FORTESCUE METALS GROUP LIMITED
Christmas Creek Life of Mine Expansion Surface Water Investigation and Impact Assessment
301012-01527-SS-REP-0001
18 March 2014
Level 7, QV1 Building, 250 St Georges Terrace Perth WA 6000 Australia Telephone: +61 8 9278 8111 Facsimile: +61 8 9278 8110 www.worleyparsons.com ABN 61 001 279 812 © Copyright 2014 WorleyParsons Services Pty Ltd
FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
CONTENTS
1 INTRODUCTION ...... 5 1.1 This Document ...... 5 1.2 Purpose and Scope ...... 5 1.3 Relevant Legislation ...... 5 1.4 Definitions and Abbreviations ...... 6 2. SITE DETAILS ...... 7 2.1 Life of Mine Plan ...... 7 2.2 Development Scenario Assumptions ...... 8 2.3 The Study Area ...... 8 3. HYDROLOGY ...... 9 3.1 Regional Hydrology...... 9 3.1.1 Fortescue Marsh ...... 9 3.1.2 Sheet Flow Areas and Dependent Vegetation ...... 9 3.1.3 Cultural Significance ...... 10 3.2 Site Hydrology ...... 10 3.2.1 Hillslope Runoff ...... 10 3.2.2 Channel Flow ...... 12 3.2.3 Diverging Flow ...... 15 3.2.4 Sheet Flow ...... 16 3.3 Catchment Characteristics ...... 17 4. SURFACE WATER ASSESSMENT ...... 18 4.1 Qualitative Sheet Flow Impact Assessment ...... 18 4.2 Quantitative Hydraulic Assessment ...... 19 4.2.1 Hydraulic Model Setup ...... 20 4.2.2 Modelling Hydrology ...... 22 4.2.3 Model Scenarios ...... 24 4.2.4 Sensitivity Analysis ...... 24
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4.3 Fortescue Marsh Catchment Model...... 25 5. SURFACE WATER IMPACTS ...... 27 5.1 Directly and Indirectly Impacted Sheet Flow Areas ...... 27 5.2 Hydraulic Regime Impacts ...... 27 5.2.1 Flood Extents ...... 27 5.2.2 Flow Velocities ...... 28 5.2.3 Implications ...... 28 5.2.4 Flood Extent Differences ...... 28 5.2.5 Sensitivity Analysis ...... 29 5.2.6 Limitations ...... 29 5.3 Cumulative Development Impacts ...... 30 5.4 Areas of Cultural Significance ...... 32 6. CONCLUSIONS ...... 34 REFERENCES ...... 35 Appendices
APPENDIX A: CHRISTMAS CREEK LIFE OF MINE DEVELOPMENT AND MAJOR WATERWAYS APPENDIX B: YINTA LOCATIONS AND CATCHMENT ASSESSMENT APPENDIX C: DIRECT AND INDIRECT SHEET FLOW IMPACTS APPENDIX D: MODELLED FLOOD EXTENTS APPENDIX E: MODELLED FLOOD EXTENT CHANGES APPENDIX F: MODELLED FLOOD VELOCITIES APPENDIX G: MODELLED FLOOD VELOCITY CHANGES APPENDIX H: SENSITIVITY ANALYSIS – FLOOD EXTENTS APPENDIX I: SENSITIVITY ANALYSIS – FLOOD VELOCITIES APPENDIX J: RAINFALL LOSS ESTIMATION FIELD TRIALS APPENDIX K: FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
1 INTRODUCTION
1.1 This Document
This report describes the impacts on the existing hydrological processes of the Christmas Creek Life of Mine Expansion. The report also describes the expected level of impact of the development after the application of the proposed surface water management strategies. This report is intended to guide ongoing development of the Project Surface Water Management Plan.
1.2 Purpose and Scope
This report provides information to support the development of management strategies to be applied during construction and operation of the proposed Christmas Creek Life of Mine Expansion.
The guiding objectives relating to surface water management, as stated in the Fortescue Surface Water Management Plan (45-PL-EN-0024) includes:
• Maintain the integrity of flow paths and water quantities to protect surface water dependent ecological systems;
• Prevent and minimise turbidity & sedimentation caused by erosion;
• Prevent and minimise impacts to discharged surface water quality;
• Minimise impact of storm surge and flooding; and
• Monitor and report sufficiently to demonstrate compliance and enable management to make informed decisions that minimise environmental impacts to surface water dependent ecological systems.
In achieving these objectives, the report will also assist in maintaining functions addressed through the Project Groundwater Management Plan.
1.3 Relevant Legislation
• Rights in Water and Irrigation (RiWI) Act 1914 (WA)
• Wildlife Conservation Act 1950 (WA)
• Dangerous Goods Safety Act 2004 (WA)
• Environmental Protection Act 1986 (WA)
• Environmental Protection (Unauthorised Discharge) Regulations 2004 (WA)
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1.4 Definitions and Abbreviations
Table 1-1 - Definitions and Abbreviations
Abbreviation Description
ANZECC Australian and New Zealand Environment Conservation Council
DoW Department of Water
EMP Environmental Management Plan
EMS Environmental Management System
FMG Fortescue Metals Group Limited
GMP Groundwater Management Plan
SWMP Surface Water Management Plan
TPI The Pilbara Iron Ore and Infrastructure Project
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2. SITE DETAILS
2.1 Life of Mine Plan
The disturbance footprint associated with current and proposed mining at Christmas Creek is shown in Appendix A. This includes an indicative outline of the current and proposed disturbance areas approved under ministerial statement 707. This report concerns the impacts of the proposed development outside the existing approved disturbance areas. This includes future activities that take place within the existing approved disturbance areas that may have impacts further downstream, away from the development.
The Christmas Creek Life of Mine plan includes a series of pit developments, waste dumps, haul roads, dewatering infrastructure and a proposed above ground ore conveyor. Expanded mining is anticipated to occur over the next 15 years, commencing in mid-2013. The initial development is concentrated around the existing disturbed area and gradually extends eastwards into the hilly terrain of the Chichester Range and westward where pits are typically located on flat terrain south of the Chichester Ranges. While pits progressively open and close, this study assumes that some waste dumps are retained and remain after the completion of the project.
Infrastructure associated with the proposed Christmas Creek Life of Mine Expansion is sited on the band south of the Chichester Ranges and within the foothills of the ranges themselves. The proposed infrastructure includes:
• Pit developments and waste dumps, typically located at least 6 km north of the Fortescue Marsh shoreline within the steeper foothills of the Chichester Ranges and occasionally on the band of low relief terrain further south;
• De-watering infrastructure including settlement and transfer ponds, typically located just outside the southern extremity of the proposed future pit expansions;
• Groundwater re-injection infrastructure including pipes, pumps and bores typically located south of the de-watering infrastructure, in some cases within 1 km of the Fortescue Marsh land system boundary;
• Ancillary facilities including administration buildings, workshops, crib rooms and fuel farms;
• Access and haul roads connecting the various elements of the mine site; and
• An above ground conveyor transporting ore back to the Christmas Creek Ore Processing Facility.
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Existing infrastructure including railways, existing pits and dumps and the Ore Processing Facility are represented within the indicative current and proposed disturbance areas approved under ministerial statement 707.
2.2 Development Scenario Assumptions
Mine planning activity associated with the Christmas Creek mine site can be broadly split into short, medium and long term planning. The Christmas Creek Life of Mine plan falls within long term planning, while medium term planning addresses a period 6 to 18 months ahead. Short term planning is effectively operational planning, assessing a window from 2 weeks to 12 months in advance of current developments. This distinction is important because this study addresses the impact of the Life of Mine plan. The operating reality is slightly more detailed and assumptions have been made to enable assessment at the Life of Mine timescale.
The Life of Mine plan provides an overview of the full extent of the development footprint for mine pits, waste dumps and associated land disturbance. It does not include details of the disturbance footprint at spatial scales smaller than an entire pit shell, and does not describe the sequence of development within a given mining stage. Therefore the following assumptions are required to estimate the impacts of pit developments on surface hydrology:
1. The entire area of a pit footprint in a given phase is developed (and therefore acting as a hydraulic obstruction) at the same time.
2. Pits are developed (opened, mined and closed) within 2 years.
These assumptions are necessarily conservative, such that the potential impacts discussed in section 5 are likely to be over-estimated.
2.3 The Study Area
The studies that make up this investigation (discussed in section 4) examined the likely impact of the development at two distinct spatial scales. The specific examination of surface water flow characteristics and likely changes resulting from the proposed development took place at a hillslope scale, and considered parts of the landscape downstream of the development to which this impact was likely to extend. Overall water balance modelling took place at the catchment scale and included the entire catchment of the Fortescue Marsh.
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3. HYDROLOGY
3.1 Regional Hydrology
The Christmas Creek Life of Mine Expansion covers an area of the Chichester Range which drains in a southerly and south westerly direction towards the Fortescue Marsh. Over time, the larger catchments draining the Chichester Ranges have formed a series of floodplains, alluvial fans and sheet flow zones that form a band of low relief terrain between the ranges and the Fortescue Marsh. The most prominent of these is Christmas Creek itself, which discharges through the eastern section of the proposed development. The creek has formed an alluvial fan along the south eastern section of the development which retains some large channel forms all the way to the Fortescue Marsh. The band of low relief terrain runs east-west along the northern edge of the marsh, between 5 and 10 km from the base of the Chichester Ranges and sloping at around 0.3%.
3.1.1 Fortescue Marsh
The marsh effectively constitutes the terminus of the Upper Fortescue River catchment, which includes an area of approximately 29,300 km2. Following significant rainfall events, runoff from the surrounding catchment drains to the marsh resulting in transient ponding. This water contributes to a shallow aquifer system beneath the marsh, with ponding slowly dissipating through the processes of seepage and evaporation. Groundwater discharge from topographically driven flow derived from the surrounding landscape is low, due to the poor hydraulic connection between the marsh surface and underlying aquifers.
3.1.2 Sheet Flow Areas and Dependent Vegetation
Mulga woodland communities are common on the plains surrounding the Fortescue Marsh. Vegetation dominated by Mulga is generally considered to rely on overland flow to help meet its ecological water requirements. The occurrence of Mulga south of the Chichester Range is linked to landscape drainage patterns, with communities commonly associated with drainage tracts and localised depressions. In some areas of low relief and poorly defined drainage, banded communities occur. This distinctive vegetation pattern is comprised of bands or groves of Acacia anerua trees of about 30% canopy cover and an intergrove area of grass or forb-land (Anderson & Hodgkinson, 1997).
The banded vegetation patterns, (Figure 1 and Figure 4), are thought to be dependent on sheet flow from the intergrove areas immediately upslope of each band and on the high infiltration of water flowing overland into the soil of the mulga bands. The water transports nutrients and organic matter creating fertile patches of land in the mulga groves where the flow is concentrated and distributed around the plants that act as obstructions to flow across the slopes (Anderson & Hodgkinson 1997). The groves are the fertile patches of land where water and nutrients are concentrated in the mulga ecosystems. Grove/Intergrove mulga communities are mainly concentrated on the lower flanks of the Chichester and Hamersley Ranges adjacent to the Fortescue Marsh. Due to their reliance on sheet
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT flows, banded vegetation communities are believed to be particularly vulnerable to disrupted surface drainage.
3.1.3 Cultural Significance
The Fortescue Marsh and some semi-permanent water pools along its northern shoreline have been identified as having high cultural significance. The semi-permanent water pools or “yinta” are typically located near where major creeks such as Goman Creek and Christmas Creek discharge into the Fortescue Marsh. The yinta are thought to be sustained predominantly by surface water inputs, however these features are relatively poorly understood. The locations of the yinta can be seen in Appendix B.
3.2 Site Hydrology
Within the development site itself, there are several different forms of surface water flow, each requiring a unique management approach. In a hydrological sense, the catchment of the study area and surrounds can be divided into several zones based on runoff generating mechanisms, including:
• Hillslope Runoff;
• Channel Flow;
• Diverging Flow; and
• Sheet flow.
Some areas, including those closer to the shore of the Marsh, may exhibit one or more of these characteristics.
3.2.1 Hillslope Runoff
Hillslope runoff zones are located in the portion of catchments where the majority of runoff is contained within small creeks, broad swales or gullies. Naturally, flows are generally convergent which concentrates flows, increases velocities, promotes scour and enhances channel formation. Catchment sizes are usually small but can be larger in cases where the terrain is flat and velocities are insufficient to maintain well defined channels. Areas with Hillslope runoff characteristics are shown in Figure 1.
Location ‘A’ is an area typical of the broader Chichester Ranges including most of the catchments with concentrated flows and small, well defined channels with characteristics of gullies and small creeks. These catchments have steep slopes and surface runoff travels short distances before reaching the channel.
Location ‘B’ is more typical of waterways with large catchment areas and mainly low relief terrain. Most of these catchments are characterised by channels which have a similar appearance to broad swales. In some cases channels are not easily distinguished, so preferential flow paths can be
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT identified through analysis of vegetation patterns. This is distinct from sheet flow areas where there are no preferred flow paths and vegetation forms banded mosaic patterns (Figure 1).
