Western Australian Marine Science Blueprint Marine...AUSTRALIAN VENTURE CONSULTANTS PTY LTD 1 Western Australian Marine Science Blueprint Online Appendix 2: The Western Australian

AUSTRALIAN VENTURE CONSULTANTS PTY LTD

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Western Australian Marine Science

Blueprint

Online Appendix 2: The Western Australian Marine

Environment

January 2015


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CONTENTS

1. Physical Oceanography ................................................................................................................... 4

1.1. Physical Oceanography of the Northern Region ................................................................. 4

1.2. Physical Oceanography of the Southern Region ............................................................... 10

2. Marine Ecosystems ........................................................................................................................... 14

3. River Catchments ............................................................................................................................. 16

3.1. Kimberley River Catchments .................................................................................................. 17

3.2. Pilbara Region ............................................................................................................................ 17

3.3. Gascoyne-Murchison ............................................................................................................... 17

3.4. Midwest Region ......................................................................................................................... 17

3.5. Swan-Avon ................................................................................................................................. 18

3.6. Peel – Harvey ............................................................................................................................. 18

3.7. South West Region .................................................................................................................... 19

3.8. Great Southern Region ............................................................................................................ 19

4. Key Western Australian Rivers ......................................................................................................... 20


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Disclosure and Disclaimer

This report has been prepared by Australian Venture Consultants Pty Ltd (ACN: 101 195 699) (‘AVC’). AVC has

been commissioned to prepare this report by the Western Australian Marine Science Institution, and has received

a fee from the Western Australian Marine Science Institution for its preparation.

While the information contained in this report has been prepared by AVC with all reasonable care from sources

that AVC believes to be reliable, no responsibility or liability is accepted by AVC for any errors, omissions or

misstatements however caused. Any opinions or recommendations reflect the judgment and assumptions of AVC

as at the date of the document and may change without notice. AVC, its officers, agents and employees exclude

all liability whatsoever, in negligence or otherwise, for any loss or damage relating to this document to the full extent

permitted by law. Any opinion contained in this report is unsolicited general information only. AVC is not aware that

any recipient intends to rely on this report or of the manner in which a recipient intends to use it. In preparing this

information it is not possible to take into consideration the information or opinion needs of any individual recipient.

Recipients should conduct their own research into the issues discussed in this report before acting on any

recommendation.


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The intended audience of the Blueprint is diverse and will demonstrate varying degrees of

familiarity with the key physical, chemical and biological features of the Western Australian

marine environment. The purpose of this Appendix is to provide a high level overview of these

features for the less informed reader.

1. Physical Oceanography Physical oceanography describes the physical aspects of the marine environment such as

waves, currents and water temperature. An understanding of physical oceanography is

critical. It determines the physical conditions and forces that marine infrastructure must

withstand and operate within, as well as setting the conditions in which marine ecosystems

exist and connect with each other.

While the physical Western Australian marine environment is interconnected along the coast

and indeed to the wider regional and global ocean environment, for practical reasons this

Appendix will describe the key physical ocean features of the Western Australian marine

environment according to the northern and southern regions.

1.1. Physical Oceanography of the Northern Region

North West Shelf

The north western margin of Western Australia is formed by a continental shelf known as the

North West Shelf. This is a wide, 2,500 kilometre long ramp comprised mostly of carbonate

sediments that starts from a narrow base on the North West Cape, substantially widening in a

northward direction. It is one of the largest structures of its kind existing in the modern world. In

fact, the large area of continental shelf and continental slope across the northwest is a key

feature that differentiates the northwest from other marine regions in Australia.

The North West Shelf hosts immense biodiversity as well as significant hydrocarbon resources in

the Carnarvon, Browse and Bonaparte Basins (see Appendix Error! Reference source not

found.)

Major Currents

Large scale regional ocean currents play a key role in ocean circulation patterns on and

adjacent to the North West Shelf. Figure 11 below illustrates the main currents that effect ocean

circulation in the northern region.

1 Adapted from the Integrated Marine Observing System

http://imos.org.au/httpimosorgauwasci1html.html (accessed 5th September 2014)

http://imos.org.au/httpimosorgauwasci1html.html


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FIGURE 1 – MAJOR OCEAN CURRENTS OF THE NORTHWEST

The following subsections describe the main current affect ocean circulation in the northwest.

Indonesian Through Flow

The Indonesian Through Flow (ITF), or the Indo-Pacific Through Flow as it is also known, delivers

a flow of warm, low salinity, oligotrophic tropical water from the western Pacific Ocean to the

North West Shelf. The flow is driven by a gradient difference between the western Pacific

Ocean and the Indian Ocean and enters the Indian Ocean through passages between the

islands of Eastern Indonesia2.

Once in the Indian Ocean, the ITF flows in two directions, both of which impact on the North

West Shelf. South of Java, ITF surface waters join the South Java Current to form the westward

flowing South Equatorial Current, with a portion of this re-curving and flowing by circuitous

routes southward, delivering mixed Pacific Ocean and central Indian Ocean water to the

western end of the North West Shelf3.

The ITF passes through the East Indies Triangle which hosts an immensely species rich benthic

shelf and reef habitats serving as an important mechanism for transporting planktotrophic

marine species from an important centre of marine biodiversity to the North West Shelf4.

During El Nino, the thermocline rises, sea level differentials drop, sea surface temperatures fall

and the strength of the ITF weakens. Conversely, during La Nina, higher sea level differentials,

warmer sea surface temperatures and deeper thermoclines result in a stronger ITF5.

