Flow thresholds
Whittington et al. (2002), Sims and Thoms (2002), and Sims (2004) provide information on the flow
thresholds used to inform the ecological target associated with ensuring the current extent of
native vegetation of the riparian, floodplain and wetland communities is sustained in a healthy,
dynamic and resilient condition within the Lower Balonne Floodplain. This information is also used
to address the ecological target concerning the provision of a flow regime which supports key
ecosystem function related to connectivity between the Balonne, Culgoa, Bokhara, Ballandool,
Birrie and Narran Rivers and the connected floodplain.
Using satellite images captured between September 1989 and April 1999, Sims (2004) analysed
floodplain inundation patterns under a range of flow conditions for the Queensland portion of the
Lower Balonne floodplain. Flood magnitudes required to inundate different areas of the floodplain
were determined based on gauged flows at St. George 14 days before image capture. Based on this
analysis, floodplain inundation commences when flows exceed approximately 26,000 ML/d (Sims
and Thoms 2002; Sims 2004) with flows at this level inundating around 12,000 ha or around 3% of
the floodplain.
Flows of between 45,000 ML/d and 65,000 ML/d at St. George inundate approximately 75,000 ha
(Sims 2004). Flows between 60,000 – 65,000 ML/d ensure a significant improvement in connectivity
between the systems rivers and channels and its floodplain (Sims and Thoms 2002; Sims 2004). This
connectivity is important for a range of ecosystem functions such as nutrient and carbon exchange.
Sims (2004) found that in general, vegetation communities grade laterally from riparian forests
adjacent to river channels, to lignum and coolibah open woodland associated with infrequent
inundation, with open grassland dominant in rarely inundated areas on the floodplain fringes.
To connect most of the main channels within the Lower Balonne Floodplain, including Birrie River
and a number of secondary channels, a flow of 26,000 ML/d at St.George is required (Sims 2004).
The author showed that a flow of around 26,000 ML/d would inundate around 12,000 hectares.
Based on Sims (2004) analysis of vegetation communities, the MDBA has determined that the
12,000 ha would consist mainly of riparian forest dominated by river red gum and coolibah (Tables 1
and 6).
10
Table 3 Site-specific targets for the Lower Balonne River Floodplain System
Site-specific ecological
targets
Justification of targets

Protecting the water-dependent ecosystems and their vital habitat requires
retaining the current state of the wetlands and the surrounding vegetation.



Provide a flow regime
which ensures the current
extent of native vegetation
of the riparian, floodplain
and wetland communities is
sustained in a healthy,
dynamic and resilient
condition
Provide a flow regime
which supports the habitat
requirements of waterbirds
Provide a flow regime
which supports a range of
native aquatic species (e.g.
fish, frogs, turtles,
invertebrates)
Provide a flow regime
which supports key
ecosystem functions,
particularly those related to
connectivity between the
river and the floodplain
Coolibah – Black Box Woodland of the northern riverine plains in the Darling
Riverine Plains and Brigalow Belt South bioregions is listed as Endangered
Ecological Community under the Threatened Species Conservation Act 1995.
Coolibah is typically the dominant tree species in these woodlands and may occur
in association with a wide range of other species including river cooba (Acacia
stenophylla), black box and river red gum (NSW Scientific Committee 2011). It is
common for a dense understorey of lignum to also form in these Woodland
communities (Hunter 2005).
Coolibah-Black Box Woodland provides habitat features important to a range of
fauna (NSW Scientific Committee 2011). These features include grassy
understorey, patches of thick regenerating Eucalyptus saplings and large hollow
bearing trees (NSW Scientific Committee 2011).
The Lower Balonne has high ecological and hydrological connectivity to the
Ramsar-listed Narran Lakes Nature Reserve which is as an important site for
colonial waterbird breeding. The link between waterbird breeding and inundation
of habitat which provides foraging and nesting opportunities is relatively well
understood. The broader Lower Balonne floodplain is likely to provide foraging
habitats and in doing so supports major bird breeding events in the Narran Lakes
system.
Key ecosystem functions support fish, birds and invertebrates through habitat
maintenance, energy transfer and facilitating connections between rivers and
floodplains. Overbank flows supply the floodplains with nutrients and sediments
from the river, accelerate the breakdown of organic matter and supply water to
disconnected wetlands, billabongs and oxbow lakes. As the floodwaters recede,
the floodplains provide the main river channel with organic matter.
The hydrological connection between watercourses and their associated floodplain
provides for the exchange of carbon and nutrients (Thoms 2003). The connections
are considered essential for the functioning and integrity of floodplain-river
ecosystems.
The maintenance of natural patterns of longitudinal and lateral connectivity is
essential to the viability of populations of many aquatic species (Bunn and
Arthington 2002). Vital habitat within the Lower Balonne includes in-channel
waterholes and billabongs that act as refugia during drought. The use of drought
refugia by aquatic organisms is often the key to the survival of population stocks
and strongly influences the capacity of populations to recover when the drought
breaks and connectivity is restored, such as endangered fish and invertebrate
species (Lake 2003).