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Figure 1 - Example of Flow Type Mapping in the Christmas Creek Project Area i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology part 2\reporting\rev2\301012-01527-ss-rep-0001_rev2.docm Page 12 301012-01527-SS-REP-0001 : Rev 2 : 18 March 2014
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3.2.2 Channel Flow
Channel Flow zones are located in the portion of catchments with large channels and adjacent floodplains. These zones are associated with large catchments that predominantly drain the steep areas of the Chichester Range rather than the low relief terrain closer to the Fortescue Marsh. Large convergent flows, high velocities and large, well defined channels are typical of these creeks. Smaller, more frequent flows are mostly confined to the channel while larger and less frequent flood flows break out onto the adjacent floodplain. These zones can be identified using topographic information and vegetation patterns in aerial photos. Channels are usually devoid of vegetation due to bed load movement during flood events. Vegetation on the banks and adjacent floodplains is maintained either by periodic inundation or has rooting depths sufficient to access the superficial fresh aquifer replenished by more frequent smaller flows.
Areas with concentrated Channel Flow are shown in Figure 1. Two large channels discharge floodwater south from the Chichester Range onto the low relief terrain north of the Marsh. Catchment areas for creeks at location ‘C’ and ‘D’ are 12 and 18 km2 respectively. The aerial photo shows that the resulting creeks have main channels widths between 30 and 40 m and adjacent floodplains between 100 and 200 m in width. As the creeks flow further south, the low gradient reduces stream velocities and the creeks transition into diverging flow.
The results from 2D hydraulic flood modelling conducted for the TPI Project are shown in Figure 2 and Figure 3 with an aerial image of the area shown in Figure 4. These figures show modelled inundation extents for a 20 and 100 year average recurrence interval (ARI) design storm event. In the 20 year ARI flood, the model predicts that the inundated area would be confined to the floodplain with no connectivity with the adjacent sheet flow area. Some shallow inundation of sheet flow areas is shown resulting from the 100 year ARI flood. The two creeks shown in these figures have larger catchments (22 and 40 km2 respectively) with 50 m wide creeks and 500 m wide floodplains.
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Christmas Creek OPF - 20 year ARI Flood 7525600
7525400
7525200
7525000
7524800
7524600
7524400
7524200
7524000
7523800
7523600
7523400
7523200
7523000
7522800
H Water Depth m [m] 7522600 Above 1.50 0.80 - 1.50 7522400 0.50 - 0.80 0.20 - 0.50 0.05 - 0.20 7522200 Below 0.05 Undefined Value 776500 777000 777500 778000 778500 779000 779500 780000 01/01/08 00:00:00, Time step 0 of 0 Figure 2 – Estimated 20 year ARI Flood Extent for two creeks discharging from the north into the Fortescue Marsh
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Christmas Creek OPF - 100 year ARI Flood
7525600
7525400
7525200
7525000
7524800
7524600
7524400
7524200
7524000
7523800
7523600
7523400
7523200
7523000
7522800
H Water Depth m [m] 7522600 Above 1.50 0.80 - 1.50 7522400 0.50 - 0.80 0.20 - 0.50 0.05 - 0.20 7522200 Below 0.05 Undefined Value 776500 777000 777500 778000 778500 779000 779500 780000 01/01/08 00:00:00, Time step 0 of 0 Figure 3 - Estimated 100 year ARI Flood Extent for two creeks discharging from the north into the Fortescue Marsh
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Figure 4 - Aerial Imagery of for two creeks discharging from the north into the Fortescue Marsh
3.2.3 Diverging Flow
Diverging flow areas are located in the portion of catchments where channel flow has become dispersed, leading to a loss of channel form. The transition from channel flow to diverging flow normally occurs on the low relief terrain after large rivers have discharged from the Chichester Ranges. The distance that the channel form is maintained is proportional to the slope of terrain and the size of the flows generated by a catchment (i.e. the greater the flow, the more well defined the channel is further downstream). Sandy Creek is an example where although flows disperse across the alluvial fan, some channel form is maintained all the way to the Marsh shoreline. The width of the main Sandy Creek channel reduces from 50 m at the base of the Chichester Ranges to around 5 m at the Marsh.
Diverging flow zones are shown in Figure 1. The initial transition from channel flow to diverging flow is seen at ‘C’ and ‘D’, where breakout channels begin to form and the floodplains become wider. Other breakouts and bifurcation occur further upstream, but within a clearly defined floodplain of a
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT relatively constant width. As the creeks progress downstream, a higher proportion of flows are conveyed over the floodplains and the channels become narrower. At ‘F’ the floodplain is over 1 km wide with the two main creeks having transformed into a series of small, interconnected swales which combine to convey the flow.
Banded grove-intergrove vegetation patterns typical of sheet flow areas are not normally found downstream of areas where diverging flows intersect with sheet flow zones. Sheet flow zones form in ‘fan’ like terrain such as seen at location ‘B’ on Figure 1. Once sheet flow reaches a swale, the flows are concentrated, which supports continuous tracts of vegetation.
3.2.4 Sheet Flow
Sheet flow zones form in areas where overland flow moves down slope while maintaining a broad shallow front. This is the initial hillslope response to infiltration excess prior to channel initiation. Channel initiation is dependent on a threshold level of stream power, controlled in part by the extent of flow convergence and gradient. There are many examples in the study area where the terrain has been formed by remnant alluvial fans. These areas do not promote convergence of flows and are relatively flat, causing sheet flow zones to be maintained over large areas.
The banded Mulga (Acacia aneura) formations common throughout the study area as discussed in section 3.1.2, are part of an ecological response to the sheet flow patterns. The banded patterns, shown in Figure 1, are thought to be a result of ecohydrological processes that concentrate water and nutrients at the grove areas. The “trigger-transfer-reserve-pulse” concept (Ludwig, et al. 2005, Ludwig, et al. 1997) suggests that following rainfall (the “trigger”), low infiltration rates at intergrove areas result in sheet flow and the transport (“transfer”) of water and nutrients (via leaf litter) downstream to the grove areas. Higher infiltration rates at the grove areas enable storage of water and nutrients (“reserve”) leading to a “pulse” of plant growth. These points of accumulation are critical for arid rangeland ecology, they form biological hot spots in which organic matter and nutrient cycling processes are prevalent. The accumulation of moisture and nutrients provide the conditions for biogeochemical cycling required to sustain arid rangeland ecosystems.
Other papers have suggested that mulga groves are less dependent for survival on intergrove processes and more dependent on direct rainfall. Dunkerley (2002) suggests that the leaf structure and inward sloping stems of Mulga trees promote “stem flow”, directing rainfall towards the stem at the base of the trees where infiltration capacity is highest. This is due to not only the direct physical distribution of water along the stem but also the improved soil structure due to higher organic matter. Infiltration rates were shown to decrease as distance away from the stem increases. Dunkerley (2002) also states based on earlier studies that “…rather than the survival of groves being consequent upon the additional water supplied from the intergrove upslope, there was considerable dependence on the internal processes of canopy interception and stem flow, together with marked spatial variability of grove soil properties.”
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3.3 Catchment Characteristics
A series of large catchments run through the site, from north to south. The headwaters of these catchments are located in the Chichester Ranges, where hillslope processes initiate surface runoff. Typically, channel form is enhanced as flows move further south before water discharges onto the flatter zones closer to the Fortescue Marsh. Channel form diminishes as water flows over the flat terrain becoming more distributed. The proposed Christmas Creek Life of Mine Expansion includes areas within the hilly terrain of the Chichesters and on the lower slopes of the flat area adjacent to the Fortescue Marsh. This means all flow types discussed in section 3.2 are encountered. Catchment outlines and mainstreams are shown in Appendix A.
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4. SURFACE WATER ASSESSMENT
Three separate studies were conducted to estimate the likely impact of the development on aspects of the surface water characteristics around the proposed development area. By identifying sheet flow areas, modelling flood hydraulics and developing a Fortescue Marsh catchment rainfall-runoff model, the studies were able to estimate:
• Areas of sheet flow directly impacted by the development (requiring clearing of vegetation); • Areas of sheet flow “shadow” – where the development impacts sheet flow zones indirectly; • Changes to flood depths, extents and velocities; • Changes to the overall volume of flow passing through the site and reaching the Fortescue Marsh; and • The cumulative impact of the three major developments of the Chichester Range (Cloudbreak, Christmas Creek and Roy Hill) on the water balance of the Fortescue Marsh.
For each of the studies, impacts have been assessed based on the assumption that the principles of the Fortescue Surface Water Management Plan have been applied to the development.
4.1 Qualitative Sheet Flow Impact Assessment
The first of the three studies was a qualitative assessment of the impact the development is estimated to have on sheet flow dependent vegetation around the site and downstream to the Fortescue Marsh. The areas of sheet flow dependent vegetation were identified via aerial photo interpretation and assessed as either directly impacted, indirectly impacted or not impacted by the development.
Sheetflow areas were mapped according to the topography of the area and the location of sheetflow dependent mulga groves in grove/intergrove structure. A number of assumptions were made to determine the impact areas associated with the mine development. • Direct impacts are classified as areas impacted by haul roads, pit shells, waste dumps, topsoil dumps, go lines and ROM areas. • Sheet flow will be restored at a 45° angle from direct impact zones down gradient of the direct impact. The areas intercepted by the 45° angles from the disturbed sites will be classified as being indirectly impacted. This is based on the approximate angle of spread of water exiting the downstream end of a typical environmental culvert. The areas outside this impact zone will be classified as being undisturbed. • Pits were mapped to assume a mine life of 2 years. This assumption was based on the pits being active for one year starting at any stage during its starting year, causing the impact to potentially occur at any stage over a two year period. • Once pits are backfilled, there will be no impact and sheetflow conditions will be restored. • Current infrastructure has been assumed to have no additional direct or indirect impacts on sheetflow areas.
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• A 50m buffer of indirect impacts has been applied to haul roads. This buffer is conservative and represents the largest possible extent of impact with the placement of environmental culverts. The precise extent of impacts will be able to be estimated once the location and sizing of culverts has been determined.
Sheet flow impact areas were mapped for the life of mine proposed development using these assumptions and spatial extents of pit areas, dumps and supporting infrastructure supplied by FMG. The sheet flow impact maps are shown in Appendix C and the outcomes of the assessment are discussed in section 5. An example of the sheetflow impacts mapping outputs is shown below in Figure 5.
Figure 5 - Example of Sheetflow Impacts Mapping
4.2 Quantitative Hydraulic Assessment
A series of 1D and 2D hydraulic models have been developed for the study area. These models have been used to demonstrate the changes to the hydraulic regime that can be expected to occur as a result of the development, including changes to the spatial extent of inundation, flow velocity distributions and runoff volumes. By ensuring the hydraulic regime is not significantly altered, the
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT proposed development can also maintain existing natural scour patterns, watering frequency of surface water dependent vegetation and flow volumes reaching the Fortescue Marsh.
4.2.1 Hydraulic Model Setup
The study area was divided into one domain for the 1D modelling component and five separate 2D model domains. The single 1D domain covered the Christmas Creek mining development, including pits, drainage and infrastructure. The 2D domains extended approximately 7km downstream from the mine site just north of the Fortescue Marsh. Separate 2D model domains were necessary as running the model in a single domain would have been too computationally intensive for the resolution required. Domains were divided to ensure that there was comprehensive coverage downstream of the mine site and no overlap of upstream catchments between adjacent domains.
1-dimensional modelling
The 1D modelling component was completed using XP Storm software. The software has both runoff routing capabilities and a comprehensive hydraulic component which models the performance of hydraulic infrastructure such as drains and culverts (XP Software 2011). XP Storm was considered the most appropriate 1D model for this exercise as it would generate the hydrographs required as input to the 2D models. Additionally it would easily include the in situ infiltration data, a feature that would have been problematic had MIKE 11 been used instead. XP Storm has 2D modelling capabilities however this is limited to small domains and therefore considered inappropriate for modelling the Christmas Creek mine site
A series of networks were set up in XP Storm with a total of 26 outfalls. These networks corresponded to the main channels and existing drains located across the Christmas Creek mine site and the seven outfall locations were then adopted as the input boundaries for the 2D hydraulic model.
In the Runoff Mode of the model, all catchment nodes were set to use the Laurenson routing method and assigned the area and slope estimated from the catchment geometry and terrain data. Rainfall, infiltration and runoff parameters are discussed in Section 4.2.2.
In the Hydraulic mode of the model, a combination of natural channels and trapezoidal drains were used to define the channel network. Cross sections for the natural channels were generated using LIDAR data. This data was also used to assign upstream and downstream inverts of all conduits. Manning’s n values of 0.03 and 0.04 were assigned to the drains and natural channels, respectively. Bunds were also included in the model where required; they were included in the profile of the drain and set to an infinitely high value.
2-dimensional modelling
The 2D modelling component was completed using DHI’s MIKE-FLOOD software package. MIKE- FLOOD is a coupled 1D-2D hydrodynamic model comprising of MIKE11 and MIKE21. MIKE11 uses an implicit, finite difference scheme to solve unsteady flows in well-defined channels and structures such as culverts (DHI, 2005a). MIKE21 solves 2-dimensional hydraulics for sheetflow and areas such as floodplains using a finite difference solution to the Navier-Stokes equations (DHI 2005b). MIKE-
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FLOOD couples these two models to enable modelling of large areas while including the required level of detail at localised structures and waterways.