2 Wilson, B. (2013) The Biogeography of the Australian North West Shelf: Environmental

Change and Life Response, Elsevier, Massachusetts 3 Domingues, C., Maltrud, M., Wijffels, S., Church, J., Tomczak, M. (2007)’Simulated lagrangian

pathways between the Leeuwin Current System and the upper ocean circulation of the

southeast Indian Ocean, Deepsea Research, Vol.2(54), pp.797-817 4 Wilson, B. (2013) The Biogeography of the Australian North West Shelf: Environmental

Change and Life Response, Elsevier, Massachusetts 5 Department of Environment, Water, Heritage and the Arts (2008), The Northwest Marine

Bioregional Plan: Bioregional Profile, Australian Government, Canberra


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Holloway Current

Driven by a steric height gradient and augmented by easterly winds during the autumn-winter

monsoon season, the Holloway Current flows along the North West Shelf margin6. It is a narrow

surface current that flows most strongly and persistently along the shelf break during the

southeast trade wind season from March to July. In response to the reversal of the regional

winds during the spring and summer months, the Holloway Current weakens and frequently

reverses its direction of flow7.

Eastern Gyral Current

The Eastern Gyral Current is an anticyclonic recirculation that flows eastward near latitude 15o

South. In the upper ocean, a strong salinity front exists between fresh water from the ITF in the

South Equatorial Current (see below) and salty subtropical waters. In that region, salinity

overwhelms the temperature contribution to density gradients generating eastward

geostrophic shear and establishing the Eastern Gyral Current8.

During the Southeast Monsoon (April to September), the pressure gradient between the Pacific

and Indian Oceans is more intense, strengthening the South Equatorial Current.

The Eastern Gyral Current is an upstream source for the Leeuwin Current (see subsequent

section on the Key Oceanographic Features of the Southern Region).

South Java Current

The South Java Current is a semi-annually reversing boundary current. It is controlled by the

monsoon over the Indian Ocean and Indonesian archipelago, flowing generally in a south-

east direction along the Java coast during December to April, a northwest direction during

June to October, and goes through a period of transition during two weeks in May and

November9.

South Equatorial Current

The South Equatorial Current flows westward along the northern flank of the Eastern Gyral

Current. During the Southeast Monsoon (April to September), the pressure gradient between

the Pacific and Indian Oceans is more intense, strengthening the South Equatorial Current.

Eddy Currents

Flooding of water from the ITF onto the continental shelf is believed to be assisted by local

eddy currents which facilitate cross-shelf transport. Along with internal tides, these eddy

6 Kronberg, M. (2004), Ocean Circulation over the North West Shelf of Western Australia: Does

it Impact on the Leeuwin Current (PhD Thesis), University of Copenhagen, Denmark 7 Wilson, B. (2013) The Biogeography of the Australian North West Shelf: Environmental

Change and Life Response, Elsevier, Massachusetts 8 Menezes, V., Phillips, H., Schiller, A., Domingues, C. and Bindoff, N. (2013), ‘Salinity

dominance of the Indian Ocean Eastern Gyral Current’, Geophysical Research Letters, Vol.

40 (21), pp 5716-5721 9 Sprintall, J., Chong, J., Syamsudin, F., Morawitz, W., Hautala, S., Bray, N. and Wijffels, S.

(1999), ‘Dynamics of the South Java Current in the Indo-Australian Basin’, Geophysical

Research Letters, Vol. 26(16), pp. 2493-2496


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currents modify the characteristics of the water on the shelf through facilitating vertical

mixing10.

Coastal Currents

Coastal currents on the North West Shelf are typically along-shore, wind driven flows that

reverse direction on a seasonal basis according to the winter south easterly trade winds and

the summer monsoon11. Regardless, these general trends are overridden by the impact of

astronomic semidiurnal tides.

Other Currents

Other seasonal surface currents in the northern region include the Ningaloo current, Shark Bay

Outflow and the Capes Current.

Tides

Tides in the northwest are among the largest tides along a coastline adjoining an open ocean

in the world. They increase in amplitude from south to north, corresponding to the increasing

width of the northwest shelf12. Spring tide amplitudes range from 4 metres on the Pilbara coast

to over 11 metres on the Kimberley coast.

Solitons

Solitons are waves that travel within the interior of the ocean. They occur as the result of

stratified density structure of two fluids, with a very sharp density change occurring along the

interface and with the properties that the smaller the density contrast, the lower the wave

frequency and slower the propagation speed.

Solitons are generally ubiquitous where strong tides and stratification occur in the

neighbourhood of irregular topography. The combination of tides, temperature stratification

and the sloping seabed on the North West Shelf create perfect conditions for soliton

propagation.

Ocean Circulation and Mixing

By virtue of the turbulence caused by the interaction of the main and eddy currents and

solitons discussed above, there is an area of intense boundary mixing along the shelf margin.

When the Holloway Current is flowing most strongly during autumn and winter, oligotrophic ITF

oceanic water and shelf coastal water mix by means of eddies associated with the large-

scale, regional, oceanic circulation and possibly cyclonic storms. When the Holloway Current

weakens or reverses, the water column along the North West Shelf may stratify, facilitating the

ability of complex tidal currents to dominate water circulation patterns of the outer and middle

shelf.

