[paper] design philosophy statement – freshwater and recycle dams – escarpment mine project.pdf

November 2010

DESIGN PHILOSOPHY STATEMENT

Freshwater and Recycle Dams - Escarpment Mine Project

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RT

Report Number. 1078101422-001-R-Rev1-3

Distribution:

Bathurst - Les McCracken

Submitted to: Bathurst Resources Ltd

FRESHWATER AND RECYCLE DAMS - DESIGN PHILOSOPHY STATEMENTS

November 2010

Report No. 1078101422-001-R-Rev1-3 i

Table of Contents

1.0 INTRODUCTION ................................................................................................................................................. 1

1.1 Background ............................................................................................................................................ 1

1.2 Scope of Document ................................................................................................................................. 1

2.0 POTENTIAL IMPACT CLASSIFICATION............................................................................................................. 2

2.1 New Zealand Society of Large Dams Potential Impact Category ............................................................... 2

2.2 Potential Incremental Consequences of Failure ........................................................................................ 3

2.2.1 Effects on stream flow ........................................................................................................................ 4

2.2.2 Risk to structures ............................................................................................................................... 4

2.2.3 Risk to human life .............................................................................................................................. 4

2.2.4 Socio-economic, financial & environmental risk ................................................................................... 5

2.3 PIC classification ..................................................................................................................................... 5

3.0 DESIGN CRITERIA ............................................................................................................................................. 6

3.1 General Design Requirements ................................................................................................................. 6

3.1.1 Inflow design flood ............................................................................................................................. 7

3.1.2 Seismic design criteria ....................................................................................................................... 7

3.2 Hydraulic Design of Dams ....................................................................................................................... 8

3.2.1 Design floods ..................................................................................................................................... 8

3.2.2 Embankment freeboard ...................................................................................................................... 8

4.0 EMBANKMENT DESIGN AND CONSTRUCTION ................................................................................................ 9

4.1 Site Geology ........................................................................................................................................... 9

4.2 Foundation Preparation ........................................................................................................................... 9

4.2.1 Embankment shoulder ....................................................................................................................... 9

4.2.1 Liner and core/filter .......................................................................................................................... 10

4.2.1 Cutoff trench .................................................................................................................................... 10

4.3 Embankment Cross Section .................................................................................................................. 10

4.3.1 Dam type ......................................................................................................................................... 10

4.4 Available Construction Materials ............................................................................................................ 11

4.5 Embankment Construction .................................................................................................................... 12

4.5.1 Core (Zone 3A) ................................................................................................................................ 12

4.5.2 Drainage fingers (Zone 2B) ............................................................................................................ 12

4.5.3 Shoulder (Zone 3) material ............................................................................................................... 12


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4.5.4 Liner filter (Zone 2A) ........................................................................................................................ 12

4.5.5 Rip rap (Zone 4) .............................................................................................................................. 13

4.5.6 Embankment crest and laydown construction ................................................................................... 13

4.6 Access for Machinery ............................................................................................................................ 13

5.0 SPILLWAY DESIGN .......................................................................................................................................... 13

5.1 Spillway Design..................................................................................................................................... 13

5.1.1 Design criteria ................................................................................................................................. 13

5.1.2 Design ............................................................................................................................................. 14

5.1.3 Reservoir drawdown arrangement .................................................................................................... 14

5.1.4 Temporary stream diversion arrangements ....................................................................................... 14

6.0 DAM OPERATION AND REHABILITATION ...................................................................................................... 15

6.1 Dam Operation...................................................................................................................................... 15

6.2 Proposed Rehabilitation ........................................................................................................................ 15

7.0 REFERENCES .................................................................................................................................................. 16

TABLES

Table 1: Preliminary dimensions of the Recycle and Freshwater dams. .......................................................................... 2

Table 2: Potential Impact Categories for dams in terms of failure consequences (NZSOLD, 2000). ................................. 2

Table 3: Modelled flood levels and channel velocities - Freshwater Dam sunny day failure (Golder, 2010). ...................... 3

Table 4: Modelled flood levels and channel velocities Recycle pond sunny day failure (Golder, 2010)........................... 3

Table 5: Preliminary seismic design loads. .................................................................................................................... 8

Table 6: Estimated dam peak inflows #. ......................................................................................................................... 8

Table 7: Spillway design criteria. ................................................................................................................................. 14

APPENDICES

APPENDIX A Report Limitations

APPENDIX B Freshwater and Recycle Dam Concept Drawings

APPENDIX C Dam Break Analysis


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Report No. 1078101422-001-R-Rev1-3 1

1.0 INTRODUCTION

1.1 Background

Bathurst has entered into an agreement with L&M Mining Ltd (L&M) to purchase and develop a mining lease

covering the Escarpment Mine Project (EMP) part of the Buller Coalfield on the Denniston Plateau, New

Zealand. Bathurst and L&M are proposing to consent and develop the EMP, with the proposed mine area

covering 148 hectares. The bulk of the mining operations will be carried out within the current Mining

Permits, and concessions will be sought to establish roads and pipelines within Department of Conservation

lands.

The EMP area is estimated to contain approximately 6.1 million tonnes of recoverable coal. It is proposed to

extract up to 1.5 million tonnes per year and according to projections the life of the mine is estimated to be

just over five years.

Bathurst and L&M have applied to the West Coast Regional Council and Buller District Council for several

consents to construct and operate the EMP mine. During the consenting process, Bathurst has been

required to provide some additional information to the councils, specifically to address the design of the

recycle pond (20,000 m3) and freshwater pond (152,000 m

3), which this document addresses.

The EMP will require the construction of two dams to form each pond. The recycle pond is required to

recover and recycle water from the coal processing plant (CPP). While the freshwater pond is a buffer pond,

temporarily storing the water extracted from the Waimangaroa River, before being used in the CPP (as

makeup water) to transport the coal slurry from the plateau to the dewatering and stockpile facility, or to

augment the river flows in the Whareatea River. The EMP is proposing to replace the catchment water that is

intercepted by the mining operation and mitigate any potential effects on the downstream Kawatiri Energy

Power Scheme.

1.2 Scope of Document

This Design Philosophy Statement has been prepared to summarise the basis for the design of the recycle

and freshwater dams.

Several dam cross-sectional design options have been considered. Both dams will be upstream lined earth

and rockfill structures. There are many examples nationally and around the world of lined earth and rockfill

embankment dams that have been successfully designed, constructed and operated.

As noted above, the primary purpose of the dams is to retain water for mining purposes. The Freshwater

Dam will store treated freshwater from the Waimangaroa River. Storage is required to accommodate the

variable flow in the Waimangaroa River and therefore buffer abstraction rates. A clean water supply is

required to primarily transport the processed coal within a slurry line from the CPP to the dewatering and

stockpile facility. Secondary purposes include, (1) the supply of makeup water for the CPP operation, and

(2) augment the river flows in the Whareatea River for the Kawatiri Energy Power Scheme.

The Recycle Dam will store the recirculation plant water as well as act as a stormwater detention basin for

the CPP, ROM and general workshop area.

Coal slurry and process water will be pumped from the Freshwater and Recycle Dams respectively, the

design of these pump stations is outside the scope of this document. The duty, configuration and operational

control philosophy will be developed during the detailed design phase.

The Freshwater and Recycle Dams have a nominal operating life of 35 years, following which then will be

backfilled and landscaped and any stormwater inflows redirected to a stable channel. It may be possible that

the operation life of the Freshwater Dam could be extended if an alternative application for the storage of

water could be identified (e.g. power generation, potable water etc.).

The approximate physical dimensions of the proposed dams are summarised in Table 1. The location of the

dams and typical cross sections are shown in Appendix B.


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Table 1: Preliminary dimensions of the Recycle and Freshwater dams.

Dimension Freshwater Dam Recycle Dam

Maximum height (m) 18 14

Fill volume (m3) 73,100 TBA

Crest level (mRL) 672 655

Spill sill level (mRL) 670.5 654

Water storage volume (m3) (reservoirs at spillway sill

level) 152,000 25,000

*

Normal water storage volume 152,000 (670 mRL) 10,000

Notes: * 10,000 m

3 active storage volume + 15,000 m

3 flood storage (Envirolink, 2010)

During the detailed design phase, a Dam Design Report, construction issue drawings, and technical

specifications will be produced based on the concepts outlined in this document.

2.0 POTENTIAL IMPACT CLASSIFICATION

The likelihood of failure of a properly engineered and constructed dam is extremely low. However, the New

Zealand Society of Large Dams (NZSOLD) Dam Safety Guidelines (NZSOLD, 2000) require dams to be

ranked in terms of the severity of downstream effects (potential impact) in the unlikely event of a dam failure.