11
The flow thresholds of 45,000 ML/d and 70,000 ML/d at the St George gauge were selected to
provide a flow regime able to inundate lignum and coolibah communities. Hunter (2005) found that
major changes in native vegetation composition across the Culgoa National Park were correlated to
flood frequency and the period of inundation. In particular, Hunter (2005) found that the ability for
certain sections of the floodplain to retain water for an extended period was an important feature
in determining vegetation patterns. Based on this observation, the MDBA has assumed that areas
which are flooded regularly and retain water for extended periods contain high proportions of
lignum and river cooba which are more flood dependent, while areas which do not retain water are
likely to contain less flood dependent species like coolibah. The MDBA has concluded flows of both
45,000 ML/d and 70,000 ML/d at the St George gauge are required to inundate areas that retain
water for extended periods for the different vegetation communities.
At the lower end of 45,000 to 70,000 ML/d range the three main flood-dependent vegetation
communities (coolibah open woodland, lignum and riparian forests) have at least 50% of their total
area wetted (Whittington et al. 2002). A threshold of 70,000 ML/d encompasses an important
transition in floodplain inundation where floodwaters emerge from the Culgoa River and travel
across the floodplain to re-enter the Culgoa downstream, enabling a substantial exchange of
material between the floodplain and its adjoining aquatic ecosystems (Sims 2004). Around this
threshold is the point where inundation patterns go from being relatively disconnected into a more
highly integrated network of patches (Sims 2004) where approximately 40% of the total floodplain is
inundated (Whittington et al. 2002).
The largest flow threshold adopted for the Lower Balonne Floodplain is a flow of 120,000ML/d at
the St George gauge for one day. At this threshold, around 70% of the floodplain between St George
and the New South Wales – Queensland border is inundated, with flows greater than this resulting
in proportionally larger increases in flow depth rather than increases in floodplain area inundated
(Whittington et al. 2002). Therefore, this flow provides a balance between the flood event
magnitude and floodplain area inundated.
The key thresholds presented by Whittington et al. (2002), Sims and Thoms (2002), and Sims (2004)
are described at the St George gauge, which is the closest upstream gauge from the Lower Balonne
Floodplain (above the first bifurcation). Flows suggested at this gauge therefore take account of the
total amount of flow entering the Lower Balonne Floodplain. However, a large proportion of
diversions under Condamine and Balonne Resource Operations Plan occur downstream of St.
George (almost 40% of all diversions within the Queensland section of the Condamine-Balonne
system occur downstream of Jack Taylor Weir). The gauge located downstream of St. George at
Brenda on the Culgoa River more accurately reflects the full impact of diversions and for this reason
this gauge has been selected as a better location to assess and specify proposed environmental
water requirements.
To relate the key floodplain vegetation community flow thresholds associated with flows at St
George to flows on the Culgoa River at Brenda, MDBA undertook a correlation analysis of modelled
without-development flow data for the period 1895–2009 (Figure 4). The analysis compared
modelled peak flows at Brenda and St. George based on an 8 day flow lag between the two sites.
The analysis focused on flows in the target range of 26,000 – 120,000 ML/d at St. George and so the
range encompasses the inundation threshold as indicated by Whittington et al. (2002). A 2nd order
polynomial trend analysis was used as the most appropriate fit (regression co-efficient of R2=0.86).
However, as the scatter in Figure 4 indicates, there is a substantial degree of variability in the
modelled peak flows between St George and Brenda.
12
45,000
Culgoa River Flow at Brenda (ML/d)
40,000
35,000
30,000
25,000
20,000
15,000
y = -1E-06x2 + 0.4284x + 1377.7
R² = 0.86
10,000
5,000
0
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
Balonne River Flow at St.George (ML/d)
Figure 4
Correlation between modelled flow at St. George and Brenda under without
development conditions
The variability in the modelled peak flows between St George and Brenda (as shown in Figure 4) is
reflected in gauged flows at the two sites. A comparison of peak discharges gauged at St. George
(gauge number 422201E) and the Culgoa River at Brenda (gauge number 422015) for the period
October 1971 to August 2011 is shown in Table 5. An example of the variability is shown by the
1974, 1976, 1981 and 1984 flow events. Each event shows a similar peak in gauged flows at St.
George (71,651, 77,538, 74,286 and 65,838 ML/d respectively) however corresponding flows as
gauged at Brenda show significant variability (28,205, 14,889, 8,639 and 20,977 ML/d respectively).
The significant variability in the relationship between flows at St. George and Brenda (as shown by
both modelled and gauged data) is consistent with the complexity of the hydrology of the Lower
Balonne floodplain and the highly variable climatic patterns of the system.
The regression analysis equation was applied to determine for each vegetation community a flow
threshold at Brenda equivalent to key thresholds at St. George (Table 6). These flow thresholds
estimated for peak flows at Brenda were used to determine the site-specific flow indicators for the
Lower Balonne Floodplain to achieve the ecological target of providing a flow regime which ensures
the current extent of native vegetation of the riparian, floodplain and wetland communities is
sustained in a healthy, dynamic and resilient condition.
