Spillways Project - Wagerup · The recommendation for a spillway is supported. The general premise that installation of spillways at each operation reduces the risk of embankment

Spillways Project - Wagerup Hydrological and Ecological Review Alcoa of Australia

TE18077 Alcoa spillway Wagerup.1d March 2019 | Page 1

Assets | Engineering | Environment | Noise | Spatial | Waste

Spillways Project - Wagerup

Hydrological and Ecological Review

Prepared for Alcoa of Australia

March 2019

Project Number: TE18077


TE18077 Alcoa spillway Wagerup.1d March 2019 | Page i

DOCUMENT CONTROL

Version Description Date Authors Reviewer

0a Internal Review GBa/SW/GBo JM

1a Draft report for client 18/12/2018 GB AM

1b Final report 4/1/2019 GB GB

1c Minor edits 4/1/2019 GB DD

1d Minor edit 20/3/2019 GB

Approval for Release

Name Position File Reference

Dr Greg Barrett Senior Environmental Consultant TE18077 Alcoa spillway Wagerup.1d

Signature

Copyright of this document or any part of this document remains with Talis Consultants Pty Ltd and cannot be used,

transferred or reproduced in any manner or form without prior written consent from Talis Consultants Pty Ltd.


TE18077 Alcoa spillway Wagerup.1d March 2019 | Page ii

Executive Summary Alcoa’s Australian operations represent one of the world’s largest integrated bauxite mining, alumina

refining and aluminium smelting systems.

In Western Australia, Alcoa operates two bauxite mines (Huntly and Willowdale) and three refineries

(Kwinana, Pinjarra and Wagerup). As part of the refining process, each refinery has residue storage

facilities (RSAs) and water storage dams for fresh water and process contaminated water.

Alcoa has recently reviewed the management of its RSAs against regulatory guidelines, Australian

technical standards (ANCOLD) and international standards (ICOLD) for the design and management of

RSAs and dams. This review process has identified that best practice management of these dam

facilities should include the installation of a spillway so that, should overtopping occur under

exceptional circumstances, it occurs in a controlled manner and significantly reduces the risk of a

major loss of containment event through dam wall failure.

Alcoa has now completed the preliminary design engineering works on the spillways and are finalising

the detailed design. As part of the preliminary design engineering works on the spillways, Alcoa also

completed a hydrological assessment of the likelihood of a discharge occurring from each spillway at

Kwinana and Pinjarra and the likely downstream inundation zones that may result. An assessment to

determine the spillway location and dimensions at Wagerup has been conducted.

The objective of this assessment was to evaluate the potential hydrological and ecological impacts

associated with the fitting of a spillway at Wagerup.

The spillway assessment identified the optimal locations for the spillway and the likely rainfall events

and scenarios under which it would operate. Engagement of the spillway would only occur under

extreme rainfall conditions.

The approach to identifying the spillway location at Wagerup appears sound and is consistent with

ANCOLD guidelines. Should the spillway be engaged, the discharge would be directed to a perimeter

drain and then to surrounding farmland (held by Alcoa). The farmland contains some remnant

vegetation that is likely to support some conservation significant fauna from time to time.

The assessment does not consider runoff from outside of the catchment of the RSAs. Under the rainfall

conditions considered in developing the spillway design, very significant runoff could be expected

from the broader catchment area. We conclude that the installation of a spillway at Wagerup is

unlikely to lead to environmental impacts in its own right, and may reduce risk to the environment by

reducing the potential for an embankment wall failure.