As summarised below, the dams have been subject to a qualitative dam break assessment to determine

their Potential Impact Category (PIC).

2.1 New Zealand Society of Large Dams Potential Impact Category

NZSOLD (2000) provides broad guidelines for assessing the PIC of new dams, as reproduced in summary

Table 2 below.

Table 2: Potential Impact Categories for dams in terms of failure consequences (NZSOLD, 2000).

Potential Impact Category

Potential incremental consequences of failure

Life Socio-economic, Financial and

Environmental

High Fatalities Catastrophic damages

Medium A few fatalities are possible Major damages

Low No fatalities expected Moderate damages

Very-low No fatalities Minimal damages beyond owners

boundary

The NZSOLD New Zealand Dam Safety Guidelines (NZSOLD, 2000) suggest that the dam height and

reservoir volume parameters are useful for an initial screening of PIC, yet should not necessarily control the

PIC designation. They suggest that low PIC dams are likely to have dam heights less than 10 m, medium PIC dams are likely to have dam heights in the order of 10 20 m, but not exceeding 15 m if the stored volume of water exceeds 1,000,000 m

3. If the dam height and storage exceeds those for medium category,

then the dam classification is probably a high PIC.

Both dams are in the order of 10 20 m high and will store about less than 1,000,000 m3.


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2.2 Potential Incremental Consequences of Failure

A qualitative preliminary dam break analysis was performed by Golder (2010) for both the Freshwater Dam

and Recycle Dam (Appendix C). The analysis assessed the potential incremental consequences of failure of

both dams during a sunny day failure scenario. The analysis was undertaken using a hydraulic model based on the HEC-RES modelling system. Parameters describing the breach formation time and breach

geometry were obtained from a literature review and conservative values adopted. As Bathurst are

proposing to use the Recycle Dam crest as a plant laydown and car parking area. As the crest width is

considerable longer than typical, a longer breach formation time and narrower breach width were adopted.

The dam break analysis predicted the following flood level and channel velocities for a sunny day failure of the Freshwater Dam (Table 3) and Recycle Dam (Table 4).

Table 3: Modelled flood levels and channel velocities - Freshwater Dam sunny day failure (Golder, 2010).

Location Channel velocity (m/s)

Flood level (mRL)

Minimum channel elevation (mRL) (est.)

Bridge soffit (mRL) (est.)

Surface level road/track (mRL) (est.)

SH 67 road bridge

Upstream 1.9 11.74 * 7.80 9.50 10.00

Downstream 4.4 10.54 * 7.80 9.50 10.00

Westport Ngakawau Railway Bridge

Upstream 0.5 2.81 -0.20 #

5.50 6.00

Downstream 0.5 2.78 -0.25 #

5.50 6.00

Notes: * denotes overtopping of the bridge.

# a negative reduced level denotes minimum channel elevation below datum adopted in the analysis

Table 4: Modelled flood levels and channel velocities Recycle pond sunny day failure (Golder, 2010).

Location Channel velocity (m/s)

Flood level (mRL)

Minimum channel elevation (mRL) (est.)

Bridge soffit (mRL) (est.)

Surface level road/track (mRL) (est.)

SH 67 Road Bridge

Upstream 1.4 9.58 #

7.80 9.50 10.00

Downstream 1.7 9.34 7.80 9.50 10.00

Westport Ngakawau Railway Bridge

Upstream 0.4 2.24 -0.20 #

5.50 6.00

Downstream 0.4 2.22 -0.25 #

5.50 6.00

Notes: # denotes wave impinges on bridge deck.

# a negative reduced level denotes minimum channel elevation below datum adopted in the analysis


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2.2.1 Effects on stream flow

A dam break will result in an uncontrolled release to the Whareatea River of rapidly increasing flow, heavily

entrained with sediment. Because simultaneous and instantaneous failure of both dams is considered highly

unlikely, a simultaneous failure has not been specifically calculated.

Golder (2010) has determined that the dam break flows would be generally be confined to the Whareatea

River both within the plateau river system and on the lower terrace and flats of the Fairdown area, during a

sunny day (normal weather condition) failure scenario.

2.2.2 Risk to structures

A failure of the Freshwater Dam, whilst it will result in complete or partial destruction of the dam, should not

result in additional damage to the mining infrastructure due to the location of the mining infrastructure being

located upstream of the dam. However failure of the Recycle Dam could result in the loss/damage of one or

more of the following infrastructure items, due to their location being on the crest of this dam:

Workshop buildings

Laydown area

Heavy equipment parking and any equipment in the park

Office, ablution and amenities complex

Staff car park and vehicles

Sewage treatment system

Employee car park and vehicles

The Kawatiri Energy Power Scheme is proposing to construct an intake weir in the Whareatea River, at

approximately 5376605 mE, 1497412 mN. It is highly likely that a dam break wave from either the

Freshwater or Recycle Dam will damage and/or compromise the operation of the intake weir.

Golders dam break analysis (2010) indicates that the bridge on SH 67 across the Whareatea River is subject to overtopping in the simulation of the breach of the Freshwater Dam. The wave is estimated to

arrive at the bridge 17 minutes after dam-break with the water level rising from the creek bed to maximum

level in 2 minutes. The modelled flood depth and velocity suggests that the flood wave may be a hazard to bridge. Whilst further investigations are required, it is likely that the flood wave will wash away the bridge and/or its embankments.

2.2.3 Risk to human life

It is not expected that mine staff will normally operate in the vicinity of the Freshwater Dam crest or

downstream of the dam. However breaching of the Recycle Dam, with significant mining infrastructure

located on the crest of the dam, presents a hazard to between 10-100 people operating within the vicinity of

the dam crest. Due to the breach timing and width, 15 minutes and 15 m respectively, it is expected that the

signs of the dams distress will be evident as the failure develops allowing time for evacuation. Consequently it is estimated that less than 2 lives could be lost.

Persons using the Whareatea River system would be at risk in the event of a flood wave. As outlined in the EMP AEE (L&M Coal, 2010) tourism, mountain biking, tramping and four wheel driving is focused to the

north of the EMP project and does not appear to extend down into the Whareatea River system. As a

consequence the probability that someone will be present in the river system during the flood wave is low.


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Report No. 1078101422-001-R-Rev1-3 5

The flats of the Fairdown area in the vicinity of the SH 67 Road Bridge across the Whareatea River will be

inundated. Currently no residential properties are located near the Whareatea River, and hence the

probability that someone will be near and at risk of the flood wave is low.

Due to the sudden nature of the predicted flood wave that will result due to failure of the Freshwater Dam, and that the wave will peak at 1.7 m above the SH 67 Road Bridge deck, it is likely that motorists who

happened to be on the bridge at the time would be at risk.

2.2.4 Socio-economic, financial & environmental risk

The damage of the SH 67 Road Bridge is expected to take more than three months to reinstate, which would

result in major damage and inconvenience to a major public infrastructure component on the upper West

Coast of the South Island of New Zealand. A temporary bridge e.g. Bailey Bridge would need to be installed.

Environmentally, the dam breaks would result in a significant release of stored sediment, in the order of a

few thousand cubic metres, into the Whareatea River. Whilst the implication to aquatic species in the river

has not been assessed, the financial cost to restore the river would be significant and possibly technically

impossible due to the deeply incised nature of the Whareatea River descending from the Denniston Plateau.

The failure of either of the dams will adversely affect the operation of the coal processing plant. Without the

Freshwater dam, the CPP will be unable to continue to process and slurry coal to the dewatering and

stockpile facility at Fairdown. The loss of the recycle pond would temporary halt the CPP and mining

operations due to the lack of support infrastructure (workshops, offices and/or equipment).

Failure of either dam has significant direct financial risks to Bathurst, the socio-economic environmental

effects may also have a financial risk to Bathurst, in terms of either loss of reputation or non-compliance with

environmental standards and possible prosecution by the West Coast Regional Council.

2.3 PIC classification

Specific guidance on assessing the PIC is provided in Dam Safety Scheme Guidance for Regional Authorities and Owners of Large Dams (DHB, 2008). This document sets out a formalised means to derive the potential impact classification of a dam. It is based on the population at risk (defined as the number of

people who would experience 0.5m or greater of inundation in the event of a dam breach) and the degree of

damage expected.