10 Department of Environment, Water, Heritage and the Arts (2008), The Northwest Marine

Bioregional Plan: Bioregional Profile, Australian Government, Canberra 11 Condie, S., Andrewartha, J. (2008) ‘Circulation and connectivity on the Australian North

West Shelf’, Continental Shelf Research, (28), pp. 1724-1739 12 Holloway, P. (1983) ‘Tides on the Australian Northwest Shelf’, Australian Journal of Marine

and Freshwater Research, (34), pp.213-220


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Internal waves generated by barotropic tides along the shelf break may cause bottom

turbulence, whereby colder, nutrient rich water from the deep sea to raise higher in the water

column.

On the shelf slope, the surface layer of warm, oligotrophic ITF water overlays the cooler, more

nutrient-rich waters of the deep sea. The boundary between these two water bodies is marked

by a sharp thermocline that is a barrier to convective mixing of nutrients.

Mobile Seabed

Much of the seabed off the Western Australian coastline is mobile. Over timescales of

decades, seafloor sediments are likely transported southward along the continental shelf, by

cyclone induced (see below) currents at the seabed. Physical indicators of this regional

pathway include submarine dune systems and sediment tails behind islands and reefs. The

regional bed sediment transport pathway is an important indication of the dynamic nature

of the shelf, the connectivity between various shelf ecosystems, and forms part of the long-

term natural resilience of these systems13.

Thermal Structure

In the Kimberley surface sea temperatures of coastal waters and offshore near the shelf margin

average approximately 28.5 oC. There is some noted seasonal variation. For example, near the

Ichthys gas field sea surface temperatures are consistently approximately 30 oC in March and

26 to 27 oC in July. Bottom temperatures of as low as 12 oC have been measured in the Browse

Basin14.

Surface sea temperatures of coastal waters in the Pilbara average approximately 27.3 oC in

coastal waters and 28.6 oC offshore near the shelf margin. There is seasonal variation in the sea

surface temperatures as well, with seasonal variation at the Pilbara mid-shelf location ranging

from 35oC in March-April to 24oC in July. Bottom temperatures as low as 20 oC have been

measured15.

Offshore waters are stratified with a distinct thermocline at depths of approximately 30 to 50

metres in summer and 70 to 120 metres in winter. The shelf break is an area of intense boundary

mixing, where mixed water intrudes onto the continental shelf16.

Salinity

Salinity on the North West Shelf is largely influenced by the ITF. Salinity along the margins of the

shelf is in the 34 to 35 ppt range. The salinity of coastal waters is generally higher in the range

of 34.8 to 35.2, but with some seasonal and spatial variability. For example, temporary dilution

occurs on the tropical monsoonal Kimberley coast and close to major river discharge points

on the Pilbara coast.17

13 Buchan, S. (2014), RPS Metocean 14 INPEX, Biological and Ecological Studies of the Bonaparte Archipelago and Browse Basin

Marine Sediment and Water Quality, INPEX, Perth 15 INPEX, Biological and Ecological Studies of the Bonaparte Archipelago and Browse Basin

Marine Sediment and Water Quality, INPEX, Perth 16 Brewer, D., Lyne, V., Skewes, T., Rothslisberg, P. (2007), Trophic Systems of the North West

Marine Region, Department of Environment and Water Resources 17 Wilson, B. (2013), The Biogeography of the Australian North West Shelf: Environmental

Change and Life’s Response, Elsevier, Massachusetts


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Nutrients

Nutrient concentrations in the surface waters of the North West Shelf are generally low,

especially near the shelf margin. Nutrient concentrations below the thermocline are

significantly higher and seasonal nutrient enrichment of benthic habitats on the outer and

middle shelf may be expected as a result of upwelling.

Nutrient concentrations in near-shore coastal waters of the North West Shelf are relatively high,

where they are derived from benthic primary production in the photic zone of the inner shelf

and inputs from the adjacent terrestrial environment, primarily through river discharge.

Turbidity

Turbidity is usually either measured as Light Attenuation Coefficient or concentration of Total

Suspended Solids (TSS). Offshore waters of the shelf margin are generally clear with low

concentrations of suspended particles and high light penetrations. Whereas coastal waters

receive fine terrestrial sediment and with increased nutrient concentrations, tend to be more

turbid18.

In the shallows of the inner-shelf turbidity is greatly influenced by disturbance and re-suspension

of fine sediments on the seafloor by tidal flows and waves (particularly those caused by

cyclones). Re-suspension of the seafloor sediments during periods of spring tide is a major

determinant of the high turbidity of coastal waters of both the Kimberley and the Pilbara where

macrotidal conditions prevail. The turbidity of coastal waters tends to be higher in summer

than in winter as a result of variation in seasonal wave conditions19.

Tropical Cyclones

Tropical cyclones in the northwest are frequent and often severe, with 75 percent of all severe

tropical cyclones crossing the Australian coast occurring in the Pilbara Region. The Pilbara

Region experiences an average of approximately five tropical cyclones per season, with an

average of two tropical cyclones crossing the coast, one of which is likely to be a severe

tropical cyclone.

Figure 220 below illustrates the pathway and intensity of tropical cyclones that crossed the

Australian coast between 1970 and 2009.