TE18077 Alcoa spillway Wagerup.1d March 2019 | Page iii

Table of Contents 1 Introduction ......................................................................................................................... 1

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

1.2 About this assessment ............................................................................................................ 1

2 General approach ................................................................................................................. 3

3 Review of spillway design report ........................................................................................... 4

4 Ecological characteristics of potential discharge areas ........................................................... 6

4.1 Wagerup.................................................................................................................................. 6

4.2 Threatened Ecological Communities ...................................................................................... 6

4.3 Rare and Priority flora ............................................................................................................. 6

4.4 Rare and Priority Fauna .......................................................................................................... 7

4.5 Other environmental features of significance ........................................................................ 7

4.6 Heritage values ....................................................................................................................... 7

5 Conclusions .......................................................................................................................... 9

6 References ......................................................................................................................... 10

Tables Table 5-1: Summary of spillway location and sizing study

Table 5-2: Key environmental features of discharge area


TE18077 Alcoa spillway Wagerup.1d March 2019 | Page iv

Figures Figure 1-1: Wagerup Residue Storage Area – layout and surrounds

Figure 3-1: Wagerup ROWS pond – proposed spillway location

Figure 4-1: Wagerup – environmental values of the area west of the ROWS



1 Introduction

1.1 Background

Alcoa’s Australian operations represent one of the world’s largest integrated bauxite mining, alumina

refining and aluminium smelting systems.

In Western Australia, Alcoa operates two bauxite mines (Huntly and Willowdale) and three refineries

(Kwinana, Pinjarra and Wagerup). As part of the refining process, each refinery has residue storage

facilities (RSAs) and water storage dams for fresh water and process contaminated water. The

refineries are licensed under Part V of the Western Australian Environmental Protection Act 1986 as

follows:

L5245/1967/14 (Kwinana);

L5271/1983/14 (Pinjarra); and

L6217/1983/15 (Wagerup).

Alcoa has recently reviewed its management of its RSAs against regulatory guidelines, Australian

technical standards (ANCOLD) and international standards (ICOLD) for the design and management of

RSAs and dams. The Australian National Committee on Large Dams (ANCOLD) issues various

guidelines which are applicable for water or tailings dams with the potential to cause loss of life or

significant environmental or physical damage through operation or failure. Although prepared for

dams which would normally be at least 10 to 15 m high, ANCOLD guidelines can also be used to assist

with decisions on smaller dams, particularly where a dam or series or dams creates the potential for

loss of life or significant damage. These guidelines include risk assessment and dam design modules.

This review process has identified that best practice management of these dam facilities should

include the installation of a spillway so that, should overtopping occur under exceptional

circumstances, it occurs in a controlled manner and significantly reduces the risk of a major loss of

containment event through embankment wall failure.

Alcoa has now completed the preliminary design engineering works on the spillways and are finalising

the detailed design. As part of the preliminary design engineering works on the spillways, Alcoa also

completed a hydrological assessment of the likelihood of a discharge occurring from each spillway at

Kwinana and Pinjarra and the likely downstream inundation zones that may result. An assessment to

determine the spillway location and dimensions at Wagerup has also been conducted.

1.2 About this assessment

The objective of this assessment was to evaluate the potential hydrological and ecological impacts

associated with the fitting of a spillway at the RSA at Wagerup (Figure 1-1). The assessment will

support a submission to the WA Department of Water and Environmental Regulation (DWER) in

relation to the licensing requirements under Part V of the EP Act.

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Harvey RiverMain Drain

Samson SouthDiversion Drain

Yalup BrookDrain

South

Wes

tern H

wy

Willowdale Rd

Bristol Rd

Some

rs Rd

ROWS

ResidueStorage

Area

BullerNature

Reserve

390,000

390,000

392,000

392,000

394,000

394,000

396,000

396,000

398,000

398,000

6,356

,000

6,356

,000

6,358

,000

6,358

,000

6,360

,000

6,360

,000

6,362

,000

6,362

,000

LEGEND

© Talis Consultants Pty Ltd ("Talis") Copyright in the drawings, information and datarecorded in this document ("the information") is the property of Talis. This document andthe information are solely for the use of the authorised recipient andthis document may not be used, transferred or reproduced in whole or partfor any purpose other than that which it is supplied by Talis withoutwritten consent. Talis makes no representation, undertakes no duty andaccepts no responsibility to any third party who may use or rely upon thisdocument or the information.