As summarised in Table 1, both dams are in the order of 10 to 20 m in height and will store 53,000 m3 and

152,000 m3 of water in the recycle dam and freshwater dam respectively. In terms of NZSOLD (2000) size-

volume screening criteria, the recycle and freshwater dam would be broadly classified as medium PIC structures. However based on the evaluation outlined above, in the event of a dam failure, then:

A Freshwater dam failure could result in the following:

Although a few fatalities are possible, none are expected.

Socio-economic and environmental consequences are expected to be major due to the damage of the SH 67 Road Bridge.

Damage beyond the owners property will be significant and may result in the lost of the SH 67 bridge.

Financial consequences may be major in terms of bridge repair costs and loss of mine production.


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A Recycle dam failure could result in the following:

In excess of 10 fatalities if the crest is washed away without warning, but less than 2 fatalities are expected due to the likelihood that a warning can be given for evacuation.

Socio-economic and environmental consequences are expected to be moderate.

Damage beyond the owners property will be minimal, as the resulting flood wave should be retained within the Whareatea River banks and should not result in damage to downstream bridges or

embankments.

Financial consequences may be significant due to loss of mine production.

Based on the NZSOLD (2000) potential impact guidelines summarised in Table 2, the Freshwater Dam may

be classified as high, while the Recycle Dam may be classified as a medium-high" PIC structure.

3.0 DESIGN CRITERIA

3.1 General Design Requirements

The NZSOLD Dam Safety Guidelines (2000) addresses the design, construction, and long-term

maintenance and operation of water retaining structures, irrespective of the size or type of dam. These

guidelines are intended to outline general measures to achieve successful design, construction, operation

and maintenance of safe dams that are economically viable and fit for the purpose. These guidelines provide

the industry general guidance on dam engineering, but it is not a prescriptive standard. The 2004 Building

Act introduced specific legislation covering dam safety.

The likelihood of failure of a properly engineered and constructed dam is extremely small. However, as a

means of comparison, both the NZSOLD guidelines and Building Act require dams to be assessed and

classified in terms of their PIC. The potential impact rating for a structure is based on an evaluation of the

potential incremental consequences of failure to human life, and the socioeconomic, financial, and

environmental effects that could result from a potential release of an impounded reservoir. As the level of

downstream impacts (due to a potential dam failure resulting in the uncontrolled release of the reservoir)

increases, so does the potential impact classification. Depending on the level of this classification, guidelines

are provided for different levels of effort required during design, and in the selection of critical design criteria

of the dam, foundations and abutments as listed below:

Be able to safely pass the Inflow Design Flood (IDF).

Be able to withstand the Maximum Design Earthquake (MDE) without uncontrolled release of the reservoir.

Be able to withstand the Operating Basis Earthquake (OBE) with only minor, repairable damage.

Have a sliding factor of safety greater than 1.5 under static loading with steady state seepage and maximum storage pool.

Have a sliding factor of safety greater than 1.2 under static loading with rapid draw down from maximum storage pool.

Have a sliding factor of safety greater than 1.3 under static loading at the end of construction and before reservoir filling.


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Report No. 1078101422-001-R-Rev1-3 7

Have sufficient freeboard such that the percentage of waves that could overtop the dam would not lead to dam failure. Sufficient freeboard should also be provided to ensure the dam is not overtopped

subsequent to an earthquake.

3.1.1 Inflow design flood

For a medium PIC dam, the IDF usually has an Annual Exceedance Probability (AEP) of between a 1 in 1,000 and 1 in 10,000 while a high PIC dam, the IDF AEP is usually between 1 in 10,000 and PMF. For the Freshwater and Recycle Dams, it is intended that the IDF event will have an AEP of 1 in 10,000 and 1 in

7,500 respectively. This decision is supported by the following probabilistic assessment.

Freshwater Dam: If 1 in 10,000 is selected as the AEP for the IDF, then:

Probability of a flood exceeding the IDF in any single year = 0.00010

Probability of no flood exceeding the IDF in any single year = 1 - 0.00010 = 0.99990

If (say) the design life is 35 years, probability of no flood exceeding the IDF in 35 years, equates to the following:

Probability of 1 or more floods exceeding the IDF in 35 years, equates to the following: .

This is judged to be acceptable for the Freshwater Dam.

Recycle Dam: If 1 in 7,500 is selected as the AEP for the IDF, then:

Probability of a flood exceeding the IDF in any single year = 0.00013

Probability of no flood exceeding the IDF in any single year = 1 - 0.00013 = 0.99987

If (say) the design life is 35 years, probability of no flood exceeding the IDF in 35 years, equates to the following:

Probability of 1 or more floods exceeding the IDF in 35 years, equates to the following: .

This is judged to be acceptable for the Recycle Dam.

3.1.2 Seismic design criteria

The New Zealand Dam Safety Guidelines do not give specific design levels of earthquake shaking for dams.

However, they do note that for high PIC dams a site specific seismic risk study should be undertaken. The NZSOLD (2000) guidelines indicate that Medium and High PIC dams should be designed for two levels of

earthquake. These are the maximum design earthquake (MDE) and the Operating Basis Earthquake (OBE).

The MDE is the maximum level of ground motion for which the dam should be designed or analysed. Based

on PIC criteria of the dams, the MDE shall be the Maximum Credible Earthquake (MCE) or 1 in 10,000 AEP.

Bathurst has yet to undertake a site specific probabilistic seismic hazard assessment of the EMP site. As a

consequence no site specific seismic loadings are currently available for the dams. For the purposes of the

conceptual design only, it is likely that the peak ground acceleration (PGA) for the MDE and ODE will be

similar to those determined for the Mangatini Dam at Stockton Coal Mine (URS, 2005), as summarised in

Table 5.


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Report No. 1078101422-001-R-Rev1-3 8

Table 5: Preliminary seismic design loads.

Design seismic load Peak ground acceleration (g)

Operating Basis Earthquake (OBE)

1 in 150 year AEP 0.38

Maximum Design Earthquake (MDE)

1 in 10,000 year AEP 0.82

Note: A site specific seismic hazard assessment is required before detail design.

3.2 Hydraulic Design of Dams

Both dams will require a spillway to pass large flows up to the maximum design flood. It is anticipated that

the spillways will be formed in open channels cut through rock on the abutments to the dams, and allow the

Incremental Damage Flood (IDF) flows to pass safely.

3.2.1 Design floods

The proposed dams will be designed to a 1:10,000 AEP criteria for an IDF. This is consistent with the

maximum IDF criteria for a medium PIC dam classification in which the minimum IDF is usually between 1:1,000 and 1:10,000 AEP (NZSOLD, 2000) and at the minimum end for a high PIC dam, where the IDF AEP is usually between 1 in 10,000 and PMF.

Table 6: Estimated dam peak inflows #.

Parameter Freshwater Dam Recycle Dam

Catchment Area (Ha) 15.3 4.0

Peak Inflow (m3/s) 1:1 AEP 1.7 0.5

1:10 AEP 2.7 0.7

1:50 AEP 4.4 1.1

1:100 AEP 5.6 1.5

1:1,000 AEP

TBA

TBA

1:10,000 AEP

TBA TBA

Probable maximum flood (PMF) 16.6 4.5 # This data from Envirolink (2010) will need to be verified and possibly adjusted for the detailed dam design

phase.

3.2.2 Embankment freeboard

The spillway system for each dam will be designed to ensure the reservoir level during the IDF is at least

0.4 m below the crest of the dam.

The Freshwater Dam will be designed so that the spillway intake sill is at 670.5 mRL, being 1.5 m below the

crest of the dam and 0.5 m above the maximum operating level. If the spillway were designed to pass the

PMF of 16.6 m3/s, then the spillway breadth will be in the order 8.6 m.

The Recycle Dam will be designed so that the spillway intake sill is at 654.0 mRL, being 1.0 m below the

crest of the dam. A 3.5 m wide spillway, operated at a water level of 655 mRL is able to discharge

approximately 5.8 m3/s, which is greater than the predicted PMF for this dam.

Design levels for the crest and spillway intake sill for each dam are summarised in Table 1.


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4.0 EMBANKMENT DESIGN AND CONSTRUCTION

The design of the embankments provide for a level of protection appropriate for a high PIC dam against instability, seepage, erosion and deformation under all normal and potential loading conditions.

4.1 Site Geology

The EMP dams are located on the Denniston Plateau, a gently undulating plateau that generally slopes to

the north and east and is deeply incised by north-east sloping streams.

Basement rocks on the plateau comprise Greenland Group greywacke and argillite of Ordovician age, locally

intruded by porphyritic granites, associated gneiss and younger intrusives of quartz porphyry. During the late

Cretaceous and early Tertiary, these rocks were eroded to form an erosional surface with relief that had a

major influence on coal measure deposition. Basement rocks are extensively exposed where erosion has

removed Tertiary rocks.

