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Department of Employment, Economic Development and Innovation
Southern Gulf Catchments
Barrier Prioritisation
Report
September 2010
Alana O’Brien Tim Marsden Matthew Moore Melinda Scanlon
i
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 ii
Information contained in this publication is provided as general advice only. For application to
specific circumstances, professional advice should be sought.
Fisheries Queensland has taken all reasonable steps to ensure the information contained in this
publication is accurate at the time of publication. Readers should ensure that they make
appropriate enquires to determine whether new information is available on the particular subject
matter.
For further information contact:
Tim Marsden
Fisheries Biologist
Fisheries Queensland
A Service of the Department of Employment, Economic Development and Innovation
Ph: (07) 4967 0724
© The State of Queensland, Department of Employment, Economic Development and Innovation,
2010.
Except as permitted by the Copyright Act 1968, no part of the work may in any form or by any
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Enquiries about reproduction, including downloading or printing the web version, should be
directed to ipcu@dpi.qld.gov.au or telephone +61 7 3225 1398.
Cover image: Clockwise from top image: Leichardt River causeway; Flinders River, Richmond,
pipe and culvert crossing; Road crossing at L Creek; and Doomadgee Weir on the Nicholson
River
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 iii
Contents
Glossary of Terms 1
Acronyms 1
Introduction 2
The Southern Gulf Region 2
Fish Communities and Passage Requirements 3
GIS Prioritisation 4
Methods 5
Stage 1 – GIS Prioritisation of Biological Criteria 5
Stage 2 – Full Biological Criteria Prioritisation 7
Stage 3 – Social, Economic and Technical Feasibility Prioritisation 8
Results 10
Stage One 10
Stage Two 12
Stage Three 14
Discussion 16
Conclusion 17
Recommendations 17
References 18
Appendix 1 – The 28 Barriers to Fish Migration in SGC 19
Appendix 2. Total barriers (7992) identified in Southern Gulf Catchments before a Stage 1
criterion was applied. 29
Appendix 3 – Barriers Previously Assessed in 2005 30
Appendix 4 - Fish Species of the Southern Gulf Region 31
Appendix 5 – Fishways completed 2008 & 2009 within the SGC 33
Appendix 6 – Stream Order 37
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 iv
Glossary of Terms
Diadromous - These fish are true migratory species whose distinctive characteristics include
migrating between freshwaters and the sea. Their movement is usually obligatory migration takes
place at fixed seasons or life stages. There are three distinctions within the diadromous category,
catadromous, amphidromous and anadromous.
Catadromous - Diadromous fishes which spend most of their lives in fresh water, and
migrate to sea to breed.
Amphidromous - Diadromous fishes in which migration between freshwater and the sea
is not for the purpose of breeding, but occurs at some other stage of the life cycle.
Anadromous - Diadromous fishes which spend most of their lives at sea, and migrate to
freshwater to breed.
Potamodromous - fish species whose migrations occur wholly within freshwater for breeding and
other purposes.
Acronyms
SGC – Southern Gulf Catchments Natural Resource Management Group
1
Introduction
In 2005 Fisheries Queensland (formally Queensland Primary Industries and Fisheries) completed a
‘Gulf Catchments Fish Passage Assessment’ that examined potential fish barriers within the
Southern Gulf Region. This report, funded by the Mount Isa Stocking Group, identified 15 priority
barriers that required fish passage remediation. In 2008 and 2009 four of these barriers were
retrofitted with fishways – Gregory River Doomadgee Road Crossing (rock ramp fishway), Gin Arm
Creek (rock ramp fishway), Escott Causeway Nicholson River (concrete cone fishway) and the
Flinders River Burketown-Normanton Road Crossing (concrete cone fishway).
In 2009, Southern Gulf Catchments approached Fisheries Queensland to undertake a complete
prioritisation of all barriers in the Southern Gulf Region. This report details the prioritisation process
and lists the current top 20 barriers within the region based on this prioritisation, outlining
recommended remediation works.
The Southern Gulf Region
The Southern Gulf region covers approximately 200,000 square kilometres of Gulf Savannah
country in northwest Queensland. This region is comprised of a number of major and minor river
catchments including the Mornington Inlet, Flinders, Bynoe, Leichhardt, Nicholson, Gregory, Albert,
Saxby, Cloncurry, Gilliat, Woolgar, O’Shannassy, Thornton, Cameron, Malbon and Williams
Rivers. The major settlements within the Southern Gulf region include Burketown, Doomagee,
Mount Isa, Julia Creek, Cloncurry, Richmond, Hughenden and the Wellesley Islands.
Essentially, the region is a large coastal plain comprised of over two million hectares of wetlands
and extensive floodplains that surround each of the major river systems (Southern Gulf NRM
2010). The three major bioregions including the Gulf Plains, the Mitchell Grass Plains and the
North West Highlands make up the Southern Gulf Region. The Gulf Plains, the largest of the
bioregions, covers almost 12% of Queensland’s land area and consists primarily of coastal salt
flats, mangroves, and grass and woodland areas (Australian Government 2010). The Mitchell
Grass Downs bioregion is dominated by Mitchell Grass tussock on its large undulating plains, while
the rugged, hilly country of the North West Highlands is dominated by eucalypt and spinifex
communities (Australian Government 2010). Land usage in the Southern Gulf is primarily cattle
and sheep grazing (93.7%) with mining (copper, silver, lead, zinc, gold and phosphate), national
parks/reserves and urban centres making up the remainder (Southern Gulf Catchments 2010).
The Southern gulf region can be described as semi-arid in the south and southwest sections to
tropical monsoon in the north (Southern Gulf Catchments 2010). It is generally cool and dry in the
winter and hot and wet in the summer, with 80% of the annual rainfall arriving with the monsoon
between December and March (Southern Gulf Catchments 2010). Average annual rainfalls vary
from 350mm in the southern areas, up to 900mm along the coast. Mornington Island has slightly
higher rainfall than the mainland, having recorded 1200mm in recent years (Southern Gulf
Catchments 2010).
