Olympic Dam Expansion Draft Environmental Impact Statement 2009 315 SURFACE WATER 11 11.1 INTRODUCTION The area around Olympic Dam receives very little rainfall (the annual average is 167 mm) and has a high evaporation rate (the annual average is around 3,000 mm). However, when it does rain it is often in high intensity events, which can lead to localised flooding given the flat terrain of the area. Stormwater is held temporarily in swales or clay pans before it evaporates or infiltrates. In large events it may fill the saline lakes that occur in the region; for example, the flooding event of 1989 filled Lake Torrens for the first time in 100 years. Records of floods dating from 1836, and incidental observations of surface water flows during the last 20 years of operation at Olympic Dam, have provided an understanding of flooding and drainage patterns in the area. This chapter describes the natural and constructed landform features that currently influence stormwater drainage patterns, and identifies how the various components of the proposed expansion have been designed to reduce impacts and how they may change surface water flows. The chapter also explains the potential for water to accumulate in the bottom of the open pit and, should this occur, the predicted depth and quality of such water. Stormwater management around proposed infrastructure is also discussed within the SML, for the expanded Roxby Downs, along the infrastructure corridors, and at the site of the desalination plant. The current Olympic Dam EM Program records the effectiveness of the existing stormwater management controls in achieving compliance with applicable limits. The amendments required to the program to account for the expanded operation are addressed in Chapter 24, Environmental Management Framework. 11.2 ASSESSMENT METHODS 11.2.1 SURFACE WATER ASSESSMENT The assessment of surface water for the gas pipeline corridor options was undertaken by RPS Ecos Pty Ltd, and the assessment for the southern infrastructure corridor was conducted by ENSR Australia Pty Ltd (ENSR). The methods employed are described below and detailed in Appendix J1. The broad physiographic features of the Andamooka–Torrens region in the northern portion of the project area have been examined by Johns (1968), and detailed terrain mapping has been undertaken in the vicinity of Roxby Downs and the mine site as part of the 1982 EIS (Kinhill-Stearns Roger 1982). More recently, detailed digital elevation models have been produced for the expanded SML. Finer-scaled work on land systems undertaken by the Department of Primary Industries and Resources, South Australia (PIRSA) provides a consistent approach to defining and mapping recurring patterns of topography, soil, geology and vegetation. The descriptions of land systems and mapping for the project area are provided in Chapter 10, Topography and Soils. In addition to reviewing the above publications, the desktop investigation undertaken for the Draft EIS involved: reviewing the surface water chapters and appendices from • the 1982 and 1997 Olympic Dam EIS (Kinhill-Stearns Roger 1982; Kinhill 1997) reviewing the BHP Billiton annual environmental reports to • obtain information relevant to the surface water assessment discussions with Olympic Dam site personnel to gain a first • hand understanding of rainfall intensities and durations, and the existing water catchments and flow paths on-site and at Roxby Downs
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Olympic Dam Expansion Draft Environmental Impact Statement 2009 315
11Surface water 11
11.1 IntroductIonThe area around Olympic Dam receives very little rainfall (the
annual average is 167 mm) and has a high evaporation rate
(the annual average is around 3,000 mm). However, when it
does rain it is often in high intensity events, which can lead to
localised flooding given the flat terrain of the area. Stormwater
is held temporarily in swales or clay pans before it evaporates
or infiltrates. In large events it may fill the saline lakes that
occur in the region; for example, the flooding event of 1989
filled Lake Torrens for the first time in 100 years.
Records of floods dating from 1836, and incidental observations
of surface water flows during the last 20 years of operation at
Olympic Dam, have provided an understanding of flooding and
drainage patterns in the area.
This chapter describes the natural and constructed landform
features that currently influence stormwater drainage patterns,
and identifies how the various components of the proposed
expansion have been designed to reduce impacts and how they
may change surface water flows.
The chapter also explains the potential for water to accumulate
in the bottom of the open pit and, should this occur, the
predicted depth and quality of such water. Stormwater
management around proposed infrastructure is also discussed
within the SML, for the expanded Roxby Downs, along the
infrastructure corridors, and at the site of the desalination plant.