Each of the 2-D domains used a common set of model parameters. Grid size was set at 10 metres and was derived from LIDAR flown over the area extending from Cloudbreak to Christmas Creek in September 2011. Based on this grid size, a model time step of 1 second and constant velocity based eddy viscosity of 5 m2/s were chosen to minimize numerical instabilities. A uniform Manning’s n value for roughness of 0.036 was chosen. Values of n were estimated based on tables, photographs and formulas presented by Chow (1959), Henderson (1966) and Barnes (1967), as well aerial photographs of the site and field observations of the land surface, soils and vegetation density. While small channels are unlikely to be well defined by a 10 metre grid, overland flow delivery to Mulga groves forming banded grove-intergrove patterns in low relief terrain or continuous tracts in broad swales, are adequately represented at this scale.
Inflow hydrographs were applied at the upstream boundary of the model domain while rainfall excess was applied directly to the grid itself. Using a rain-on-grid technique requires that the parameters which control at what depth a cell is considered “wet” or “dry” are lower than normal. For each model, the wetting and drying depths were set at 2mm and 1mm respectively. The areas of each of the 2D domains are outlined in Table 4. Time to flood peak varied for each of the inflow streams so the duration of model runs was varied accordingly. Each of the model domains is shown in Figure 6
Figure 6 - 1D and 2D Model Domains
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4.2.2 Modelling Hydrology
Temporal Patterns & Rainfall
Rainfall Intensity Frequency Duration (IFD) data for Christmas Creek was obtained from the Bureau of Meteorology. The temporal patterns for the 5, 20 and 100 year ARIs were included in the XP Storm model to generate runoff in order to produce a hydrograph for each catchment. All typical storm durations (1hr – 72hr) were initially run through the model in order to identify the critical storm (the rainfall intensity and duration combination that produces the greatest peak flow) associated with each catchment. The critical storm duration would then be adopted for the rainfall over the grid in the 2D model.
Since each 2D model domain would have several catchments flowing into the grid, criteria for the most appropriate duration to use was required. It was decided that the critical storm associated with the dominant catchment within each 2D model domain was the most appropriate duration to adopt as it would typically generate the most volume of runoff and therefore have the most downstream effects. Based on the variation of catchment sizes and shapes associated with each 2D model, unique storm durations were identified for each ARI. These critical storms are outlined in Table 1.
Table 1: Critical storm durations for 2D model domains
5yr 20yr 100yr Model Domain ARI ARI ARI CC3 24hr 24hr 24hr CC1 West 6hr 6hr 2hr CC1 East 4.5hr 4.5hr 4.5hr CC2 12hr 12hr 4.5hr CCreek 24hr 24hr 24hr
Infiltration & Runoff
Several infiltration methods are available for use in XP Storm. The Green and Ampt Method was adopted for this model to account for different infiltration rates at natural catchment areas compared to backfilled pit areas and waste dumps. Values for the required parameters were based on results yielded from the Rainfall Loss Estimation Field Trials (301012-01527-SS-REP-0002) which formed part of this study and is included in Appendix J. Parameters for the different land types used in the model are summarised in Table 2.
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Table 2: Green and Ampt Parameters used for 1D modelling
Average Capillary Suction 150 mm Initial Moisture Deficit 0.18 Saturated Hydraulic Conductivity 33.9 mm/hr
To represent surface runoff occurring within the entire domain of each model, design rainfall excess was applied directly to the model cells. The design rainfall events chosen for each model domain reflect the critical storm durations identified for the major catchments and are shown in Table 1.
Runoff coefficients were applied to the rainfall data in order to account for expected loss due to infiltration. These coefficients were calculated using the ratio of the total surface runoff generated in the XP-Storm model domain and the total rainfall calculated for each critical storm duration shown in Table 1. Adopted runoff coefficients for each ARI are shown in Table 3.
Table 3: Runoff coefficients applied to rainfall data
5yr 20yr 100yr Model Domain ARI ARI ARI CC3 0.4 0.5 0.7 CC1 West 0.6 0.7 0.8 CC1 East 0.8 0.85 0.9 CC2 0.5 0.6 0.8 CCreek 0.4 0.5 0.6
Hydrographs
Several inflow boundaries were incorporated into each of the 2D model domains representing the major flow paths affecting the mine site; Table 4 includes the number of inflow boundaries used for each model.
Table 4: Summary of 2D model areas and inflows
Domain Area No. of Inflows Model Domain (km2) CC3 53 9 CC1 West 47 4 CC1 East 56 4 CC2 21 6 CCreek 45 3
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Several hydrological methods were used to estimate peak flows for the catchments delineated in the area, including Rational Method, Regional Flood Frequency Procedure (RFFP) and the Laurenson runoff routing method which is used by XP Storm. Inflow hydrographs for 5 year, 20 year and 100 year ARI design flood events were generated in XP Storm and the peaks compared to Rational Method and RFFP estimates. It was determined that the uncalibrated XP Storm generated hydrographs were more appropriate to use for the 2D modelling than scaling a unit hydrograph to either of the other methods’ peak estimates. XP Storm would account for infiltration specific to each subcatchment area and would therefore produce hydrographs that better represented the characteristics of the area.
4.2.3 Model Scenarios
Scenarios were modeled for the 5 year, 20 year and 100 year ARI flood events for year 1 and year 5. Due to the progression of pit locations planned across the site, some model domains did not require additional runs for particular years of development. As a result, a total of 24 scenarios were run in MIKE21 across the five model domains. Table 5 summarises these scenarios.
Table 5: Summary of the Christmas Creek Mine Modeled Scenarios
Year 1 Year 5 CC3 5yr, 20yr, 100yr CC1 West 5yr, 20yr, 100yr 5yr, 20yr, 100yr CC1 East 5yr, 20yr, 100yr 5yr, 20yr, 100yr CC2 5yr, 20yr, 100yr 5yr, 20yr, 100yr CCreek 5yr, 20yr, 100yr
4.2.4 Sensitivity Analysis
A sensitivity analysis was completed to demonstrate the sensitivity of the un-calibrated model against changes in the roughness co-efficient, Manning’s n. The use of an un-calibrated model is not ideal, though with the addition of a sensitivity analysis, increased confidence can be placed in the model provided the model isn’t highly sensitive to parameters such as roughness. Each of the year 1 models were run again in both the 1D and 2D domains with the Manning’s n value increased and decreased by 20%. This was completed for the 5 year, 20 year and 100 year ARI flood events and resulted in an additional 30 runs being completed, as seen in Table 6. The purpose of the sensitivity analysis was to determine whether having a uniform roughness coefficient throughout the model domains is a suitable assumption and whether or not the conclusions drawn from the modelling are applicable.
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Table 6: Scenarios Completed for Christmas Creek Mine Sensitivity Analysis
Year 1 Year 1 Manning’s n +20% Manning’s n -20% CC3 5yr, 20yr, 100yr 5yr, 20yr, 100yr CC1 West 5yr, 20yr, 100yr 5yr, 20yr, 100yr CC1 East 5yr, 20yr, 100yr 5yr, 20yr, 100yr CC2 5yr, 20yr, 100yr 5yr, 20yr, 100yr CCreek 5yr, 20yr, 100yr 5yr, 20yr, 100yr
4.3 Fortescue Marsh Catchment Model
A hydrological model was developed for the entire Fortescue Marsh Catchment to demonstrate the relative importance of inflows received from the Chichester Ranges. This model was used to estimate the cumulative impact of the Cloudbreak, Christmas Creek and Roy Hill developments on the water balance of the Fortescue Marsh. The model setup and outcomes are presented in detail in Fortescue Marsh Catchment Water Balance Study (301012-01527-SS-REP-0003), which is included in Appendix K.
The modelling process was comprised of a rainfall-runoff model developed using the Source Catchments software, developed by eWater. Source Catchments allows for hydrologic modelling at the whole of catchment scale, with subcatchments being allocated specific parameters which represent the hydrological processes which occur within each catchment. The results from this modelling were then incorporated into a spreadsheet based water balance model to determine the marsh characteristics over the modelled period.
The modelling process included:
• Catchment delineation, where the Fortescue Marsh Catchment was split into 35 subcatchments for routing analysis; • Rainfall analysis, where the sparse network of rainfall gauges were used to estimate variable rainfall across the catchment – each subcatchment was allocated one of 10 rainfall gauges; • Streamflow gauging analysis – where the significant gauged parts of the catchment were calibrated and used to estimate rainfall runoff parameters which were then allocated to ungauged catchments with similar terrain characteristics; • Storage analysis – where the impact of Opthalmia Dam on the rainfall runoff and routing model was assessed; and
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• Water balance modelling – where the estimated runoff from the catchment was calibrated against observed water levels and storage volumes in the Fortescue Marsh derived from a previous study.
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5. SURFACE WATER IMPACTS
This section describes the outcomes of the studies discussed in section 4 and presents the likely impact of the development and how this varies as the mining sequence progresses.
5.1 Directly and Indirectly Impacted Sheet Flow Areas
Impact areas have been identified for the development of the Christmas Creek mine site with the impact areas mapped in Appendix C. The estimates of impact have been based on the combined development layout over the entire life of mine.
Table 7 shows the impact areas expressed as both hectares and percentage of the total sheetflow area for the life of the Christmas Creek Mine. These percentages relate to the total mapped areas shown in Appendix C. Other Mulga areas outside this zone, such as those further south, are not considered to be subject to direct impact (clearing) or indirect impact (sheetflow shadow) by the development.
Table 7: Estimated Sheetflow Impact Areas for the Christmas Creek Mine.
Level of Impact Area (ha) Percentage
No Impact 3,415 56%
Indirect Impact 439 7%
Direct Impact 2,288 37%
5.2 Hydraulic Regime Impacts
5.2.1 Flood Extents
Current development flood scenarios for Christmas Creek mine site (Year 1) were undertaken for the 5 year, 20 year and 100 year ARI design flood events in order to provide a baseline for comparing the results of the proposed life of mine development for Year 5. Flood extent maps for each of these years of development are included in Appendix D.
The model results support the hydraulic characterisation of the area presented in section 3. Areas where depths reach 1 to 2 metres indicate areas of channel flows. These flows are typically confined to the channels in low flows and immediate adjacent floodplains during high flows. Shallow sheetflow, typically not exceeding 0.2 m depth is common across the flatter sections of the site. Flows become distributed towards the southern end of the model domain.
A series of difference maps have been generated to depict the effects of development on the flood extents for each modeled scenario. The maps in Appendix E show the net increase in flood levels in Year 5 compared to Year 1 as a result of the development. Changes in water level are mainly
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT associated with the larger channels and water depths typically change by less than half a metre. The modelling suggests that water depths remain unchanged in sheetflow areas.
5.2.2 Flow Velocities
The same scenarios presented in Appendix D and E were used to develop flow velocity maps shown in Appendix F. During low flow scenarios, channel velocities typically do not exceed 1 to 1.5 m/s. In high flow scenarios, extensive parts of the larger channels and some areas associated with major culvert outlets exceed 2 m/s. Few of these channels however, maintain a flow velocity exceeding 1 m/s around the southern sections of the model domain as flows become more distributed. Flow velocities exceeding 0.2 m/s were uncommon in sheetflow areas.
Difference maps for flow velocities are shown in Appendix G for Year 5 compared to Year 1 as a result of the development. As with flow depths, the major changes are confined to the main channels, in some cases changing by as much as 0.5 m/s. Areas of distributed flow and sheetflow were not typically subject to significant changes in velocity as a result of the development.
5.2.3 Implications
The changes in water depth as the development progresses can be attributed to changes in the upstream catchments. As the mine expands, open pit areas move from catchment to catchment and the overall amount of backfilled area increases. Other significant changes are associated with the planned diversions of key waterways. In these cases, the new receiving waterway shows an increase in water levels while the former receiving waterway, now having been diverted upstream, shows a decrease in water levels. These changes to the flow regime in drainage tracts are not expected to significantly affect the delivery of water to mulga fringing the drainage tracts, as flooding events and direct rainfall will still be capable of replenishing stored soil water in the soil profiles beneath this vegetation.
The model results can be used in the implementation of Fortescue’s Surface Water Management Plan. Flood depths and extents can be used to ensure future development avoids areas subject to inundation and prevent significant ponding. The modelling also identifies areas of high velocity and therefore high scour potential. Potential changes to the scour regime resulting from the development can then be identified and mitigated.
5.2.4 Flood Extent Differences
The flood extent differences between year 5 and year 1 for the 5, 20 and 100 year ARI events are presented in Appendix E. The differences within these domains are an indirect result of impacts upstream, where there has been a reduction in catchment area upstream or a diversion has redirected water into a different creek in an attempt to maintain flows to the downstream area. Appendix E illustrates that flood extents downstream of the local inflows are only marginally affected and flood extent differences being isolated to the inflow areas.
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Table 8 presents the estimated impact areas for inundation extents in the CC1 West, CC1 East and CC2 model domains. The areas presented below display the changes to inundation extents in the following aspects:
a) Areas subject to inundation in year 1 which have become dry in year 5; b) Areas not subject to inundation in year 1 which have become wet in year 5; c) Areas which remain inundated (not impacted); and d) The total inundated area (b+c).