13
Table 5 Gauged Flows at St. George and Brenda (1971 – 2011)
Balonne River at St. George (422201E)
Culgoa River at Brenda (422015)
Gauged Flow (ML/d)
Date
Gauged Flow (ML/d)
Date
97,956
2/01/1972
20,759
21/01/1972
45,342
15/11/1972
8,845
3/12/1972
71,651
3/02/1974
28,205
28/02/1974
77,538
11/01/1976
14,889
24/01/1976
84,836
2/03/1976
33,082
16/03/1976
123,490
17/03/1977
20,400
4/04/1977
74,286
23/02/1981
8,639
6/03/1981
54,320
7/06/1981
10,688
20/06/1981
82,175
8/03/1982
12,456
28/03/1982
177,021
16/05/1983
53,658
26/05/1983
112,784
7/07/1983
39,570
17/07/1983
121,321
4/12/1983
20,403
19/12/1983
65,838
6/02/1984
20,977
25/02/1984
84,876
13/08/1984
40,288
27/08/1984
71,133
5/03/1988
8,260
17/03/1988
120,931
25/04/1988
40,248
4/05/1988
43,777
3/05/1989
10,761
20/05/1989
218,897
25/04/1990
47,852
4/05/1990
44,490
15/12/1993
4,192
15/12/1993
63,327
16/03/1994
13,685
31/03/1994
28,083
7/12/1995
5,506
1/01/1996
160,669
21/01/1996
29,327
3/02/1996
119,928
20/05/1996
28,181
2/06/1996
32,699
9/02/1997
3,137
15/02/1997
58,596
21/02/97
10,269
10/03/1997
39,146
16/02/1998
2,649
1/03/1998
101,467
9/09/1998
16,378
21/09/1998
44,201
26/09/1998
10,633
8/10/1998
49,272
26/01/2008
3,246
6/02/2008
261,128
8/03/2010
28,795
19/03/2010
255,706
10/01/2011
78,026
18/01/2011
38,644
27/03/2011
8,370
11/04/2011
44,867
26/04/2011
8,246
7/05/2011
14
Table 6 The relationship between ecologically relevant thresholds as defined for the Balonne
River at St. George as expressed at Brenda on the Culgoa River using the regression
equation in Figure 4
Target
Ecologically relevant threshold
at St. George (ML/d)
Correlated flows at Brenda
(ML/d) (see Figure 4)
Inundation of riparian river red gum and
coolibah forests
26,000
11,840
Inundation of lignum communities and
coolibah open forest / woodland
45,000
18,630
Floodplain connections
70,000
26,465
Significant floodplain inundation
120,000
38,385
Frequency and duration of flow thresholds
To inform the frequency and duration of flow indicators, the MDBA has collated available
information on the inundation patterns needed by flood dependent vegetation communities which
occur within the Lower Balonne floodplain (Table 7). Generally, there is a lack of site-specific
information for the vegetation communities of the Lower Balonne and information on the general
water requirements of key vegetation species from throughout the Murray-Darling Basin has been
drawn upon.
Generally, the flow indicator metric with the greatest level of uncertainty across the Basin is the
definition of the desirable inundation frequency. This uncertainty is due to a number of reasons.
Firstly, it is likely that there are thresholds for many plants and animals beyond which their survival
or ability to reproduce is lost, but the precise details of those thresholds are mostly unknown or
where there is information (for instance river red gum communities) our knowledge is evolving.
Secondly, vegetation communities are located across the floodplain and would have experienced
some variability in their inundation frequency under pre-development conditions which
subsequently makes specification of a single frequency metric deceptively certain. For many species
and ecological communities the relationship between water provisions and environmental
outcomes may not be threshold based, rather there could be a linear relationship between flow and
the extent of environmental outcomes or the condition of a particular ecological
species/community.
Recognising the degree of confidence in specifying a desirable frequency, ‘low‐uncertainty’ and
‘high‐uncertainty’ frequency of flow events have been specified (Table 8). For the low‐uncertainty
frequency, there is a high likelihood that the environmental objectives and targets will be achieved.
The lower boundary of the desired range is referred to here as the high uncertainty frequency which
is effectively the best estimate of the threshold, based on current scientific understanding, which, if
not met, may lead to the loss of health or resilience of ecological communities, or the inability of
species to reproduce frequently enough to sustain populations. The high‐uncertainty frequencies
attempt to define critical ecological thresholds. The high uncertainty frequency is considered to
represent a boundary beyond which there is a high likelihood that the objectives and targets will
not be achieved.
15
Table 7 Flood frequency and duration for selected flood-dependent species
River Red Gum (Eucalyptus camaldulensis)
River red gums are opportunistic water users and are able to meet their needs using water from a variety of sources. They
are also tolerant of elevated salinity levels (Roberts and Marston 2011). River red gums have mechanisms to avoid serious
water deficit including a deep root system that allows them to access soil water and groundwater (Roberts and Marston
2011).
Frequency of inundation – About every one to three years for forests and about every two to four years for woodlands
(Roberts and Marston 2011).
Critical Interval between inundations – Do not form a seed bank, hence it is important to maintain trees in good condition
so that a good supply of seed is available. Inundation required after about three years for forests and five to seven years
for woodlands (Roberts and Marston 2011). Longer intervals may be tolerated periodically, but if these become routine
then tree condition is likely to deteriorate in the long term (Roberts and Marston 2011).
Duration of inundation - About five to seven months for forests, and about two to four for woodlands (Roberts and
Marston 2011).
Lignum (Muehlenbeckia florulenta)
Water regime is a very strong influence on lignum growth and reproduction. Frequency and duration of inundation are the
most important components for maintaining adult lignum in good condition (Roberts and Marston 2011).
Frequency of inundation – About every one to three years for large shrubs with vigorous canopy; every three to five years
for healthy shrubs (Roberts and Marston 2011). For maintenance of small shrubs less frequent inundation of every seven
to 10 years is tolerable however these will not be suitable as nesting platforms (Roberts and Marston 2011).
Duration of inundation - About three to seven months for vigorous canopy (Roberts and Marston 2011).
Critical Interval between inundations – inundation required after five to seven years to maintain vigour (Roberts and
Marston 2011).