The major rivers within the SGC are long, low gradient systems with intermittent flows that often
dry up to form refuge pools in the dry season. Much of the riparian zones of these rivers are well
vegetated often with areas of overhanging vegetation, instream habitat such as snags, undercut
banks and submerged vegetation. The majority of the rivers and streams within the SGC are still
natural in form i.e. unmodified by realignment, farming or mining practices.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 2
Fish Communities and Passage Requirements
Several fish community surveys have been conducted within the Southern Gulf NRM region,
including the most recent by Hogan and Vallance (2005) that found 50 species of freshwater fish
within the Flinders, Leichardt and Nicholson Rivers (see Appendix 4). A number of these species,
including barramundi, sawfish, fork-tailed catfish, long-tom, mullet, and the nurseryfish are
diadromous, meaning that they migrate between freshwater and the sea at some point in their life
cycle. A number of potamodromous species, those that migrate wholly within freshwater, were
also found in the study, including rainbow fish, giant glassfish, sleepy cod, sooty grunter and fly-
speckled hardyhead. Hogan & Vallance’s list also contains species endemic to the Southern Gulf
region, including the gulf grunter, elongate glassfish, strawman, saltpan sole, small mouth catfish,
river gar, mariana’s hardyhead, carpentaria catfish, neil’s grunter, tadpole goby, golden goby,
square-blotched goby, giant glassfish and the freshwater anchovy. As they are found nowhere
else except the SGC passage requirements are very important.
There are a number of commercial and recreational species found within the SGC including
barramundi, sooty grunter, mullet, archerfish, sleepy cod and the salmon catfish. A number of
these species are also important to the aquarium industry including rainbowfish, hyrtl’s tandan,
mariana’s hardyhead, fly-speckled hardyhead, strawman and mouth almighty being very attractive
in captivity.
The fish communities within the SGC in some areas have been impacted by mining, agriculture
and some river regulation. However as much of this development is limited and due to the very
large size of the catchments the SGC remains in relative good condition, (Marsden and Stewart,
2005). However, barriers to migration have had an impact on the fisheries condition.
Streams of the SGC are mostly ephemeral systems where flows can be extremely high during the
wet season and very low during the dry season. With peak flows many of the barriers are drowned
out allowing free passage for fish migration. However when these flows decrease to medium and
low flows passage becomes very limited. As many of the fish species found within the SGC move
on lower flows, they require passage towards the end of the wet season when flows have started
to recede and often fall below the level of the barrier. Quite often these lower flows can continue
for extended periods of time, leaving many fish (adults and juveniles) stranded below barriers.
Barriers found in the SGC including pipes, culverts, road crossings and weirs constructed for water
storage. These can affect fish communities as they prevent the free movement of migratory fish
species (Figures 1 and 2). Barriers such as these can often cause local extinctions upstream of the
obstruction and can also cause a reduction in fish populations downstream of the barrier
(Thorncraft and Harris, 2000). Pipes and culverts can cause considerable modification to channel
form and flow conditions with increased velocities, turbulence and also a reduction of water depth
within the structure, (NSW DPI, 2006). Scouring at the culvert or pipe outlet can create a drop that
is often impassable to fish, this can also indicate a velocity barrier existing inside the structure
during higher flows (Bates, 2003).
Causeways, although they can drown out, cause obstructions to migration with excessive headloss
height and depth of water over the structure (NSW DPI, 2006). Scouring can also occur on the
downstream side of the causeway created by high velocity flow. Weirs cause a distinctive barrier
in-stream with drown-outs rarely occurring and connectivity often limited due to the short duration
floods, and the high velocities associated with flooding, (Gehrke, 1995). The ability to negotiate
barriers at peak flows may be limited to a very select suite of fish species, (Gehrke, 1995).
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 3
Figures 1 and 2. Culvert/pipe fish barrier Flinders River, Richmond (left); Burketown-Normanton
Road causeway crossing of the Little Bynoe River (right).
Of particular concern are the tidal barriers affecting fish migrating upstream from the estuary.
Estuaries provide spawning and nursery grounds for many riverine species and also operate as a
buffer zone between the fresh and salt water for freshwater fish washed downstream during high
flows. At tidal barriers, many fish, particularly juveniles, can easily become trapped below the
structure if it is too large to negotiate. Subsequent barriers upstream of tidal barrages have similar
effects on fish communities and can often isolate seasonal or ephemeral habitats in wetlands and
floodplains (NSW Department of Primary Industries 2006).
Barriers can have serious implications for the conservation of threatened and vulnerable species
such as the freshwater sawfish, Pristus microdon, found in the Southern Gulf region. Listed as
vulnerable under the national Environment Protection and Biodiversity Conservation (EPBC) Act
1999, the sawfish is a diadromous species where both adults and juveniles utilise freshwater
(DEWHA 2010). It is believed that juvenile sawfish spend up to 5 years in freshwater steams
before returning to the estuary (Thorburn et al 2007). Barriers to migration can potentially prevent
the successful breeding of such important species leading to problems in their management.
GIS Prioritisation
GIS Prioritisation of potential barriers is a fast and efficient way to analyse large numbers of
barriers to identify the highest priority sites for remediation investment. This process is a good way
to obtain a manageable number of barriers to ground-truth in the field, by eliminating those with
poor or limited habitat, time in the field can be maximised on those of highest priority.
A three stage selection criteria process was used to prioritise barriers from most important through
to least important based on the biological, social and economic benefits and the cost of
remediation. The selection criteria process has taken into consideration the importance of various
migration patterns and the likelihood of localised extinctions caused by barriers. The process was
designed to favour barriers located close to the estuarine interface in large coastal river systems as
they may prevent diadromous species from migrating to upstream freshwater habitats. The impact
of barriers on diadromous fish communities is considered to be more critical than the effect on
potamodromous fish communities as the species that migrate wholly within freshwater can
maintain populations despite the presence of barriers.