18 Wilson, B. (2013), The Biogeography of the Australian North West Shelf: Environmental

Change and Life’s Response, Elsevier, Massachusetts 19 Wilson, B. (2013), The Biogeography of the Australian North West Shelf: Environmental

Change and Life’s Response, Elsevier, Massachusetts 20 Haig et al (2013) IN: Pattiaratchi, C. (2013), An Overview of the Oceanography of Northern

Australia


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FIGURE 2 – PATHWAY AND INTENSITY OF TROPICAL CYCLONES CROSSING THE AUSTRALIAN COASTLINE

(1970 TO 2009)

Squalls

Squalls are high wind, wave and current events that escalate in intensity and travel very

rapidly. Driven by strong convection, they can occur in conjunction with tropical cyclones or

independently. A recent squall approximately 30 kilometres north of Onslow saw near calm

conditions escalate to a swell of two metres and wind speed of 75 kilometres per hour (40

knots) in a matter of hours.

1.2. Physical Oceanography of the Southern Region

South West Australian Shelf

The southwest region is characterised by a narrow continental shelf hosting numerous near-

shore islands and reefs. The continental slope is incised by many, well developed submarine

canyons, has mid-slope terraces, an extensive continental rise and the deepest marginal

plateau on the Australian margin, the Naturaliste Plateau21.

21 Richardson, L., Mathews, E. and Heap, A. (2005), Geomorphology and Sedimentology of

the South Western Planning Area of Australia: Review and Synthesis of Relevant Literature in

Support of Regional Marine Planning, Geoscience Australia, Australian Government,

Canberra


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South Westerly Swells

South westerly swells, originating in the Southern Ocean have significant impact on the

oceanographic processes in the southwest and contribute to a relatively high energy

environment22.

Offshore regions of the South West Australian Shelf are dominated by oceanic swells and seas

with an average significant wave height of about 3 metres and period from 5 to 20 seconds.

For most of the year, the waves arrive from the south west. However, winter storms often result

in waves from the west and north-west bringing high energy conditions for short periods of

time23. Inshore, much of the coastline is sheltered from the direct impact of swell and wave

activity by an extensive chain of reefs, which attenuate ocean waves24.

South Westerly Storms

South westerly storms, typically originating in the Southern Ocean during the winter months,

have a significant impact on oceanographic processes in the southwest, contributing to the

high energy environment25.

Major Currents

Figure 326 below illustrates the main currents that impact on the physical oceanography of

the south west.




Canberra 23 Feng, M., Weller, E. and Hill, K. (2009), ‘The Leeuwin Current’, Marine Climate Change in

Australia: Impacts and Responses, 2009 Report Card 24 Steedman, R. (1993), ‘Collection of wave data and the role of waves in nearshore

circulation’, Report Prepared for Water Authority of Western Australia 25 Richardson, L., Mathews, E. and Heap, A. (2005), Geomorphology and Sedimentology of



Canberra 26 Richardson, L., Mathews, E. and Heap, A. (2005), Geomorphology and Sedimentology of



Canberra


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FIGURE 3 – MAIN CURRENTS OF THE SOUTH WEST REGION

West Australian Current

As the West Wind Drift approaches the coast of Western Australia, it turns north to parallel the

coast as the West Australian Current. It is weak during the winter and strong during summer.

Leeuwin Current

The Leeuwin Current is a warm, pole-ward flowing ocean eastern boundary current off the

west and south coasts of Australia. It is weaker during summer when there are opposing winds

and stronger in the winter months when these winds cease. In later autumn – early winter the

Leeuwin Current accelerates and rounds Cape Leeuwin and enters the waters of South

Australia, continuing as an eastward shelf current along the southern coast of Australia. During

the summer months, sporadic wind-driven northward inshore current and coastal upwelling

events occur in limited shelf regions off the west coast, while wind-driven upwelling is more

persistent off the southern coast of Australia.27

27 Feng, M., Weller, E. and Hill, K. (2009), ‘The Leeuwin Current’, Marine Climate Change in

Australia: Impacts and Responses, 2009 Report Card


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The headwaters of the Leeuwin Current lie at the western end of the North West Shelf, fed by

both tropical Pacific and central Indian Ocean water via the ITF, Holloway, South Equatorial

and Eastern Gyral Currents28

El Nino Southern Oscillation in the tropical Pacific Ocean has induced strong responses in the

Leeuwin Current off the west and south coasts of Australia, due to the existence of equatorial

and coastal waveguides. During La Nina events, deep anomalies in thermocline depth are

transmitted along the west and south Australian coasts, including high sea level anomalies,

strengthened Leeuwin Current volume transport, eddy energetics and pole-ward transport of

warm waters. Conversely, the event of El Nino, results in a weaker Leeuwin Current.

The headwaters of the Leeuwin Current lie at the western end of the North West Shelf and are

fed by both tropical Pacific Ocean and central Indian Ocean waters. The source of the

Leeuwin Current is understood to be complex. Waters from the Holloway Current are believed

to be a major source of the Holloway Current, as well as indirect flows from the branches of

the South Equatorial and Eastern Gyral Currents29.

The Leeuwin Current contributes to the maintenance of generally low levels of biological

productivity in the southwest region, as well as playing a crucial role in transporting tropical

and subtropical species to areas further south than would otherwise occur30.

Eddy Currents

The Leeuwin Current is intrinsically unstable and mesoscale eddy currents are an ubiquitous

feature of the Leeuwin Current. Indeed the Leeuwin Current has the highest eddy energy

among all eastern boundary currents in the world31. They are a major driver of ocean

circulation in the south west marine environment.

West Wind Drift

The West Wind Drift is a surface current that circulates around Antarctica, flowing from east to

west. It influences the south westerly direction of ocean swells affecting the south west Western

Australian marine environment32.