Brunner Coal Measures of Mid-Late Eocene age unconformably overlie basement rocks. The measures are

variable in thickness, averaging 40 to 60 m in the west and thickening to more than 270 m near Mt Rochfort.

Thickness variations can be very rapid, as can vertical and lateral changes in lithology. Throughout the Buller

Coalfield, only one major interval contains coal of workable thickness, either resting directly on basement or

on a conglomerate-sandstone succession. The interval comprises carbonaceous mudstones and lenticular

coal seams up to 17m thick which are often split in several directions by sandstones.

Conformably overlying Brunner Coal Measures (BCM) are thick (originally several kilometres) dark coloured,

micaceous, marine siltstones with some sandy layers. Coarse beds exposed along the western edge of the

coalfield are the Torea Breccia Member consisting of closepacked boulders of granite and gneiss. Erosion

has stripped most of the original thickness of soft Kaiata Mudstone from the coalfield.

The Buller Coalfield is preserved as a distorted, eastward-dipping plateau between the Papahaua Overfold in

the west and the Glasgow Fault in the east. The two structures converge to the north. The intervening

structure is complex and largely responsible for the present physiography that exposed coal measures form.

The plateau is cut by faults, and generally slopes to the north. Much of the plateau is underlain by early

Tertiary sediments, with local windows of the underlying Pre-Tertiary rocks exposed by erosion.

There is a good quality geological database available within the mining permit areas. This database includes

good quality geological maps at 1:10,000 scale based on in excess of 50 drill holes and old mine maps.

4.2 Foundation Preparation

The prepared foundation surface will be mapped by an engineering geologist prior to placement of any fill,

and specific defects will be treated as described below. As noted above, finger drains will be provided

beneath the downstream shoulders to drain potential seepage from rock defects exposed during foundation

preparation that are judged to be amenable to foundation seepage.

4.2.1 Embankment shoulder

The entire foundation area will be cleared of all plant matter, organic soils and other unsuitable material (as

assessed by the Engineer). Large projecting knobs of rock, steep bluffs and overhangs will be treated to

ensure no areas are left that could cause differential settlement or the formation of voids within the placed

rockfill. The Engineer will inspect and approve the cleared foundation and any treated areas before

placement of any fill commences.

All prominent open defects or joints in the foundation rock below the upstream shoulder that could present

preferential flow paths will be treated to reduce the potential for foundation seepage. Below the downstream


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shoulder, open joints and potentially erodible features will have filter material (Zone 2A) and finger drains

(Zone 2B) placed over them to ensure free drainage of any seepage to the downstream toe.

4.2.1 Liner and core/filter

A liner with a low permeability core possibly formed of graded sandstone will likely form the key water detaining element within the dam body. The liner and core / filter foundation requires special attention and

will be cleaned and prepared thoroughly in order to prevent uncontrolled seepage along the fill-foundation

boundary, or through the underlying jointed rock mass. The strip to be prepared will be marked out by the

dam surveyors. Preparation of this area will include the following measures, where appropriate:

Water or air blasting equipment and hand labour to clean all soil and loose material from the rock surface.

Geological mapping to document the foundation conditions and identify defects that require treatment.

Dental treatment of any open joints, weathered seams, fault zones or other features that could adversely impact on future dam performance. This will involve water or air blasting the defects clean,

then back-filling and sealing with slush grout, concrete or compacted select fine soil. In some cases it

may be necessary to shape the rock surface to ensure that protrusions and overhangs are treated,

thereby allowing good compaction of the core materials.

The Engineer will inspect and approve the cleared foundation and each stage of this operation before

placement of any core material commences.

4.2.1 Cutoff trench

Any core material will be placed on a prepared foundation surface of slightly to moderately weathered rock. It

is anticipated that construction of a cutoff trench will be necessary, to provided adequate foundation

treatment and that a good seal is provided between the rock and the liner material.

4.3 Embankment Cross Section

4.3.1 Dam type

Dam options studies (Golder, 2010) considered several dam options to identify the preferred least cost, fit for purpose, quickest construction option. The following provides a summary of the five dam type options considered viable for the EMP.

a) Zoned Earth and Rockfill Dam - constructed of well-compacted earth and rockfill materials that are

placed in distinct zones based on material properties. This could consist of:

Outer shells of free-draining large particle granular material (or rockfill) surrounding a central

low-permeability core flanked by free-draining granular filter and drain zones or

Low permeability zone near the upstream face, protected by upstream filter and rip rap

layers and separated from permeable, free draining granular material downstream by free-

draining granular filter and drain zones

The size of the various zones is optimised to reduce cost, while maintaining stability and adequately

controlling seepage.

b) Upstream Lined Earth and Rockfill Dam with Geomembrane Liner - consists of a rockfill

embankment with a liner typically composed of High-Density Polyethylene (HDPE) sheets that are

welded together to form a relatively impermeable barrier on the upstream face. Free-draining granular


November 2010

Report No. 1078101422-001-R-Rev1-3 11

filter and drain layers are constructed adjacent below the liner to collect and remove seepage. A

concrete plinth is constructed along the upstream toe of the dam to provide a seal between the

geomembrane and rock foundation.

c) Upstream Lined Earth and Rockfill Dam with Geocomposite Liner (GCL) - similar to option B,

however, a different type of liner is used. All other aspects including filters, drains, and plinth remain the

same. A GCL is a composite material comprising a layer of low permeability bentonite surrounded by

two layers of non-woven geotextile filter fabric.

d) Concrete Faced Rockfill Dam (CFRD) - similar to options B and C, however, an impervious concrete

slab or facing element is used instead of a geomembrane or geocomposite liner. All other aspects

including filters, drains, and plinth remain the same. Typically the size of the plinth constructed for a

CFRD is larger to provide additional foundation support.

e) Roller Compacted Concrete (RCC) Dam - consists of a hybrid concrete dam construction (zero-slump

concrete that is placed and compacted in lifts). RCC dams typically require a large quantity of sound

aggregate for concrete production, and significant foundation excavation to develop a suitable

foundation shape with excellent bearing strength.

Preliminary cost estimates indicated that Option A was relatively the least expensive of the options

considered. However, this type of construction can be quite sensitive to wet weather, and the frequent

rainfall on the Denniston Plateau could force frequent delays in the embankment placement schedule,

lengthen the overall construction timeframe, and potentially increase the construction management costs

associated with dam construction.

Subject to further investigations, there may also be a limited supply of potential low permeability core

material available on the mine site and accessible at the time of dam construction. While RCC or CFRD

dams would be suitable for the proposed dam sites, initial analyses indicate that they would be less cost

effective than options B and C, and incur an additional 30-50% construction cost premium.

Of the five embankment options considered by Golder (2010), the upstream lined earth and rockfill dams

(Option B and C) with a 1:3 upstream slope profile appeared feasible and offer the best balance of the

performance, constructability and cost objectives. Golder recommends that the selection of the liner should

be deferred to the detailed design phase. Possible liner materials could include:

HDPE (high-density polyethylene) or LLDPE (linear low-density polyethylene)

Bentonite geocomposite liner

Geotextile reinforced PVC

Bitumen impregnated geotextile

Due to the high PIC rating of the dams, in addition to the water retaining liner, a secondary level of protection is proposed. In this case it is possible that the Zone 3a core could be constructed of a BCM

Sandstone. Previous experience on the Stockton Plateau suggests that similar geological units exhibited

low-moderated permeability following working of the sandstone (permeability of between 10-5

10-6

m/s).

Roller Compacted Concrete dams may be considered further during detailed design as while they are more

expensive then Options B and C this construction form offers benefits in a more rapid construction and

robustness to overtopping. Further, overtopping of the crest can be designed as the spillway.

4.4 Available Construction Materials

An extensive evaluation has yet to be undertaken of the potential construction materials available on site.

This evaluation should include the characterising of material properties based on field observations,

laboratory testing and if time allows field trials.


November 2010

Report No. 1078101422-001-R-Rev1-3 12

Due to the conceptual mine plan, many of the construction materials, for example the weathered granites will

not be made available till Year 3-4 of the mine life. As a consequence some of the earth fill materials may

need to be imported into the mine.

4.5 Embankment Construction

4.5.1 Core (Zone 3A)

The core material placed immediately behind the liner will likely be a compacted graded sandstone derived

material that has all rock size particles greater than 225 mm removed from it to form a low to moderate

permeability material in the order of 10-6

to 10

-7 m/s.