The three stage prioritisation process includes undertaking an automated GIS prioritisation of five
biological criteria (see methods) to refine the list of barriers. Then field validation and further
refinement of the barriers by four more biological criteria is to be completed. From this social,
economic, environmental and technical criteria are evaluated and the list is refined further and
finally the GIS program can analyse all the criteria for each barrier and rank them in priority order.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 4
Methods
Stage 1 – GIS Prioritisation of Biological Criteria
The aim of Stage 1 was to identify all potential barriers within the Southern Gulf Region and to
provide an initial prioritisation to allow further field investigation of high priority sites. Using
OziExplorer software and NATMAP Raster 250K map (2005) from Geosciences Australia,
waypoints were created at all intersecting roads/rail lines and water bodies. ArcMap 9.3 GIS
software was utilised to validate these barriers using Spot 5 satellite imagery. This imagery was
also used to identify any further barriers not found using the NATMAP software. All waypoints
originally created in OziExplorer were replaced with shape file points (in ArcMap), so that a GIS
analysis could be performed. Every potential barrier was assigned a unique identification number
to maintain quality assurance.
Once all potential in-stream barriers had been cross checked using Spot 5 satellite imagery and
assigned a shape file point, they were analysed using an automated GIS program. The GIS
program was created specifically to prioritise the large quantity of potential in-stream barriers
identified during the study. To achieve this, five biological criteria questions were incorporated into
the GIS program. For each question, a score was assigned relating to how the barrier fulfilled the
biological criteria. Barriers were then prioritised based on their total score, with the top scoring
barrier becoming the highest priority.
All scores were based on the premise that free access to and from the sea is essential to the
breeding of diadromous species and they cannot survive without this access. Therefore habitats
and barriers close to the sea gain higher scores as they have the greatest impact on the movement
of diadromous species. Upper habitats and barriers score lower as the potamodromous species
found there can still maintain populations, even though they may become fragmented, while
diadromous species become extinct without access to the sea.
The following are fundamental for a potential in-stream barrier to attain a high score in stage one:-
• High Stream order
• Located lower down in the system, closer to the estuary
• Catchment condition has minimal adverse surrounding land use practices
• A large area of the catchment will be opened up above the barrier to the next barrier (or to
the top of the catchment) if the barrier is removed
• Minimal or no barriers downstream
The software utilised for this process includes ESRI ArcGIS 9.3 and ArcGIS Extension tools that
include Network Analyst, Spatial Analyst, EtGeowizards and X-Tools.
The five biological questions and associated scoring system incorporated into the automated GIS
program for the first round of the prioritisation process were as follows:
Question 1.
Stream Type
The first GIS question determined the stream order of the stream segment on which the barrier
was located. Higher stream orders (large streams) gained a higher score, while minor stream
orders (small streams) gained a lower score. (Appendix 6 outlines the Strahler stream order
method). Stream orders 1 and 2 within the first 50km of the important coastal zone and stream
orders 1, 2, 3 and 4 from beyond the coastal zone to the head waters of the catchment were
removed from the barrier prioritisation process as they contained little or poor fish habitat.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 5
Stream orders 3 to 11 within the Coastal Zone and Stream orders 5 to 11 from the coastal zone to
the headwaters were scored as follows:-
Stream order in the
Coastal zone
Score Stream orders inland
from the coastal zone
Score
3 2 5 4
4 4 6 6
5 6 7 8
6 8 8 10
7 10 9 12
8 12 10 14
9 14 11 16
10 16
11 18
Question 2.
What is the stream length (km) cut off by the barrier, expressed as a proportion (%) of the total
stream network within the entire catchment?
The total stream network should take into account all tributaries of the catchment upstream and
downstream (to the saltwater interface) of the barrier, not just the tributary in which the barrier is
located. The greater the percentage of stream network cut-off by the barrier then the likelihood for
a greater benefit from removing the barrier.
a. 80% or more of total stream network (5 points)
b. 60-79% of total catchment. (4 points)
c. 40-59% of total catchment. (3 points)
d. 21-39% of total catchment. (2 points)
e. ≤20% of total catchment. (1 point)
Question 3.
What stream length (km) exists upstream of the barrier that is not impeded by further barriers?
Include all tributaries if there are no further barriers. If there is another barrier upstream, then only
measure to this point. If it is the uppermost barrier in the system and there are barriers below, take
3 points off of the score (lowest score possible is 0). This takes into account that uppermost
barriers often have large stream networks, but of relatively low value habitat.
a. 500+ km’s. (5 points)
b. 100 - 499 km’s. (4 points)
c. 50 - 99km’s. (3 points)
d. 10 - 49 km’s. (2 Points)
e. 0.6 – 9 km’s (1 Point)
f. 0 – 0.5 km’s. (0 Points)
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 6
Question 4
Number of barriers downstream.
a. No barriers downstream. (7 points)
b. One barrier downstream. (5 points)
c. Two to four barriers downstream. (3 points)
d. Five to Nine barriers downstream. (2 points)
e. Ten or more barriers downstream. (0 points)
Question 5
Catchment Condition
Take into account the whole catchment downstream to the declared downstream limit, not just the
sub-catchment the barrier is located. E.g. if a barrier is located on the Flinders River, then its
catchment condition would include the entire Flinders catchment include the Saxby, Cloncurry and
any other associated rivers.
a. No intensive cropping/urban. (7 points)
b. 1%-4% intensive cropping/urban. (4 points)
c. 5%-14% intensive cropping/urban (3 points)
d. 15-29% intensive cropping/urban. (2 points)
e. 30%-39% intensive cropping/urban. (1 point )
f. ≥40% intensive cropping/urban. (0 points)
Stage 2 – Full Biological Criteria Prioritisation
Stage two of the barrier prioritisation process involved field validation of the top 100 ranked barriers
from stage one. To achieve this, a GPS (Garmin GPS map 76) tracking system was set up on a
laptop computer using the moving map function of OziExplorer mapping software. Together with
remotely indentified and prioritised waypoints, allowed field staff to systematically locate the
geographical position of each barrier in relation to identifiable locations (towns, roads, streams),
allowing for efficient validation of potential barriers.
Once a potential barrier was located and confirmed as a barrier to fish passage, information about
the relevant physical and biological (surrounding habitat) aspects were recorded. These aspects
included: the type of barrier; number of culverts/pipes; head loss (difference between upstream
and downstream water levels); length, height and width of the structure, and; access information.
Additionally, video footage and photos of the barrier were taken. Detailed biological information on
stream condition, water supply, habitat for migratory fish upstream of the barrier, fish passage
status downstream and distance to tidal interface was also recorded for use in the second stage
scoring process.
The second stage scoring process involved allocating a score to all barriers for each of the
biological criteria. Scores were collated and added to the stage one scores, the barrier with the
highest combined score became the highest ranking barrier.