Subtropical Convergence

The subtropical convergence is the zone in the Southern Ocean where two water masses meet

and sharp changes in sea surface temperature are observed. The subtropical convergence

28 D’Admo, N., Fandry, C., Buchan, S. Domingues, C. (2009) ‘Northern Sources of the Leeuwin

Current and the Holloway Current on the North West Shelf’, Journal of the Royal Society of

Western Australia, (92), pp. 53-66 29 Wilson, B. (2013), The Biogeography of the Australian North West Shelf: Environmental

Change and Life’s Response, Elsevier, Massachusetts 30 Department of Environment, Water, Heritage and the Arts (2008), The Northwest Marine

Bioregional Plan: Bioregional Profile, Australian Government, Canberra 31 Feng, M., Weller, E. and Hill, K. (2009), ‘The Leeuwin Current’, Marine Climate Change in

Australia: Impacts and Responses, 2009 Report Card 32 Richardson, L., Mathews, E. and Heap, A. (2005), Geomorphology and Sedimentology of



Canberra


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shifts latitude through time, moving northwards closer to southern Australia during glacial

periods33.

Ningaloo Current

The Ningaloo Current is a wind-driven, northward, inshore flow of cooler water from the west

coast, which in summer extends onto the western end of the North West Shelf.

2. Marine Ecosystems This section provides a brief overview of the biodiversity and ecosystems that are characteristic

of the Western Australian marine environment. It is deliberately brief in this introductory section,

as Appendix Error! Reference source not found., Sections Error! Reference source not found.

and Error! Reference source not found. provide a detailed discussion on the key habitats and

ecosystems of the northern and southern bioregions respectively.

Biodiversity is defined as the variety of life forms within a defined geographical area, including

the genetic and species diversity of plants, animals and microorganisms, as well as the variety

of habitats, ecological communities and ecological processes that exist in that geographical

area.

Ecosystems are comprised of biodiversity, habitats and nutrient cycling that support that

biodiversity. The physical ocean systems described in the previous sections shape the marine

environment in which those ecosystems exist, as well as providing connectivity between those

ecosystems.

The majority of the Western Australian coast line has a north-south orientation between the

latitudes 15o South and 25o South, with approximately 1,000 kilometres of coastline interfacing

with the Southern Ocean and a relatively small portion of the coastline interfacing with the

Timor Sea. Along this coastline exist a diverse range of physical features. These physical

features are summarised in Table 1 below.




Canberra


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Physical Feature Description/Examples

Estuaries Leschenault, Peel Harvey, Swan-Canning,

Sounds Campden, Cockburn, King George

Bays Jurien Bay, Shark Bay, Roebuck Bay, Geographe Bay, Esperance

Bay

Island and island systems Recherche Archipelago, Rottnest Island, Bonaparte Archipelago,

Buccaneer Archipelago, Dampier Archipelago, Houtman-

Abrolhos Islands, Dirk Hartog Island, Barrow Island, Kimberly Islands

Coastal and Offshore Coral

reefs

Scott Reef, Rowley Shoals, Mermaid Reef, Montgomery Reef,

Ashmore Reef, Seringapatam Reef, Glomal Shoals and Ningaloo

Reef

Temperate Reefs Network of temperate reefs on the southwest coastline that host

significant biological productivity

Seagrass Meadows Western Australia has some of the most diverse seagrasses in the

world. Meadows of perennial seagrass species cover extensive

areas of Shark Bay, Cockburn Sound, Geographe Bay and Flinders

Bay and can be found along much of the southern coast. They

are less diverse and abundant and tend to be seasonal in northern

parts of the State.

Mangroves The climatic range in which mangroves exist in Western Australia

results in a complex ensemble of mangrove species that form

important habitats for a wide range of organisms and are quite

different to mangrove ecosystems elsewhere in Australia.

Sponge Gardens The Western Australian marine environment host extensive sponge

biodiversity. For example, the estimated number of sponge

species on Ningaloo Reef is 500 to 800 (the number of sponge

species known in the world is approximately 8,500)

Continental shelf A very wide, mostly sandy continental shelf

Shelf and deep ocean features Carbonate banks, continental slopes, Exmouth Plateau, Wallaby

Saddle, Naturalist Channel, Naturalist Plateau, Albany Canyons

and the Diamantina Fracture Zone

TABLE 1 – KEY PHYSICAL FEATURES OF THE WESTERN AUSTRALIAN MARINE ENVIRONMENT

The fact that these features exist in very diverse climatic and, as discussed in 1 above,

oceanographic conditions, means that they host diverse habitats and immense biodiversity

and ecosystems. This includes a wide range of iconic and listed marine fauna and flora,

significant endemism and short range endemic species.


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This includes a number of marine mega-fauna (whale sharks, blue whales, humpback whales,

southern right whales and sperm whales), numerous species of dolphin, dugong, a variety of

shark species, Australian sea lions, New Zealand fur seal, marine turtles, sawfish and sea snakes

as well as a large number of seabird species including the soft plumed petrel, Australian lesser

noddy and the Indian yellow-nosed albatross and species of coral. It also hosts significant

marine flora biodiversity including the most diverse seagrasses in the world and a large number

of sponge species. In addition to the large number of iconic and listed species, there is a

significant amount of marine fauna and flora endemism and short range endemic species in

the Western Australian marine environment. Furthermore, by virtue of the dominance of the

Leeuwin Current along the length of the Western Australian coast, these systems are highly

interconnected.

