Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Page 1
Our ref: FM-EcoConcept_v8.docx
1
Introduction
1.1
Study description
BHP Billiton Iron Ore Pty Ltd (BHP Billiton Iron Ore) commissioned MWH to develop an ecohydrological
conceptualisation of the Fortescue Marsh and surrounding catchment areas contributing to the Marsh.
This study informs BHP Billiton Iron Ore
’s Strategic Environmental Assessment (SEA) process and has
been undertaken in parallel with three other ecohydrological studies in adjacent landscapes: referred to
as the Central Pilbara, Eastern Pilbara and Marillana Creek Regions.
The ecohydrological conceptualisation provides an integrated understanding og groundwater, surface
water and ecological regimes in the vicinity of BHP Billiton Iron Ore
’s mining and infrastructure
development activities. BHP Billiton Iron Ore has no current mining operations near the Fortescue
Marsh; however, potential projects in the Marillana, Mindy, Coondiner and Roy Hil l tenement areas are
at various stages of assessment and development.
The ecohydrological conceptualisation is supported by maps of the region and study area which have
been compiled into a map book
(Fortescue Marsh Ecohydrological Conceptualisation Map Book)
. The
map book should be referred to in conjunction with this document.
1.1.1
Location and extent
The Fortescue Marsh (the Marsh) is located in the Pilbara Region of Western Australia and is the largest
ephemeral wetland in the region (Map 1-01). It is an extensive intermittent wetland within a broad valley,
bound by the Chichester Range to the north and the Hamersley Range to the south.
The Marsh has formed at the terminus of the Upper Fortescue River catchment, which constitutes the
upper portion of the Fortescue River Basin (Map 1-01). The Fortescue River Basin covers an area of
49,710 km
2
. The Upper and Lower Fortescue River catchments occupy areas of 29,820 km
2
and 19,890
km
2
, respectively. The Goodiadarrie Hills form the catchment divide between the Upper and Lower
Fortescue Catchments. To the west of the Goodiadarrie Hills, the Lower Fortescue River catchment
drains into the Indian Ocean.
The Upper Fortescue River catchment is an internally-draining catchment and is considered to have
negligible or limited hydraulic connectivity, either via surface water or groundwater, to the Lower
Fortescue River catchment. Flood flows are delivered to the Marsh by the Upper Fortescue River, Weeli
Wolli Creek and numerous small creeks emanating from the surrounding ranges.
Study area delineation
MWH developed an appropriate spatial domain for the ecohydrological co nceptualisation. A pragmatic
approach was adopted, based on catchment scale hydrology and the location of BHP Billiton Iron Ore
’s
proposed mining projects within the vicinity of the Marsh. The defined Fortescue Marsh study area
(hereafter referred to as the study area) covers an area of 11,971 km
2
(Map 1-02).
The study area boundary depicted in Map 1-02 was selected
with due consideration of:
the purpose of the ecohydrological conceptualisation;
areas encompassing prospective BHP Billiton Iron Ore
’s proje
cts;
ecophysiographic boundaries and broadly anticipated hydrological stresses on the Marsh and other
ecosystems;
sites of recognised ecological significance;
hydrological requirements (reflected in catchment boundaries) for potential future construction of
numerical models (including ecohydrological models); and
potential stresses imposed by any existing or proposed mining/dewatering
operations including
those associated with parties other than BHP Billiton Iron Ore.
Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Page 2
Our ref: FM-EcoConcept_v8.docx
The project area encompasses the management zones described in the Environmental Protection
Authority (EPA)
Guidance for environmental and water assessments relating to mining operations in the
Fortescue Marsh area (EPA, 2013). This is discussed in more detail in Section 2.6.6 of this report. It is
generally bound to the north and south by surface water catchment divides along the Chichester and
Hamersley Range, respectively. The eastern boundary is broadly defined by the Fortescue River course.
The western boundary is defined by an inferred surface water and groundwater divide to the west of the
Goodiadarrie Hills.
Key assumptions and limitations inherent in the delineation of the study area are as follows:
The southern boundary extends sufficiently beyond the proposed BHP Billiton Iron Ore mine sites to
enable assessment of flow contributions primarily from Weeli Wolli, Mindy Mindy and Coondiner
Creeks into the study area.
The study area boundary extends significantly beyond the inferred groundwater divide in the vicinity
of the
Coondiner mine site; delineation of the boundary in this area was designed to coincide with
the surface water catchment boundary further south. Surface water contributions captured in the
ecohydrological conceptualisation will be evaluated in some detail within this extended area,
however, detailed characterisation of the hydrostratigraphy beyond the inferred groundwater divide
will not be
undertaken, and will be limited to a brief description of the stratigraphic sequence and
groundwater flow interpretation primarily as a flux input into the Fortescue Marsh.
The area to the west
of the Goodiadarrie Hills, which includes the Goodiadarrie Swamp, constitutes
an internally draining system disjunct from the Fortescue Marsh. Subsequent discussions regarding
the Goodiadarrie Swamp throughout this document will reflect the functional difference between the
Goodiadarrie Swamp and Fortescue Marsh.
There are currently three active mine sites within the study area, and one in the initial stages of
operations (Table 1-1, Map 1-02). In addition, there are several proposed mining operations within the
study area (Table 1-2). Public reports associated with project site characterisation and feasibility studies
are available for the Christmas Creek, Cloudbreak, HPPL Roy Hill, Nyidinghu, Brockman, Marillana and
Koodaideri projects. Data relevant to this study have been used where appropriate, and all reports are
catalogued in Appendix A: Data Inventory and Catalogue.
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