4.5.2 Drainage fingers (Zone 2B)

Drainage (Zone 2B) material will be placed in fingers or as a blanket beneath the downstream shoulder to direct seepage flows from the chimney drain into the seepage collection system. Further finger drain(s) will

be positioned and sized on site by the Engineer, following preparation of the foundation. These finger

drain(s) will be positioned in natural depressions on the prepared foundation surface and also over areas of

exposed open defects in the downstream shoulder footprint. Alignment of the drain(s) will be approximately

perpendicular to the embankment axis.

4.5.3 Shoulder (Zone 3) material

The shoulder material will be stripped overburden rock with a maximum dimension of 1.5m. Shoulder

material will be placed in lifts with a maximum thickness of 1.5 m and compacted by suitable plant as agreed

with the Engineer. Regular visual monitoring will be performed by the Engineer to check that adequate

compaction of the shoulder material is being achieved.

The shoulder material requires compaction to develop sufficient shear strength to protect against sliding

instability, limit post construction settlements to acceptable levels, and provide resistance to internal and

surface erosion. Blocks larger than 1.5 m will be pushed to the outside of the fill for use as rip rap. Removal

of large boulders (> 0.5 m) from adjacent to the upstream edge of the filter material (Zone 2A) will be

undertaken to reduce the risk of voids or poor compaction adjacent to these material interfaces.

Placement will commence by filling low points and providing as much compaction to these areas as practical.

Given the expected space restrictions at such low points, compaction with mine trucks will be impractical.

Compaction using a vibrating roller with reduced layer thickness may be required to ensure effective

compaction of the shoulder material in this area. The second stage will involve shoulder material placement

on the downstream part of the footprint until the entire footprint area is essentially level. Shoulder material

will then be placed in regular lifts across the entire footprint area.

Similarly, in other areas where compaction of shoulder (Zone 3) material with mine trucks is impractical,

compaction will be performed using a vibrating roller, with a thinner layer thickness before compaction.

The Zone 3A material will be compacted BCM Sandstone. Working and/or screening of this material to < 225

mm particle size will reduce the particle size of this material and result in a decrease in permeability.

4.5.4 Liner filter (Zone 2A)

The main issues that need to be addressed in construction of the liner filter are:

Grading of the material to ensure it is a cohesionless material with < 2% fines to perform the dual function of drainage and filtering action to trap any eroded fine material in seepage flows.


November 2010

Report No. 1078101422-001-R-Rev1-3 13

Ensuring that the filter is constructed as a continuous element with a minimum width of 0.5 m.

Ensuring that the material is not compacted such that it forms a bridge in the event of a crack developing within the dam.

Preventing segregation of filter material during placement.

Compaction of filter material will be achieved with either one pass of an approved vibratory roller or two

passes with hand held compaction equipment. Visual monitoring will be performed by the Engineer to check

that the filter material has been compacted to an appropriate degree, and also to confirm that the method of

placement of filter material does not result in segregation of that material.

4.5.5 Rip rap (Zone 4)

Water levels in the reservoir are expected to vary during normal operation as the inflow rate varies in

proportion to the decant rate. A layer of rip rap (Zone 4) will be constructed to protect the reservoir face of

the dam against wave erosion.

The rip rap will be formed from boulder sized rock from the Zone 3 (shoulder) material, selectively placed at

the outer edge of the upstream shoulder during placement of Zone 3. The need for a bedding layer will be

determined prior to placing any riprap, and will depend on the grading of the material at the margins of the

upstream embankment slope.

4.5.6 Embankment crest and laydown construction

A requirement for the mine operations is to construct a laydown and workshop facility on the Recycle Dam.

This surface will be prepared in accordance with normal civil engineering practice, with a basecourse/running

course placed once the embankment is complete.

4.6 Access for Machinery

The proposed access routes will be within the CPP Dam area as delineated in Appendix B. In the case of the Freshwater Dam, the primary access of the dam site will be via a temporary haul road that will connect to

the public

c road and mine road adjacent to the CPP.

5.0 SPILLWAY DESIGN

5.1 Spillway Design

The spillway for the Freshwater and Recycle Dams will be sized to provide at least 0.4 m freeboard below

the dam crest in the event of the IDF. As summarised in Section 3.2.1 the IDF for the Freshwater and

Recycle Dam are still to be determined, however for the purposes of conceptual design the spillway has

been designed to convey the PMF. This may be overly conservative, and a more appropriate AEP may be

ultimately adopted.

5.1.1 Design criteria

Initial calculations indicate that the required spillway channel dimensions at the spillway intake for both dams

are as shown in Table 7. These are based on the Inflow Design Flood (IDF), a water depth of 0.5 m at the


November 2010

Report No. 1078101422-001-R-Rev1-3 14

spillway sill and allowance of a 0.4 m freeboard below the dam crest under the ID flood condition for the

Freshwater and Recycle Dam respectively.

Table 7: Spillway design criteria.

Parameter Freshwater Dam Recycle Dam

Design Crest Level (mRL) 672 655

Spillway Intake Sill Level (mRL) 670.5 654

IDF (ARI) (m3/s) TBA (1:10,000)

# TBA (1:10,000)

#

PMP (m3/s) 16.6 4.5

Water Depth at Sill (at IDF) (m) 0.55 0.55

Required Channel Width at Dam (m) 8.6 3.5

Hydraulic Coping Capacity (m3/s) 15.3 5.8

# To be confirmed during the detailed design phase

5.1.2 Design

The intention is that the primary spillway channels for both dams will be open channels cut into competent

rock and aligned to be well away from the embankment dams.

The intention is that the primary spillway channel for each dam will be cut deeper into rock as soon as

possible after the spillway intake, to allow a transition to a narrower channel width. This will be clarified as

part of detailed design.

Channel protection requirements to prevent excessive erosion downstream from the spillways will be

determined as part of the final design process.

5.1.3 Reservoir drawdown arrangement

There will not be any specific provision of a low level outlet capable of lowering the water level in the dams in

an emergency. To facilitate rapid water level drawdown in an emergency, a combination of the process

withdrawal pumping and additional pumping or syphoning over the dam crest will be required.

5.1.4 Temporary stream diversion arrangements

The general requirement from NZSOLD (2000) regarding design of temporary diversion arrangements for

during construction is that diversion arrangements should be carefully considered in relation to the risks of overtopping and the expected consequences of the dam being overtopped at any stage of construction. This requirement will be considered in the detailed design phase.

It is intended that normal stream flows will be diverted around the dam footprints during construction most

likely utilising a diversion culvert through the dam body. This will be grouted up on completion of the dam

construction to fully seal it and prevent the entry of reservoir water.


November 2010

Report No. 1078101422-001-R-Rev1-3 15

6.0 DAM OPERATION AND REHABILITATION

6.1 Dam Operation

Once the dams are operating regular inspection and maintenance will be carried out to ensure that the dams

perform to specification. Ongoing embankment monitoring will likely include seepage collection and

recording, piezometer installation and surface settlement monitoring. This will be detailed in the dam

surveillance plan to be developed during the detailed design and construction phases. The surveillance plan

will also detail routine dam safety inspection requirements, personnel responsibilities and procedures for

reacting to unusual observations or events.

6.2 Proposed Rehabilitation

It is currently intended that post-closure the dams will be filled with mine waste rock and capped with

available materials to promote site revegetation. The surface will be built up to enable armoured channels to

be developed to carry runoff across the surface of the capped area and down the spillways. Species tolerant

of the local environmental conditions will be selected and planted on permanent landform slopes, wherever

possible.

The downstream shoulder of the Freshwater Dam will be flattened to a slope of 1V:3H by placing additional

waste rock. Exposed embankment surfaces on both dams will be rehabilitated by placing a soil capping layer

and revegetated with species tolerant of local conditions.

It is intended that inflows to these dams will be directed to the respective the spillway channels, this may

require providing additional spillway capacity depending on the detailed design for these post-closure

landforms, and material consideration to avoid erosion risk along the spillway channel.


November 2010

Report No. 1078101422-001-R-Rev1-3 16

7.0 REFERENCES

DBH (2008): Dam Safety Scheme: guidance for regional authorities and owners of large dams. Prepared by

Department of Building and Housing.

Envirolink (2010): Escarpment Mine Project: Assessment of Runoff from Catchment within Mine Area. Report

prepared for Resource and Environmental Management Nelson Limited by Envirolink Limited. 8 November

2010.

