before the board of inquiry in the matter of the … · a concrete face rockfill dam (“cfrd”)...

Sainsbury Logan & Williams Ref: Lara J Blomfield Solicitors Fax: 06-835 6746 Cnr Tennyson Street and Cathedral Lane Phone: 06-835 3069 PO Box 41 Napier

BEFORE THE BOARD OF INQUIRY

IN THE MATTER of the Resource Management Act 1991

AND

IN THE MATTER

of the Tukituki Catchment Proposal

STATEMENT OF EVIDENCE OF

Phillip Richard CARTER

TABLE OF CONTENTS

1. INTRODUCTION ................................................................................................... 1 2. SUMMARY AND CONCLUSIONS ......................................................................... 2 3. OVERVIEW OF REPORT ..................................................................................... 4 4. COMMENTS ON SUBMISSIONS .........................................................................23 5. REFERENCES .....................................................................................................26

1. INTRODUCTION

1.1 My name is Phillip Richard Carter

1.2 My formal engineering qualifications consist of a Bachelor of Engineering, 1967,

University of NSW and a Master of Engineering Science, 1972, University of

NSW in water engineering. I have 47 years of continuous experience in dam

engineering and hydraulic structures such as large gated weirs, irrigation

structures and river management works. This has included direct site

investigation and design experience with most types of major dams including

earthfill, earthcore rockfill, concrete face rockfill and mass concrete including

prestressed dams. I have directed multi-disciplinary project teams for a number

of major dam engineering projects.

1.3 Until August 2004, I was Principal Engineer & Manager Water Technologies for

the NSW Department of Public Works. This required overall management and

direction of a team of 100 professional and technical staff providing a

commercial engineering consultancy service covering water supply and

irrigation infrastructure, urban drainage and flood protection, river management,

roads, bridges and tunnels.

1.4 Since August 2004, I have worked as a consulting engineer on dam and

irrigation projects working for various clients including several major consulting

firms such as Tonkin & Taylor.

1.5 Purpose and scope of evidence

1.6 I assisted with preparation of the report entitled “Ruataniwha Water Storage

Scheme Project Description” (“PD”) in relation to the proposed Ruataniwha

Water Storage Scheme (“RWSS”) comprising part of the Tukituki Catchment

Proposal (“TCP”) being considered by the Board of Inquiry. In particular, my

involvement was centred on the development of the concept, feasibility and in

turn Application Design (as described in the PD) for the dam component of the

RWSS.

1.7 The purpose of my evidence is to provide an overview of the PD in relation to

the dam, and to address issues raised by submitters to the RWSS component

of the TCP in relation to the dam. Given the relationship between issues raised

in submissions and the considerations applied in the development of the

Application Design, I have integrated much of the response I consider needs to

be made to submissions within the overview of the PD in relation to the dam set

out below.

1.8 I note for assistance of the Board that the discussion in this evidence of the

principal design considerations for the dam and its auxiliary structures and

components, along with the construction sequence, essentially covers the

information in Section 4 of the PD, commencing at page 44 though to page 57.

Where relevant, e.g. to respond to issues raised by submissions, I go into more

detail than the PD on a given topic, with reference to background assessments

and reports that informed that document. On other topics, the converse applies,

and the PD is more detailed in its account.

Expert Code of Conduct

1.9 I have read the Code of Conduct for Expert Witnesses in section 5 of the

Environment Court’s Practice Note (2011). I agree to comply with that Code of

Conduct. Except where I state that I am relying upon the specified evidence of

another person, my evidence in this statement is within my area of expertise. I

have not omitted to consider material facts known to me that might alter or

detract from the opinions which I express.

2. SUMMARY AND CONCLUSIONS

2.1 The proposed total water storage requirement of 90 million m3 at the site results

in a dam of approximately 83 m height at the river’s deepest point. A Concrete

Face Rockfill Dam (“CFRD”) has been selected for the Application Design. The

crest is 505 m long and 8 m wide.

2.2 Two spillways are provided to pass flood flows. A concrete lined chute spillway

controlled by a 25 m wide arc-crested concrete ogee crest is located on the

right abutment. This spillway terminates in a hydraulic jump dissipator located

within the rockfill quarry for the embankment. An outlet channel excavated into

the quarry floor takes flows back to the river. This channel is located well away

from any rockfall that may result from earthquake induced damage to the area

of dilated, potentially unstable rock on the left bank wall of the gorge.