Coolibah (Eucalyptus coolabah)
In their review of literature for selected wetland and floodplain species, Roberts and Marston (2011) found that the
importance of flooding for adult coolibah had not been established. Roberts and Marston (2011) found that inundation is
probably important for seedling establishment, and a sequence of floods, or flood and wet years, may be necessary to
ensure seedlings are well established.
As a summary Roberts and Marston (2011) found that although tolerant of hot dry conditions and infrequent flooding,
coolibah is unlikely to persist if flow regime or regional hydrology becomes substantially drier.
Frequency of inundation – About every 10 to 20 years.
Duration of inundation – Not known.
Critical Interval between inundations – Uncertain. Can maintain fair to good condition for possibly as long as 10 – 20
years.
River Cooba (Acacia stenophylla)
In their review of literature for selected wetland and floodplain species, Roberts and Marston (2011) found that flooding was
important in determining the vigour of river cooba and implicated in germination and establishment of the species.
The following information is taken from (Roberts and Marston 2011).
Frequency of inundation – About every three to seven years for large shrubs with vigorous canopy (Roberts and Marston
2011).
Duration of inundation - About two to three months (Roberts and Marston 2011).
Critical Interval between inundations – Not known, possible maintains vigour up to five years without flooding, with trees
near creeks and waterholes able to maintain vigour for much longer periods (Roberts and Marston 2011).
16
Proposed flow indicators
Based on information outlined in the previous two sections, the following summarises the
judgements made on how the flow indicators will achieve the ecological target of providing a flow
regime which ensures the current extent of native vegetation of the riparian, floodplain and
wetland communities is sustained in a healthy, dynamic and resilient condition in the Lower
Balonne Floodplain. This information also informs the flow indicators needed for a flow regime
which supports key ecosystem functions related to connectivity between the river and the
floodplain.
Riparian Forest
As detailed in previous sections a flow at Brenda of 12,000 ML/day is a key threshold at which
inundation occurs for this vegetation community.
Key flood dependent species found within this community include river red gum and coolibah as
well as river cooba and lignum (Table 1). Generally the vegetation species that make up this
community need to be inundated for periods up to several months. In defining water requirements
for this community, the MDBA has assumed that river red gums are able to access other sources of
water and that floodplain wetlands will retain water for extended periods (at least 90 days)
following inundation. Given this, the MDBA concluded that the required duration for the 12,000
ML/d event is significantly shorter than 90 days. This is supported by analysis of modelled flows
under without development conditions, which indicates that flows with a minimum threshold of
12,000 ML/d at Brenda have a maximum duration of 47 days and a median duration of 11 days. The
MDBA has chosen the median duration (under a without development scenario) of 11 days as the
flow indicator and believe that this should be representative of events which would typically
inundate the Riparian forest of the Lower Balonne.
The MDBA has also assumed that an event lasting 11 days is sufficient to fill secondary channels and
adjacent floodplain waterholes close to the main rivers as well as provide a sufficient period of
inundation for riparian forests. Table 7 presents information on the inundation requirements of
individual species.
Given that the riparian forest of the Lower Balonne contain a mix of species, the MDBA has
reviewed existing literature related to inundation patterns for vegetation communities containing a
mix of river red gum and coolibah as well as river cooba and lignum. Inundation mapping
undertaken as part of developing the Gwydir Wetlands Adaptive Environmental Management Plan
Floodplain showed that lignum, river red gum and some coolibah woodland occurring on the Gwydir
River floodplain were inundated by moderate floods with a 1-4 year average recurrence interval
(NSW Department of Environment, Climate Change and Water 2011). This regime is broadly
consistent with the species requirements described by Roberts and Marston (2011) (see Table 7).
The MDBA has assumed that the hydrology and climatic patterns of the Gwydir Wetlands and Lower
Balonne are sufficiently similar to allow the inundation mapping undertaken on Gwydir River
floodplain to be used to inform the frequency of flows required to inundate riparian forests on the
Lower Balonne.
Given previous assumptions and analysis, the MDBA has specified that an event with a minimum
threshold of 12,000 ML/d at Brenda and a duration of at least 11 days needs to occur on average
once every 3 to 4 years.
17
Lignum Shrublands and Coolibah Woodlands
As detailed in previous sections flows at Brenda of between 18,500 and 26,500 ML/d represent a
key range for inundation of these vegetation communities.
Key flood dependent species found within these communities include coolibah, lignum and river
cooba (Table 1). Hunter (2005) found on the section of the Culgoa River floodplain within the Culgoa
National Park that there was a correlation between major changes in native vegetation composition
and the retention of water for extended periods. The MDBA has assumed that areas that are
flooded regularly and retain water for extended periods contain high proportions of lignum and
river cooba, while areas which do not retain water are likely to contain less flood dependent species
such as coolibah.
As shown in Table 7, Roberts and Marston (2011) report that the minimum period of inundation
required to maintain lignum and river cooba in a healthy condition (as defined by the maintenance
of vigorous canopy) is between two and three months. In defining flow indicators for these
communities, the MDBA has assumed that once inundated, floodplain wetlands will retain water for
at least two to three months and has determined that the required duration for the 18,500 ML/d
and 26,500 ML/d events is significantly shorter than two – three months. This is supported by
analysis of modelled flows under without development conditions which indicates that flows with a
minimum threshold of 18,500 ML/d at Brenda have a maximum duration of 40 days and a median
duration of 9 days. Similarly analysis of modelled flows under without development conditions
indicates that flows with a minimum threshold of 26,500 ML/d at Brenda have a maximum duration
of 36 days and a median duration of 7 days. The MDBA has assumed that an event with a median
duration (under a without development scenario) is representative of events which would typically
inundate lignum shrublands and coolibah woodlands of the Lower Balonne.
