Existing and potential stressors
Existing mining projects proximal to the Marsh include the FMG Cloudbreak and Christmas
Creek operations along the northern margins. To the east, the RHIO Roy Hill project is under
development with various early preparation works now completed. Additional mining proposals
south of the Marsh including FMG Nyidinghu and Brockman Mining Limited Marillana. BHP
Billiton Iron Ore and Rio Tinto have existing and proposed mines in upper catchment areas of
the Weeli Wolli Creek.
Key indicators
Based on the ecohydrological conceptualisation of the Marsh, t he following key indicators for the
preservation of the ecological values of the Marsh are proposed:
Volumes of surface and groundwater inflows to the Marsh.
Flooding frequency, duration and spatial extent.
Depth to watertable.
Samphire vegetation health.
Aquatic invertebrate assemblages (species diversity and abundance).
Waterbird species diversity and abundance.
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
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Figure 4-15: Ecohydrological conceptualisation of the Fortescue Marsh
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
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4.3
Ecological receptor - Freshwater Claypans of the Fortescue
Valley PEC (EHU 9)
This section of the report addresses the freshwater claypans of the Fortescue Valley PEC, including
restating some information presented in earlier sections. Ecological information on the Freshwater
Claypans is included in Sections 4.3.1 to 4.3.3, with hydrological and ecohydrological aspects presented
in later sections.
4.3.1
Overview
The Freshwater Claypans of the Fortescue Valley is recognised as a Priority 1 Ecological Community
(PEC) by the Department of Parks and Wildlife (DPaW) (DPaW, 2013). There are five occurrences of
this PEC in the Fortescue Valley west of the Goodiadarrie Hills, with three in the study area summarised
as follows (Map 4-02):
East Claypan - located approximately 2 km west of the BHP Billiton Iron Ore railway line;
Central Claypan - located 13 km west of the BHP Billiton Iron Ore railway line; and
West Claypan - located approximately 4 km west of the Great Northern Highway.
All of these claypans are relatively small in size and are situated south of the BHP Billiton Iron Ore Roy
Hill tenements (Map 4-02).
4.3.2
Previous work
There is little published information on the hydrology and ecology of the claypans constituting the
freshwater claypans of the Fortescue Valley PEC. Between 2003 and 2006, Pinder et al. (2010) sampled
water quality and aquatic invertebrates in the two PEC claypans west of the study area, as a component
of the Pilbara Biological Survey (Table 4-5). A high diversity of aquatic invertebrates was observed, with
major differences in assemblages between sampling dates (for each claypan respectively less than 15%
of the total number of sampled taxa were collected on every sampling date).
Between 2004 and 2005, Halse et al. (2010) measured the depth to groundwater and sampled water
quality in a station bore 2.5 km south west of the West Claypan ( Table 4-6). The depth to groundwater
was about 4 m and groundwater salinity around 4000 µs/cm EC.
4.3.3
Ecological description
The Freshwater Claypans of the Fortescue Valley PEC are important for waterbirds, invertebrates and
some poorly collected plants (Eriachne spp, Eragrostis spp. grasslands) (DPaW, 2013). It is a unique
community characterised by having relatively few Western Coolibah trees ( Eucalyptus victrix) and
expansive bare clay flats (Map 4-02).
The fringing Western Coolibah trees at the claypans, although at low density, may provide an important
structural element for waterbird roosting and nesting. The flood regime may influence tree water use,
through soil water replenishment and vegetation population dynamics (e.g. recruitment and
senescence). Flood frequency has been correlated with overstorey tree health in semi -arid wetlands in
eastern Australia (McGinness et al., 2013); and has also been linked to flowering, seed production, seed
germination and seedling recruitment dynamics (Jensen et al., 2008). The long -term persistence of such
wetland woodland communities requires sufficient recruitment/regeneration to compensate for adult tree
mortality.
The ephemeral nature of the claypans is an important factor affecting aquatic invertebrate assemblages
and use of the claypans by waterbirds. The high diversity of aquatic invertebrates may be related to high
biotic diversity in riverine refugia, which promote high floodplain diversity following floods (Pinder et al.,
2010). High turbidity may also be an important factor affecting the aquatic invertebrate species
assemblages. Turbidity can limit macrophyte growth and affect algal production through light limitation,
resulting in benthic primary productivity being largely restricted to the edge of the waterbody (Bunn et
al., 2003; Fellows et al., 2007). Turbidity may assist some invertebrate species to more easily evade
predation by waterbirds (Pinder et al., 2010).
The claypans and their surrounding catchments have been subjected to an extended period of pastoral
land use, which is likely to have influenced catchment characteristics and vegetation communities.
