Caroona Coal Project Floodplain Definition
Presentation to the Community Consultative Committee
1 August 2011
Caroona Coal Project – Floodplain Definition
Introduction Purpose of presentation: Why is a floodplain definition required? Introduction to scientific studies Floodplain land use planning tools Geomorphology preliminary results Flood model input Where are we now? Where to from here?
Caroona Coal Project – Floodplain Definition
Introduction • Caroona Exploration Licence (EL6505) covers approximately 344 square kilometres within the Liverpool Plains. • Land within the EL area varies from near-flat floodplain to elevated grazed and timbered ridge country. • Floodplains sustain highly productive agriculture – irrigated and dryland cropping and livestock production. • Highly productive alluvial aquifers beneath the floodplains support irrigated agriculture and potable water supplies. • Protection of this underground water and the high agricultural productivity of the floodplains are high priority issues for the local community, BHP Billiton and other stakeholders in the region.
Caroona Coal Project – Floodplain Definition
What is a floodplain? Literal definition • Macquarie dictionary: A nearly flat plain along the course of a stream that is naturally subject to flooding at high water.
Other characteristics • Floodplains are characterised by sediment deposited by alluvial processes (e.g. rivers) – referred to as alluvium. • Floodplains associated with the Mooki River/Quirindi Creek system and the Yarraman Creek system are the focus of this study. These systems make up the ‘black soil plains’ within the EL area.
Caroona Coal Project – Floodplain Definition
Why is a floodplain definition required? •
Determining the extent of the floodplain will provide certainty for the community on how BHP Billiton will deliver on its commitments, including that there will be: no longwall mining under the floodplains; no longwall mining under the deep alluvial aquifers; no open cut mining anywhere on the floodplain.
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The NSW Government has subsequently amended the special conditions of the EL to reflect these commitments.
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Exploration has been restricted to a targeted area within the EL and consists mainly of ridge country.
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BHP Billiton has declared that land outside the targeted area for further exploration is a ‘no go zone’ for mining of any description.
Caroona Coal Project – Floodplain Definition
Targeted Exploration Area
Caroona Coal Project – Floodplain Definition
Why is a floodplain definition required? • Clear delineation of the floodplain is required to assist BHP Billiton: deliver on commitments to avoid potential impact; design a potential mine plan within the scope of the commitments.
• The delineation of the floodplain must be based on sound scientific studies and consultation to ensure that these commitments are met.
Caroona Coal Project – Floodplain Definition
Introduction to scientific studies • There are various land use planning tools used to assist in defining floodplains for various purposes. • These tools alone are not adequately definitive, given the importance of the floodplains and the highly productive alluvial aquifers they contain. • The floodplain areas within the EL are a very old system and cannot accurately be mapped using these broad planning tools.
Caroona Coal Project – Floodplain Definition
Floodplain land use planning tools • The land use planning tools that historically have been used as a method of defining a floodplain include: 2% slope definition; 1980 Flood Atlas; 50-year Average Recurrence Interval (ARI) flood; 100-year ARI flood; Probable Maximum Flood (PMF).
• These approaches define only the surface extent of alluvium, not the subsurface extent, or where the water currently flows.
Caroona Coal Project – Floodplain Definition
Floodplain land use planning tools 2% slope definition • Based on report by Burton, Junor & Whitehouse (June 1994) – Floodplain Management on the Liverpool Plains. • Intent was to address past floodplain management issues by broadening the previous definition of the floodplain used by government agencies for licensing/flood management purposes: ‘There is a clear need for an extension of the concept of what constitutes a floodplain for licensing purposes … in the case of the Liverpool Plains, we have suggested that this area should include all land having a slope of 2 percent or less.’
• This is a planning tool and does not clearly define the extent of the actual floodplain on a location specific basis and therefore not considered adequately definitive for use in this context.
Caroona Coal Project – Floodplain Definition
2% Planning tool
Caroona Coal Project – Floodplain Definition
Floodplain land use planning tools Flood event based planning tools: • Various definitions based on different flood events (theoretical and actual). • Flood extent information alone is not considered appropriate as it shows only where the water runs now, not where it would have run hundreds and thousands of years ago. • Flood event modelling results will provide one input to the definition, but cannot be used in isolation of other scientific studies.
Caroona Coal Project – Floodplain Definition
Comparison – Flood Atlas and 100-year ARI Flood 1980 Flood Atlas
100-year ARI Flood Event
• As indicated above, a very different floodplain boundary results from using the 1980 flood atlas or the 100-year ARI flood event.
Caroona Coal Project – Floodplain Definition
Scientific Studies • Geomorphology studies are being undertaken as the primary scientific tool to define the extent of the floodplain alluvium. • The geomorphology information will be cross-checked with the flood model information. • This is the most accurate way of defining the floodplain for this project.
Geomorphology Studies
Caroona Coal Project – Floodplain Definition
Introduction to geomorphological studies • Objective is to define the extent of floodplain alluvium associated with Mooki River/Quirindi Creek and Yarraman Creek. • Alluvium – sediment deposited by flowing water, e.g.: river bed and bank deposits (coarse, rounded) – floodplain alluvium; flood and backwater deposits (very fine) – floodplain alluvium; gully deposits (moderately coarse, angular) – non-floodplain alluvium; slope wash (well sorted, moderately fine, angular) – non-floodplain alluvium.