The current Olympic Dam EM Program records the effectiveness
of the existing stormwater management controls in achieving
compliance with applicable limits. The amendments required to
the program to account for the expanded operation are addressed
in Chapter 24, Environmental Management Framework.
11.2 aSSeSSment methodS
11.2.1 Surface water aSSeSSment
The assessment of surface water for the gas pipeline corridor
options was undertaken by RPS Ecos Pty Ltd, and the
assessment for the southern infrastructure corridor was
conducted by ENSR Australia Pty Ltd (ENSR). The methods
employed are described below and detailed in Appendix J1.
The broad physiographic features of the Andamooka–Torrens
region in the northern portion of the project area have been
examined by Johns (1968), and detailed terrain mapping has
been undertaken in the vicinity of Roxby Downs and the mine
site as part of the 1982 EIS (Kinhill-Stearns Roger 1982). More
recently, detailed digital elevation models have been produced
for the expanded SML. Finer-scaled work on land systems
undertaken by the Department of Primary Industries and
Resources, South Australia (PIRSA) provides a consistent
approach to defining and mapping recurring patterns of
topography, soil, geology and vegetation. The descriptions of
land systems and mapping for the project area are provided in
Chapter 10, Topography and Soils.
In addition to reviewing the above publications, the desktop
investigation undertaken for the Draft EIS involved:
reviewing the surface water chapters and appendices from •
the 1982 and 1997 Olympic Dam EIS (Kinhill-Stearns Roger
1982; Kinhill 1997)
reviewing the BHP Billiton annual environmental reports to •
obtain information relevant to the surface water assessment
discussions with Olympic Dam site personnel to gain a first •
hand understanding of rainfall intensities and durations, and
the existing water catchments and flow paths on-site and at
Roxby Downs
Olympic Dam Expansion Draft Environmental Impact Statement 2009316
identifying legislation, policies and guidelines including •
water resource plans, and/or land management plans of
relevance to the EIS Study Area. The primary sources
of relevance are the South Australian Government
Environmental Protection (Water Quality) Policy 2003 and
Natural Resources Management Plan 2006
reviewing the drainage basins developed by the Department •
of Water, Land and Biodiversity Conservation
reviewing the topographic maps and aerial photography for •
the project area to identify existing creeks, rivers, wetlands
and surface drainage patterns within each drainage basin,
and to assess channel slope
reviewing the Bureau of Meteorology (BOM) data to gain an •
appreciation of flooding history and flood levels across the
project area
reviewing stream gauging stations and previous water •
quality monitoring data where available (e.g. AUSRIVAS
program)
identifying sensitive downstream environments based on •
information obtained during the ecological assessments for
the Draft EIS
identifying present surface water users within the EIS Study •
Area and downstream areas through the stakeholder
consultation and engagement program and discipline-
specific field surveys
gaining an appreciation of the climate change information •
collated for the Draft EIS to establish the implications for
stormwater management for the expanded operation.
field survey
Rainfall sufficient to create widespread ponding of surface
waters is not a common occurrence in the Olympic Dam region.
However, such an event occurred in mid-July of 2006 during an
eight-day field survey of the southern infrastructure corridor
(undertaken from 10 to 17 July) and this allowed a better
understanding of stormwater flows.
During the survey, 19.6 mm of rainfall was recorded at
Andamooka on 14 July, 15 mm at Roxby Downs and 24 mm
at Woomera on 14 and 15 July, and 17.8 mm at Port Augusta
between 14 and 16 July. The survey areas investigated during
this period were the Olympic Dam SML, the Municipality of
Roxby Downs and the southern infrastructure corridor to
Port Augusta.
The field survey entailed:
measuring the water quality of terminal lakes for dissolved •
oxygen, electrical conductivity, pH, temperature and
turbidity
examining and photographing the receiving environments of •
catchments and collecting water samples (where possible)
digging auger holes to a maximum depth of 3 m in receiving •
environments to identify the presence or absence of shallow
groundwater and to assess water quality
measuring the electrical conductivity and pH of bed •
sediments to assess the salinity of the receiving
environments and enable commentary on likely
groundwater/surface water interaction.