The areas presented are only located within the model domains of CC1 West, CC1 East and CC2 and do not include the results from CCreek and CC3 domains as there was no change in those areas.
Table 8: Estimated Impact Areas for Inundation Extents between Year 1 and Year 5 ǀĞŶƚ tĞƚƚŽƌLJƌĞĂ ƌLJƚŽtĞƚ EŽƚ dŽƚĂů ;ŬŵϮͿ ƌĞĂƐ;ŬŵϮͿ /ŵƉĂĐƚĞĚ /ŶƵŶĚĂƚŝŽŶ Ϯ Ϯ ƌĞĂ;Ŭŵ Ϳ ƌĞĂ;Ŭŵ Ϳ ϱLJƌ ϭ͘ϬϬ Ϭ͘ϯϰ ϰϭ͘Ϯϳ ϰϭ͘ϲϬ ϮϬLJƌ ϭ͘ϯϵ Ϭ͘Ϯϯ ϱϭ͘ϲϭ ϱϭ͘ϴϰ ϭϬϬLJƌ Ϭ͘ϰϵ Ϭ͘ϭϴ ϱϵ͘ϯϮ ϱϵ͘ϱϬ
5.2.5 Sensitivity Analysis
The sensitivity analysis was completed for Year 1 flood models in order to determine the impact of altering the manning’s n by plus or minus 20%. The results from the sensitivity analysis can be seen in Appendix H and I. The alteration of the roughness coefficient does not have a large impact on the results in terms of the flood extents and velocities downstream of the mine infrastructure. The changes are isolated to the channels and as such do not have an impact on the sheetflow areas. The changes that do occur are associated with small increases in the flood extents and changes to the velocities within the channels. With this in mind, the modelling results presented and the conclusions drawn from the flood modelling are acceptable even though it was not possible to calibrate the model due to a lack of suitable data.
5.2.6 Limitations
There are limitations associated with the modelling completed in both the 1D and 2D domains. These include:
• Assumptions made for roughness coefficients throughout the modelling. The sensitivity analysis showed that alterations to the roughness coefficients can cause changes with respect to flood extents and flood velocities. • The model area had to be broken into five separate models. This resulted in a conservative approach being taken in the development of these models. The areas between the models can act as a “wall” and obstruct flow that would normally spread to the other models. An
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example of this can be seen between the CC1West and CC3 models. This scenario results in additional water mounding against the boundaries resulting in conservative results. • LIDAR data was provided for the majority of the 2D model area. A small area within the CCreek model domain required the use of SRTM data. Data inconsistencies between the two sets of topographic data resulted in the data being manipulated such that they could be integrated within the model. This resulted in a sheeting effect occurring in the results of CC3. • There was no suitable data available with which to calibrate the model. The results of the sensitivity analysis indicate that the conclusions drawn from the uncalibrated modelling results are not highly sensitive to changes in roughness and are likely to be valid.
The limitations of the modelling do not impact the applicability of the conclusions made in Section 6.
5.3 Cumulative Development Impacts
The results of the Fortescue Marsh water balance model are presented in detail in Appendix K. The model was run from 1984 to 2011 and shows an average annual volume of water entering the Marsh of 281 GL per year during the undisturbed conditions scenario. The contribution from each source is shown for each scenario in Table 8 and Figures 7, 8 and 9. It can be seen that over this period the Chichester Ranges contribute approximately 17% of the total Marsh inflows. Under the worst case scenario, concurrent development of the three mines reduces the total inflow to the Marsh by approximately 1%.
Table 9: Modelled Annual Average Runoff into the Fortescue Marsh for the period 1984 to 2011
Undisturbed Scenario Disturbed Scenario Restored Scenario Contribution (%) Contribution (%) Contribution (%) Source of Inflow
GL Percentage GL Percentage GL Percentage
Chichester 48 17.2% 45 16.1% 46 16.4%
East Fortescue 128 45.6% 128 46.2% 128 46.0%
Southern Flanks 23 8.3% 23 8.5% 23 8.4%
Weeli Wolli 35 12.4% 35 12.6% 35 12.5%
East Hamersley 18 6.3% 18 6.4% 18 6.3%
Direct Rainfall 29 10.2% 29 10.3% 29 10.3%
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^ƵŵŽĨ ŚŝĐŚĞƐƚĞƌ͕ ϭϳ͘Ϯй ^ƵŵŽĨŝƌĞĐƚ ^ƵŵŽĨ ĂƐƚ ZĂŝŶĨĂůů͕ &ŽƌƚĞƐĐƵĞ͕ ϭϬ͘Ϯй ϰϱ͘ϲй ^ƵŵŽĨ ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ tĞĞůŝ &ůĂŶŬƐ͕ϴ͘ϯй tŽůůŝ͕ ϭϮ͘ϰй ^ƵŵŽĨ ĂƐƚ ,ĂŵĞƌƐůĞLJ͕ ϲ͘ϯй
Figure 7: Marsh Inflow Contributions - Undisturbed Scenario
^ƵŵŽĨ ŚŝĐŚĞƐƚĞƌ͕ ^ƵŵŽĨ ϭϲ͘ϭй ŝƌĞĐƚ ZĂŝŶĨĂůů͕ ^ƵŵŽĨ ĂƐƚ ϭϬ͘ϯй &ŽƌƚĞƐĐƵĞ͕ ϰϲ͘Ϯй ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ &ůĂŶŬƐ͕ϴ͘ϱй
^ƵŵŽĨ ĂƐƚ ^ƵŵŽĨtĞĞůŝ ,ĂŵĞƌƐůĞLJ͕ tŽůůŝ͕ϭϮ͘ϲй ϲ͘ϰй
Figure 8: Marsh Inflow Contributions - Disturbed Scenario
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^ƵŵŽĨ ^ƵŵŽĨ ŚŝĐŚĞƐƚĞƌ͕ ŝƌĞĐƚ ϭϲ͘ϰй ZĂŝŶĨĂůů͕ ϭϬ͘ϯй ^ƵŵŽĨ ĂƐƚ &ŽƌƚĞƐĐƵĞ͕ ϰϲ͘Ϭй ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ &ůĂŶŬƐ͕ϴ͘ϰй
^ƵŵŽĨ ĂƐƚ ^ƵŵŽĨtĞĞůŝ ,ĂŵĞƌƐůĞLJ͕ tŽůůŝ͕ϭϮ͘ϱй ϲ͘ϯй
Figure 9: Marsh Inflow Contributions - Restored Scenario
As discussed in Appendix K, the relative importance of each of the sub-catchment contributions varies from wet season to wet season. Three separate filling events were examined and the contribution from the Chichester catchment varied from 9% up to 32%.
The water balance showed that the three developments do not significantly reduce the volume of water reaching the Fortescue Marsh. The total marsh catchment area is 29,320 km2, whereas the combined area of the pits for the three mines is 190 km2, representing 0.64% of the total catchment. The computations undertaken for this project have assumed a worst case scenario in which all pits are active simultaneously. In reality this situation will not occur as pits will be progressively backfilled as new excavation proceeds. Hence, the maximum area of open pit is likely to be much smaller than that assumed for the calculations undertaken in this project. Modelling showed that the mines cause an average decrease of 1% in the total volume of water reaching the Marsh. During infilling events where rainfall is concentrated over the Chichester Ranges the decrease in inflows to the Marsh may be as a high as 2%. Rehabilitation of the pits after mine closure will reduce these impacts.
5.4 Areas of Cultural Significance
Impacts on areas of cultural significance were assessed based on the actual or potential reduction of catchment size as a result of the life of mine footprint. Actual reductions in catchment area were defined as a reduction in catchment size due to internally draining pits and dumps which receive direct rainfall. Potential reductions were assessed as any part of the catchment area from which flow may be restricted by pits and dumps without the implementation of any surface water management measures.
The impact assessment completed focused on the yinta located near the Fortescue Marsh, which are understood to be filled as a result of surface water flow associated with Christmas Creek and Kulbee
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Creek/Fortescue River. These yinta are referred to as “Yinta 1” and “Yinta 2” in the assessment, with their locations visible in Appendix B. The locations of other yinta in the area have also been identified in Appendix B. These yinta have not been included in this assessment as they are directly impacted by mining operations or in the case of the Takarra yinta there will be no impact from the mining operation.
The potential and actual impact in the form of reduced catchment area upstream of the Yinta areas is shown in Appendix B and in Table 9. The actual reduction in catchment area for Christmas Creek and Kulbee Creek/Fortescue River (Yinta 1 and 2) are not expected to exceed 6 and 8% over the life of mine. This estimation is conservative as it assumes that all development will be active at once, in reality these areas will be progressively disturbed, before being restored.
A combination of standard engineering practices and management controls are likely to minimise the potential impact on water balances for areas of significance. With the use of flood levees, diversions and perimeter drains, flows originating upstream are expected to pass through or around the mine area. An example of the effectiveness of these engineering practices and management controls can be seen in the difference mapping between year 5 and year 1, located in Appendix E and G.
Table 10: Potential and Actual Impacts on Catchment Area of the Yinta
Name Potential Catchment Reduction Actual Catchment Reduction
2 Yinta 1 216.8 km 84% 15.0 km2 6%
Yinta 2 74.0 km2 62% 9.2 km2 8%
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
6. CONCLUSIONS
This report describes the likely impact of the Christmas Creek Life of Mine Expansion on aspects of the hydrological processes within and around the developed area. The impacted areas have been estimated based on the spatial and temporal distribution of mine site infrastructure in relation to different landforms and the expected hydrological processes that take place within them. The assessment sought to identify impacts to three key areas:
• What was the likely impact of the development on areas of sheetflow dependent vegetation? • How does the development impact on the hydrological regime, including changes to flood extents, flow velocities and flow volumes passing through the site? • What is the potential cumulative impact of all mines proposed for the Chichester Ranges on the water balance of the Fortescue Marsh?
This assessment and the various supporting studies concluded that:
• Of a total 74 km2 of sheetflow dependent vegetation located within the study area, approximately 21% will be directly impacted by the development, with a further 13% being indirectly impacted.
• Significant changes to flow depths and velocities are likely to be confined to major waterways. No significant hydraulic changes are expected in areas of distributed flow or sheetflow outside the directly impacted zones.
• The Fortescue Marsh typically receives 260 GL of inflows and direct rainfall per year, of which approximately 17% flows of the Chichester Ranges north of the marsh. The eastern section of the Fortescue Marsh Catchment upstream of the Roy Hill pastoral station was shown to be the most important part of the catchment inflows.
• The combined effect of the Christmas Creek, Cloudbreak and Roy Hill development is not expected to reduce flows reaching the Fortescue Marsh by more than 1-2%.
This assessment has proceeded on the basis that the principles of Fortescue’s over-arching Surface Water Management Plan (SWMP) are applied with minimal variation to the proposed Christmas Creek Life of Mine development. It is expected that the outcomes of this study can be used to assist in the preparation and implementation of such a plan specific to the Christmas Creek development.
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
REFERENCES Anderson, V.J. & Hodgkinson, K.C., 1997. Grass-mediated capture of resource flows and the maintenance of banded Mulga in a semi-arid woodland in . Australian Journal of Botany Vol. 45, 331-342.
ANZECC & ARMCANZ, 2000. Australian and New Zealand guidelines for fresh and marine water quality
Barnes, H.H. Jr (1967). Roughness characteristics of natural channels. U.S. Dept of the Interior, Geological Survey Water-Supply Paper No. 1849.
Chow, V.T (1959). Open-Channel Hydraulics. McGraw Hill.
Department for the Environment, Water, Heritage and the Arts (DEWHA), 2008. Environment Protection and Biodiversity Conservation Act 1999 Protected Matters Report, available online:http://www.environment.gov.au/erin/ert/epbc/index.html, accessed 24 November 2008, Commonwealth of Australia.
Dunkerley, D., 2002. Infiltration rates and soil moisture in a groved mulga community near Alice Springs, arid central Australia: evidence for complex internal rainwater redistribution in a runoff–runon landscape, Journal of Arid Environments, 51: 199-219.
Danish Hydraulic Institute (2005a), MIKE 11 User Guide and Reference Manual, Hørsholm, Denmark.
Danish Hydraulic Institute (2005b), MIKE 21 User Guide and Reference Manual, Hørsholm, Denmark.
Engineers Australia 2006, Australian Runoff Quality – a guide to water sensitive urban design, Wong, T. H. F. (Editor-in-Chief), Engineers Media, Crows Nest, New South Wales.
Environ Australia Pty Ltd, 2005. Public Environmental Review, Pilbara Iron Ore and Infrastructure Project: E-W Railway and Mine Sites (Stage B). Report prepared for Fortescue Metals Group Ltd.
Flavell, D. 2005. Pilbara Iron Ore and Infrastructure Project, Design Flood Estimation. David Flavell Pty Ltd, June 2005.
Henderson, F.M. (1966). Open Channel Flow. Macmillan.
Ludwig, J., Tongway, D. J., Freudenberger, D., Noble, J. and Hodgkinson, K. (1997) Landscape Ecology, Function and Management: Principles from Australia's Rangelands. CSIRO Publishing, Collingwood, Australia.