The biological questions and associated scoring system for the second stage of the prioritisation
process are as follows:
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 7
Question 1.
Barrier type
a). Tidal barrage. (5 points)
b). Dam or weir ≥3m. (4 Points)
c). Dam or weir 1.5–3m high or culvert/pipes that span ≤60% of stream width. (3 Points)
d). Dam or weir ≤1.5m high or culvert/pipes that span ≥60% of stream width. (2 Points)
e). No barrier – DO NOT SCORE REMAINING CRITERIA.
Question 2.
Stream condition
a). Pristine; undisturbed (no apparent clearing of rip veg; no bank degradation). (5 Points)
b). Low disturbance (≤ 25% of upstream areas degraded as above). (4 Points)
c). Moderate disturbance (25-50% of upstream areas degraded as above). (3 Points)
d). High disturbance (51-75% of upstream degraded) (2 Points)
e). Very high disturbance (≥ 75% of upstream degraded). (1 Point)
Question 3.
Water Supply/Quantity
a). Natural, permanent or non-polluted. (5 Points)
b). Natural, permanent via supplemented flow or minimal pollution. (4 Points)
c). Stream occasionally dries up with refuge pools or some pollution. (3 Points)
d). Stream seasonally dries up with refuge pools or moderate pollution. (2 Points)
e). Stream dries seasonally with no refuge pools or heavy pollution. (1 Point)
Question 4.
Habitat for migratory fish species upstream of barrier site
a). Excellent (diverse and abundant fish habitat). (5 Points)
b). Good (reasonable amount of suitable fish habitat). (4 Points)
c). Moderate (moderate amount of suitable fish habitat). (3 Points)
d). Poor (little suitable fish habitat). (2 Points)
e). Very poor. (little or no suitable fish habitat). (1 Point)
Stage 3 – Social, Economic and Technical Feasibility Prioritisation
The third stage of the prioritisation process involved investigating the social, economic and
environmental benefits of the barrier remediation works. A very important aspect of this stage of
the process was considering the net benefits of fixing the barrier versus the economic cost of the
remediation. As much of the remediation works are funded by Natural Resource Management
groups who’s funding is often quite limited, this stage of the prioritisation is important in
understanding which barrier can be affordably fixed in line with the funding. Smaller structures are
cheaper to construct and therefore most cost affective for the investor.
This third process is achieved through analysing the top 28 barriers with a range of social,
economic and biological criteria. Like stage one and two of the prioritisation process, each criterion
contained a question with multiple answers. A score of 1 to 5 was assigned to each answer and
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 8
once all the barriers had been analysed, scores were collated, and as with stage 2, the highest
scoring barrier become the top ranked barrier of the SGC region. The end result of the third stage
is a list of the 28 barriers to fish migration in the SGC region in order of highest priority (see
Appendix 1).
The social, economic and biological questions and associated scoring system of the third stage of
prioritisation included:
Question 1.
Estimated cost
a). Low cost small/low nature-like fishway (<0.8m) or short culvert baffles
(<0.8m) (5 Points)
b). Low-moderate cost small/high nature-like fishway (0.8-1.5m) or small/low height
technical fishway (<0.8m) or tall culvert baffles (>0.8m) (4 Points)
c). Moderate cost high nature-like fishway (1.5-2.0m) or medium/low height
technical fishway (0.8-1.5m) (3 Points)
d). Moderate-high cost large/low height technical fishway (>1.5m) (2 Points)
e). High cost large/high height technical fishway (>1.5m) (1 Point)
Question 2.
What assistance by way of access, financial or in-kind support is available?
a). Easy access, good financial and in-kind support available. (5 Points)
b). Reluctant access, some financial or in-kind support available. (3 Points)
c). Reluctant access, no financial or in-kind support available. (1 Point)
d). No access, no financial or in-kind support available. (0 Points)
Question 3.
Technical viability - How difficult is the design and construct?
a). Simple installation of current design, limited engineering required. (5 Points)
b). Modest installation of current design, some engineering
(includes multi-design fishways) (3 Points)
c). Complex installation and engineering or a new concept design. (1 Point)
Question 4.
Productivity benefits
What fish species will benefit from the remediation and will this benefit commercial/recreational
fisheries and/or increase local business revenue (consider added improvement to current fish
passage as well)?
a). A high benefit to a large number of commercial and or recreational species. (5 Points)
b). A moderate benefit to a moderate number of commercial and or recreational species (3 Points)
c). A small benefit to a small number of commercial and or recreational species. (1 Point)
d). No benefit to commercial and or recreational species. (0 Point)
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 9
Sout
hern Gulf Catchments, Barrier Prioritisation Report, 2010 10
Question 5.
Conservation significance
Will the improvement have a positive impact on the conservation of species?
a). Listed (under EPBC Act 1999) species present. (5 Points)
b). Species present that are rare or restricted within the region (but not rare or restricted outside
the region). (3 Points)
c). Only common or abundant species within the region present. (1 Point)
Question 6.
How effective will the fish passage remediation be?
a). All species at all migration flows will be able to pass. (5 Points)
b). All species at some migration flows or some species at all migration flows will be able to pass.
(3 Points)
c). Some species at some migration flows will be able to pass. (1 Point)
Results
Stage One
Before removing the lower order systems 7992 in-stream road crossings were identified in the
Southern Gulf Catchments, (see appendix 2). The removal of these lower order streams by the
automated GIS programme in Stage One of the prioritisation process reduced this number to 536
potential barriers to fish migration. The ranking of the 536 barriers was achieved by using the
questions in the stage one process.
Table 1. The number of potential barriers identified at each score from the highest score to the
lowest score.
Score No. Potential Barriers Score No. Potential Barriers
35 1 20 6
34 2 19 7
30 1 18 4
28 1 17 13
27 1 16 7
24 4 15 18
21 5 14 and lower 464
Figure 3. Map of the 536 potential barriers identified within the Southern Gulf Catchments region following the Stage 1 automated GIS program.
11
12
Stage Two
A total of 60 potential barriers were validated in the field during stage two of the prioritisation
process (see figure 4). This resulted in 28 confirmed barriers to fish migration and by using the
questions set out in Stage Two. These barriers were ranked in order of priority (see Table 2.).