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
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Table 4-5: Data collected by Pinder et al. (2010) from freshwater claypans of the Fortescue Valley PEC located west of the study area
DPaW Site Code and Location
Units
PSW004
(652098E; 7549388N)
PSW005
(643987E; 7553451N)
Sampling Date
24/05/2004
18/08/2003
30/08/2006
24/05/2004
18/08/2003
30/08/2006
Altitude
mASL
404
404
404
406
406
406
Turbidity
NTU
340
0.7
7
400
490
2.1
Total dissolved solids (TDS)
mg.L
-1
120
190
75
88
140
87
Maximum depth of
invertebrate sample (Depth)
cm
62
35
60
104
70
150
Biomass of submerged
macrophytes (SubMB)
g.m
2
0
87.1
4.5
0
0.8
17.4
% Cover of submerged
macrophytes (SMC)
%
0
80
20
0
1
90
% Cover of emergent
macrophytes (EMC)
%
0.5
0
0
2
0
0
pH
pH
8.1
9.33
9.21
7.72
8.09
9.13
Total filterable nitrogen (TFN)
mg.L
-1
0.84
1
0.43
0.39
1.7
0.57
Total filterable phosphorus
(TFP)
mg.L
-1
0.03
0.01
0.02
0.02
0.21
0.02
Total chlorophyll (Chl)
mg.L
-1
0.0045
0.1495
0.002
0.0065
0.028
0.002
Water temperature (Temp)
ºC
24.7
25.6
23.9
28
22.5
24.4
Colour
TCU
37
13
15
37
17
11
Alkalinity
mg.L
-1
87
110
50
62
115
55
Hardness
mg.L
-1
23
25
20
22
359
19
Silica
mg.L
-1
11
15
3.1
7.8
11
7.9
Number of aquatic
invertebrate taxa (diversity)
98
91
81
106
91
112
Ecohydrological Conceptualisation of the Fortescue Marsh Region
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September 2015
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Table 4-6 Data collected by Halse et al. (2014) from a station bore located 2.5 km southwest of the
West Claypan
Bore ID
Units
PSS284 Mulga1
(675434E; 7536782N; Altitude 411mASL)
Sampling Date
23/06/2004
15/08/2005
Depth to water
m
3.8
4.25
Depth to bottom
m
5
5.85
Turbidity
NTU
22
0.7
Colour
TCU
2.5
2.5
TDS
mg/L
1.9
2.8
Alkalinity
mg/L
303
295
Hardness
mg/L
540
630
SiO
2
mg/L
71
94
Na
mg/L
614
692
Ca
mg/L
76.8
89.4
Mg
mg/L
83.8
99.8
K
mg/L
39
42.1
Mn
mg/L
0.0025
0.0005
Cl
mg/L
750
873
HCO
3
mg/L
369
360
CO
3
mg/L
1
1
NO
3
mg/L
5.8
9.1
SO
4
mg/L
485
577
Fe
mg/L
0.0025
0.0025
Sr
mg/L
0.55
0.67
EC
µS/cm
3757
4415
Field pH
6.81
6.79
TN
mg/L
6300
13000
TP
mg/L
30
5
Temp
°C
24.9
27.27
DO
%
41.1
61.9
DO
mg/L
3.1
4.9
Redox
mV
406
504
Ecohydrological Conceptualisation of the Fortescue Marsh Region
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September 2015
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4.3.4
Surface water
The three freshwater claypans (East, Central and West) are located within the BHP Billiton Iron Ore Roy
Hill West catchment (Map 4-02). This catchment occupies 725 km
2
of the Goodiadarrie Swamp
catchment, which has a total area 4,138 km
2
(Map 3-01). Each claypan is associated with a discrete
catchment area.
The catchment rainfall-runoff response and distribution of EHUs within the BHP Billiton Iron Ore Roy Hill
West catchment are considered to be similar to those of the catchments located on the northern fringes
of the Marsh. There is an even distribution of upland areas (EHU 1) and alluvial plains (EHU 6) in the
catchment (Map 4-01, Map 4.02, and Figure 4-16).
Runoff from the eastern and central Claypan catchments flow directly into the East and Central claypans
respectively; while the Western Claypan is located within a small localised catchment. Assessment of
the 5m DEM levels suggests that runoff from the upstream surface water sub -catchments of the BHP
Billiton Iron Ore Roy Hill West catchment will flow directly into the Fortescue River and do not contribute
any surface water inflow to this claypan.