L&M Coal (2010): Escarpment Mine Project: West Coast Regional Council Resource Consent Application

and Assessment of Environmental Effects on the Environment. Report prepared by Resource and

Environmental Management Nelson Limited for L&M Coal Limited. 31 August 2010.

NZSOLD (2000): New Zealand Dam Safety Guidelines. New Zealand Society of Large Dams. November

2000.

URS (2007) Stockton Opencast Mine: TM#2 Seismic Hazard Assessment. Report prepared by URS New

Zealand Limited for Solid Energy New Zealand Limited, March 2007.


November 2010

Report No. 1078101422-001-R-Rev1-3

APPENDIX A Report Limitations


November 2010

Report No. 1078101422-001-R-Rev1-3

REPORT LIMITATIONS

This Document has been provided by Golder Associates (NZ) Ltd (Golder) subject to the following limitations:

(i). This Document has been prepared for the particular purpose outlined in Golders proposal and no

responsibility is accepted for the use of this Document, in whole or in part, in other contexts or for any other purpose.

(ii). The scope and the period of Golders Services are as described in Golders proposal, and are subject

to restrictions and limitations. Golder did not perform a complete assessment of all possible conditions or circumstances that may exist at the site referenced in the Document. If a service is not expressly indicated, do not assume it has been provided. If a matter is not addressed, do not assume that any determination has been made by Golder in regards to it.

(iii). Conditions may exist which were undetectable given the limited nature of the enquiry Golder was

retained to undertake with respect to the site. Variations in conditions may occur between investigatory locations, and there may be special conditions pertaining to the site which have not been revealed by the investigation and which have not therefore been taken into account in the Document. Accordingly, additional studies and actions may be required.

(iv). In addition, it is recognised that the passage of time affects the information and assessment provided

in this Document. Golders opinions are based upon information that existed at the time of the production of the Document. It is understood that the Services provided allowed Golder to form no more than an opinion of the actual conditions of the site at the time the site was visited and cannot be used to assess the effect of any subsequent changes in the quality of the site, or its surroundings, or any laws or regulations.

(v). Any assessments made in this Document are based on the conditions indicated from published

sources and the investigation described. No warranty is included, either express or implied, that the actual conditions will conform exactly to the assessments contained in this Document.

(vi). Where data supplied by the client or other external sources, including previous site investigation data,

have been used, it has been assumed that the information is correct unless otherwise stated. No responsibility is accepted by Golder for incomplete or inaccurate data supplied by others.

(vii). The Client acknowledges that Golder may have retained subconsultants affiliated with Golder to

provide Services for the benefit of Golder. Golder will be fully responsible to the Client for the Services and work done by all of its subconsultants and subcontractors. The Client agrees that it will only assert claims against and seek to recover losses, damages or other liabilities from Golder and not Golders affiliated companies. To the maximum extent allowed by law, the Client acknowledges and agrees it will not have any legal recourse, and waives any expense, loss, claim, demand, or cause of action, against Golders affiliated companies, and their employees, officers and directors.

(viii). This Document is provided for sole use by the Client and is confidential to it and its professional

advisers. No responsibility whatsoever for the contents of this Document will be accepted to any person other than the Client. Any use which a third party makes of this Document, or any reliance on or decisions to be made based on it, is the responsibility of such third parties. Golder accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or actions based on this Document.


November 2010

Report No. 1078101422-001-R-Rev1-3

APPENDIX B Freshwater and Recycle Dam Concept Drawings

DRAFTS:\Graphics\Projects-numbered\2010\10781x\01xxx\1078101_422_BathurstResourcesLtd_EscarpmentDam&AMD\Nov10\Project R

1PROJECT | 1078101422NOVEMBER 2010TITLE | ESCARPMENT MINE PROJECT: GENERAL ARRANGEMENT OF THE COAL PROCESSING PLANT AND DAMS

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SOURCE: Bathurst Resources Ltd Escarpment Project. Crown Mineral Permits Relative to Project Infrastructure. Drawn LMcC July 13 2010.

FRESHWATER DAM

SPILLWAY

RECYCLE DAM

SPILLWAY

S:\Graphics\Projects-numbered\2010\10781x\01xxx\1078101_422_BathurstResourcesLtd_EscarpmentDam&AMD\Nov10\Project R

2PROJECT | 1078101422NOVEMBER 2010TITLE | ESCARPMENT MINE PROJECT: FRESHWATER DAM EMBANKMENT CONCEPT

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Schematic only, not to be interpreted as an engineering design or construction drawing

0 2 4 6 8 10Metres

APPROX. SCALE

CONCRETE TOE

3% CAMBER

ZONE 3bZONE 3a

ZONE 2a FINGER DRAIN

STRIPPED GROUND PROFILE(INDICATIVE) (BEDROCK)

FULL OPERATIONALSTORAGE LEVEL (FSL)RL 670.0m

CREST RL 672.0m (PLUS LONGITUDINAL CAMBER)

RL 654.0m

ZONE 4(RIP RAP)

CONSTRUCTION DIVERSION SLUICE(INDICATIVE, PROJECTED ONTO SECTION)(CONTINUOUSLY SUPPORTED WITH CAST-INSITU CONCRETE)

(DOWNSTREAM TOE DRAIN)

BULK FILL

ZONE 4 (RIP RAP)

2m (MIN)

2m (MIN)

ZONE 2A(FILTER)

LINER

UPSTREAM LINED EARTH & ROCKFILLDAM WITH GEOMEMBRANE LINER1:3 SLOPE PROFILE

11.75

11

3

13

1

21

5m

S:\Graphics\Projects-numbered\2010\10781x\01xxx\1078101_422_BathurstResourcesLtd_EscarpmentDam&AMD\Nov10\Project R

3PROJECT | 1078101422NOVEMBER 2010TITLE | ESCARPMENT MINE PROJECT: RECYCLE DAM EMBANKMENT CONCEPT

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Schematic only, not to be interpreted as an engineering design or construction drawing

0 2 4 6 8 10Metres

APPROX. SCALE

CONCRETE TOE

ZONE 3bZONE 3a

ZONE 2a FINGER DRAIN

STRIPPED GROUND PROFILE(INDICATIVE) (BEDROCK)

FULL OPERATIONALSTORAGE LEVEL (FSL)RL 654.0m

CREST RL 655m (PLUS LONGITUDINAL CAMBER)

RL 646.0m

ZONE 4 (RIP RAP)CONSTRUCTION DIVERSION SLUICE(INDICATIVE, PROJECTED ONTO SECTION)(CONTINUOUSLY SUPPORTED WITH CAST-INSITU CONCRETE)

(DOWNSTREAM TOE DRAIN)

BULK FILL

ZONE 4 (RIP RAP)

2m (MIN)

2m (MIN)

ZONE 2A (FILTER)LINER

UPSTREAM LINED EARTH & ROCKFILLDAM WITH GEOMEMBRANE LINER1:3 SLOPE PROFILE

11.75

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311

3 21

5m 70m

RL 640.0m


November 2010

Report No. 1078101422-001-R-Rev1-3

APPENDIX C Dam Break Analysis

Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation. 124 Pacific Highway, St. Leonards, New South Wales 2065, Australia (PO Box 1302, Crows Nest NSW 1585)

Tel: +61 2 9478 3900 Fax: +61 2 9478 3901 www.golder.com

Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America

A.B.N. 64 006 107 857 Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation.

Dear Les

1.0 INTRODUCTION Golder Associates (Golder) were engaged to provide a preliminary dam break assessment of the Recycle and Freshwater Ponds associated with the Escarpment Mine Project area (the EMP). The analysis was conducted considering sunny day failure, caused by piping of these proposed dams. Failure due to overtopping with coincident flooding was not considered in this assessment.

2.0 BACKGROUND The two ponds are located in the Whareatea River catchment, which is located in the centre of the Denniston Plateau. The plateau is bounded by the Mount William Range to the east, Mount Rochfort to the southwest and the lowland terraces and flats of the Fairdown area to the west. The Whareatea River flows in a westerly direction to the sea through a road bridge on Fairdown Road and a railway bridge on the Stillwater-Westport line. The location of the proposed dams is shown in Figure 1.

The proposed EMP area covers approximately 148 hectares. It is located on the southern edge of the Denniston Plateau, and is approximately 13 km to the east of Westport and approximately 4 km to the south of Denniston. Figure 2 shows a preliminary layout of the EMP.

Within the EMP area, there are a number of creeks and streams flowing into the Whareatea River. The proposed dams for fresh water pond and recycle water pond are located on two unnamed tributaries upstream of the Whareatea River as shown in Figure 1. Other tributaries that contribute to the Whareatea River include S Creek, V40 Stream, Conglomerate Creek and Trent Stream.