Based on a review of existing knowledge and information related to lignum communities, Roberts
and Marston (2011) found that the average flooding frequency expected to maintain healthy lignum
shrubs was every three to 5 years.
Given previous assumptions and analysis, the MDBA has specified that an event with a minimum
threshold of 18,500 ML/d at Brenda and a duration of at least 9 days needs to occur on average
once every 4 to 5 years.
Based on Sims (2004) analysis and recommendations within Whittington et al. (2002), the MDBA
has determined that a threshold of 26,500 ML/d (at Brenda) represents an important transition in
floodplain inundation where floodwaters emerge from the Culgoa River and travel across the
floodplain and re-enter the Culgoa downstream. A flow of this magnitude will enable a substantial
exchange of material between the floodplain and its adjoining aquatic ecosystems (Sims 2004) and
is likely to be important in connecting a range of floodplain wetlands to the systems main channels.
The MDBA has assumed that a flow of 7 days is sufficient to provide full connection between the
system’s main channels and its floodplain and in doing so inundate channels, depressions and low
lying areas across large sections of the floodplain. The MDBA has also assumed that these areas will
retain water for extended periods.
Roberts and Marston (2011) found that to maintain small lignum shrubs in good health, inundation
every seven to 10 years is required. Given previous assumptions and analysis, the MDBA has
specified that an event with a minimum threshold of 26,500 ML/d at Brenda and a duration of at
least 7 days needs to occur on average once every 7 - 10 years.
The water regime specified for lignum has been assumed by the MDBA to also be sufficient for the
establishment of coolibah seedlings. Broadly, this assumption is supported by work undertaken in
18
the Gwydir system. Inundation mapping undertaken in the Gwydir system as part of the Gwydir
Wetlands Adaptive Environmental Management suggests that coolibah woodlands are inundated by
large flows that occur infrequently (annual recurrence interval (ARI) of 5 - 20 years) (NSW
Department of Environment, Climate Change and Water 2011). While Wilson et al (2009) describes
the approximate flood frequency of coolibah communities in the Lower Gwydir prior to river
regulation as being once every 10 -20 years.
Significant Floodplain Inundation
The 38,500 ML/day (as measured at Brenda) flow threshold provides water for the floodplain as a
whole system and the ecosystem functions that sustained the Lower Balonne floodplain in a
healthy, dynamic and resilient condition.
Extensive areas of native grassland are found across Lower Balonne Floodplain (Smith et al. 2006)
and are commonly dominated by species such as Mitchell Grass (Astrebla spp.) and Wire Grass
(Aristida spp.) (Smith et. al 2006). As identified by Sims (2004), other common grassland species
found on the floodplain between St. George and the NSW border (Table 1) include warrego summer
grass (Paspalidum jubiflorum) and curly mitchell grass (Astrebla lappacea). Sims and Thoms (2002)
and Sims (2004) suggest these areas are generally inundated by large flood events with average
recurrence intervals of 10 years or greater.
Like the Lower Balonne system, native grasslands are common on the Gingham and Lower Gwydir
floodplains and occur on slightly elevated areas. Common species include warrego summer grass
(Paspalidum jubiflorum), native millet (Panicum decompositum), Queensland blue grass
(Dicantheum sericeum), curly mitchell grass, (Astrebla lappacea), windmill grass (Chloris truncata),
curly windmill grass (Enteropogon acicularis) and Australian cup grass (Eriochloa australiensis)
(McCosker 2007). Inundation mapping undertaken in the Gwydir system suggests that native
grasslands within the Gwydir Wetlands are inundated by large flows that occur very infrequently
(ARI of 10 - 20 years) (NSW Department of Environment, Climate Change and Water 2011).
The MDBA has used the analysis undertaken by Sims and Thoms (2002) and Sims (2004) and NSW
Department of Environment, Climate Change and Water (2011) to inform the desired frequency of
the flow indicator.
As part of an assessment of plant community responses to wetting and drying in arid floodplain
systems, Capon (2003) suggests that flooding induces increases in productivity, particularly total
cover, in floodplain grass communities. However, Capon (2003) did not indicate that a particular
duration or frequency of event was required by these communities.
Recognising that floodplain inundation is important for a range of ecosystem functions such as the
long term-persistence of fish assemblages in lowland rivers (Balcombe et al. 2005), supply of
dissolved organic carbon (Thoms 2003) and the productivity of terrestrial vegetation communities
(Capon 2003), the MDBA has specified a site-specific indicator flow to achieve broad scale floodplain
inundation. This will provide a flow regime which supports key ecosystem functions related to
connectivity between the river and the floodplain.
Analysis of modelled flows under without development conditions indicates that flows with a
minimum threshold of 38,500 ML/d at Brenda have a maximum duration of 30 days and a median
duration of 6 days.
19
As with other flow indicators, the MDBA has relied on a hydrological analysis of without
development events to determine the duration of the 38,500 ML/d flow indicator at Brenda. The
MDBA has assumed that an event with a median duration (under a without development scenario)
is representative of events which would typically achieve broad scale floodplain inundation.
Given previous assumptions and analysis, the MDBA has specified that an event with a minimum
threshold of 38,500 ML/d at Brenda and duration of at least 6 days needs to occur on average once
every 20 years to achieve this ecological target for key ecosystem functions.