Based on similarities of catchment characteristics and EHU distributions in the Newman and Claypan
catchments, the Newman catchment rainfall-runoff relationships, as discussed in Section 3.1.3, and
adjusted for shorter flow distances and differences in alluvial plain areas (Section 4.2.6) , have been
applied to the claypan catchments to simulate runoff from these catchments. Similar to the Fortescue
Marsh catchments, flooding is generally associated with cyclonic rainfall and runoff in the summer
months. As shown in Figure 4-16, runoff into the claypans is estimated to be about 3% of annual rainfall,
with significant catchment losses (infiltration, evaporation and ev apotranspiration). The assumed runoff
coefficient of around 3% corresponds to the median annual runoff for Fortescue River at Newman (i.e.
lower than the average annual runoff coefficient of 5.3%).
Figure 4-16: Conceptual water balance for the East and Central Claypans
Rainfall
CP Central
(186km
2
)
Claypan Central Catchment
68 GL/yr
Losses
71 GL/yr
2 GL/yr
100% contribution to CP Central
Runoff
Rainfall
CP East
(247km
2
)
Claypan East Catchment
91 GL/yr
Losses
94 GL/yr
3 GL/yr
100% contribution to CP East
Runoff
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
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4.3.5
Groundwater
The claypans are underlain by shallow alluvium and Tertiary Detritals, in a sequence presumed similar
to the Fortescue Valley. The depth to watertable beneath the claypans is unknown, but considered likely
to be in the range of two to four metres below ground level. The level of connectivity of the groundwater
system with the surface environment is unknown.
The position of the watertable is maintained by the balance of groundwater inflow from the Chichester
Range and evapotranspiration. Monitoring instrumentation needs to be installed to provide an
understanding of the role groundwater has, if any, in the hydrological regime of the claypans.
4.3.6
Ecohydrological conceptualisation
The key features of the ecohydrological conceptualisation of the Freshwater Claypans of the Fortescue
Valley PEC are depicted in Figure 4-17 and summarised as follows:
Surface and groundwater systems
Surface water runoff from the surrounding catchments is attenuated in the internally draining
low-relief landscape of the claypans. The estimated flooding frequency may be similar to the
Fortescue Marsh and could range between 1 in 5 years to 1 in 27 years based on the
hydrological analysis for the Marsh (Section 4.2). No information is available on flood
levels/regimes that would be required to support the claypan ecosystems.
Soil moisture in the shallow sediments of the claypans is replenished by a combination of rainfall
and surface inflows.
The ephemeral waterbodies of the claypans rapidly evaporate post flooding.
Large floods exceed the storage volume of the claypans, and via flushing prevent significant
accumulation of salts (in contrast with the Fortescue Marsh environment).
Groundwater levels may range between 2 and 4 m bgl.
Little is known of the hydrostratigraphy beneath the claypan surfaces. The claypans are
assumed to be underlain by low permeability sediments, which may constitute a barrier to
groundwater recharge and discharge. Further investigations are required to confirm this.
Ecosystem components
The expansive bare clay flats are fringed with Western Coolibah and tussock grassland
vegetation communities. The Western Coolibah trees may rely on stored soil moisture
replenished by flooding to meet their water requirements.
The claypans support diverse aquatic invertebrate assemblages during flood events. Waterbody
ephemerality, turbidity and connectivity with the broader Fortescue River floodplain may be key
factors affecting the species composition. These factors will vary interannually and between
seasons.
The claypans provide foraging habitat for waterbirds, and ma y also provide breeding habitat.
Existing and potential stressors
There are currently no mining activities in the catchments of the West , Central and East Claypans
respectively.
Key Indicators
Based on the ecohydrological conceptualisation of the Freshwater Claypans of the Fortescue Valley
PEC, the following key indicators for the preservation of the ecological values of the PEC are propos ed:
1. Flooding frequency.
2. Depth to groundwater (unless shown to be disconnected from the surface environment).
3. Tree health (Western Coolibahs).
4. Aquatic invertebrate assemblages (species diversity and abundance).
5. Waterbird species diversity and abundance.
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Page 114
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Figure 4-17: Ecohydrological conceptualisation of the Claypans
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Page 115
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5
Stressors
5.1
Marillana
The BHP Billiton Iron Ore Marillana Iron Ore Project is approximately 100 km northwest of Newman and
16 km northeast of BHP Billiton Iron Ore
’s mining
area at Yandi (Map 5-01), within the Upper Fortescue
River Catchment along the northern edge of the Hamersley Range and southern side of the Fortescue
River Valley. The project is approximately 9 km to the south of the closest part of the Fortescue Marsh.