Perth

Pinjarra

Wagerup

Kwinana

0 40 80 120 16020km

LOCALITY

LOCALITYWAGERUP RESIDUE

STORAGE DAMSSpillways Project

Alcoa Australia

0 300 600 900 1,200Metres

¤ Coordinate System: GDA 1994 MGA Zone 50Projection: Transverse Mercator, Datum: GDA 1994

A MackG BarrettReviewed:

Checked:Prepared: F Walker Date: 3/01/2019

Revision:

Scale @ A3:1:30,528

Project No: TE18077A

Data source: Roads - Main Roads WA, 2018. Imagery - Landgate, 2018

Figure

1-1

Major RiverDrainNature ReserveRemnant NativeVegetation

P: PO Box 454, Leederville WA 6903 | A: Level 1 660 Newcastle St, Leederville WA 6007 | T: 1300 251 070 | W: www.talisconsultants.com.au



2 General approach

The steps involved in undertaking this assessment were as follows:

A desktop review of spillway design work undertaken by Alcoa and its consultants for the

Wagerup operation, including requests for further information;

A brief site visit to view the expected spillway location and adjoining area;

A desktop assessment of the ecological values of the expected areas that would be inundated

should a discharge from the spillway occur; and

Synthesis of this information and formulation of some broad conclusions as to the risks posed.



3 Review of spillway design report

The following spillway design report was available:

Wagerup Alumina Refinery ROWS Pond Spillway (Advisian 2018).

This report was primarily aimed at determining the location and size of the proposed spillway. Unlike

spillway investigations undertaken for Kwinana and Pinjarra, a potential area of inundation was not

determined.

Storm events considered were 1 in 100 AEP (72 hours) through to Probable Maximum Precipitation

(PMP) (120 hours).

Three scenarios were considered:

Rainfall directly on the Runoff Water Storage (ROWS) pond only (Scenario 1);

Rainfall directly on the Runoff Water Storage (ROWS) pond plus runoff from the refinery

catchment (Scenario 2); and

Rainfall directly on the Runoff Water Storage (ROWS) pond plus runoff from the refinery

catchment plus water pumped from the ROCP2 and RSAs (Scenario 3).

The outcome of the report was a recommended spillway location and size for the ROWS pond. A

separate document (Alcoa 2016) notes that all ponds are designed to contain a 1 in 100 year AEP 72

hour event. A spillway would only be engaged toward the end of an extremely wet winter (a wet

season with a rainfall in excess of a 1 in 100 Annual Exceedance Probability).

The preferred spillway location is the south-western corner of the ROWS pond where the discharge

would be directed to a perimeter drain and then to surrounding farmland (held by Alcoa) (see Figure

3-1). Surface water across the general area west of the RSA is controlled by a network of drains (Figure

1-1), the nearest of which is the Yalup Brook Drain which connects with the Harvey River Main Drain

and ultimately to the Harvey River.

The recommendation for a spillway is supported. The general premise that installation of spillways at

each operation reduces the risk of embankment wall failure and consequently more serious

environmental outcomes compared with discharge from a spillway is sound.

One aspect that has not been addressed is the effect that an extreme rainfall event in the surrounding

catchment would have on any discharge occurring from Alcoa’s operations. It is likely that such an

event would result in significant adverse environmental impacts (flooding, erosion) in its own right

without any consideration of discharge from the RSAs.

The quality of any discharge over a spillway at Wagerup has not been considered. Assuming discharge

from the spillway at Wagerup would occur in conjunction with a very significant rainfall event, dilution

is likely to render water quality impacts such that they would be inconsequential relative to the event

itself.