5.2.2. Waterbirds
The MDBA is confident that the site-specific flow indicators determined to achieve the ecological
targets for ensuring the current extent of native vegetation of the riparian, floodplain and wetland
communities will also have valuable beneficial effects on the life-cycle and habitat requirements of
waterbirds. Recognising that major colonial waterbird breeding events in the region occur in the
Narran Lakes System, the vegetation communities found on the broader Lower Balonne floodplain
are likely to support these events by providing foraging opportunities for key waterbird species.
5.2.3. Other Biota
The high variability of flows in the Lower Balonne system means that the system experiences long
periods of low-flows or cease-to-flow periods. For aquatic fauna populations, this places greater
emphasis on sections of the channel capable of holding water for extended periods. These pools act
as vital habitat during times of low-flow, with many species of fish and invertebrates persisting in
these areas until larger flows occur (Balcombe et al. 2006; Balcombe et al. 2007; Bunn et al. 2006).
There are three major attributes of waterhole refugia which contribute to their ability to sustain
biota: the length of time they retain water during no-flow events, the quality of the refuge
(including water quality and habitat availability) and connectivity between waterholes (Balcombe et
al. 2006; Bunn et al. 2006). The maintenance of these waterholes is associated with the ecological
targets of providing flow regimes supporting key ecosystem functions and maintaining viable
populations of key aquatic species.
A reconnaissance survey conducted in November 2007 following an extended 44-month period of
low to no-flows identified 22 substantial refugia waterholes in the Lower Balonne system (Webb
2009). The majority of these waterholes (12) were located on the Culgoa River, three on the
Bokhara (behind low-level weirs) and five on the Narran River (Figure 5; Webb 2009).
DERM (2010) developed a relationship between pool depth and persistence as part of an
assessment of waterhole refugia in the nearby Moonie River catchment. DERM (2010) determined
that persistence time (measured in days) for waterholes in the Moonie system could be quickly
determined as approximately 170 days per metre of maximum depth.
20
Figure 5 Substantial refugia waterholes within the Lower Balonne Floodplain (Source: Webb
2009).
DERM (2011a) suggests that refugia waterholes in the Queensland section of the Lower Balonne
have maximum depths up to 5-6 metres. The MDBA has assumed that the relationship between
pool depth and persistence determined by DERM (2010) as part of an assessment of waterhole
refugia in the nearby Moonie River catchment are applicable to the waterholes of the Lower
Balonne. Using the above relationship, waterholes in the Lower Balonne Floodplain will retain water
for a maximum of around 28 months assuming an initial depth of 5 metres and no inflows. The
MDBA has assumed that the limited analysis of waterhole depth undertaken by DERM (2011a) is
representative of waterhole depth across the entire system.
Habitat conditions within waterholes may also decline as water levels recede, meaning that a
waterhole could become unsuitable as habitat for some species long before it dries completely
(DERM 2010). With this in mind it is assumed that pools must contain at least one metre of water in
order to provide suitable habitat. Based on the work of DERM (2010, 2011a), to ensure 1 metre of
water is retained in pools, a replenishment flow along the system is required at a maximum interval
of 680 days or 22 months.
To determine the flows required to maintain these critical refugia waterholes, observed flows were
compared between the St George gauge on the Balonne River, the gauge upstream of Collerina at
the lower end of the Culgoa River, and the Wilby Wilby gauge on the Narran River, for a five year
period (1/07/1973 – 30/06/1978) prior to major development in the system.
Analysis of flows from these gauges shows that during the five year period there were 6 events
which reached a peak flow at St. George between 4,000 and 6,500 ML/d. Generally these flows
correlated to peak flows of between 500 – 4,000 ML/d upstream of Collerina and between 600 –
21
1,600 ML/d at Wilby Wilby (Figures 6 to 11). Each of the six events maintained a flow at St. George
of 2,500 ML/d for between 4 and 11 days, and 1200 ML/d for between 3 and 7 days at Brenda.
When measured at St. George, the flow volume of these events generally range between 20,000
and 60,000 ML which is comparable to the total volume currently released from Beardmore Dam to
maintain waterholes for stock and domestic purposes (Brizga 2011). However given the outlet
capacity of Beardmore dam (1000 ML/d at full supply level – DERM 2011b), the patterns of releases
currently made from Beardmore Dam are significantly different from the events shown in the
following figures.
These flows would connect all the vital waterholes along the length of these rivers. It is assumed
that a flow of this magnitude at St George would also connect waterholes along the Bokhara River.