Table 2. The 28 confirmed barriers and their rank in order of priority after Stage Two of GIS
Prioritisation process.
Barrier
Number Stream Name Barrier Type/Name Stage 2
Rank
411 Bynoe River Pipe causeway 1
412 Little Bynoe River Pipe causeway 2
106 Nicholson River 1st Escott causeway 3
186 Flinders River Walkers Bend causeway 4
514 L Creek Inverleigh Station weir 5
152 Leichardt River Augustus Downs causeway 6
104 Pear Tree Creek Culvert crossing 7
253 Flinders/Saxby Rivers junction Earth bund – single pipe 8
122 Big Oaky Creek Low bridge crossing 9
535 Nicholson River Doomadgee Weir 10
408 Leichardt River Lake Julius Dam 11
534 Alexandra River Causeway 12
177 Armstrong Creek Culvert crossing 13
118 Nicholson River Pipe causeway 14
250 Saxby River Wondoola Road causeway 15
176 L Creek Causeway – single pipe 16
147 Leichardt River Coolullah Station causeway 17
348 Flinders River Richmond culvert and pipe crossing 18
150 Cloncurry River Fort Constantine causeway 19
182 Magowra Creek culvert crossing 20
525 Flinders River Punchbowl Waterhole causeway 21
157 Lagoon Creek Earth causeway – single pipe 22
259 Flinders River Pipe Causeway 23
103 Crooky Creek Culvert crossing 24
417 Saxby River Millungera Station culvert crossing 25
466 Lagoon Creek Earth causeway – single pipe 26
65 Cloncurry River Cloncurry Anabranch culvert crossing 27
225 Eastern Creek Culvert crossing 28
13
Figure 4. Map of top 60 barriers validated in the field during Stage 2.
14
Stage Three
The final stage of the prioritisation process involved analysing the 28 confirmed barriers using the
economic, social and technical questions in Stage Three. This resulted in the prioritisation of the
28 barriers to fish migration in the SGC (see Table 3 and figure 5). Appendix 1 outlines the
recommended remediation activities for each of the 28 barriers.
Table 3. Final scores for the top priority barriers in SGC.
Barrier
Number Stream Name Barrier Type/Name
Total
adjusted
Rank
411 Bynoe River Pipe causeway 1
412 Little Bynoe River Pipe causeway 2
106 Nicholson River 1st Escott causeway 3
152 Leichardt River Augustus Downs causeway 4
186 Flinders River Walkers Bend causeway 5
514 L Creek Inverleigh Station weir 6
104 Pear Tree Creek Culvert crossing 7
534 Alexandra River Causeway 8
122 Big Oaky Creek Low bridge crossing 9
253 Flinders/Saxby Rivers junction Earth bund – single pipe 10
177 Armstrong Creek Culvert crossing 11
176 L Creek Causeway - single pipe 12
250 Saxby River Wondoola Road causeway 13
147 Leichardt River Coolullah Station causeway 14
535 Nicholson River Doomadgee weir 15
182 Magowra Creek Culvert crossing 16
118 Nicholson River Pipe causeway 17
103 Crooky Creek Culvert crossing 18
408 Leichardt River Lake Julius Dam 19
259 Flinders River Causeway – four pipes 20
150 Cloncurry River Fort Constantine causeway 21
157 Lagoon Creek Earth causeway – single pipe 22
417 Saxby River Millungera Station culvert crossing 23
525 Flinders River Punchbowl Waterhole causeway 24
466 Lagoon Creek Earth causeway – single pipe 25
348 Flinders River Richmond culvert and pipe crossing 26
65 Cloncurry River Cloncurry Anabranch culvert crossing 27
225 Eastern Creek Culvert crossing 28
15
Figure 5. Map of the top 28 barriers identified in the Southern Gulf Catchment.
Discussion
Of the 7992 potential barriers identified in Stage One of the prioritisation process, 7456 were found to
be in systems that our GIS program deemed to have limited or poor fish habitat and by providing
passage beyond that potential barrier would not be beneficial to fish populations.
After removing these potential barriers from the prioritisation process, there remained a further 536
potential barriers that were ranked in accordance of priority that would be most beneficial to
maintaining fish populations.
Of those barriers identified in the 2005 study, six out of the fifteen sites were included in the current
study as they met all the criteria of the prioritisation. Four of the fifteen sites have had fishways
retrofitted to them and therefore passage is no longer an issue, one is a natural barrier and one is no
longer considered to be within the SGC (boundaries have changed since the council amalgamation in
2008). Three that did not rate high in the prioritisation process as they where found in the upper
catchment and were eliminated in stage one. Nevertheless, as they are barriers to fish migration,
appendix 3 lists these barriers with remediation activities that could be undertaken.
Although validation of only the top 50 to 100 potential barriers was required, the top 200 sites were
identified for field validation to ensure that as many potential barriers could be surveyed as possible.
As expected, of the top 200 potential barriers only 60 were actually validated in the field. This was due
to the extended wet season leaving many roads impassable (especially those close to the coast).
Future validation of these sites should be considered, however, communication with landholders
suggests that the majority are bed level crossings and are not barriers to fish migration. Landholders
indicated that they did not access these areas during the wet season and therefore there was no
requirement for in-stream structures (large or small) for access. Other sites that could not be accessed
were on remote properties and along roads that were closed to the public and communication with
landholders could not be made.
From the field validation 28 of the 60 sites surveyed were found to be actual barriers to fish migration.
These were mostly culvert and pipe crossings, weirs and causeways. The highest priority barriers
were generally lower in the system usually on large creeks and rivers, and had been installed for either
in-stream water storage or where the system was too wide or too deep for bed level and rock
crossings. The 28 confirmed barriers were ranked according to impact on fish communities, cost of
construction, effectiveness of the remediation, conservation issues (e.g. freshwater sawfish), access
and financial support from all parties involved.
The top 6 priority sites were, The Bynoe River, The Little Bynoe River, The Nicholson River at Escott
Station, The Leichardt River at Augustus Station, Walkers Bend on the Flinders River and Inverleigh
Station weir on L Creek. To remedy these 6 barriers would cost $ 485,000.00 and would result in over
900 km of stream becoming available to fish migration.
