Ecohydrological Conceptualisation of the Fortescue Marsh Region
Status: Final
September 2015
Project No.: 83501069
Page 45
Our ref: FM-EcoConcept_v8.docx
3
Regional hydrology
This section presents a conceptual understanding of regional hydrology, both surface and
subsurface (hydrogeology), within the study area. Functional relationships and interactions
between hydrological processes and ecosystems are evaluated where possible; particularly where
applicable to the Fortescue Marsh. This forms the conceptual basis for assessing how potential
changes (natural or anthropogenic) to the hydrological system may affect ecosystems, and which
factors may be important for the formulation of mitigation strategies.
3.1
Surface water
3.1.1
Setting and key features
The Fortescue River Basin (49,750 km
2
) is defined by the Chichester Range to the north and the
Hamersley Range to the south (Map 3-01). It is divided into the Upper Fortescue River Catchment
(30,279 km
2
) and the Lower Fortescue River Catchment (19,890 km
2
).
A small portion of the study area (in proximity to BHP Billiton Iron Ore
’s proposed Roy Hill
operations) lies within the Lower Fortescue River Catchment, in a sub -catchment which drains into
Goodiadarrie Swamp (Map 3-01). The remainder of the study area lies within the Upper Fortescue
River Catchment, for which the Marsh is the drainage terminus.
Goodiadarrie Hills, which separate the Marsh from the Goodiadarrie Swamp, constitutes a surface
water and potential groundwater divide. A second groundwater and surface water divide exists to
the west of the Goodiadarrie Swamp, separating the Goodiadarrie Swamp from the Lower
Fortescue River. Shallow groundwater in the internally draining Goodiadarrie Swamp is brackish to
saline; whereas groundwater in the lower portion of the Fortescue River is fresh, implying the
presence of a groundwater and surface water divide between the two hydrogeological systems.
Fresh water may collect on the surface of playa lakes or clay pans within the Goodiadarrie Swamp
during prolonged 'wet' periods.
Two major drainage systems, the Fortescue River and Weeli Wolli Creek, contribute point source
surface water inflows (Map 3-01). All other sub-catchments receive no inflows from external
catchments. Significant drainages include the Weeli Wolli Alluvial Fan and Mindy Mindy /
Coondiner Creek catchments in the Hamersley Range, and Kulbee Creek / Christmas Creek /
Kulkinbah Creek catchments in the Chichester Range (Map 3-01).
The Upper Fortescue River, with a total catchment area of 16,281 km
2
, contributes significant
surface water flow volumes into the eastern end of the Marsh. These flows are largely derived
from upland areas, and delivered through numerous tributaries such as Homestead Creek,
Whaleback Creek and Jimblebar Creek. Since the completion of Ophthalmia Dam in December
1981, natural flows emanating from the upper catchment have been partially attenuated.
Downstream of Ophthalmia Dam, at the entrance of the Fortescue River to Fortescue River Valley
(Ethel Gorge), there is a major deltaic feature.
Weeli Wolli Creek has a catchment area of 4,982 km
2
and drains into the central-southern part of
the Fortescue Marsh, forming an extensive and broadly-shaped alluvial fan at the foot of the
Hamersley Range. Weeli Wolli Creek receives contribution from Weeli Wolli Spring located higher
in the catchment (outside the study area), as well as Yandicoogina and Marillana Creeks which
discharge into Weeli Wolli Creek at approximately 25 km upstream of the point where the creek
exits the Hamersley Range (Map 3-01). Where the creek enters the study area, it drains into a
braided channel system within a more extensive delta (referred to as Weeli Wolli Alluvial Fan
Catchment for the purpose of this study). Since the 1990s, natural surface water flow in the Weeli
Wolli Creek has been supplemented by surface discharge from mining operations located
upstream of the study area.
The drainage systems are ephemeral and flow in direct response to rainfall. Streamflow mainly
occurs during the summer months of December to March and is generally associated with the
major rainfall events such as the passage of tropical cyclones. Runoff can persist for periods of
weeks to months.