A detailed description of the key marine ecosystems that comprise the Western Australian

marine environment is contained in Appendix 13.

3. River Catchments The marine ecosystems discussed in the previous section are also affected, to an extent, by

the volume and chemical and sediment composition of river catchments that discharge into

the marine environment through river mouths and estuaries along the Western Australian

coast.

Compared to many other coastlines around the world, Western Australia has relatively few

large rivers that discharge into the marine environment. Indeed, the volume of run-off from

Australian rivers as a whole is among the lowest in the world and unlike the rest of the world, in

Australia, there is an inverse relationship between annual variation in the volume of run-off of

a river and the size of its catchment34. Indeed there is considerable inter-annual variation in

the flow of many Western Australian rivers, particularly those in the Gascoyne-Murchison,

Pilbara and Kimberley Regions.

Nevertheless, there are approximately 50 rivers in Western Australia that are over 100 kilometres

in length that either directly, or indirectly through a river system, discharge into the Timor Sea,

Indian Ocean and Southern Ocean from the Western Australian hinterland (see Section 4).

Only a handful of these rivers are significant in terms of flow and many draw from relatively

pristine catchments. However, there are a number of river systems, particularly the Ord River,

Swan-Canning Rivers, Serpentine-Murray-Harvey Rivers and several rivers in the South West of

the State whose catchment is characterised by significant agricultural, mining and urban

development.

The following subsections describe the main rivers in each of the regions of Western Australia

as well as the main river systems.

34 Finlayson, B. and McMahon, T. (1988) ‘Australia versus the rest of the world: a comparative

analysis of streamflow characteristics’, IN: Fluvial Geomorphology of Australia’, Warner, R.

(Ed.), Academic Press, Sydney


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3.1. Kimberley River Catchments The main rivers in the Kimberley Region that discharge to the Timor Sea are the Berkeley,

Durack, Forrest, King George, King, Ord, Pentecost and Sale Rivers. The Ord is the most

significant river in this region and one of the most regulated in Western Australia, with dams at

Lake Argyle and Lake Kununurra used for both irrigation and hydroelectricity. The irrigation

network covers 150km² of farmland (with plans for significant expansion currently being

implemented) supporting the production of a wide variety of crops, including tropical fruit,

vegetables and seed crops. Efforts to grow sugar, rice and cotton have not been sustainable.

Most of the other rivers in this region are largely in pristine condition due to their remoteness.

In addition, the Charnley, Drysdale, Fitzroy, Isdell, King Edward, Lennard, Mitchell, Prince

Regent and Robinson Rivers discharge into the Indian Ocean. The Fitzroy River is in a semi-

arid/monsoonal climate and has, on average, the greatest volume of annual flow and the

largest floods in WA. It remains an unregulated river and its catchment is dominated by

pastoral leases. There have been proposals for establishing an irrigation scheme in the region

and a pipeline to transport water to the Perth metropolitan area, albeit neither have

progressed.

Mining activities in the Kimberley region have the potential to impact on water quality.

However, there are very few operations and there interaction with rivers and the ground water

system is highly regulated and intensively managed.

3.2. Pilbara Region Rivers that discharge into the Indian Ocean from the Pilbara Region include the Ashburton,

Cane, De Grey, Fortescue, Harding, Robe, Sherlock, Turner and Yule Rivers. The Pilbara Region

is characterised by a semi-arid climate and a number of its rivers are ephemeral yet prone to

flooding. There are competing pressures on water resources in the region, the most significant

been from the resources, primarily iron ore, industry. However, increasing populations in

Karratha, Onslow and Port Hedland also potentially place pressure on water resources.

3.3. Gascoyne-Murchison The Gascoyne and Murchison are significant rivers in Western Australian. Although in a semi-

arid region and only flowing for around 120 days a year, the Gascoyne River is the longest river

in Western Australia. It is joined by the 561 kilometre long Lyons River about 16km from its mouth,

and together they have a catchment area of 68,326km².

There is significant horticulture activity carried out along the banks of the river near Carnarvon

on 170 plantations covering an area of 15km². This area produces a range of crops including

tropical fruit and vegetables. Pastoral activity is also significant with over 80 stations in the

region. Mining production is limited, with activity centred on salt production north of

Carnarvon (see Appendix Error! Reference source not found., Section Error! Reference source

not found.)

3.4. Midwest Region Rivers in the Midwest region include the Chapman, Greenough, Irwin and Moore Rivers. The

coastal areas of the Mid West experience a mild, Mediterranean climate with inland areas a

more arid climate.


18

Broad-acre cropping and livestock operations are a significant land-user in the region and

within river catchments. There is also a small amount of horticulture undertaken near coastal

areas. Mining operations that could potentially impact on water quality include operations in

the iron ore, gold, copper, nickel and mineral sands sectors.

3.5. Swan-Avon The Perth Metropolitan Area and parts of the Wheatbelt region revolve around the Swan-

Canning-Avon river system. The combined Swan-Avon River is 280 kilometres long and flows

from a location near the town of Wickepin to the Indian Ocean at Fremantle. The Swan-Avon

River drains a total catchment of around 126,000km².

The lower reaches of the Swan and Canning rivers form an estuary that was mostly brackish

water before the Fremantle sand bar was removed in the late 1800s and a large flood delta

dredged. The estuary is now a permanently open and changes from fresh/brackish conditions

in winter and spring, to salty conditions during summer and autumn.