7000
6000
Flow (ML/D)
5000
4000
3000
2000
1000
0
13/07/1973
23/07/1973
2/08/1973
BALONNE RIVER AT ST. GEORGE
12/08/1973
22/08/1973
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
5000
4500
4000
Flow (ML/D)
3500
3000
2500
2000
1500
1000
500
0
14/09/1973
24/09/1973
4/10/1973
BALONNE RIVER AT ST. GEORGE
14/10/1973
24/10/1973
3/11/1973
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
22
4500
4000
3500
Flow (ML/D)
3000
2500
2000
1500
1000
500
0
11/11/1973
21/11/1973
1/12/1973
BALONNE RIVER AT ST. GEORGE
11/12/1973
21/12/1973
31/12/1973
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
7000
6000
Flow (ML/D)
5000
4000
3000
2000
1000
0
21/04/1974
1/05/1974
BALONNE RIVER AT ST. GEORGE
11/05/1974
21/05/1974
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
23
6000
5000
Flow (ML/D)
4000
3000
2000
1000
0
18/11/1974
28/11/1974
8/12/1974
BALONNE RIVER AT ST. GEORGE
18/12/1974
28/12/1974
7/01/1975
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
5000
4500
4000
Flow (ML/D)
3500
3000
2500
2000
1500
1000
500
0
28/10/1975
7/11/1975
17/11/1975
BALONNE RIVER AT ST. GEORGE
27/11/1975
7/12/1975
17/12/1975
CULGOA RIVER AT U/S COLLERINA (MUNDIWA)
NARRAN RIVER AT WILBY WILBY (BELVEDERE)
Figures 6 to 11
Observed flows from six events at St. George, upstream of Collerina at the lower
end of the Culgoa River, and the Wilby Wilby gauge on the Narran River
24
Proposed flow indicator
A flow indicator to maintain critical in-channel habitat has been proposed for the Culgoa River at
Brenda given that the majority of identified refugia waterholes are located on the Culgoa River and
also due to its location downstream of major diversions for consumptive use. To ensure waterholes
within the Lower Balonne system retain at least one metre of water, flows of 1,200 ML/d for 7 days
at Brenda should occur at a maximum interval of 22 months (1.8 years). A maximum interval
between flows of 28 months (2.3 years) is likely to ensure that a number of deeper waterholes will
be maintained as drought refuges. However, it is expected that increasing the maximum interval
between flows of 1,200 ML/d for 7 days at Brenda from 1.8 to 2.3 years is likely to reduce the
number of waterholes able to adequately support critical in-channel habitat.
The proposed flow indicators are consistent with the hydrology of the Lower Balonne system prior
to development. In order to achieve the objective of maintaining key waterholes as drought refugia
the volume of an event is likely to be the key driver. As such, water could be delivered in a different
pattern to the proposed flow indicator and still achieve the objective.
5.2.4. Summary
By analysing modelled flow data for the period 1895-2009, the frequency of specified flow
indicators under without development and current development scenarios has been determined.
In summary, the MDBA has prescribed the site-specific flow indicators (Table 8) for the Lower
Balonne Floodplain based on available information and analysis of flow data. As the floodplain
system is less studied than other locations in the Basin, its environmental water requirements have
a higher degree of uncertainty compared to other hydrologic indicator sites.
25
Table 8 Site-specific ecological targets and associated flow indicators for the Lower Balonne River Floodplain System
Without development and baseline
event frequencies
Site-Specific Flow Indicators
Average period between events (years)
except where labelled
Event
Site-Specific Ecological Targets
Provide a flow regime which ensures the current
extent of native vegetation of the riparian, floodplain
and wetland communities is sustained in a healthy,
dynamic and resilient condition
Provide a flow regime which supports the habitat
requirements of waterbirds
Provide a flow regime which supports a range of
native aquatic species (e.g. fish, frogs, turtles,
invertebrates)
Provide a flow regime which supports key ecosystem
functions, particularly those related to connectivity
between the river and the floodplain
Flow rate
required
(measured at
Brenda ML/d)
Duration –
minimum
continuous
(days)
Timing
1,200
7
12,000
11
18,500
9
26,500
7
Preferably
summer /autumn
but timing not
constrained to
reflect that high
flows depend on
occurrence of
heavy rainfall and
will be largely
unregulated
events
38,500
6
Average period
between events
(except where
labelled) under
modelled without
development
conditions (years)
Average period
between events
(except where
labelled) under
modelled
baseline
conditions (years)
Low uncertainty
(years)
High uncertainty
(years)
1.8 (maximum
period between
events)
2.3 (maximum
period between
events)
1.7 (maximum
period between
events)
3.5 (maximum
period between
events)
3
4
1.7
6.7
4
5
2.4
8.7
7
10
4.5
8.7
20
20
10.3
28.5
Note: Multiplication of the flow rate by the duration and frequency does not translate into the additional volume of water the site needs to be
environmentally sustainable. This is because part of the required flow is already provided under baseline conditions. Additional environmental water
required is the amount over and above the baseline flows.
26
6. Summary and conclusion
The Lower Balonne Floodplain is a key environmental asset within the Basin and is an important site
for the determination of the environmental water requirements of the Basin. MDBA has undertaken
a detailed eco-hydrological assessment of the Floodplain’s environmental water requirements.
Specified flow indicators are indicative of a long-term flow regime required to enable the
achievement of site-specific ecological targets at the Lower Balonne Floodplain and for the broader
river valley and reach. Along with other site-specific flow indicators developed across the Basin at
other hydrologic indicator sites, these environmental flow requirements were integrated within
hydrological models to inform the ESLT. This process is described in further detail within the
companion report on the modelling process ‘Hydrologic modelling to inform the proposed Basin
Plan: Methods and results’ (MDBA 2012).
The flow indicators in this report are used to assess potential Basin Plan scenarios. MDBA (2012)
summarises how the proposed draft Basin Plan released in November 2011 performs against flow
indicators for the Lower Balonne Floodplain.
27
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larvae, growth and biomass relationships in an Australian arid zone river: links between floodplains
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Nathan, Queensland, Australia
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from the CSIRO Murray–Darling Basin Sustainable Yields Project, CSIRO, Australia. 169pp.