Catchments and watercourses on the gas pipeline corridor
options were examined and photographed during a ground-
based ecological survey undertaken in October 2006 and a
helicopter and ground-based survey in January 2008. Conditions
were dry during these surveys, so sampling was restricted to
collecting surface water samples at four locations in the EIS
Study Area, where it was present in waterholes or springs.
11.2.2 water accumulatIon In the open pIt
The size of the proposed open pit would grow over time,
ultimately spanning an area 3.5 km long, 4.1 km wide and about
1 km deep (see Chapter 5, Description of the Proposed
Expansion, Section 5.4.1 for details). An assessment was
undertaken to predict the volume of water entering the open pit
after mine closure in order to determine whether water would
accumulate at the bottom of the pit and eventually form a
permanent pit lake. The possibility of this outcome depends on
the relationship between incident rainfall, surface run-off from
local catchments draining to the pit, groundwater inflow to the
pit, and evaporation. An assessment of potential impacts to
fauna from the accumulation of water in the open pit after
closure is provided in Chapter 15, Terrestrial Environment.
A water balance model was developed to predict the likely rate
at which water would enter the pit, whether evaporation would
exceed water entry and, if it doesn’t, the steady state water
level condition that would eventually develop. The model was
run to simulate the water balance for 3,000 years, which
was found to be well in excess of the required duration to
reach steady state conditions in all scenarios considered.
The key components of the assessment methods were (see
Appendix J2 for details):
estimating water inputs into the pit from groundwater, •
incident rainfall and surface water run-off from the pit walls
and small external catchments
estimating evaporative loss of water within the pit•
conducting sensitivity analysis to assess the effect of •
uncertainty regarding the input parameters on the model
outputs. Consideration was also given to the impact of
changing weather conditions due to climate change
characterising the chemistry of input waters (groundwater, •
surface water run-off, incident rainfall) based on
groundwater and surface water monitoring and tailings
storage facility (TSF) and rock storage facility (RSF) seepage
predictions (see Chapter 12, Groundwater)
undertaking limnological analysis to estimate the physical •
characteristics (salinity gradient, temperature gradient and
circulation patterns) of a potential pit lake
estimating the chemical characteristics (i.e. pH, redox, major •
anions and cations, and metal concentrations) of pit waters
using a geochemical model, including sensitivity analysis.
Olympic Dam Expansion Draft Environmental Impact Statement 2009 317
11
11.2.3 Impact and rISk aSSeSSment
The assessment of impacts and risks for the proposed
expansion has been undertaken as two separate, but related,
processes (see Section 1.6.2 of Chapter 1, Introduction, and
Figure 1.11).
Impacts and benefits are the consequence of a known event.
They are described in this chapter and categorised as high,
moderate, low or negligible in accordance with the criteria
presented in Table 1.3 (Chapter 1, Introduction). A risk
assessment describes and categorises the likelihood and
consequence of an unplanned event. These are presented in
Chapter 26, Hazard and Risk.
11.3 exIStIng envIronment
11.3.1 draInage regIonS
The Olympic Dam operation and associated infrastructure are
located in the Cooper Creek, Lake Frome, Gairdner, Torrens and
North St Vincent–Spencer Gulf drainage regions (see
Figure 11.1). These regions, particularly Cooper Creek, Lake
Frome, Gairdner and Torrens are lowland interior basins of
Australia where rainfall generally ponds on the surface for short
periods of time, prior to infiltration or evaporation. Following
large rainfall events, surface water collects in terminal surface
water features such as clay pans, small fresh or brackish lakes
(e.g. Coorlay Lagoon) and ephemeral salt lakes such as Lake
Eyre South and Lake Gregory (along the gas pipeline corridor
options) and Lake Torrens, Lake Windabout, Pernatty Lagoon
and Island Lagoon (along the southern infrastructure corridor)
(see Plates 11.1, 11.2 and 11.3). In dunefield areas, typical of
the areas surrounding Olympic Dam, stormwater flows often
occur at very low velocities and over short distances, a result of
the flat terrain and small closed catchments formed by the
dune-swale systems. Rainfall in the North St Vincent–Spencer
Gulf drainage region is generally higher and more seasonal
than the Gairdner and Torrens regions, with surface water
run-off trending towards the sea via Spencer Gulf.