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ROWS

ResidueStorage Area

394,000

394,000

396,000

396,000

6,356

,000

6,356

,000

6,358

,000

6,358

,000

LEGEND

© Talis Consultants Pty Ltd ("Talis") Copyright in the drawings, information and datarecorded in this document ("the information") is the property of Talis. This document andthe information are solely for the use of the authorised rec ipient andthis document may not be used, t ransferred or reproduced in whole or partfor any purpose other than that which it is supplied by Talis withoutwritten consent. Talis makes no representat ion, undertakes no duty andaccepts no respons ibility to any third party who may use or rely upon thisdocument or the information.

Perth

Pinjarra

Wagerup

Kwinana

0 40 80 120 16020km

LOCALITY

INUNDATION AREAWAGERUP RESIDUE

STORAGE DAMSSpillways Project

Alcoa Australia

0 150 300 450 600Metres




Revision:

Scale @ A3:1:15,000



Figure

3-1

Spillway


View from proposed spillway location looking west



4 Ecological characteristics of potential discharge areas

The information in this section was compiled by searching the following databases:

Threatened and Priority Flora Database (TPFL) and WA Herbarium database (WAHerb)

(through DBCA);

Threatened Fauna Databases (DBCA);

Threatened Ecological Communities database (DBCA);

The Commonwealth Government’s Directory of Important Wetlands; and

Other relevant documentation.

Also considered were heritage values assessed by interrogating:

The Heritage Council’s Inherit database; and

The Aboriginal Heritage Inquiry System (AHIS) (Department of Planning, Lands and Heritage).

4.1 Wagerup

4.2 Threatened Ecological Communities

The following Priority Ecological Community (PEC) occurs in remnant vegetation within farmland west

of the RSA:

Banksia-dominated Woodlands of the Swan Coastal Plain IBRA Region (P3).

This PEC extends from Jurien Bay in the north to Dunsborough in the south and has been impacted by

land clearing and fragmentation. It commonly occurs north-west of the Wagerup RSA. It is listed as

Endangered under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).

Other TECs occur in the area around the Wagerup operations but were not recorded on the database

in the area west of the RSA. Furthermore, the majority of trees occurring near the RSA have been

planted as wind breaks and generally occur along fence lines and roads (Alcoa 2012). These vegetated

areas will not have the conservation value of remnant vegetation.

Given the likelihood of any discharge, should it occur, would be restricted to farmland near the RSA

(bounded by the Samson South Diversion Drain to the north and the Yalup Brook Drain to the south),

the risk to vegetation communities of conservation significance appears low.

4.3 Rare and Priority flora

The database search did not identify any flora of conservation significance occurring in the area west

(between the Samson South Diversion Drain to the north and the Yalup Brook Drain to the south). The

search did record some species of conservation significance occurring in remnant vegetation east of

the refinery and in the Buller Nature Reserve north west of the RSA (Figure 4-1). Neither of these areas

would be affected by any discharge from the RSA.



4.4 Rare and Priority Fauna

The database search identified one fauna species of conservation significance occurring in the area

west of the RSA (between the Samson South Diversion Drain to the north and the Yalup Brook Drain

to the south) (Figure 4-1). There was a single record of the South-western Brush-tailed Phascogale, or

Wambenger (Phascogale tapoatafa subsp. wambenger) recorded in remnant vegetation near Somers

Road. This species is Specially Protected under the Biodiversity Conservation Act 2016 (BC Act).

While not recorded in the immediate area, other species that could utilise remnant vegetation include:

Forest Red-tailed Black Cockatoo (Calyptorhynchus banksii subsp. naso) (Vulnerable under BC

Act and EPBC Act);

Baudin's Cockatoo (Calyptorhynchus baudinii), (Endangered under the BC Act and EPBC Act);

and

Carnaby's Cockatoo (Calyptorhynchus latirostris), (Endangered under the BC Act and EPBC

Act).

It appears very unlikely any discharge from the spillway under extreme rainfall conditions would result

in direct impacts on any of these species.