The Swan river system sits within a large urban and agricultural catchment and has relatively

shallow and slow-moving river conditions. These factors, as well as sandy soils, a climate of

diminishing rainfall and long, hot summers make the system vulnerable to a suite of

environmental issues. The most significant of these is the large amounts of nutrients that may

fuel algal blooms such as phosphorus and nitrogen flowing into the river from the agricultural

catchment.

The river is also a significant site of recreation for visitors and residents of the surrounding

metropolitan area and boating activities in particular.

3.6. Peel – Harvey The Harvey, Murray and Serpentine rivers discharge to the Peel Estuary, which is the focus of

the town of Mandurah and urban development in its surrounds.

The Harvey River discharges into the southern end of the elongated Harvey Estuary, which has

an area of about 56 km². This in turn feeds into the south west corner of the more northerly Peel

Inlet, which is roughly circular and occupies an area of about 75 km². The Serpentine River and

Murray Rivers discharge into the eastern edges of Peel Inlet.

The catchment area, approximately 11,500km², encompasses high quality coastal dune and

lake environments, the largest estuarine system in the south west, and an extensive back-plain

and foothills area. The coastal plain portion of the catchment supports many relatively small

sized farms and areas of irrigated horticulture. It also includes the rapidly growing city of

Mandurah and southern parts of the Perth metropolitan region with the associated urban, peri-

urban, and industrial land uses.

Both irrigated and non-irrigated intensive agriculture, in particular beef production, dominate

the coastal plain, and almost the entire coastal area has been cleared for agricultural, mining

or urban land use. Conserved areas and cropping dominate the broader catchment,

particularly on the Darling Plateau.

The estuary is also a significant site of recreation for visitors and residents of the surrounding

metropolitan area, including boating and fishing activities.


19

After several decades of severe algal blooms in the estuary caused by discharge of nutrients

from agricultural land and piggeries, the Dawesville Cut was constructed and opened in 1994.

Recent surveys have shown that levels of phosphorous and sulphidic sediments remain high.

3.7. South West Region The main rivers in the South West Region are the Blackwood, Collie, Donnelly and Warren Rivers.

The Leschenault Estuary catchment covers approximately 4,808km² with land use in the area

highly diversified. Runoff from the catchment enters the estuary via the Collie and Preston

rivers and the Parkfield Drain. The lower Collie catchment has been extensively cleared and

drained for agriculture. Irrigated pastures in the central and eastern area support grazing of

dairy and beef cattle, while horticulture, industrial and residential development characterise

the western area near the estuary and coastline. Land use within the Preston catchment

ranges from broad-acre agriculture (cropping and grazing), to intensive orcharding, viticulture

and horticulture. Approximately 33 per cent of the catchment is cleared, with the land east

of the Darling Scarp remaining largely forested. Works to service the requirements of the

Bunbury Port undertaken in the 1950s included closing the natural outlet to the ocean at Point

MacLeod and excavating a connection to the ocean through the dunes opposite the mouth

of the Collie River. Rivers within the catchment are subject to algal blooms and fish kills from

excess nutrients in run off. Surveys have also shown the inlet has high levels of heavy metals in

sediment.

The Vasse Wonnerup Estuary and Geographe Bay catchment occupies some 2,000 km² along

the Busselton coast. The bulk of the land in the catchment is utilised by intensive agricultural

industries, with dairy and beef grazing dominant and intensifying, along with horticulture and

viticulture. Algal blooms caused by excessive nutrients have been known to cause fish kills in

the estuary. Population growth in the Busselton, Dunsborough and Capel town sites may also

contribute to the water quality problems.

The Blackwood, Donnelly and Warren Basins are largely cleared and used for horticulture,

viticulture and grazing as well as forestry. Salinity and nutrient run are a threat for some parts

of these rivers. Algal blooms have occurred in the Hardy Inlet, being the Blackwood River

mouth at Augusta.

Swimming, canoeing and fishing are popular recreational pursuits in many of the rivers of the

South West region.

3.8. Great Southern Region Rivers of the Great Southern Region include the Deep, Frankland, Gairdner, Kalgan, Kent, Lort,

Pallinup and Phillips Rivers.

The Deep River is one of a few rivers in WA that remains in almost pristine condition. Large

sections of catchment areas of the Great Southern are State Forest or National Park, and much

of the coastal area is remote and inaccessible. The region is becoming increasingly attractive

to visitors for nature based tourism activities.

There are large areas of cleared land for agricultural use and forestry, with the most significant

agricultural use being broad-acre cropping (wheat and barley), livestock and dairy, egg and

wool production.


20

There are a number of significant estuaries in the region, including the Broke Inlet, Fitzgerald

Inlet, Gordon Inlet, Irwin Inlet, Stokes Inlet, Wilson Inlet and Walpole-Nornalup Inlet, which all in

relatively good condition.