The topography of the plateau area is typically gently rolling scrub. The majority of the area has an elevation of between 600 and 700 m above sea level.

3.0 SITE DESCRIPTION The two dams proposed within the EMP are described below:

Freshwater Pond Freshwater Pond is to be located on the western side of the proposed plant area within the EMP (Figure 2). Proposed crest level is 672 mRL, with a top width of 10 m and embankment length of 180 m. The height of the embankment (dam wall) is approximately 18 m. The proposed spillway sill level is 670 mRL.

12 November 2010 Project No. 107622088-001-R-Rev0-5

Les McCracken Bathurst Resources Ltd c/- Les McCracken Consulting Ltd 70 Aitken Street ASHBURTON

PROPOSED MINE DEVELOPMENT AT DENNISTON, NEW ZEALAND DAM BREAK ANALYSIS FRESHWATER AND RECYCLE PONDS

Les McCracken 107622088-001-R-Rev0-5Bathurst Resources Ltd 12 November 2010

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There are two potential construction options for this dam:

Upstream Lined Earth and Rockfill Dam Rolled Compacted Concrete (RCC) For the purposes of this analysis, it was assumed that the Freshwater Pond will be earth and rockfill dam.

Recycle Pond Recycle Pond is to be located on the eastern side of the proposed plant area (Figure 2). The dam crest is very wide at 70 m and the crest is proposed to be used as a laydown area, parking as well as the location of the workshop. The proposed crest level is 655 mRL, with a top width of 70 m and an embankment length more than 150 m. The height of the embankment (dam wall) is 14 m. A spillway and diversion channel will be designed to direct stormwater away from this structure. The elevation of the spillway sill is 654 mRL.

4.0 MODEL SETUP Hydrologic Engineering Centre River Analysis System (HEC-RAS) models, Version 4.1.0 (United States Army Corp of Engineers, January 2010), were prepared for the Freshwater Pond and the Recycle Pond.

4.1 Model Data The datasets upon which the model was constructed included:

2 m topographic contours for the whole Whareatea River catchment (topo_nzam_2_10_m.dwg received 20 October 2010)

Mine Model Layout (Mine Model 28 Sept 2010.dwg received 14 October 2010) preliminary layout of the mine including location of the Freshwater Pond and Recycle Pond as well

as proposed plant footprint.

1 m topographic contours within the EMP area 5 m topographic contours within the Whareatea River catchment

Updated dam dimensions Freshwater and Recycle Pond (via email 25 October 2010) Topographic Maps (derived from nztopomaps.com) Aerial Imagery (derived from Google Earth) 4.2 Model Construction Model Geometry Two HEC-RAS models were constructed:

Freshwater Pond Recycle Pond Each model consisted of a single reach commencing from above the relevant structure and proceeded downstream through Fairdown Road Bridge onto the floodplain and through the Stillwater Westport Railway Bridge to the Pacific Ocean.

Cross-sections for each of the models were derived from the 2 m contour dataset, except in the vicinity of the EMP area, where the 1 m contour dataset was used wherever available. In the lowland terraces and flats of the Fairdown area, at the western extent of the model, the topographic definition is very broadscale. The 2 m dataset at this location was interpreted, where required, to derive hydraulically appropriate cross-sections and the minimum channel elevations were assumed below the tidal limit.

There are two hydraulic structures of interest in this analysis:


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Fairdown Road Bridge Stillwater Westport Railway Bridge Detailed topographic survey of these structures has not been undertaken at this stage. Table 1 presents geometric details that were adopted in the model.

Table 1: Adopted Hydraulic Structure Details

Description Fairdown Road Bridge Stillwater Westport Railway Bridge

Average Opening Width 35 m 30 m Top Level of Road or Track 10.00 mRL 6.00 mRL Soffit Level of Bridge 9.50 mRL 5.00 mRL Central Pier Width 1.0 m N/A

Figure 3 presents the layout of the Freshwater Pond model, including the location of primary cross-sections. Figure 4 presents the layout of the Recycle Pond model. Primary cross-sections in each model were then interpolated at a 10 m interval within HEC-RAS.

Relevant hydraulic parameters adopted in the HEC-RAS models are presented in Table 2.

Table 2: Adopted Model Hydraulic Parameters Parameter Freshwater Pond Recycle Pond

Left Bank Mannings Roughness 0.09 0.09 Main Channel Mannings Roughness 0.06 0.06 Right Bank Mannings Roughness 0.09 0.09 XS Interpolation Interval 10 m 10 m US Boundary Full Pond Full Pond DS Boundary 0 mRL 0 mRL

Table 3 presents the properties of each of the reservoirs to be included in the model. Breach parameters adopted for use in the model are presented in the following section.

Table 3: Reservoir Geometric Properties

Reservoir Property "Sunny Day" Failure

Freshwater Pond Recycle Pond Maximum Dam Height 18 m 14 m Dam Crest Level 672 mRL 655 mRL Spill Sill Level 670 mRL 654 mRL

Water Storage Volume (at spillway level) 152,000 m3 53,000 m3

Depth of Dam at Time of Failure 16 m 16 m1

1 Depth of dam adjusted in the model such that Water Storage Volume for Recycle Dam was approximately 53,000 m3.

Boundary Conditions A known water surface was used as the downstream boundary condition for each HEC-RAS model. The assumed level was 0 mRL.


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At the upstream end, an assumed inflow of 5 m3/s was adopted for each model. An inflow of 5 m3/s was selected as being sufficient:

to stabilise the model simulation be insignificant compared to modelled discharges caused by the dambreak flood wave. The dams were also assumed to be full up to sill level as an initial condition of the model simulation.

Dam Breach Parameters A literature review was undertaken and relevant empirical equations used to predict breach formation time and average breach width. The empirical equations presented in Wahl (2004) and Froehlich (2008) were then processed using geometric data presented in Table 3.

It is noted that breach formation time is defined as the time for the breach to completely form once the breach has initiated. In the case of piping failure, the breach formation time is not the time taken for the pipe to form; rather it is the time for the breach to form once the breach has been initiated.

Table 4 presents the predicted value for each of the breach parameters.

Table 4: Dam Breach Parameter Predictions (Wahl, 2004 and Froehlich, 2008)

Average Breach Width (m)

95% UCL5 95% LCL5 Breach Formation Time (hr)

95% UCL5 95% LCL5

Freshwater Pond Bureau of Reclamation (1988) 48 22 158 0.53 0.13 14.3

Von Thun and Gillette (1990)1 46 17 83 0.24 0.10 9.6

Froelich (1995)2 14.2 5.7 34 0.11 0.04 0.77 MacDonald and Langrige-Monopolis (1984)3 3.2 0.5 22 0.29 0.07 3.2

Froehlich (2008)4 14.4 N/A N/A 0.12 N/A N/A

Recycle Pond Bureau of Reclamation (1988) 39 17.5 128 0.43 0.1 11.6

Von Thun and Gillette (1990)1 39 14.3 69 0.24 0.1 9.6

Froelich (1995)2 9.7 3.9 23 0.11 0.03 0.55 MacDonald and Langrige-Monopolis (1984)3 1.4 0.2 9.8 0.20 0.05 2.3

Froehlich (2008)4 8.8 N/A N/A 0.09 N/A N/A 1 Dam type assumed to be highly erodible; 2 Failure mechanism assumed to be piping (Ko = 1); 3 Assumed to be earthfill type; 4 From Froehlich, 2008. All others from Wahl, 2004; 5 95% Upper Confidence Limit, 95% Lower Confidence Limit.

From Table 4, there is a considerable range in predicted values of the breach parameters. The 95% UCL and 95% LCL highlight the significant uncertainty inherent in these empirical equations.

For the purposes of this analysis, a conservative approach was therefore adopted wherein the lower end of the range of values presented in Table 4 were adopted. Table 5 presents the parameters adopted for use in the model.


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It is noted that the values adopted for the Recycle Pond reflect the proposed use of the crest as a plant layout and car parking area. The crest length, in a downstream direction, is therefore considerably longer than typical and hence longer breaching time would be more suitable.

Table 5: Adopted Breach Parameters Parameter Freshwater Pond Recycle Pond

Breach Formation Time 10 min 15 min Average Breach Width 20 m 15 m Final Breach Elevation 655.5 mRL 647.5 mRL Side Slope1 0.7H:1.0V 0.7H:1.0V Failure Mode Piping Piping Piping Orifice Coefficient 0.5 (default) 0.5 (default) Initial Piping Elevation 657 mRL 649 mRL Breach Progression Mode Linear Linear Breach Trigger Mode Specified Time Specified Time 1 Side slope for piping failure of 0.7H:1.0V adopted from Froehlich (2008).