Darwin is located within the Timor Sea drainage region, an area
which drains more than 50 million megalitres of water from the
Northern Territory each year. Surface water run-off in the
tropical areas of the Northern Territory is dominated by well
defined rivers and drainage features, rather than by surface
ponding and evaporation. River flow and surface water run-off
is highly seasonal, being highest during October and April,
when more than 95% of the annual rainfall occurs.
On a local scale, the Port of Darwin lies within the Darwin
Harbour catchment. This catchment can be further divided
into the sub-catchments of the Howard River, Elizabeth River,
Blackmore River and the minor creeks and streams of the West
Arm and Woods Inlet (Haig and Townsend 2003). The East Arm
of the Port of Darwin is located within the Elizabeth River
sub-catchment.
11.3.2 Surface water catchmentS
While the drainage regions identify broad drainage boundaries,
greater definition of surface water catchments on a local scale
is required to understand the implications for the proposed
expansion. As surface water flow in much of the South Australian
portion of the EIS Study Area is not dominated by drainage to
defined channels and rivers, the finer-scaled land system mapping
developed by PIRSA better represents the local catchment
characteristics. Land systems in the region were described in
Chapter 10, Topography and Soils, and the location and extent
of each land system was shown in Figures 10.3 and 10.4.
Plate 11.3 Lake Gregory and the dunefields of the Strzelecki Desert
Plate 11.2 Lake Windabout
Plate 11.1 Lake Torrens
Olympic Dam Expansion Draft Environmental Impact Statement 2009318
OLYMPIC DAM
SpencerGulf
Woomera
Port Augusta
WhyallaPointLowly
Spencer GulfBasin
Mambray CoastBasin
Broughton RiverBasin
GairdnerBasin
Lake TorrensBasin
Roxby Downs
Andamooka
Willochra CreekBasin
LakeTorrens
LakeWindabout
LakeBlanche
IslandLagoon
PernattyLagoon
PimbaSW1
SW4
SW3SW2
Lake EyreSouth
Lake EyreNorth
Moomba
Marree
Lyndhurst
Port Pirie
Lake FromeBasin
Cooper CreekBasin
DiamantinaBasin
Lower River MurrayBasin
GC1
GC2
GC128
GC134
LakeFrome
0 20 40 60 80 100km
Moomba
Adelaide
Port Pirie
Roxby s
Port Augusta
Surface water sample locations
EIS Study Area
Surface Water Drainage Regions
Channel Country
Lower Murray
Cooper Creek
Lake Frome
Gairdner
Torrens
North St Vincent-Spencer GulfSource: DWLBC 2004
Down
Whyalla
Figure 11.1 Surface water drainage regions and basins
Olympic Dam Expansion Draft Environmental Impact Statement 2009 319
11
There are 28 land systems in the EIS Study Area within South
Australia. Twelve of these cover the Olympic Dam region and
the project area south to Point Lowly, and a further 16 occur to
the north, within the gas pipeline corridor options.
The Olympic Dam area and southern infrastructure corridor
mainly fall within four land systems:
Roxby – this includes the existing SML, Roxby Downs •
township and the adjacent sections of the southern
infrastructure corridor
Arcoona – this includes the proposed Hiltaba Village, •
relocated airport, large sections of the southern
infrastructure corridor between kilometre points (kp)
170 and 270 and a small section of the gas pipeline corridor
options
Hesso – this includes the southern infrastructure corridor •
between kp 80 and 170
Tent Hill – this includes the southern infrastructure corridor •
between kp 30 and 80 and the proposed desalination plant
at Point Lowly.
The gas pipeline corridor options traverse two broad groups of
land systems with similar landforms and drainage patterns:
Stony plains and tablelands – Oodnadatta, Kalatinka, •
Mumpie, Flint, Kopi and Cooryaninna
Dunefields – Stuarts Creek, Wirringina, Collina, Hope, •
Tingana, Strzelecki and Cooper.
The relationships between these land systems and surface
water catchments is described below.
roxby land system
The Roxby land system is characterised by many small, enclosed
catchments, individually bound by east–west trending dunes,
generally up to eight metres high. Typically, each catchment
contains a boundary formed by the crest of sand dunes, an
upper interdunal corridor (swale) and a lower depression, often
a clay pan (see Plates 11.4 and 11.5 and Chapter 10, Topography
and Soils, Plate 10.1).