Providing passage these barriers would improve the fish community and provide the most cost effective
remediation for investors.
The 32 crossings that were found not to be barriers were either bed level crossings or bridges. These
do not obstruct fish migration as they promote natural unimpeded stream flow, allowing the free
movement of fish during a wide range of hydrological conditions (Fairfull and Witheridge, 2003; NSW
DPI 2006).
16
Conclusion
The study clearly demonstrates what while there are thousands of barriers with the SGC NRM region,
remediation of a small number of the highest priority barriers will significantly increase the habitat
available fro fish. By restoring fish passage to these priority sites, free passage between tidal zones,
wetlands floodplains and instream lagoons will be greatly enhanced, maximizing the productivity of
these systems and ensuring that the fishermen of the Gulf have many more healthy and well fed fish to
catch.
Recommendations
• Prepare an investment strategy for the highest priority sites based on the information contained
within this report
• Landholder negotiations should be commenced to permit rehabilitation of the highest priority
sites.
• Detailed surveys should be undertaken to produce suitable fishway designs
• Contracts should be initiated to detail ongoing maintenance and monitoring agreements to
ensure the success of any fishway installed.
• Fish community sampling should be undertaken to monitor population sizes and species
diversity after remediation activities have been completed.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 17
References
Australian Government. 2010. Southern Gulf - Natural Resource Management region
http://www.nrm.gov.au/nrm/qld-sgul.html
Bates, K. 2003. Design of Road Culverts for Fish Passage, Washington Department of Fish and
Wildlife
DEWHA, 2010:
http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=66182
Fairfull, S. and Witheridge, G. 2003. Why do fish need to cross the road? Fish passage requirements
for waterway crossings. NSW Fisheries, Cronulla
Gehrke, P.C. 1995. Fish need corridors too: The importance of connectivity in riverine ecosystems.
Presentation to the ‘Corridors Seminar’ at the University of Western Sydney, Richmond Campus
Hogan, A. and Vallance, T. 2005. Rapid Assessment of Fish Biodiversity in Southern Gulf of
Carpentaria Catchments, QLD DPI & F, Mackay
Marsden, T., Stewart, R., 2005, Gulf Catchments and Fish Passage Assessment, QLD DPI & F,
Mackay
NSW Department of Primary Industries. 2006. Reducing the impact of road crossings on aquatic
habitat in coastal waterways – Northern Rivers, NSW. Report to the New South Wales Environmental
trust. NSW Department of Primary Industries, Wollongbar, NSW
Southern Gulf Catchments, 2010. The Land, http://www.southerngulf.com.au/page/The%20Land
Thornburn, D., Morgan, D., Rowland, A. and Gill, H. 2007. Freshwater Sawfish Pristis microdon
Latham, 1974 (Chondrichthyes : Pristidae) in the Kimberley Region of Western Australia, Zootaxa ISSN
1175-5334 (online edition) pp 27-42
Thorncraft, G. and Harris, J.H. 2000. Fish passage and fishways in NSW: A status Report.
Cooperative Research for Freshwater Ecology Technical Report 1/2000
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 18
Appendix 1 – The 28 Barriers to Fish Migration in SGC
Rank 1
Barrier Id number 411
System Name Bynoe River
Barrier Type Causeway and Pipes
Barrier Height 1.3m
Location 40km west of Normanton
Fishway Option Concrete cone Fishway
Approximate cost $45 000.00
Rank 2
Barrier Id number 412
System Name Little Bynoe River
Barrier Type Causeway and pipes
Barrier Height ~2m
Location 35km west of Normanton
Fishway Option Concrete cone fishway
Approximate cost $75 000.00
Rank 3
Barrier Id number 106
System Name Nicholson River
Barrier Type Causeway
Barrier Height ~2m
Location Escott Station
Fishway Option Concrete Cone
Approximate Cost $ 40 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 19
Rank 4
Barrier Id number 152
System Name Leichhardt River
Barrier Type Causeway
Barrier Height 700mm
Location Augustus Downs station
Fishway Option Rock Ramp Fishway
Approximate cost $25 000.00
Rank 5
Barrier Id number 186
System Name Flinders River
Barrier Type Causeway
Barrier Height 2m
Location Walkers Bend
Fishway Option Partial Removal & / or
Culvert installation
Approximate cost $ 150 000.00
Rank 6
Barrier Id number 514
System Name L Creek
Barrier Type Weir
Barrier Height 1.8m
Location Inverleigh Station
Fishway Option Vertical Slot Fishway or
Concrete cone Fishway
Approximate cost $150 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 20
Rank 7
Barrier Id number 104
System Name Pear Tree Creek
Barrier Type Culvert Crossing
Barrier Height 1.2m
Location 9km south of Burketown
Fishway Option Baffles
Approximate cost $15 000.00
Rank 8
Barrier Id number 534
System Name Alexander River
Barrier Type Causeway
Barrier Height 400mm
Location 73km SE of Burketown
Fishway Option Rock Ramp fishway
Approximate cost $25 000.00
Rank 9
Barrier Id number 122
System Name Big Oaky Creek
Barrier Type Low Bridge Crossing
Barrier Height 1m
Location 38km SW of Burketown
Fishway Option Rock Ramp & Baffles
Approximate cost $ 40 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 21
Rank 10
Barrier Id number 253
System Name Flinders/Saxby Rivers
Junction
Barrier Type Earth-bund Crossing
Barrier Height 600mm
Location Warrenvale Station
Fishway Option Culverts & baffles & rock
ramp fishway
Approximate cost $ 75 000.00
Rank 11
Barrier Id number 177
System Name Armstrong Creek
Barrier Type Boxed Culverts
Barrier Height 1.2m
Location 54km west of Normanton