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ecological condition of the Lower Balonne system, report to the Queensland Government
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2008,http://asdd.ga.gov.au
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national guidelines for Ramsar wetlands — implementing the Ramsar Convention in Australia,
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Dick, R 1993, The vegetation of the Wombeira land system and the floodplains of the Culgoa, Birrie
and Narran Rivers in NSW,November 1990, New South Wales National Parks & Wildlife Service,
Hurstville, NSW.
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29
Roberts, J & Marston, F 2011, Water regime for wetland and floodplain plants. A source book for the
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30
Appendix A
Data used in producing hydrologic indicator site maps
Data
Dataset name
Sourcea
Basin Plan regions
Draft Basin Plan Areas 25 May 2010
Murray–Darling Basin Authority (2010)
Dam walls/barrages
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia 2006
Gauges
100120 Master AWRC Gauges
Icon sites
Living Murray Indicative Icon Site Boundaries
Murray–Darling Basin Commission
(2007)
Irrigation areas
Combined Irrigation Areas of Australia Dataset
Bureau of Rural Sciences (2008)
Lakes
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia (2006)
Maximum wetland
Wetlands GIS of the Murray–Darling Basin Series 2.0
Murray–Darling Basin Commission
extents
(Kingsford)
(1993)
National parks/nature
Digital Cadastral Database
New South Wales Department of
reserves
Lands (2007)
National parks/nature
Collaborative Australian Protected Areas Database —
Department of the Environment,
reserves
CAPAD 2004
Water, Heritage and the Arts (2004)
Nationally important
Directory of Important Wetlands in Australia Spatial
Department of the Environment,
wetlands
Database
Water, Heritage and the Arts (2001)
Ocean and landmass
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia (2006)
Ramsar sites
Ramsar wetlands in Australia
Department of the Environment,
Water, Heritage and the Arts (2009)
Rivers
Surface Hydrology (AUSHYDRO version 1-6)
Geoscience Australia (2010)
Roads
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia (2006)
State border
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia (2006)
State forests
Digital Cadastral Database
New South Wales Department of
Lands (2007)
Towns
GEODATA TOPO 250K Series 3 Topographic Data
Geoscience Australia (2006)
Weirs
Murray–Darling Basin Weir Information System
Murray–Darling Basin Commission
(2001)
Weirs 2
a
River Murray Water Main Structures
Murray–Darling Basin Authority (2008)
Agency listed is custodian of relevant dataset; year reflects currency of the data layer.
31
Appendix B
Species relevant to criteria 1 and 4: Lower Balonne River Floodplain System
Species
Environment Protection
and Biodiversity
Conservation Act 1999
(Cwlth)
Fisheries
Management Act
2004 (NSW)
Threatened Species
Conservation Act
1995 (NSW)
Amphibians and reptiles
Western blue-tongued lizard (Tiliqua occipitalis)3
V
Birds
Australasian bittern (Botaurus poiciloptilus)3
V
Australian bustard (Ardeotis australis)2
E
Barking owl (Ninox connivens)3
V
Black-chinned honeyeater (eastern subspecies) (Melithreptus
V
gularis
gularis)3
Blue-billed duck (Oxyura australis)1
V
Brolga (Grus rubicundus)1, 2
V
Brown treecreeper (Climacteris picumnus)3
V
Freckled duck (Stictonetta naevosa)1, 2
V
Grey falcon (Falco hypoleucos)2
V
Grey-crowned babbler (eastern subspecies) (Pomatostomus
V
temporalis
temporalis)3
Hall’s babbler (Pomatostomus halli)2
V
Hooded robin (Melanodryas cucullata)3
V
Major Mitchell's or pink cockatoo (Cacatua leadbeateri)3
V
Painted honeyeater (Grantiella picta)2
V
Painted snipe (Rostratula australis or R. benghalensis)1
Red-tailed black cockatoo (Calyptorhynchus banksii)2
V
E
V
Fish
32
Species
Environment Protection
and Biodiversity
Conservation Act 1999
(Cwlth)
Fisheries
Management Act
2004 (NSW)
Silver perch (Bidyanus bidyanus)1
V
Olive perchlet (Ambassis agassizii)1
E
Murray cod (Maccullochella peelii peelii)1
Threatened Species
Conservation Act
1995 (NSW)
V
Purple spotted gudgeon (Mogurnda adspersa)1
E
Mammals
Inland forest bat (Vespadelus baverstocki)3
V
Koala (Phascolarctos cinereus)3
V
Little pied bat (Chalinolobus picatus)2
V
Sandy inland mouse (Pseudomys hermannsburgensis)2
V
Stripe-faced dunnart (Sminthopsis macroura)3
V
Yellow-bellied sheathtail bat (Saccolaimus flaviventris)3
V
Plants
Narrow-leafed bumble (Capparis loranthifolia var. loranthifolia)1, 2
E
Climbing caustic (Euphorbia sarcostemmoides)2
E
Desert cow-vine (Ipomoea diamantinensis)1
E
Winged peppercress (Lepidium monoplocoides)3
E
E
Communities
Lowland Darling River aquatic ecological community1
Coolibah–black box woodland of the northern Riverine Plains in the
E
E
Darling Riverine Plains and Brigalow Belt South bioregions1
Brigalow–gidgee woodland/shrubland in the Mulga lands and
Darling Riverine Plains
E
bioregion1
V = vulnerable E = endangered
1 Smith et al. (2006)
2 NSW National Parks and Wildlife Service (2003)
3 NSW Department of Environment, Climate Change and Water (2009)
33