The proposed project comprises fourteen open-cut pits (MA-A to MA-N), eight proposed OSAs (MA-1 to
MA-8) and three proposed infrastructure areas (MI-1 to MI-3). The proposed study area plan also
includes a conceptual railroad alignment (Map 5-01). The proposed footprint covers an area of 31 km
2
out of the total mining tenement M 270SA area of 115 km
2
.
BHP Billiton Iron Ore have undertaken preliminary hydrogeological field investigations (RPS, 2012)
enabling the development of a conceptual hydrogeological model. This has been incorporated into a
numerical groundwater model that predicts groundwater response to dewatering scenarios related to a
proposed mining plan and schedule (based on Preliminary_Mine_Sequence_hydrology.xlsx an d 054
alignments.dxf).
No detailed surface water investigations have been undertaken to evaluate the potential impacts and
influence of episodic flow events in the Weeli Wolli and Koodiaderi Creeks, as they discharge into the
Fortescue River Valley and towards Fortescue Marsh.
Table 5-1 provides an overview of the Marillana orebody.
5.1.1
Conceptualisation
5.1.1.1 Surface water
The Weeli Wolli Creek is the main surface water feature that episodically flows through and adjacent to
the south east corner of the tenement. The main creek channel flows in a north to north westerly
direction terminating in the Fortescue Marsh.
At a regional scale, the Fortescue Marsh located to the north is the most significant surface water
feature being an evaporative sink and regional termini for surface water catchments. There is no direct
surface water flow from the Marillana deposit that reaches the Marsh.
5.1.1.2 Groundwater
The Marillana iron ore deposits consist of a combination of bedrock mineralisation within the Brockman
Iron Formation members and localised overlying Tertiary detrital, scree, pisolite and CID deposits that
occur along the northern flank of the Hamersley Range. An interpretive geological cross-section is
presented in Figure 5-1.
The main bedrock aquifers are the mineralised orebodies within the Brockman Iron Formation (Dales
Gorge Member, Whaleback Shale and Joffre Member), that have undergone preferential leaching
resulting in enhanced secondary permeability within the ore zones and the associated partially
mineralised halo zone. The unmineralised BIF and underlying shale units (Mt McRae Shale and Mount
Sylvia Formation) have generally low permeability which restricts vertical and in some locations
horizontal hydraulic connection.
To the north and outside the Marillana tenements, the Poonda Fault is concealed by the Tertiary
sediments. This fault may contribute to hydraulic connection between orebody aquifers and the
potentially highly weathered and cavernous dolomite of the Wittenoom Formation.
Aquifers within the Tertiary sedimentary sequence include localised, ephemerally saturated colluvium
and detrital deposits generally marginal to the northern edge of the Hamersley Range (may be perched
aquifers). Aquifers exist within the Weeli Wolli Creek alluvium, pisolites, gravels and CID deposits have
highly variable extents and continuities. A broad scale calcrete aquifer, considered to be the Oakover
Formation, is present within the Tertiary sediment sequence at or below the regional watertable
extending from the south and outcropping near the edge of the Fortescue Marsh. These aquifers are
expected to become increasingly confined with depth.
Ecohydrological Conceptualisation of the Fortescue Marsh Region
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Groundwater flow is generally to the north towards the Fortescue Marsh, with water levels broadly
mimicking topography. Depth to water potentially ranges from more than 150 m bgl at the top of
Hamersley Range to about 20 m bgl in proximity to Weeli Wolli Creek.
The orebodies occurring at higher elevations in the Hamersley Range are likely to have limited or no
hydrological connectivity with the detritals in the Fortescue Valley. Orebodies at lower elevations are
likely to be at least partly connected with detritals in the Fortescue Valley.
Faults and dolerite dykes are known to propagate through the tenement and may act as conduits or
barriers to groundwater flow. The Wittenoom Formation containing upper horizons of enhanced
permeability may, in places, be in direct connection with orebody aquifers, notably where associated
with the Poonda Fault.
Recharge contribution to the shallow aquifer from the Weeli Wolli Creek is expected to be small, given
that median flows in the Weelli Wolli Creek within the Fortescue Valley are relatively small (2 to 4 GL/yr)
and the depth to watertable is greater than 30 m bgl. High flows that occur infrequently have a greater
potential to provide recharge to the underlying shallow aquifer.
Recharge from incidental rainfall, localised streamflow and sheetflow may occur along the foothills of the
range into the detrital units (RPS, 2012).
Groundwater quality within the orebodies is generally fresh to brackish with salinity increasing slightly
with depth. A significant regional saline-hydersaline groundwater body is known to exist to the north of
the Marillana Project associated with the Fortescue Marsh, however its on impact on dewatering
activities at Marillana is considered to be limited.
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