Fishway Option Concrete Cone Fishway
Approximate cost $45 000.00
Rank 12
Barrier Id number 176
System Name L Creek
Barrier Type Causeway and Pipe
Barrier Height 700mm
Location Inverleigh Station 80km
west of Normanton
Fishway Option Concrete cone Fishway
Approximate cost $ 45 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 22
Rank 13
Barrier Id number 250
System Name Saxby River
Barrier Type Causeway
Barrier Height 1m
Location Wondoola station
Fishway Option Rock Ramp Fishway
Approximate cost $ 35 000.00
Rank 14
Barrier Id number 147
System Name Leichhardt River
Barrier Type Causeway
Barrier Height 1.1m
Location Coolullah Station
Fishway Option Rock Ramp Fishway
Approximate cost $35 000.00
Rank 15
Barrier Id number 535
System Name Nicholson River
Barrier Type Weir
Barrier Height 1.5m
Location 5km south of
Doomadgee
Fishway Option Vertical Slot Fishway
Approximate cost $750, 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 23
Rank 16
Barrier Id number 182
System Name Magowra Creek
Barrier Type Culvert crossing
Barrier Height ~1m
Location 25km west of Normanton
Fishway Option Baffles
Approximate cost $ 15 000.00
Rank 17
Barrier Id number 118
System Name Nicholson River
Barrier Type Pipe causeway
Barrie Height ~1m
Location 5km south of
Doomadgee
Fishway Option Concrete cone
Approximate cost $55 000.00
Rank 18
Barrier Id number 103
System Name Crooky Creek
Barrier Type Culverts
Barrier Height ~600mm
Location 25km SE of Burketown
Fishway Option Baffles & cleanout
Approximate cost $ 15 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 24
Rank 19
Barrier Id
number
408
System Name Leichhardt river
Barrier Type Dam
Barrier Height 30m
Location Lake Julius
Fishway Option Fish Lift
Approximate cost $ 14 million
Rank 20
Barrier Id number 259
System Name Flinders River
Barrier Type Pipe Causeway
Barrier Height 1.15m
Location 75km north of Julia Creek
Fishway Option Removal
Approximate cost $ 30 000.00
Rank 21
Barrier Id number 150
System Name Cloncurry river
Barrier Type Causeway and Pipe
Barrier Height 1.8m
Location Fort Constantine
Fishway Option Concrete cone fishway
Approximate cost $ 75 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 25
Rank 22
Barrier Id number 157
System Name Lagoon Creek
Barrier Type Earth-bund causeway
Barrier Height ~600mm
Location Wernadinga Station
Fishway Option Rock Ramp
Approximate cost $ 20 000.00
Rank 23
Barrier Id number 417
System Name Saxby River
Barrier Type Culvert Crossing
Barrier Height 600mm – 2m
Location Millungera Station
Fishway Option mp Fishway and Rock Ra
Baffles
Approximate cost $30 000.00
Rank 24
Barrier Id number 525
System Name Flinders River
Barrier Type Culvert Crossing
Barrier Height 2.4m - 4m
Location Punchbowl Waterhole
Fishway Option Rock Ramp & Baffles
Approximate cost $ 65 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 26
Rank 25
Barrier Id number 466
System Name Lagoon Creek
Barrier Type Earthbund causeway
Barrie Height ~600mm
Location Wernadinga Station
Fishway Option Rock Ramp Fishway
No Photo Available
Approximate cost $20 000.00
Rank 26
Barrier Id number 348
System Name Flinders River
Barrier Height 3.4m
Barrier Type Culvert & Pipe Crossing
Location Richmond
Fishway Option Rock Ramp and Baffles
Approximate cost $100 000.00
Rank 27
Barrier Id number 65
System Name Cloncurry River
Anabranch
Barrier Type Culvert crossing
Barrier Height 3.7m
Location Cloncurry
Fishway Option Removal
Approximate cost $ 25 000.00
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 27
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 28
Rank 28
Barrier Id number 225
System Name Eastern Creek
Barrier Type Culvert Crossing
Barrier Height 3m?
Location Gilliat river, 93km NW of
Julia Creek
Fishway Option Baffles and Rock Ramp
Approximate cost $ 20 000.00
29
Appendix 2. Total barriers (7992) identified in Southern Gulf Catchments before a Stage 1 criterion was applied.
30
Appendix 3 – Barriers Previously Assessed in 2005
These Barriers did not score high enough to be included in the 2010 prioritisation
System Name East Leichhardt River
Barrier Type Dam
Barrier Height ~30m
Location East Leichhardt Dam
Fishway Option Rock ramp and By-pass
channel
Approximate cost $ 200 000.00
System Name Leichardt River
Barrier Type Large Dam spillway
Barrier Height ~40m
Location Lake Moondarra Spillway
Fishway Option Downstream fish
protection and smoothing
of spillway
Approximate cost $ 1 million
System Name Leichhardt River
Barrier Type Culvert Causeway
Barrier Height 1m
Location Lake Moondarra Road
Fishway Option Concrete cone fishway
Approximate cost $ 45 000.00
Appendix 4 - Fish Species of the Southern Gulf Region
Seasonal Movements Flows
Species Flinders
River
Leichhardt
River
Nicholson
River Summer Autumn Winter Spring Low Mod High
Reason for
movement
Potamodromous Species
Archerfish (Toxotes chatareus) ® ∞ 29 36 22 ? ? ? ? R, D
Banded Grunter (Amniataba percoides) ∞ 26 46 28 ? D
Gulf Grunter (Scortum ogilbyi) 31 14 10 ? ? ? ? ? ? ? ?
Boney Bream (Nematolosa erebi) 124 70 67 D, S
Spangled perch (Leiopotherapon unicolour) ∞ 51 34 45 D, S
Rainbow Fish (Melanotaenia splendida) ∞ 53 40 64 R, D
Sleep Cod (Oxyeleotris lineolatus) ® 64 48 39 ? ? ? ?
? D
Striped sleepy cod (oxyeleotris selheimi) 13 6 33 ? ? ? ? ? ? ? ?
Mouth Almighty (Glossamia aprion) ∞ 23 45 37 D, S
Giant Glassfish (Parambassi gulliveri) 52 17 2 ? ? ? ? ? ? ? ?
Reticulated Glass Fish (Ambassis macleayi) 6 29 40
?
Square-blotched goby (Glossogobius sp. 2) ∞ 18 12 2 ? ? ? ? ? ?
Unidentified goby (Glossogobius sp) 1 4 4 ? ? ? ? ? ? ? ?
Berney’s catfish (Arius berneyi) 13 3 5 ? ? ? ? ? ?
Black Catfish (neosilurus ater) ® 4 4 3
? ?
? ?