Ludwig, J. A., Wilcox, B. P., Breshears, D. D., Tongway, D. J. and Imeson, A. C. (2005) Vegetation patches and runoff-erosion as interacting ecohydrological processes in semiarid landscapes, Ecology, 86(2), 288-297.
Muller Consulting Pty Ltd, 2005. Water Flow in Mulga Areas Adjoining Fortescue Marsh. Report of observations from field trips undertaken for Fortescue Metals Group Limited.
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
US Army Corps of Engineers – Hydrologic Engineering Centre, 2006. HEC-RAS River Analysis System User’s Manual, Version 4.0 Beta
XP Software Inc (2011). XP Storm Stormwater Management Model Getting Started Manual
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FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT
Appendix A: Christmas Creek Life of Mine Development and Major Waterways
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Appendix B: Yinta Locations and Catchment Assessment
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Appendix C: Direct and Indirect Sheet Flow Impacts
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Appendix D: Modelled Flood Extents
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KARRATHA MARBLE BAR /,)(2)0,1( &RS\ULJKW )/22''(37+6$1'(;7(176 :RUOH\3DUVRQV6HUYLFHV3W\/WG PA NN AW ON ICA )< 5(9 '$7( 5(9,6,21'(6&5,37,21'51 &+.' '(6(1*&+. $335' &867 *,6'6. 3/27'$7( 7,0( )(% 30 /2&$7,21 , ?352-(&76?)0*&+5,670$6&5((.3(5?B(1*,1((5,1*?+<+<'52/2* FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT Appendix I: Sensitivity Analysis – Flood Velocities i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology part 2\reporting\rev2\301012-01527-ss-rep-0001_rev2.docm Appendix 301012-01527-SS-REP-0001Rev 2 : 18 March 2014 765000 770000 775000 780000 785000 790000 795000 m 7525000 7525000 7520000 7520000 7515000 7515000 UNCONTROLLED COPY PRELIMINARY 6$9('$7( 7,0( )(% 30 UNCHECKED 7510000 7510000 .LORPHWHUV INFORMATION ONLY NOT TO BE USED 3URMHFWLRQ *'$ 0*$=RQH FOR CONSTRUCTION 765000 770000 775000 780000 785000 790000 795000 $6+((7 6&$/( /2&$7,213/$1 &86720(5 PORT HEDLAND 1 1 &+5,670$6&5((. KARRATHA MARBLE BAR /,)(2)0,1( &RS\ULJKW )/22'9(/2&,7,(6$1'(;7(17 :RUOH\3DUVRQV6HUYLFHV3W\/WG PA NN AW ON ICA $%1 )<\HDU$5, 0DQQLQJ VQ :25/(<3$56216352-(&71R 0+ ,QIRUPDWLRQ2QO\ Cloudbreak Mine CHRISTMAS '5*1R 5(9 CREEK TOM PRICE 5(9 '$7( 5(9,6,21'(6&5,37,21'51 &+.' '(6(1*&+. $335' &867 *,6'6. 3/27'$7( 7,0( )(% 30 /2&$7,21 , ?352-(&76?)0*&+5,670$6&5((.3(5?B(1*,1((5,1*?+<+<'52/2* UNCONTROLLED COPY PRELIMINARY 6$9('$7( 7,0( )(% 30 UNCHECKED 7510000 7510000 .LORPHWHUV INFORMATION ONLY NOT TO BE USED 3URMHFWLRQ *'$ 0*$=RQH FOR CONSTRUCTION 765000 770000 775000 780000 785000 790000 795000 $6+((7 6&$/( /2&$7,213/$1 &86720(5 PORT HEDLAND 1 1 &+5,670$6&5((. KARRATHA MARBLE BAR /,)(2)0,1( &RS\ULJKW )/22'9(/2&,7,(6$1'(;7(17 :RUOH\3DUVRQV6HUYLFHV3W\/WG PA NN AW ON ICA $%1 )<\HDU$5, 0DQQLQJ VQ :25/(<3$56216352-(&71R 0+ ,QIRUPDWLRQ2QO\ Cloudbreak Mine CHRISTMAS '5*1R 5(9 CREEK TOM PRICE 5(9 '$7( 5(9,6,21'(6&5,37,21'51 &+.' 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'(6(1*&+. $335' &867 *,6'6. 3/27'$7( 7,0( )(% 30 /2&$7,21 , ?352-(&76?)0*&+5,670$6&5((.3(5?B(1*,1((5,1*?+<+<'52/2* UNCONTROLLED COPY PRELIMINARY 6$9('$7( 7,0( )(% 30 UNCHECKED 7510000 7510000 .LORPHWHUV INFORMATION ONLY NOT TO BE USED 3URMHFWLRQ *'$ 0*$=RQH FOR CONSTRUCTION 765000 770000 775000 780000 785000 790000 795000 $6+((7 6&$/( /2&$7,213/$1 &86720(5 PORT HEDLAND 1 1 &+5,670$6&5((. KARRATHA MARBLE BAR /,)(2)0,1( &RS\ULJKW )/22'9(/2&,7,(6$1'(;7(17 :RUOH\3DUVRQV6HUYLFHV3W\/WG PA NN AW ON ICA $%1 )<\HDU$5, 0DQQLQJ VQ :25/(<3$56216352-(&71R 0+ ,QIRUPDWLRQ2QO\ Cloudbreak Mine CHRISTMAS '5*1R 5(9 CREEK TOM PRICE 5(9 '$7( 5(9,6,21'(6&5,37,21'51 &+.' '(6(1*&+. $335' &867 *,6'6. 3/27'$7( 7,0( )(% 30 /2&$7,21 , ?352-(&76?)0*&+5,670$6&5((.3(5?B(1*,1((5,1*?+<+<'52/2* UNCONTROLLED COPY PRELIMINARY 6$9('$7( 7,0( )(% 30 UNCHECKED 7510000 7510000 .LORPHWHUV INFORMATION ONLY NOT TO BE USED 3URMHFWLRQ *'$ 0*$=RQH FOR CONSTRUCTION 765000 770000 775000 780000 785000 790000 795000 $6+((7 6&$/( /2&$7,213/$1 &86720(5 PORT HEDLAND 1 1 &+5,670$6&5((. KARRATHA MARBLE BAR /,)(2)0,1( &RS\ULJKW )/22'9(/2&,7,(6$1'(;7(17 :RUOH\3DUVRQV6HUYLFHV3W\/WG PA NN AW ON ICA $%1 )<\HDU$5, 0DQQLQJ VQ :25/(<3$56216352-(&71R 0+ ,QIRUPDWLRQ2QO\ Cloudbreak Mine CHRISTMAS '5*1R 5(9 CREEK TOM PRICE 5(9 '$7( 5(9,6,21'(6&5,37,21'51 &+.' '(6(1*&+. $335' &867 *,6'6. 3/27'$7( 7,0( )(% 30 /2&$7,21 , ?352-(&76?)0*&+5,670$6&5((.3(5?B(1*,1((5,1*?+<+<'52/2* FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT Appendix J: Rainfall Loss Estimation Field Trials i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology part 2\reporting\rev2\301012-01527-ss-rep-0001_rev2.docm Appendix 301012-01527-SS-REP-0001Rev 2 : 18 March 2014 FORTESCUE METALS GROUP Christmas Creek Life of Mine Expansion Rainfall Loss Estimation Field Trials 301012-01527-SS-REP-0002 20-Apr-12 Infrastructure & Environment Level 7, QV1 Building 250 St Georges Terrace Perth WA 6000 Australia Tel: +61 8 9278 8111 Fax: +61 8 9278 8110 www.worleyparsons.com WorleyParsons Services Pty Ltd ABN 61 001 279 812 © Copyright 2012 WorleyParsons Services Pty Ltd FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS SYNOPSIS This study comprised of a series of infiltration tests to estimate changes in rainfall loss as a result of mining activity associated with the Christmas Creek Life of Mine expansion. The field program assessed the likely change to the surface runoff from backfilled sites and waste dumps and compared these to natural conditions. This report presents the outcomes of the field program and the estimated soil hydraulic parameters. . PROJECT 301012-01527-SS-REP-0002 - CHRISTMAS CREEK LIFE OF MINE EXPANSION REV DESCRIPTION ORIG REVIEW WORLEY- DATE CLIENT DATE PARSONS APPROVAL APPROVAL A Issued for Internal N/A 10-Apr-12 N/A Review M.Heyting P Bussemaker B Issued for Client 20-Apr-12 Review M.Heyting P S Atkinson Bussemaker i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page ii FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS CONTENTS 1. INTRODUCTION ...... 1 2. METHODOLOGY...... 2 2.1 Site Selection ...... 2 2.2 Infiltration measurements ...... 3 2.3 Data Analysis ...... 4 3. RESULTS ...... 6 3.1 Visual Analysis ...... 6 3.1.1 Backfilled Sites ...... 6 3.1.2 Waste Dump Sites ...... 6 3.1.3 Intergrove Areas...... 8 3.1.4 Groves ...... 8 3.2 Hydraulic Conductivity Analysis ...... 10 3.3 Sorptivity ...... 12 4. DISCUSSION ...... 15 4.1 Visual Observations ...... 15 4.2 Saturated Hydraulic Conductivity ...... 15 4.3 Sorptivity ...... 16 5. CONCLUSION ...... 17 6. REFERENCES ...... 18 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page iii 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 1. INTRODUCTION This study aims to quantify the effects that the Christmas Creek mine operations are likely to have on the volume of surface runoff generated following rainfall. A field program was undertaken to gain an understanding of the hydraulic soil properties of both disturbed and undisturbed areas. The use of a tension infiltrometer enabled the property of saturated hydraulic conductivity (Ksat) to be estimated for each of the disturbed and undisturbed areas. The outcomes of this analysis will provide an estimation of runoff generation from these soil types and the typical changes resulting from mine development. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 1 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 2. METHODOLOGY 2.1 Site Selection Following completion of mining operations in a given area within the Christmas Creek mine development, former pits are filled backfilled and some waste dumps are retained. Since these cover a significant proportion of the mine area at any given time during operations, it is important to understand how these surfaces respond to rainfall and how this compares to natural conditions. A series of sites were chosen across the Chichester operations, at both Cloudbreak and Christmas Creek to conduct infiltration testing on. The field program aimed to conduct infiltration tests on a number of waste dump sites, backfilled areas and grove and intergrove areas around the Christmas Creek and Cloudbreak area. Figure 1 and Figure 2 show the sampled sites at Cloudbreak and Christmas Creek respectively. Figure 1: Sample sites at Cloudbreak, Hamilton waste dump and Hamilton Backfilled area. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 2 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Figure 2: Christmas Creek sample locations, including two banded mulga areas and Vasse and Windich waste dumps. 2.2 Infiltration measurements Tension infiltrometers are designed to measure the near-saturated flow of water into a given soil, providing properties relevant to infiltration. The system applies water to the surface at a chosen tension to allow the water to be infiltrated into the soil profile, through the soil matrix rather than large macropores or cracks. Site work was completed in two stages, from the 12th of July 2011 to the 14th of July 2011, and from the 26th of March 2012 to the 30th of March 2012. The first field trip (July 2011) targeted areas undisturbed from the mine operations in sheetflow areas. The testing divided the natural environment into two areas, groved areas and intergrove areas. These areas are common throughout the Pilbara particularly in the flats near the Fortescue Marsh. The second field trip (March 2012) targeted areas impacted by mine operations such as backfilled pits and waste dumps. Commonly negative tensions ranging from -10mm to -40mm were applied to the soil, with a 20mm difference in tension were used in most cases to measure the unsaturated flow of water into the soil. Maintaining negative tensions prevents water flowing through large macropores and prevents pooling occurring on the soil surface (Soilmoisture Equipment Corp 2008). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 3 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 2.3 Data Analysis The Ksat is the coefficient of proportionality in Darcy’s law and can be used to describe the way water moves through saturated and unsaturated soils at constant water content (McKenzie & Cresswell 2002). Darcy’s Law is given below in equation (3.1): (3.1) Using the procedure of Reynolds and Elrick (1991) in combination with the Soil Measurement Systems User Manual for the Tension Infiltrometer it is possible to determine the unsaturated and Ksat for a paired data set. For these equations a series of measurements of flow will be taken at steady state and at successive negative potentials. The final equation shown below will determine the unsaturated hydraulic conductivity of the average tension: (Soil moisture Equipment Corp 2008) (3.2) Where or Ksat is given by (Mckenzie, Cresswell & Green 2002) (3.3) And is governed by (McKenzie, Cresswell & Green 2002) (3.4) Į is a constant that is representative of the ratio between flow rates at differing tensions. In equation 3.2 to 3.4 Gd is a shape parameter (usually measured as 0.25 (McKenzie, Cresswell & Green 2002), i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 4 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS is the negative potential supplied on the tension infiltrometer (cm), and q is the steady state flow at each supplied tension. Field work conducted provided a time series of infiltration quantities against time. At each sample location, infiltration quantities were taken at two different tensions. Flow rates at a given time intervals were calculated using the following equation: (McKenzie, Cresswell & Green 2002) (3.5) Where C is the reservoir calibration factor, ǻR is difference in the scale reading for a time interval, ǻt (McKenzie, Cresswell & Green 2002). For the disc infiltrometers used in the field, the C value was calculated from having a radius of 2.08cm to be 1.36×103 mm3/mm. Cumulative infiltration can be determined by dividing the total infiltration over the given time and dividing it by the cross-sectional area of the contact material, as shown below. (McKenzie, Cresswell & Green 2002) (3.6) C is the supply reservoir calibration, Ri is the initial scale reading and R is the reading at the time of interest (McKenzie, Cresswell & Green 2002). When cumulative infiltration rates have been identified it is possible to plot infiltration vs. time graphs, which can be used to identify steady state conditions and sorptivity rates. Steady state conditions occur when a there is a state of equilibrium in the system, i.e. no change over time (Adrien 2003). Taking the steady-state flow rate at both tensions can be done by calculating the average flow rate once steady state conditions have been achieved (McKenzie, Cresswell & Green 2002). Once this is determined it is possible to substitute the parameters into equations 3.2-3.4 to determine the unsaturated and Ksat. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 5 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 3. RESULTS 3.1 Visual Analysis 3.1.1 Backfilled Sites The Hamilton backfilled site had a clay layer over the top surface which was experiencing cracking on the surface as seen in Figure 3. The soil texture was fine and within the immediate area of the testing was fairly uniform. An area at the backfilled site showed evidence of more site traffic, it had a different texture, with areas of smaller stones imbedded in a clay layer (Figure 3) Figure 3: The backfilled areas characterized by cracked clay layers (left) and the compressed stone areas associated with higher traffic areas (right) 3.1.2 Waste Dump Sites Waste dump sites were visited at both the Cloudbreak and the Christmas creek mine sites. At Cloudbreak, the Hamilton dump was visited, while at Christmas Creek the Vasse and Windhich dumps were assessed. Each of the waste dumps consisted of different waste soils. The Hamilton dump, contained a yellow sand which was well compacted and consisted of small stones Figure 4. The Vasse dump consisted of an earthy coloured soil which was well compacted and contained both small and larger stones as seen in Figure 4. Windhich waste dump contained the largest range of stone sizes, which ranged from small pebbles to larger stones about 5cm in diameter and had an earthy colour to the soil (Figure 4). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 6 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Figure 4: The waste dump areas had varying characteristic from waste dump to waste dump. The Hamilton dump had a yellow colour with smaller stones (top left), the Vasse dump contained earthy soils with smaller stones (top right) and the Windhich dump contained larger stones (bottom). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 7 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 3.1.3 Intergrove Areas The intergrove surface was covered in small pebbles and had very few surface discontinuities, such as cracks. The pebbles, seen in Figure 5, vary in size across the intergrove areas, with some being up to 100 mm in diameter. The stones or pebbles are mainly embedded into the surface of the soil, though are still raised above the surface level. Underneath the surface there was evidence of soil moisture though this was minimal in comparison to the water content observed within the grove. The stones continued down the soil profile until approximately 200 mm depth. Figure 5: The intergrove areas of the banded mulga system are characterised by stony pebbles ranging in size. Limited vegetation and ecological activity is seen in these areas 3.1.4 Groves The groves had a silty/clay feel, were covered in surface litter and contained a number of holes created by termites. Figure 6 illustrates the evidence of biological activity that occurs within the groved systems, with termite holes and leaf litter spread throughout the grove. The leaf litter in Figure 6 is arranged in a way that suggests that there had been water flow in the area prior to the photograph. Within the grove, there were notable differences in the texture of the surface soils, silty/clays and did not contain any pebbles as seen in the intergroves. Some cracking was evident in some places within i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 8 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS the grove, which can be attributed to the clayey properties of the soil (Figure 7). In the subsoil, there was evidence of the prior rainfall event with the soil moisture being notably damper than the soils felt in the intergrove area. The mulga vegetation in the area contained leaves which were angled in such a way to promote interception and stemflow (Figure 7). Figure 6: Leaf litter and termite holes are evident throughout the groved areas of the banded mulga systems. Figure 7: Evidence of cracking on the surface of the silty clays that occur in the groves of the banded mulga systems (Left). Angled leaves and the mulga plant structure promotes interception and stem flow (Right). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 9 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 3.2 Hydraulic Conductivity Analysis The values calculated for the Ksat of the proposed sites can be seen in Table 1 and have been calculated using the procedure outlined in Section 2.3. Seven values for the Ksat could not be used in the analysis and have been labeled in red as the results violate the conventions of the testing. Overall averages for Ksat were equal to 35.06mm/hr (Std Dev of 30.94) for grove sites, 18.17 mm/hr (Std Dev of 11.80) for intergrove sites, 33.95 mm/hr (Std Dev of 8.1) for backfilled areas and 25.93 mm/hr (Std Dev of 12.49) for Wastedumps. Site 1 of the groved areas exhibited the highest average KSat with 60.5 mm/hr. A graphical display of the sites specific averages and standard deviations are shown in Figure 8. A single factor Anova test showed that there was not a significant difference in the means of the groups (P-value of 0.16). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 10 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Table 1: Hydraulic conductivity calculated using the procedure outlined in Section 2.3. The conductivity has been calculated in mm/hr for all sites. Values in red have been omitted from the analysis. Grove Ksat (mm/hr) Intergrove Ksat (mm/hr) Backfilled Ksat (mm/hr) Wastedump Ksat (mm/hr) Site1-Sample1 88.82 Site1-Sample1 26.12 Site1-Sample1 14.53 Site1-Sample1 16.65 Site1-Sample2 -3.26 Site1-Sample2 6.43 Site1-Sample2 39.31 Site1-Sample3 32.65 Site1-Sample3 5.48 Site1-Sample3 32.61 Site1-Sample4 30.38 Site1-Sample5 52.91 Site1 – Average 60.41 Site1 – Average 12.68 Site1 – Average 33.95 Site1 – Average 16.65 Site1 – Std Dev 27.77 Site1 – Std Dev 9.51 Site1 – Std Dev 12.49 Site1 – Std Dev 0.00 Site2-Sample1 45.37 Site2-Sample1 27.53 Site2-Sample1 26.65 Site2-Sample2 45.21 Site2-Sample2 15.44 Site2-Sample2 26.87 Site2-Sample3 2.07 Site2-Sample3 14.92 Site2-Sample3 41.53 Site2-Sample4 1.51 Site2-Sample5 6.10 Site2 – Average 25.65 Site2 – Average 19.30 Site2 – Average 31.68 Site2 – Std Dev 19.56 Site2 – Std Dev 5.83 Site2 – Std Dev 6.96 Site3-Sample1 1.86 Site3-Sample1 1.64 Site3-Sample1 14.20 Site3-Sample2 3.18 Site3-Sample2 14.62 Site3-Sample2 17.50 Site3-Sample3 -3.1 Site3-Sample3 10.98 Site3-Sample3 26.36 Site3 – Average 3.18 Site3 – Average 9.08 Site3 – Average 19.35 Site3 – Std Dev 0.00 Site3 – Std Dev 5.46 Site3 – Std Dev 5.13 Site4-Sample1 13.31 Site4-Sample2 37.31 Site4-Sample3 42.93 Site4-Sample4 19.52 Site4 – Average 33.25 Site4 – Std Dev 9.98 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 11 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Figure 8: Ksat average for each of the sample areas. The standard deviations are shown using the error bars. 3.3 Sorptivity The values calculated for sorptivity of the proposed sites can be seen in Table 2and have been calculated using the procedure outlined in Section 2.3. Overall averages for sorptivity were equal to 0.41 mm/hr0.5 (Std Dev of 0.14) for grove sites, 0.38 mm/hr0.5 (Std Dev of 0.20) for intergrove sites, 0.13 mm/hr0.5 (Std Dev of 0.05) for backfilled areas and 0.21 mm/hr0.5 (Std Dev of 0.07) for wastedumps. Site 2 of the intrergrove area exhibited the highest average sorptivity with 0.58 mm/hr0.5. A graphical display of the sites specific averages and standard deviations are shown in Figure 9: A single factor Anova test showed that there was a significant difference in the means of the groups (P-value of 0.003). i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 12 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Table 2: Sorptivity values based on the initial curves produced from cumulative infiltration graphs. The sorptivity values have been calculated in mm/h0.5 for the intergroves, groves, backfilled areas and waste dumps at -40mm tension. Groves (mm/hr0.5) Intergrove (mm/hr0.5) Backfilled (mm/hr0.5) Wastedumps (mm/hr0.5) Site1-Sample1 0.28 Site1-Sample1 0.39 Site1-Sample1 0.08 Site1-Sample1 0.36 Site1-Sample2 0.11 Site1-Sample2 0.20 Site1-Sample2 0.17 Site1-Sample3 0.33 Site1-Sample3 0.29 Site1-Sample3 0.12 Site1-Sample4 0.07 Site1-Sample5 0.19 Site1 – Average 0.24 Site1 – Average 0.29 Site1 – Average 0.13 Site1 – Average 0.36 Site1 – Std Dev 0.10 Site1 – Std Dev 0.08 Site1 – Std Dev 0.05 Site1 – Std Dev 0 Site2-Sample1 0.52 Site2-Sample1 0.80 Site2-Sample1 0.17 Site2-Sample2 0.64 Site2-Sample2 0.40 Site2-Sample2 0.21 Site2-Sample3 0.56 Site2-Sample3 0.54 Site2-Sample3 0.18 Site2-Sample4 0.45 Site2-Sample5 0.47 Site2 – Average 0.53 Site2 – Average 0.58 Site2 – Average 0.19 Site2 – Std Dev 0.07 Site2 – Std Dev 0.16 Site2 – Std Dev 0.02 Site3-Sample1 0.35 Site3-Sample1 0.42 Site3-Sample1 0.15 Site3-Sample2 0.41 Site3-Sample2 0.72 Site3-Sample2 0.19 Site3-Sample3 0.35 Site3-Sample3 0.35 Site3-Sample3 0.18 Site3 – Average 0.37 Site3 – Average 0.21 Site3 – Average 0.17 Site3 – Std Dev 0.03 Site3 – Std Dev 0.16 Site3 – Std Dev 0.02 Site4-Sample1 0.14 Site4-Sample2 0.13 Site4-Sample3 0.26 Site4-Sample4 0.29 Site4 – Average 0.21 Site4 – Std Dev 0.07 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 13 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS Figure 9: Sorptivity average for each of the sample areas. The standard deviations are shown using the error bars. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 14 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 4. DISCUSSION 4.1 Visual Observations Visually the soils of the waste dumps and the intergroves are similar, with the majority of them earthy in colour and contain varying amounts of stones. The waste dumps and the intergrove areas contained a number of stones and were relatively smooth, they were partially armoured with stones and sealed by crusts of silts and clays. These characteristics prevent high amounts of infiltration occurring and promote runoff. The backfilled site visited had a thin clayey topsoil, with areas subject to traffic the clay layer was removed. Under the clayey topsoil, there was a stony layer similar to the conditions evident in the intergrove and waste dump areas. The grove areas contained a clayey topsoil similar to the backfilled areas, with the addition of macropores due to the surrounding environment. Termite mounds and ants nests were scattered throughout the groved areas, which were surrounded by a network of macropores created by the activity of the invertebrates. Macropores could be also seen created by the roots of the mulga vegetation and through the shrinkage of the soil once the surface had dried. The macropores caused by biological activity would increase the infiltration capacity of the soil greatly. 4.2 Saturated Hydraulic Conductivity The Ksat values determined from the analysis of the tension infiltrometer data resulted in values that were within the range supplied by the Australian Soil Resource Information System (ASRIS) database. ASRIS compiles the best publically available information on soil properties. Values from ASRIS suggested that Ksat values should range from a highly permeable rate near the marsh (30- 300mm/hr to moderately permeable higher up in the catchment (3-30mm/hr). Comparison between the calculated values of Ksat for grove, intergrove, waste dumps and backfilled areas did not indicate any statistically significant differences. There was no significant difference between the saturated hydraulic conductivities of the soils, which suggests through Darcy’s Law that there would not be a difference in the infiltration rates of the sites. The testing conducted in the field did not incorporate the Ksat of the soil attributed to macropore flow. Macropore flow would dramatically impact the results for the saturated hydraulic conductivities for the groved areas in particular, where the macropores were seen throughout the groved area. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 15 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 4.3 Sorptivity Sorptivity rates were determined from the analysis of the cumulative infiltration rates of each sit and displayed a result that did deliver significant differences between the soils in the groves and intergroves, and the backfilled areas and waste dumps. This suggests that water initially infiltrates faster in the undisturbed sites than on wastedumps and backfilled areas. After the initial minutes of rainfall, it is Ksat and preferential flow that control the differences between runoff and infiltration rates. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 16 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 5. CONCLUSION This study aimed to determine the likely change to the surface runoff as a result of the mine works. A visual assessment of the soil was undertaken as well as Ksat calculations for the soil matrix of each of the main areas of the mining development (Grove, intergrove, backfilled sites and waste dumps). Visually the areas were different, with the groved areas and the backfilled sites having a clayey texture, and the waste dumps and the intergrove sites being stony and having a natural armouring on the surface promoting runoff. The sorptivity calculations that were undertaken, displayed significant results between the four areas tested. From the sites that were tested, there was a significant difference between the natural sites and the disturbed sites, with the natural grove and intergrove sites recording higher sorptivity rates. This will result in initially water infiltrating faster into the grove and intergrove sites. Infiltration testing used to calculate the Ksat of each of the soils did not return significantly different results between the soils at each site. Grove areas and backfilled areas displayed the highest Ksat, followed by waste dumps and intergrove areas. The calculations and measurements of Ksat do not include the effects of macropore flow which would be a major differentiator when analyzing the difference between groved areas and other areas. The groved areas contained large amounts of macropores which would have increased the recorded infiltration rates through preferential flow if this component of infiltration was included in the testing and analysis. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 17 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION RAINFALL LOSS ESTIMATION FIELD TRIALS 6. REFERENCES Adrien, NG 2003, 'X-Y-Z', in Computational Hydraulics and Hydrology, CRC Press, p. 401[2011/08/14]. CSIRO Land and Water, 2001, Australian Soil Resource Information System. Australian Collaborative Land Evaluation Program [24/04/2012] Heyting M., Honours Thesis (2011). Hydrological Processes in Sheetflow Dependent Mulga Groves in the Central Pilbara, Western Australia. [12/04/2012] McKenzie, NJ, Cresswell, HP & Green, TW 2002, 'Chapter 8: Field Measurement of Unsaturated Hydraulic Conductivity Using Tension Infiltrometers', in Soil Physical Measuremnet and Interpretation for Land Evaluation, eds NJ McKenzie, K Coughlan & HP Cresswell, CSIRO Publishing, Collingwood, pp. 119-131. Soil Measurement Systems, Tension Infiltrometer. Available from: i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\fieldwork report\301012-01527-ss-rep-0002_rev b.doc Page 18 301012-01527-SS-REP-0002 : Rev B : 20-Apr-12 FORTESCUE METALS GROUP LIMITED CHRISTMAS CREEK LIFE OF MINE EXPANSION SURFACE WATER INVESTIGATION AND IMPACT ASSESSMENT Appendix K: Fortescue Marsh Catchment Water Balance Study i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology part 2\reporting\rev2\301012-01527-ss-rep-0001_rev2.docm Appendix 301012-01527-SS-REP-0001Rev 2 : 18 March 2014 FORTESCUE METALS GROUP Christmas Creek Life of Mine Expansion Fortescue Marsh Catchment Water Balance Study 301012-01527-SS-REP-0003 18 March 2014 Level 7, QV1 Building, 250 St Georges Terrace Perth WA 6000 Australia Telephone: +61 8 9278 8111 Facsimile: +61 8 9278 8110 www.worleyparsons.com ABN 61 001 279 812 © Copyright 2012 WorleyParsons Services Pty Ltd FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY CONTENTS 1 INTRODUCTION ...... 1 2. METHODOLOGY...... 2 2.1 Overall Approach ...... 2 2.2 Source Catchments Model ...... 3 2.2.1 Catchment Delineation ...... 3 2.2.2 Functional Units ...... 4 2.2.3 Rainfall Runoff Model ...... 5 2.2.4 Rainfall Data ...... 5 2.2.5 Streamflow Data...... 7 2.2.6 Ophthalmia Dam ...... 8 2.2.7 Spreadsheet Water Balance Model ...... 9 2.3 Scenarios ...... 9 2.4 Assumptions ...... 10 3. RESULTS ...... 11 3.1 Overall Water Balance ...... 11 3.2 Selected Inflow Periods ...... 13 4. DISCUSSION ...... 15 4.1 Significance of Impacts ...... 15 4.2 Modelling Limitations ...... 15 5. CONCLUSION ...... 17 REFERENCES ...... 18 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page iii301012-01527 : 301012-01527-SS-REP-0003 Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 1 INTRODUCTION Christmas Creek Mine lies to the north of Fortescue Marsh within catchments that drain the Chichester Ranges. Development of Christmas Creek Mine will impact the supply of water to the Marsh at different stages of its life cycle as the result of the following processes: • Direct rainfall on open pits will not generate any runoff, effectively reducing the catchment area; • Infiltration on spoils dumps and back filled pits are likely to be higher than those from natural terrain, producing less runoff. Although this effect will be compensated by reduce infiltration and by high runoff paved areas and heavily traffic areas (which will become more consolidated than natural ground conditions). This study aims to estimate the impact that development of Christmas Creek Mine will have on the Fortescue Marsh. A spreadsheet based daily water balance model was established to determine the water volumes that reach the marsh during predevelopment, developed and post closure scenarios. A separate rainfall runoff model was established to estimate surface flows into the marsh from ungauged catchments, based on Source Catchments which was developed by eWater CRC. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 1301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 2. METHODOLOGY 2.1 Overall Approach The primary tool applied in this project was a spreadsheet based daily water balance model of Fortescue Marsh. The water balance model computes the following components: • Rainfall directly on the water surface of the Marsh: • Runoff inflows to the Marsh; • Evaporation losses from the water surface of the Marsh Based on groundwater modelling undertaken by Fortescue (FMG 2011) groundwater interactions with the Marsh were assumed to be insignificant. The water balance model was established for the period from 1999 to 2010. During this period 40 satellite images were obtained at discrete points in time and used to estimate the extent of inundation in the Marsh. An accurate digital terrain model was established for the Marsh, based on LIDAR information, and this was combined with the satellite imagery to estimate the storage volumes when the images were taken. A daily rainfall runoff model was established and used to estimated surface runoff into the Marsh. There are four stream flow gauging stations within Weeli Wolli Creek and one stream flow gauging station on the Fortescue River. A rainfall runoff model was established and calibrated for each of these catchments. These gauging stations are all located to the south of the Marsh in hilly terrain. The calibrated model parameters were found to be similar for each of these gauging stations. Median parameters from these gauged catchments were applied to the ungauged catchments draining the Chichester Ranges and East Hamersley’s, which were considered to have similar terrain and hydrologic properties. These computed flows were input to the water balance model. The gauged flows for Weeli Wolli Creek (measured at Waterloo Bore) were also entered into the water balance model. (Note that Waterloo is located approximately 30 kilometres south of the Marsh and Weeli Wolli Creek traverses an alluvial fan between Waterloo and the Marsh incurring significant transmission losses during low flows. However, during major inflow events it was considered that transmission losses would be minor.) The gauging station on the Fortescue River is located at Newman, just upstream of Opthalmia Dam which was constructed in 1981. Opthalmia Dam has a storage capacity of 32 GL, and has only overflowed 3 times since construction. There is no stream flow gauge downstream of Opthamia Dam and so flows downstream of the dam were estimated by use of the Source Catchments model. This model utilized observed stream flows at Newman and then simulated the storage behaviour of the dam to compute the spills which were then entered into the water balance model. The only input (or output) missing from the water balance model at this stage was the ungauged inflow from the remainder of the catchment. The water balance model was then applied to estimate i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 2301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY this ungauged inflow. A rainfall runoff model was then established and calibrated to match the ungauged inflows. The rainfall runoff model parameters for the catchment affected by the proposed Christmas Creek mine were then modified to represent conditions during the life of the mine and following closure in order to estimate the change in runoff from these catchments. 2.2 Source Catchments Model Source Catchments is a rainfall runoff modelling package developed by eWater CRC which operates on a daily time step. Source Catchments incorporates a number of different hydrological models for simulating the rainfall runoff process and the user can select the package that best suits their application. For this project the Sacramento model was adopted. Details of the model established for this project are provided below. 2.2.1 Catchment Delineation Sub-catchments for Fortescue Marsh were delineated using topographic information from Shuttle Radar Topographic Mission (SRTM) data. The catchment was broken into 35 sub-catchments, are shown in Figure 2-1. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 3301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Figure 2-1: The Fortescue Marsh sub-catchments 2.2.2 Functional Units The catchment was divided into five functional units which were considered to have different hydrologic properties. The adopted functional units were: • Fortescue Marsh, • hills, • lowlands, • mine areas, and • backfilled areas. The hill areas were considered to have higher rates of runoff than the lowlands which generally had very low gradients and alluvial materials. The mine areas are characterised by pit shells which do generate runoff, while backfilled areas are expected to have reduced runoff compared to natural conditions. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 4301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 2.2.3 Rainfall Runoff Model Sacramento was adopted as the rainfall runoff model for all catchments within the model. The parameters used in the modelling of each functional unit are provided in Table 2.1. Table 2.1: Sacramento rainfall runoff model parameters Sacramento Marsh Lowlands Hills Restored parameter Adimp 0.01 Ϭ͘ϲϲ 0.52 0.34 Lzfpm 40 ϰϴ 29.67 31 Lsfsm 23 ϭϯ 31.67 27.2 Lzpk 0.009 Ϭ͘ϱϳ 0.82 0.598 Lzsk 0.043 Ϭ͘ϱϵ 0.37 0.63 Lztwm 130 ϮϳϬ 290 383.6 Pctim 0.01 Ϭ 0.02 0.002 Pfree 0.063 Ϭ͘ϭϯ 0.08 0.03 Rexp 1 Ϭ͘Ϯ 1.79 1.64 Rsev 0.3 Ϭ͘ϯ 0.30 0 Sarva 0.01 Ϭ͘Ϭϭ 0.01 0 Side 0 Ϭ 0.00 0 Ssout 0 Ϭ 0.00 0 Uzfwm 40 ϳϱ 48.33 30.2 Uzk 0.245 Ϭ͘ϭϳ 0.66 0.43 Uztwm 50 ϲϲ 65.00 96.4 Zperc 40 ϰϱ 29.00 51.2 2.2.4 Rainfall Data There are seven daily rainfall gauging stations located within the Fortescue marsh catchment and a further seven stations located near the catchment boundary, but outside the catchment. The gauging station locations can be seen in Figure 2-2. Data at these stations varied in quality, with rainfall data in some areas missing for significant periods of time. There are also periods where rainfall from multiple days has been accumulated into a single reading (generally during holidays and weekends). The rainfall data was therefore processed to disaggregate the accumulated readings into individual days and to infill missing records. The approach for disaggregation was to use the proportion of rainfall recorded on individual days from the nearest rainfall station to apportion the accumulated readings. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 5301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Figure 2-2: Rainfall gauging station locations The process for infilling missing data was based on the Inverse Distance Weighted Interpolation Method (Lynch and Schulze 1995), using the following equations: σୀଵ ܼܹ ܼ ൌ σୀଵ ܹ ͳ ܹ݅ ൌ ʹ ݀݅ Where: Zp = interpolated value at the station of interest Zi = rainfall value at location (xi,yi), Wi = weighting function, n = number of rainfall stations with recorded values, and di = distance between Zp and Zi. A Thiessen polygon was constructed for the Fortescue Marsh catchment and used to determine which rainfall gauging station should be assigned to individual sub-catchments, refer to Figure 2-3. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 6301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Figure 2-3: Thiessen polygon used to allocate rainfall stations to specific subcatchments 2.2.5 Streamflow Data Recorded stream flow data was available from five gauging stations within the Fortescue Marsh catchment, which are listed below: • Gauge No. 708001 on Marillana Creek at Flat Rocks (tributary of Weeli Wolli Creek) • Gauge No. 708016 on Weeli Wolli Cree at Weeli Wolli Springs • Gauge No. 708014 on Weeli Wolli Creek at Tarina • Gauge No. 708013 on Weeli Wolli Creek at Waterloo Bore • Gauge No. 708011 on Fortescue River at Newman The locations of the gauging stations are shown in Figure 2-4. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 7301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Figure 2-4:Streamflow gauging stations locations 2.2.6 Ophthalmia Dam Ophthalmia Dam is located on the Fortescue River downstream of Newman. The dam has a maximum capacity of 32 GL and a surface area of 1260 ha (Water and Rivers Commission 2000). The purpose of the dam is to recharge underlying aquifers, which provide water supply for the township of Newman. The dam is represented in the model as a storage area, releasing water once the dam fills. The dam also intercepts inflow from both the main branch of the Fortescue River, (gauged at Newman) and significant ungauged catchments between Newman and the Dam. Inflows from the ungauged catchment were estimated in the Sacramento model using parameters for hilly terrain. The dimensions for the dam are provided in (Table 2.2). An infiltration rate of 10 mm/day was adopted. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 8301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Table 2.2: Key Dimensions of Opthalmia Dam Level (m) Volume (ML) Area (Hectare) 0 0 0 2.54 3556 420 5.08 14224 840 7.62 32000 1260 2.2.7 Spreadsheet Water Balance Model The water balance model represents three distinct areas in the Marsh (east, central and west), which are hydraulically separate at low water levels, but merge to form a single storage when water levels exceed 406.4 m AHD. Water enters each section of the Marsh through direct rainfall and streamflow. Sub-catchments 1, 7 and 8 contribute to the western cell, sub-catchment 2 contributes to the central cell and sub-catchments 3, 4, 5, 9 and 10 contribute to the eastern cell (refer to Figure 2.1). When the water level is below 406.5 m AHD flow between the cells was estimated using the broad crested weir equation taking into account the head difference between cells. Daily evaporation losses were computed using the surface area of the Marsh and the daily pan evaporation measured at Marble Bar. A pan factor of 0.65 was used to convert the pan evaporation to an open water evaporation value. The interaction between groundwater and the Marsh was assumed to be negligible. 2.3 Scenarios The following three scenarios were run to determine the effect of combined mining operations at Cloudbreak, Christmas Creek and Roy Hill on the Marsh water balance: • Undisturbed conditions: No mines at Cloudbreak Christmas Creek or Roy Hill, with the remainder of the catchment in current conditions i.e. Opthalmia Dam in place); • Disturbed conditions: Full development at Cloudbreak, Christmas Creek and Roy Hill with zero runoff from pit areas; and • Restored conditions: with reduced runoff from infilled pit areas. Under disturbed conditions, it was assumed that all mine pits are active at the same time. The pit areas applied for the study were 51.2 km2, 81.41 km2 and 55.84 km2 for Roy Hill, Christmas Creek and Cloudbreak, respectively. This is an unrealistic scenario since only a small fraction of the developed areas will be actively mined at any point in time. Based on in-situ field measurements taken during the Rainfall Loss Estimation Field Trials (301012- 01527-SS-REP-0002) runoff from the infilled pit areas is expected to be reduced by 23% from current conditions, due to higher rates of infiltration rates. The Sacramento model parameters were modified accordingly. Inflows to the Marsh are reported for five separate contributing areas, namely the Chichester Ranges, Weeli Wolli Creek, East Hamersley and East Fortescue. These areas are shown below in Figure 2-5. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 9301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Figure 2-5: Main contributing catchments within the Fortescue Marsh catchment 2.4 Assumptions A number of assumptions were made in application of the Source catchments and water balance models, which are listed below: • Flows measured at Waterloo Bore in Weeli Wolli Creek were assumed to reach the Marsh during wet infilling periods. • Spill over Ophthalmia Dam is assumed to reach the Marsh. • Runoff from sub-catchments 1, 3, 4, 5 and 6 go directly into the Marsh. • A uniform set of model parameters have been applied to the hill areas, based on calibration results from the five stream flow gauging stations. • A uniform set of model parameters has been applied to all lowland areas, i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 10301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 3. RESULTS 3.1 Overall Water Balance The water balance model was run for the period from 1/12/1984 to 30/04/2011. The average volume of water entering the Marsh is 281 GL per year for the undisturbed scenario. The contribution from each source is shown for each scenario in Table 3.1 and Figures 2.6 to 2.8. It can be seen that over this period the Chichester Ranges contribute approximately 17 % of the total Marsh inflows. Development of the three mines reduces the contribution from the Chichester Ranges by approximately 6%, which reduces the total inflow to the Marsh by approximately 1%. Table 3.1: Results for period 1984 to 2011 Undisturbed Scenario Disturbed Scenario Restored Scenario Source of Inflow Contribution (%) Contribution (%) Contribution (%) GL Percentage GL Percentage GL Percentage Chichester 48 17.2% 45 16.1% 46 16.4% East Fortescue 128 45.6% 128 46.2% 128 46.0% Southern Flanks 23 8.3% 23 8.5% 23 8.4% Weeli Wolli 35 12.4% 35 12.6% 35 12.5% East Hamersley 18 6.3% 18 6.4% 18 6.3% Direct Rainfall 29 10.2% 29 10.3% 29 10.3% i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 11301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY ^ƵŵŽĨ ŚŝĐŚĞƐƚĞƌ͕ ϭϳ͘Ϯй ^ƵŵŽĨŝƌĞĐƚ ^ƵŵŽĨ ĂƐƚ ZĂŝŶĨĂůů͕ &ŽƌƚĞƐĐƵĞ͕ ϭϬ͘Ϯй ϰϱ͘ϲй ^ƵŵŽĨ ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ tĞĞůŝ &ůĂŶŬƐ͕ϴ͘ϯй tŽůůŝ͕ ϭϮ͘ϰй ^ƵŵŽĨ ĂƐƚ ,ĂŵĞƌƐůĞLJ͕ ϲ͘ϯй Figure 3-6: Marsh Inflow Contributions - Undisturbed Scenario ^ƵŵŽĨ ^ƵŵŽĨ ŝƌĞĐƚ ŚŝĐŚĞƐƚĞƌ͕ ZĂŝŶĨĂůů͕ ϭϲ͘ϭй ϭϬ͘ϯй ^ƵŵŽĨ ĂƐƚ &ŽƌƚĞƐĐƵĞ͕ ϰϲ͘Ϯй ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ &ůĂŶŬƐ͕ϴ͘ϱй ^ƵŵŽĨ ĂƐƚ ^ƵŵŽĨtĞĞůŝ ,ĂŵĞƌƐůĞLJ͕ tŽůůŝ͕ϭϮ͘ϲй ϲ͘ϰй Figure 3-7: Marsh Inflow Contributions - Disturbed Scenario i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 12301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY ^ƵŵŽĨ ŚŝĐŚĞƐƚĞƌ͕ ϭϲ͘ϰй ^ƵŵŽĨ ^ƵŵŽĨ ĂƐƚ ŝƌĞĐƚ &ŽƌƚĞƐĐƵĞ͕ ZĂŝŶĨĂůů͕ ϰϲ͘Ϭй ϭϬ͘ϯй ^ƵŵŽĨ ^ŽƵƚŚĞƌŶ &ůĂŶŬƐ͕ϴ͘ϰй ^ƵŵŽĨ ĂƐƚ ^ƵŵŽĨtĞĞůŝ ,ĂŵĞƌƐůĞLJ͕ tŽůůŝ͕ϭϮ͘ϱй ϲ͘ϯй Figure 3-8: Marsh Inflow Contributions - Restored Scenario 3.2 Selected Inflow Periods Examination of the water balance model results shows that the significance of different inputs to the Marsh inflows varies from one filling event to another. This is demonstrated by the results in Table 3- 2 to 3-4. It can be seen that the contribution of the Chichester Ranges varies from 9% to 32% of the total Marsh inflows. Their highest contribution was during the December 2001 to March 2002 inflow event. In a repeat of this event the impact of the mines would be to reduce the total Marsh inflows by just under 2%. The Chichester catchment made the smallest contribution during the December 2002 to March 2003 event where the effect of the mines would be to reduce the total Marsh inflows by less than 1%. Table 3.2: Inflow Period November 1999 to June 2000 Source of Inflow Undisturbed Scenario Disturbed Scenario Restored Scenario Volume Contribution Volume Contribution Volume Contribution (GL) (%) (GL) (%) (GL) (%) Chichester 264.5 13.6 248.0 12.8 252.7 13.0 East Fortescue 924.5 47.4 924.5 47.8 924.5 47.7 Southern Flanks 106.3 5.5 106.3 5.5 106.3 5.5 Weeli Wolli 372.0 19.1 372.0 19.2 372.0 19.2 East Hamersley 163.1 8.4 163.1 8.4 163.1 8.4 Direct Rainfall 119.5 6.1 119.5 6.2 119.5 6.2 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 13301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY Table 3.3: Inflow Period November 2001 to February 2002 Source of Inflow Undisturbed Scenario Disturbed Scenario Restored Scenario Volume Contribution Volume Contribution Volume Contribution (GL) (%) (GL) (%) (GL) (%) Chichester 161.0 32.0 148.6 30.3 152.7 30.9 East Fortescue 308.2 61.3 308.2 62.8 308.2 62.3 Southern Flanks 9.4 1.9 9.4 1.9 9.4 1.9 Weeli Wolli 0.4 0.1 0.4 0.1 0.4 0.1 East Hamersley 9.8 1.9 9.8 2.0 9.8 2.0 Direct Rainfall 14.2 2.8 14.2 2.9 14.2 2.9 Table 3.4: Inflow Period December 2002 to March 2003 Source of Inflow Undisturbed Scenario Disturbed Scenario Restored Scenario Volume Contribution Volume Contribution Volume Contribution (GL) (%) (GL) (%) (GL) (%) Chichester 70.4 8.6 62.5 7.7 64.6 7.9 East Fortescue 188.9 23.0 188.9 23.3 188.9 23.2 Southern Flanks 169.2 20.6 169.2 20.8 169.2 20.8 Weeli Wolli 150.0 18.3 150.0 18.5 150.0 18.4 East Hamersley 47.9 5.8 47.9 5.9 47.9 5.9 Direct Rainfall 193.4 23.6 193.4 23.8 193.4 23.8 i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 14301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 4. DISCUSSION 4.1 Significance of Impacts Fortescue Marsh has a total catchment area of 29,320 km2, whereas the combined area of the combined pits for the three mines is 190 km2, representing 0.64% of the total catchment. The computations undertaken for this project have assumed a worst case scenario in which all pits are active simultaneously. In reality this situation will not occur as pits will be progressively backfilled as new excavation proceeds. Hence, the maximum area of open pit is likely to be much smaller than that assumed for the calculations undertaken in this project. Nevertheless, even with this assumption the impact of the mines on the inflows to the Marsh has shown to be relatively insignificant. Modelling showed that the mines cause an average decrease of 1% in the total volume of water reaching the Marsh. During infilling events where rainfall is concentrated over the Chichester Ranges then the decrease in inflows to the Marsh may be as a high as 2%. Rehabilitation of the pits after mine closure will reduce these impacts. 4.2 Modelling Limitations Calibration of the rainfall runoff model was hampered by the availability of gauging data. For instance, there are no stream flow gauges in the Chichester Ranges or any of the lowland areas. These ungauged areas represent approximately three quarters of the Fortescue Marsh catchment. Significantly there is no gauge recording outflows from Opthalmia Dam, which has greatly modified the flow behaviour of the Fortescue River, effectively harvesting the majority of flows from the more productive upper catchment. Another issue is that rainfall across the catchment is highly variable and localized. It was found that the available rainfall gauges did not always provide a good representation of the rainfall across the catchment and there was often a poor correlation between the pattern of recorded stream flows and recorded rainfalls. The Ophthalmia dam was constructed in 1981 on the Fortescue River upstream of Ethel Gorge near the town of Newman and has an upstream catchment of 4300 km2 (Payne & Mitchell 1999). The dam is used to recharge underlying aquifers which provide the water supply for the township of Newman. There is minimal information in regards to flow over the dam (Water and Rivers Commission 2000). In the period from construction (1981) and 1999, the dam only spilled three times (Payne & Mitchell 1999). Mines located in the Weeli Wolli Creek catchment that are operated by BHP and Rio Tinto discharge excess operational water to Weeli Wolli Creek and its tributaries. Weeli Wolli Creek was previously an ephemeral creek, only flowing during rainfall events, but it now experiences significant flows all year round (FMG 2012). As a result, daily streamflow has gone from a median of 0 ML/day to approximately 100 ML/day at the Tarina Gauging station (FMG 2012). During dry weather periods this flow is lost to infiltration and is not apparent at the Waterloo stream flow gauging station. These flows i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 15301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY seem to have impacted on the gauged low flows at the Tarina gauging station and so the parameters for this station were not considered when selecting median parameters values for the hills land units. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 16301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY 5. CONCLUSION This study compiled a water balance for the Fortescue Marsh between 1984 and 2011, based on modelled relationships between observations of rainfall, stream flow and Marsh water levels derived from satellite imagery and topographic analysis. In an average year for the undisturbed scenario, the Fortescue Marsh receives a total of 281 GL of catchment runoff and direct rainfall. Typically the contribution from the Chichester Ranges is 17.2%. Rainfall across the catchment is highly variable and from year to year, the relative importance of the contributing areas changes. Analysis of three separate wetting periods showed that the relative contribution of the Chichester Ranges varied between 9% and 32%. The study examined the combined impact of the Cloudbreak, Christmas Creek and Roy Hill mine developments on the water balance of the Fortescue Marsh. The study found that the combined pit area of 190 km2 does not significantly reduce inflows into the marsh, with modelled reductions on average not exceeding 1% of total inflow. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 17301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014 FORTESCUE METALS GROUP CHRISTMAS CREEK LIFE OF MINE EXPANSION FORTESCUE MARSH CATCHMENT WATER BALANCE STUDY REFERENCES FMG 2011, Hydrogeologic Assessment of the Christmas Creek Life of Mine Water Management Scheme, Document No. CC-RP-HY-0017 FMG 2012, Baseline Surface Water Hydrology Assessment, Weeli Wolli Creek, Document No. 60242290-RPER-001_E, Nyidinghu Project. Lynch, S.D., Schulze R.E., 1995, Techniques froe Estimating Areal Daily Rainfall, Department of Agricultural Engineering, University of Natal. Ng, R., Waugh, A., Cicero, C., Pearce, U. And Tan, B. (1991). Assessment of the impact of Ophthalmia dam on the floodplains of the Fortescue river hydrological impact of Ophthalmia dam. Water Authority of Western Australia. Report No. WS 80. Payne, A.L., Mitchell, A.A., 1999, An Assessment of the Impact of Ophthalmia Dam on the Floodplains of the Fortescue river on Ethel Creek and Roy Hill Stations. Resource Management Technical Report No.124, Department of Agriculture Western Australia. Ruprecht, J & Ivanescu, S 2000, Surface hydrology of the Pilbara region: summary report, Surface water hydrology report series, Report no. SWH 32, Perth, Water and Rivers Commission. i:\projects\301012-01527 fmg christmas creek per\4_engineering\hy-hydrology\reporting\catchment modelling report\301012-01527-ss-rep-0003 rev c.docm Page 18301012-01527 : 301012-01527-SS-REP-0003Rev C : 18 March 2014