The sand ridges are highly permeable. Rainfall infiltrates quickly
through the sandy profile, draining into the swale and clay pan
after being redirected by a thick layer of clayey soil under the
sand dunes. The clayey soils of the swales and clay pans are
less permeable and, in periods of significant rainfall, collect
water in low depressions. These dune-swale and clay pan
catchments vary in size from 10–300 ha and are typically
1–3 km long. Figure 11.2 shows examples of small, enclosed
catchment boundaries associated with the Roxby land system.
Stormwater within the swales and clay pans infiltrates the
surface cracks of the clay soils, causing them to swell. In most
instances the swelling of the clay soils reduces infiltration
significantly, leading to surface water ponding. Depending on
the rainfall event, surface water may stay in the swales and clay
pans from a few days to a few weeks, but only rainfall events of
a significant intensity and duration result in ponding for more
than one month. The ponded water in this land system is
generally fresh and of high quality.
There are no defined watercourses in the EIS Study Area in the
Roxby land system and surface waters from the small
catchments very rarely flow into the neighbouring catchments.
No stormwater from the area of the existing operation flows off
the SML.
arcoona, hesso and tent hill land systems
The southern infrastructure corridor traverses these three main
land systems.
The Arcoona land system has well defined drainage lines and
catchments that have formed several large terminal salt lakes
and ephemeral lagoons (such as Lake Torrens, Lake Windabout,
Island Lagoon and Pernatty Lagoon; see Figure 11.1). Channel
flow occurs in broad and poorly defined drainage lines during
rainfall events (see Plate 11.6). Gully erosion, while not
extensive, is evident in areas where stormwater flows are
Plate 11.5 Clay pan showing surface water drainage lines
Plate 11.4 Interdunal corridor
Olympic Dam Expansion Draft Environmental Impact Statement 2009320
concentrated, such as near roadside drains and culverts (see
Plate 11.7). Water quality is highly variable and cyclic, ranging
from fresh during rain events, to highly saline as a result of
evapoconcentration (i.e. as evaporation occurs the
concentration of salt in the remaining surface water increases).
The Hesso land system covers the area from just south of Pernatty
Lagoon (kp 170) to Port Augusta (kp 80). This system is
characterised by extensive flat sandy plains (see Plate 11.8).
Infiltration is relatively high, therefore surface ponding occurs only
Proposedopen pit
0 1 2km
Open pit catchment
Stormwater catchment
See Plate 10.10for typical sand ridge
See Plate 10.11for typical clay pan
Figure 11.2 Surface water catchments surrounding the proposed open pit
Plate 11.6 Typical drainage pattern of the Arcoona land system
after significant storm events. However, given the flat terrain,
surface ponding is widespread when such events occur. Surface
water is good quality, generally infiltrating to the groundwater
before significant changes in salinity levels can occur.
The Tent Hill land system covers the area south of Port Augusta
to Point Lowly. This system is characterised by steep
escarpments and plateaus, separated by alluvial plains (see
Plate 11.9). Well-defined drainage paths intercept these
landforms. Minor creeks from elevated areas join to form large
Plate 11.7 Erosion due to concentration of stormwater flow through culverts
Olympic Dam Expansion Draft Environmental Impact Statement 2009 321
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Plate 11.10 Screech Owl Creek and floodout area
Plate 11.9 Typical catchment composition of Tent Hill land system
Plate 11.8 Typical catchment composition of Hesso land system
Plate 11.11 Koortanyaninna Creek draining through Mumpie land system
incised creeks as they enter the broad, flat, floodplains. These
large creeks carry high water flows during storm events.
Overland flow and creek flows are often highly turbid and have
low salinity levels. Myall Creek is the most extensive catchment
in this part of the study area. The catchment terminates in a
broad floodplain that discharges to the coast via a floodway
across the Point Lowly access road. Coastal discharges also
occur at Port Augusta from an unnamed creek that runs parallel
to the Eyre Highway.
Stony plain and tableland land systems
The stony plain and tableland land systems of the gas pipeline