4.5 Other environmental features of significance

The Buller Nature Reserve occurs to the north of the potential discharge area (Figure 1-1) but would

not be affected. There are no other known environmental features of significance.

4.6 Heritage values

The site lies within Native Title held land under the Gnaala Karla Booja People Indigenous Land-Use

Agreement (ILUA), issued on the 8 June 2015.

The AHIS records one Registered Aboriginal Site (ID 3232) - Wagerup 1 (artefacts/scatter) - as located

south of the RSA, on the southern side of the Yalup Brook diversion drain (see Figure 1-1). Alcoa have

advised that these materials were recovered from the site under an approval from the Registrar of

Aboriginal Sites in 1978. No other Aboriginal sites are known in the area immediate west of the

Wagerup RSA.

There are no known sites of importance to European heritage in the area.

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South W

estern

Hwy

ROWS

ResidueStorage

Area

390,000

390,000

392,000

392,000

394,000

394,000

396,000

396,000

6,356

,000

6,356

,000

6,358

,000

6,358

,000

6,360

,000

6,360

,000

6,362

,000

6,362

,000

LEGEND

Perth

Pinjarra

Wagerup

Kwinana

0 40 80 120 16020km

LOCALITY

0 310 620 930 1,240Metres




Revision:

Scale @ A3:1:30,000



Figure

4-1

SpillwayFauna

Calyptorhynchus banksiinasoCalyptorhynchus baudiniiCalyptorhynchus latirostrisGeotria australisHydromys chrysogasterIsoodon fusciventerNotamacropus irmaPhascogale tapoatafawambenger

FloraBoronia capitata subsp.gracilisCaladenia huegeliiConostylis pauciflorasubsp. paucifloraDrakaea elasticaSynaphea odocoileopsSynaphea stenolobaSynaphea sp. Serpentine(G.R. Brand 103)


ENVIRONMENTALFEATURES

WAGERUP RESIDUESTORAGE AREASpillways Project

Alcoa Australia



5 Conclusions

Engagement of the spillway would only occur under extreme rainfall conditions (Table 5-1).

Table 5-1: Summary of spillway location and sizing study

Site Optimal spillway

location

Event required to engage

spillway Likely discharge area

Wagerup

Run Off Water

Storage (ROWS)

(south western

corner)

An extremely wet winter (a wet

season with a rainfall in excess of

a 1 in 100 Annual Exceedance

Probability).

Initial discharge to

perimeter drain, then to

surrounding farmland (held

by Alcoa).

Should the spillway be engaged and the discharge extends to the farmland, Table 5-2 outlines the key

environmental features of the area receiving the discharge.

Table 5-2: Key environmental features of discharge area

Location Likely discharge area Environmental features

Wagerup

Farmland west of the RSA,

including amenity tree plantings

and some remnant vegetation.

Some remnant vegetation, with potential for

discharge to enter drainage system - the Yalup

Brook Drain which connects with the Harvey

River Main Drain and ultimately to the Harvey

River.

Runoff from outside of the catchment of the RSA has not been considered. Under the rainfall

conditions considered in developing the spillway design, very significant runoff could be expected

from the broader catchment area. We conclude that the proposed installation of the spillway at

Wagerup is unlikely to lead to environmental impacts in its own right, and may reduce risk to the

environment by reducing the potential for an embankment failure.



6 References

Advisian (2018). Wagerup Alumina Refinery ROWS Pond Spillway. Hydrology and Spillway Sizing.

Report for Alcoa of Australia Ltd, 7 September 2018.

Alcoa (2012). Long Term Residue Management Strategy – Wagerup 2012 (PDF). Retrieved from

https://www.alcoa.com/australia/en/pdf/2012_wagerup_refinery_ltrms.pdf

Documents

Spillways Project - Wagerup · The recommendation for a spillway is supported. The general premise that installation of spillways at each operation reduces the risk of embankment