5.0 MODEL RESULTS The models for the Freshwater Pond and Recycle Pond were then executed based on the parameter values presented in Section 4.2. Table 6 presents the modelled flood levels (mRL) and channel velocities at Fairdown Road Bridge and Stillwater Westport Railway Bridge.

It is noted that the reported modelled flood level and modelled average channel velocity were obtained from

Table 6: Modelled Flood Levels and Channel Velocities

Channel Velocity

(m/s) Flood Level

(mRL)

Minimum Channel Elevation

(mRL)

Bridge Soffit (mRL)

Surface Level of

Road/Track (mRL)

Freshwater Pond (CON_FHW_26.hec) Fairdown Road Bridge Upstream ~100 m (RS99)1 4.2 12.77 9.34 N/A N/A Upstream of Structure 1.9 11.74* 7.80 9.50 10.00 Downstream of Structure 4.4 10.54* 7.80 9.50 10.00 Downstream ~200 m (RS96)1 2.1 7.78 5.70 N/A N/A Stillwater Westport Railway Bridge Upstream ~80 m (RS93)1 0.5 2.85 -0.20 N/A N/A Upstream of Structure 0.5 2.81 -0.20 5.50 6.00 Downstream of Structure 0.5 2.78 -0.25 5.50 6.00 Downstream ~400 m (RS91)1 0.9 2.42 -0.40 N/A N/A Recycle Pond (CON_RCY_13.hec) Fairdown Road Bridge Upstream ~100 m (RS99)1 2.5 11.43 9.34 N/A N/A Upstream of Structure 1.4 9.58* 7.80 9.50 10.00 Downstream of Structure 1.7 9.34 7.80 9.50 10.00 Downstream ~200 m (RS96)1 1.4 6.97 5.70 N/A N/A Stillwater Westport Railway Bridge Upstream ~80 m (RS93)1 0.7 2.26 -0.20 N/A N/A


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Channel Velocity

(m/s) Flood Level

(mRL)


(mRL)

Bridge Soffit (mRL)

Surface Level of

Road/Track (mRL)

Upstream of Structure 0.4 2.24 -0.20 5.50 6.00 Downstream of Structure 0.4 2.22 -0.25 5.50 6.00 Downstream ~400 m (RS91)1 0.7 1.84 -0.40 N/A N/A * Road overtopped; 1 RS = River Station. See Figure 3 and Figure 4 for location of RS.

HEC-RAS for the maximum water surface profile. The relevant HEC-RAS simulation filenames are noted in Table 6 for documentation purposes only.

From Table 6, the modelled flood levels from the Freshwater Pond simulation indicates Fairdown Road is overtopped to a depth of up to 1.74 m. Model results indicate that the flood level at the Stillwater Westport Railway Bridge is well below the bridges assumed soffit level, therefore the railway bridge is not overtopped during modelled dam break.

For the Recycle Pond simulation, Fairdown Road is also overtopped, with modelled depth of up to 0.08 m. Model results indicate that flood level at the Stillwater Westport Railway Bridge is well below the bridges assumed soffit level.

Figure 5 presents the modelled maximum water surface extent for the Freshwater Pond simulation. Figure 5 presents the modelled maximum water surface extent for the Recycle Pond simulation.

6.0 SENSITIVITY ANALYSIS The sensitivity of the model results to the uncertainty in the time for the breach to form was evaluated by considering longer breach formation times and increased breach dimensions.

6.1 Longer Breach Formation Time The breach formation time for the Freshwater Pond model was changed from 10 minutes to 20 minutes and the breach formation time for the Recycle Pond model was set at 30 minutes instead of 15 minutes. Other parameter values remained the same.

Each HEC-RAS model was then executed and the results extracted. Table 7 presents the modelled flood levels and channel velocities at the same reporting locations as Table 6.

Table 7: Sensitivity Analysis Longer Breach Formation Time

Channel Velocity

(m/s) Flood Level

(mRL)


(mRL)

Bridge Soffit (mRL)

Surface Level

Road/Track (mRL)

Freshwater Dam (CON_FHW_27.hec) Fairdown Road Bridge Upstream ~100 m (RS99) 4.1 12.70 9.34 N/A N/A Upstream of Structure 1.9 11.73 7.80 9.50 10.00 Downstream of Structure 4.4 10.52 7.80 9.50 10.00 Downstream ~200 m (RS96) 2.1 7.80 5.70 N/A N/A Stillwater Westport Railway Bridge Upstream ~80 m (RS93) 0.5 2.88 -0.2 N/A N/A Upstream of Structure 0.5 2.85 -0.2 5.50 6.00 Downstream of Structure 0.5 2.82 -0.25 5.50 6.00 Downstream ~400 m (RS91) 0.9 2.46 -0.4 N/A N/A Recycle Dam (CON_RCY_14.hec)


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Channel Velocity

(m/s) Flood Level

(mRL)


(mRL)

Bridge Soffit (mRL)

Surface Level

Road/Track (mRL)

Fairdown Road Bridge Upstream ~100 m (RS99) 2.5 11.38 9.34 N/A N/A Upstream of Structure 1.4 9.51 7.80 9.50 10.00 Downstream of Structure 1.7 9.30 7.80 9.50 10.00 Downstream ~200 m (RS96) 1.4 6.96 5.70 N/A N/A Stillwater Westport Railway Bridge Upstream ~80 m (RS93) 0.7 2.26 -0.2 N/A N/A Upstream of Structure 0.4 2.25 -0.2 5.50 6.00 Downstream of Structure 0.4 2.23 -0.25 5.50 6.00 Downstream ~400 m (RS91) 0.7 1.84 -0.4 N/A N/A * Road overtopped; 1 RS = River Station. See Figure 3 and Figure 4 for location of RS.

From Table 7, the modelled flood levels and average channel velocities are essentially the same as those presented in Table 6.

6.2 Increased Breach Width The average breach width for the Freshwater Pond model was increased from 20 m to 40 m and the average breach width for the Recycle Pond was increased to 30 m from 15 m. Other parameter values remained the same.

Each HEC-RAS model was then executed and the results extracted. Table 8 presents the modelled flood levels and channel velocities at the same reporting locations as Table 6.

Table 8: Sensitivity Analysis Increased Breach Width

Channel Velocity

(m/s) Flood Level

(mRL)


(mRL)

Bridge Soffit (mRL)

Surface Level

Road/Track (mRL)

Freshwater Dam (CON_FHW_32.hec) Fairdown Road Bridge Upstream ~100 m (RS99) 4.3 12.79 9.34 N/A N/A Upstream of Structure 1.9 11.75 7.80 9.50 10.00 Downstream of Structure 4.4 10.55 7.80 9.50 10.00 Downstream ~200 m (RS96) 2.1 7.77 5.70 N/A N/A Stillwater Westport Railway Bridge Upstream ~80 m (RS93) 0.5 2.84 -0.20 N/A N/A Upstream of Structure 0.5 2.80 -0.20 5.50 6.00 Downstream of Structure 0.5 2.77 -0.25 5.50 6.00 Downstream ~400 m (RS91) 0.9 2.41 -0.40 N/A N/A Recycle Dam (CON_RCY_18.hec) Fairdown Road Bridge Upstream ~100 m (RS99) 2.5 11.43 9.34 N/A N/A Upstream of Structure 1.4 9.58 7.80 9.50 10.00 Downstream of Structure 1.7 9.34 7.80 9.50 10.00 Downstream ~200 m (RS96) 1.4 6.97 5.70 N/A N/A Stillwater Westport Railway Bridge


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Channel Velocity

(m/s) Flood Level

(mRL)


(mRL)

Bridge Soffit (mRL)

Surface Level

Road/Track (mRL)

Upstream ~80 m (RS93) 0.7 2.25 -0.20 N/A N/A Upstream of Structure 0.4 2.23 -0.20 5.50 6.00 Downstream of Structure 0.4 2.21 -0.25 5.50 6.00 Downstream ~400 m (RS91) 0.7 1.82 -0.40 N/A N/A * Road overtopped; 1 RS = River Station. See Figure 3 and Figure 4 for location of RS.

From Table 8, the modelled flood levels and average channel velocities are essentially the same as those presented in Table 6.

7.0 DISCUSSION AND C

[paper] design philosophy statement – freshwater and recycle dams – escarpment mine project.pdf

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