S
Carpentaria Catfish (Arius paucus) 31 12 4 ? ? ? ? ? ? ? ?
Hyrtl’s Tandan (Neosilurus hyrtlii) ® ∞ 7 3 11
? ?
? ?
S
Toothless Catfish (Anodontiglanis dahli) 20 3 1 ? ? ? ?
Rendal’s catfish (porochilus rendahli) ® ∞ 18 -- 2 ? ? ? ? ?
S
Northwest glassfish (ambassis sp) 10 -- 8 ? ? ? ? ?
Elongate glassfish (Ambassis elongatus) -- 3 8 ? ? ? ? ?
Sooty grunter (Hephaestus fuliginosus ® -- 15 12 S
Strawman (craterocephalus stramineus) ∞ -- 7 16 ? ? ? ? ?
Northern Trout Gudgeon (Mogurnda mogumba) ∞ 1 -- --
? ?
? D
New Catfish (Porochilus sp) 1 -- -- ? ? ? ? ? ? ? ?
Fly-specked hardyhead (craterocephalus
stercusmuscarum) ∞ -- -- 26 R, D
31
Mariana’s hardyhead (craterocephalus marianae) ∞ -- -- 3 ? ? ? ? ?
?
Neil’s grunter (scortum neili) -- -- 1 ? ? ? ?
? ? ?
Diadromous Species
Barramundi (Lates calcarifer) © ® ∞ 42 18 12 C, S
Freshwater anchovy (Thryssa scratchleyi) 25 19 4 ? ? ? ? ? ? ? ?
Long tom (Strongyluar krefftii) 5 25 16 ? ? R, D
Golden Goby (Glossogobius aureus) ∞ 18 18 11 ? ? D
Forktailed Catfish (Arius graeffei) ® 27 32 -- R, D, S
Diamond Mullet (Liza alata) © ® 5 3 -- ? ? ? ? ? ?
Small-eyed Sleeper (Prionobutis microps) ∞ 5 -- -- ? ? ? ? ? ?
Speckled Goby (Redigobius bikolanus) ∞ 2 -- -- ? ? ? ? ? ? ? ?
Tadpole goby (chlamydogobius ranunculus) ∞ 7 -- -- ? ? ? ? ? ? ?
Freshwater Sole (Brachirus selheimi) ∞ 8 -- -- ? ? ? ? ? ? ? ?
Saltpan sole (brachirus salinarum) 1 -- -- ? ? ? ? ? ? ? ?
Freshwater Stingray (Himantura chaophrya) 2 -- -- ?
Crimson-tipped Flathead Gudgeon (Butis butis) ∞ 4 -- -- ? ? ? ? ? ? ? ?
Spotted Scat (Scatophagus argus) ∞ 1 -- -- ? ? ? D
Small-mouthed Catfish (Cinetodus froggatti) 3 -- -- ? ? ? ? ? ?
Salmon catfish (arius leptaspis) ® 3 -- -- R, D, S
Nurseryfish (kurtus galliveri) 1 -- -- ? ? ? ? ? ? ? D
River Gar (Zenarchopterus spp) 2 -- -- ? ? ? ? ? ? ? ?
Pony fish (leiognathus equulus) -- 3 -- ?
Silverbiddy (gerres filamentosus) -- 5 -- ? ? ? ? ? ? ? ?
Snub-nosed gar (arrhampus sclerolepis) ® -- 4 -- ? ? ? ? ? ? ? ?
Papuan River sprat (Clupeoides cf. papuensis) 15 -- -- ? ? ? ? ? ? ? ?
Total 720 578 535
© - Commercial Species ® - Recreational Species ∞ - Aquarium species - Large numbers of fish - Small numbers of fish
hern Gulf Catchments, Barrier Prioritisation Report, 2010 32
? - Limited Information S – Spawning D – Dispersal R – Re-colonisation C - Colonisation
Hogan and Vallance (2005), Renfree and Marsden (2006), Pusey, Kennard and Arthington (2004), Allen, Midgley and Allan (2002),
www.fishbase.org (2010)
Sout
Appendix 5 – Fishways completed 2008 & 2009 within the SGC
Fishway Flinders River, October 2009
Type Pre Cast Concrete Cone
Fishway
Height 1.3m
Length 11 meter slab, + 3 culverts
Cells 7 cells
Drops 67mm drops
Materials Precast concrete cones,
concrete walls, rock armouring
How long to construct 7 days
The third photo shows the cut-out section of the upstream box surrounding the culverts, this section was cut-
out (0.5m) to allow the fish that have migrated though the fish to exit into the permanent pool upstream.
33
Fishway Escott Causeway Fishway, 2008
Type Pre Cast Concrete Cone Fishway
Height 1.95m
Length 25m
Cells 17 cells
Drops 87.5 mm drops
Materials Precast concrete cones, concrete
walls
How long to construct 11 days
During construction of the fishway at Escott Causeway, the side wall was raised to ensure maximum flow through
the first cell.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 34
Fishway Gregory River Fishway, 2008
Type Rock Ramp Fishway
Height 600mm
Length 7 m
Cells 5 cells
Drops 100 mm drops
Materials Rock and Concrete
How long to construct 4 days
The Gregory river fishway during and after construction in 2008
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 35
Fishway Gin Arm Creek Fishway, 2008
Type Rock Ramp Fishway
Height 1.2m
Length 20m
Cells 13 cells
Drops 100mm drops
Materials Rock and concrete
How long to construct 4 full days
Gin Arm creek fishway during construction, the rocks were concreted in place to ensure they stayed in position
during the high flows of the wet season.
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 36
Appendix 6 – Stream Order
The Strahler stream order is the preferred method when defining stream orders. This is used to define stream
size based on the hierarchy of the streams tributaries. A first order stream is found at the headwaters of a
system; when two first-order streams come together, they form a second-order stream. When two second-
order streams come together, they form a third-order stream and so on. An increase in stream order can only
be achieved when two creeks of the same order join, if a first order stream joins a second order stream it does
not become a third order system; only when two second order streams join do they become a third order
stream. (http://www.babylon.com/definition/Strahler_Stream_Order/English)
Figure 6. The Strahler Stream Order system
Southern Gulf Catchments, Barrier Prioritisation Report, 2010 37