Caroona Coal Project – Floodplain Definition
Floodplain sediment sequence • Mooki/Quirindi and Yarraman Creek floodplains originally were a deeper basin – when the floodplain was lower. • Basin filled by materials eroded from Great Dividing Range and by locally eroded materials over tens of thousands of years. • Full extent of floodplain sediments are not visible at surface. • Ancient floodplain sediments may extend beneath footslopes (i.e. covered by slope wash and gully deposits). • Sediment sequence reflects cycles of deposition, erosion by gullies and rivers, further deposition, further erosion etc. • ‘Base level’ is the bedrock underlying all valley fill sediments.
Caroona Coal Project – Floodplain Definition
Defining the edge of floodplain alluvium • Geomorphology is the key scientific study that will define the floodplain alluvial area. • A range of evidence was used in initial investigations, including: site inspection; aerial photography; topographic information (LiDAR); soil types and soil landscapes; geology maps; satellite imagery; airborne geophysical data collection.
Caroona Coal Project – Floodplain Definition
Defining the edge of floodplain alluvium • Initial investigations largely examined the surface sediments. • These methods don’t provide information on floodplain alluvium mantled by other deposits. • Further investigations focused on these subsurface deposits.
Caroona Coal Project – Floodplain Definition
Regional soil landscape mapping Insert Figure 1 from Briefing Note – Geomorphology of the Alluvial Margins - showing soil landscapes in the EL area
Source: Tamworth & Curlewis Soil Landscape Maps. (Department of Natural Resources, 2005)
Caroona Coal Project – Floodplain Definition
Defining the edge of floodplain alluvium in subsurface • Investigation focused on sediments under footslopes to define extent of floodplain alluvium in areas of uncertainty. • Existing soil maps are of surface materials to about 2 metres. • Typically last unit of deposition is flood overbank deposits. • Subsurface investigation examines materials below 2 metres. • Drilling with auger rigs, allows sampling up to 9.5 metres.
Caroona Coal Project – Floodplain Definition
Geomorphology preliminary results • Initial identification of areas where floodplain alluvium boundary might lie. • Further investigation of areas of uncertainty with augering.
Caroona Coal Project – Floodplain Definition
Hypothetical floodplain boundary types
Caroona Coal Project – Floodplain Definition
Auger drilling in the field • Augers are similar to conventional post-hole augers, but generally narrower. • Augers drill up to 9.5 metres in depth. • Rods are 1.5 – 2 metres long. • Displaced material rises to the surface and sampled as it falls from the rod (loose) or is removed from the rod (clay). • Entire length sealed with grout. • 39 holes drilled to date.
Caroona Coal Project – Floodplain Definition
Auger holes completed
Caroona Coal Project – Floodplain Definition
Auger sediment recording Hole No: C315G
Includes grain size, grain shape, presence of clasts (rocks), pH, colour, material type.
Caroona Coal Project – Floodplain Definition
Auger sediment recording Hole No. C318G
Caroona Coal Project – Floodplain Definition
Borehole sediment interpretation Borehole No: CCP0072
Geology borehole data examined for information on floodplain sediments.
Caroona Coal Project – Floodplain Definition
Borehole sediment interpretation Borehole No: CCP0048
Caroona Coal Project – Floodplain Definition
Alluvial floodplain boundaries • Where a clear boundary is found from investigation a single line is drawn. • For locations where there is significant uncertainty about the position of the boundary further work is required to define the boundary. • Areas of remaining significant uncertainty are principally very low gradient footslopes, alluvial fans and some areas where no augering has been completed to date. • Further work will continue to be undertaken to improve the level of detail in areas of uncertainty.
Caroona Coal Project – Floodplain Definition
Auger program results to date East Doona Ridge
297G
Caroona Coal Project – Floodplain Definition
Auger program results to date Doona Vale
Caroona Coal Project – Floodplain Definition
Auger program results to date Valley north of the feedlot
Caroona Coal Project – Floodplain Definition
Auger program results to date West Nicholas Ridge
Caroona Coal Project – Floodplain Definition
Further work required • Further geomorphology studies will build on the current knowledge of the floodplain alluvium in the Caroona EL area to refine this boundary. • Access to EL areas shown as uncertain in relation to the floodplain boundary would enhance the ability to provide a more accurate floodplain boundary.
Caroona Coal Project – Floodplain Definition
Revised Preliminary Floodplain Boundary and Further Work
Caroona Coal Project – Floodplain Definition
Revised Alluvial Margin vs 2% Slope
Flood Model Input
Caroona Coal Project – Floodplain Definition
Preliminary flood model input • As discussed at the last CCC meeting the flood modeling work is currently in the verification phase. • Once verification is complete, the flood model outputs will be used to cross-check the findings of the geomorphology studies. • Preliminary model outputs for the 100-year ARI event are shown on the next slide.
Caroona Coal Project – Floodplain Definition
Preliminary flood model input – 100-year ARI
Caroona Coal Project – Floodplain Definition
Flooding Extent & Alluvial Deposit
Next Steps
Caroona Coal Project – Floodplain Definition
Where to from here? The floodplain boundary definition is not complete. • Further work is required to continue building on the existing knowledge from the geomorphology studies enabling the refinement of the floodplain boundary within the EL. • The floodplain boundary requires access to areas where drilling has not been able to occur to complete the studies, fully define the boundary and to provide certainty. • The final report of this work will be available to the community and government agencies.
Caroona Coal Project – Floodplain Definition
Where to from here? When complete the findings will: • define the floodplain boundary and in association with the information from the detailed groundwater studies be used by BHP Billiton to meet its commitments and avoid impacts to the floodplain. • be used by BHP Billiton throughout the planning process to inform any potential mine design. • be a key consideration of any future detailed environmental assessment process for a proposed mining development.
Caroona Coal Project – Floodplain Definition
Questions?