21

4. Key Western Australian Rivers The following tables summarise the main rivers in Western Australia.


22

Kimberley Region

Berkeley River

Origin Tadarida Scarp

Mouth Joseph Bonaparte Gulf

Length 180km

Source elevation 422m

Basin area 5,149km²

Durack River

Origin Durack Range

Mouth Cambridge Gulf

Length 306km


Avg. discharge 408,400 ML/yr


Forrest River

Origin near Pseudomys Hill


Length 141km


King George River

Origin W of the Ashton Range

Mouth Koolama Bay

Length 125km



23

King River

Origin Durack Range


Length 132km


Ord River

Origin Kimberley Plateau


Length 588km


Avg. discharge 3,870,000 ML/yr


Pentecost River

Origin below the Durack Range


Length 275km



Sale River

Origin Spong Pyramid

Mouth Doubtful Bay

Length 109km




24

Charnley River

Origin Caroline Ranges

Mouth Walcott Inlet

Length 148km


Drysdale River

Origin Caroline Ranges

Mouth Napier Broome Bay

Length 432km


Avg. discharge 1,080,553 ML/year


Fitzroy River

Origin King Leopold Ranges

Mouth King Sound

Length 642km


Avg. discharge 2,675,000 ML/yr


Isdell River

Origin Packhorse Range

Mouth Walcott Inlet

Length 206km




25

King Edward River

Origin Poonjurra Hill

Mouth Napier Broome Bay

Length 221km



Lennard River

Origin King Leopold Ranges

Mouth King Sound via

Meda and May Rivers

Length 240km



Mitchell River

Origin NE of Sharp Hill

Mouth Walmsley Bay

Length 117km



Prince Regent River

Origin Caroline Range

Mouth St George Basin,

Hanover Bay

Length 104km




26

Robinson River

Origin below the Van

Emmerick Range

Mouth Stokes Bay

Length 107km



Pilbara

Ashburton River

Origin 100km S of Newman

Mouth 45 km ESE of Onslow

Length 680km



Cane River

Origin Hamersley Range

Mouth Yardie Landing,

35km NE of Onslow

Length 168km





27

De Grey River

Origin confluence of

Nullagine and

Oakover Rivers

Mouth Breaker Inlet

Length 193km




Fortescue River

Origin Ophthalmia Range

Mouth 40km SW of

Dampier

Length 760km




Harding River

Origin Chichester Range

Mouth Butcher Inlet

Length 150km



28

Robe River

Origin Hamersley Range

Mouth near Robe Point

Length 276km



Sherlock River

Origin Abydos Plain

Mouth estuary at Sherlock

Bay

Length 393km




Turner River

Origin Pullcunah Hill

Mouth 40km S of Port

Hedland

Length 236km




29

Yule River

Origin Chichester Range

Mouth 60km S of Port

Hedland

Length 190km




Gascoyne Murchison

Gascoyne River

Origin Three Rivers Station near Collier Range

Mouth Shark Bay

Length 865km



Murchison River

Origin Robinson Ranges

Mouth Kalbarri

Length 820km





30

Midwest

Chapman River

Origin 150km NE of

Geraldton

Mouth Bluff Point

Length 105km



Greenough River

Origin Jingemarra Station

Mouth Cape Burney

Length 340km



Irwin River

Origin near Pindar

Mouth Arurine Bay

Length 140km




31

Moore River

Origin Perenjori

Mouth Guilderton

Length 193km




Swan-Avon

Avon River

Origin E of Pingelly

Mouth confluence with the Swan River

Length 280km




Canning River

Origin North Bannister

Mouth confluence with the Swan River

Length 107km

Avg. discharge pre-regulation (dam) estimates at

57,620 ML/yr, post 1,165 ML/yr


32

Swan River

Origin near Walyunga National Park

Mouth Fremantle

Length 60km


Peel-Harvey

Harvey River

Origin near Mt Keats

Mouth Harvey Estuary

Length 90km.



Murray River

Origin Mt Keats

Mouth Peel Inlet

Length 134km


Serpentine River

Origin Bowerling Hill

Mouth Peel Inlet

Length 111km



33

South West

Blackwood River

Origin junction of Arthur

and Balgarup Rivers

Mouth Hardy Inlet, Augusta

Length 300km




Collie River

Origin Darling Range

Mouth Leschenault Estuary

Length 154km



Donnelly River

Origin between Bridgetown

and Manjimup

Mouth 50km SE of Augusta

Length ]151km




34

Warren River

Origin Tone State Forest

Mouth near Coolyarbup

Length 137km


Avg. discharge 291,000ML/yr

Basin area 4,350 km²

Great Southern

Deep River

Origin Lake Muir

Mouth Nornalup Inlet

Length 120km



Basin area 100 km²

Frankland River

Origin Below Trollup Hill

Mouth Nornalup Inlet

Length 162km



Basin area 5722 km²


35

Gairdner River

Origin Needilup-Jacup

Mouth Gordon Inlet

Length 130km




Kalgan River

Origin Stirling Ranges

Mouth Oyster Harbour,

King George Sound

Length 140km



Basin area 2,562 km²

Kent River

Origin Tenterden

Mouth Irwin Inlet, Foul Bay

Length 140km



36

Lort River

Origin Goldfields-

Esperance; Peak

Charles National

Park

Mouth Stokes Inlet

Length 130km




Pallinup River

Origin south of Katanning

Mouth Beaufort Inlet

Length 250km




Phillips River

Origin Goldfields-

Esperance; Mt

Madden

Mouth Culham Inlet

Length 120km




http://en.wikipedia.org/wiki/River_source

http://en.wikipedia.org/wiki/Culham_Inlet

http://en.wikipedia.org/wiki/River_source

Documents

Western Australian Marine Science Blueprint Marine...AUSTRALIAN VENTURE CONSULTANTS PTY LTD 1 Western Australian Marine Science Blueprint Online Appendix 2: The Western Australian