2.3 A secondary (auxiliary) spillway consisting of a simple 50 m wide unlined

excavated channel is located on the left abutment. This spillway has a crest

level that is 3.25 m above the primary spillway and does not operate for normal

flood inflows. Discharges commence for floods that exceed the 1 in 200 AEP

inflow with a full storage.

2.4 The general design criteria for the works are based on the New Zealand Society

of Large Dams (NZSOLD) Dam Safety Guidelines and also consideration of the

Building (Dam Safety) Regulations (2008). Where the NZSOLD Dam Safety

Guidelines do not cover specific design details, the design is based on

international guidelines and practice documents.

2.5 The Ruataniwha Dam will have a high potential impact classification (PIC) and

therefore the design ground motion is required to be taken equal to the 84th

percentile level of the ground shaking associated with rupture of the Mohaka

fault. This standard is also applied to other high risk projects like nuclear power

plants.

2.6 The effect of earthquakes on concrete faced rockfill dams is to deform the

embankment with flattening of the slopes due to ravelling and sliding of shallow

materials. This produces a permanent slumping and spreading of the dam

rather than a failure along a distinct surface, i.e. a large crack or rupture.

2.7 My assessments along with preliminary theoretically based analyses of the

expected effects of earthquake ground motion on the dam undertaken by

Tonkin & Taylor indicate only moderate deformations under the Maximum

Credible Earthquake expected for the Ruataniwha Dam.

2.8 Given the close proximity of the Mohaka Fault to the dam site, there is a

possibility of secondary or sympathetic movement on pre-existing shears or

secondary faults within the footprint of the embankment itself. GNS have

investigated this weakness and have confirmed that there is no evidence of

movement along this weakness in the last 10,000 years.

2.9 Notwithstanding this, GNS consider that the possibility of secondary movement

of 0.1 m to 0.5 m here or elsewhere in the foundation remains. Defensive

measures have been applied as a precautionary measure despite there being

no evidence of movement at this feature.

2.10 Seiche effects from potential rupture of the Mohaka Fault where it crosses the

reservoir would be expected. GNS have advised that a single event vertical

displacement of 0.4 m to 1.0 m should be considered as possible. This has

been allowed for by providing adequate freeboard that includes a factor of

safety of 2 for the GNS upper limit of 1.0 m

2.11 Freeboard requirements have been determined to cater for three separate

scenarios, an extreme flood event, an extreme earthquake event and a post-

earthquake condition with a 1 in 20 AEP flood.

2.12 A river diversion strategy is outlined to ensure a diversion capacity of at least 1

in 1000 AEP at any stage where public safety and major damage are at risk.

Hold points for reservoir filling are not considered necessary from a dam

stability point of view and rapid filling of the storage is not considered a dam

safety issue.

2.13 In response to the matters raised by the submitters, I remain of the opinion that

the Application Design for the dam is appropriate, and that all reasonable

alternatives have been considered.

3. OVERVIEW OF DESIGN RATIONALE

3.1 Overview of Dam Design

(a) The proposed total water storage requirement of 90 million m3 at the

site results in a dam of approximately 83 m height at the river’s deepest

point. A Concrete Face Rockfill Dam (“CFRD”) has been selected for

the Application Design. The crest is 505 m long and 8 m wide. The top

of the parapet wall is RL 475.5 m (minimum) and extends 1.2 m above

the top of the embankment.

(b) A concrete lined primary spillway on the right abutment of the dam

passes flood inflows through a concrete lined chute to a concrete lined

stilling basin. The spillway capacity is supplemented by an unlined

auxiliary spillway located on the left abutment of the dam.

(c) A concrete intake structure located within the reservoir allows for

irrigation and flushing flows to be drawn from two levels within the

reservoir through the high level intake tower into a penstock located in a

tunnel beneath the dam. The upper tower ports can take water from the

top 4 m of storage while the lower ports would access the top 22 m of the

storage or the upper 68% of the storage volume. In addition, the lower

portion of the storage can be discharged through the outlet works by

opening a gate in the low level outlet structure. The outlet works and

hydro power station are located at the downstream end of the tunnel and

discharge into a tailrace canal that joins the spillway outlet channel.

(d) The general design criteria for the works are based on the New Zealand

Society of Large Dams (NZSOLD) Dam Safety Guidelines and also

consideration of the Building (Dam Safety) Regulations (2008). These

provide guidance on general dam design and construction practice

including the assessment of flood and seismic hazards and the provision

of appropriate spillway and diversion works and adequate defence

against earthquake events. They also provide guidance on the

establishment of dam safety surveillance practices to be adopted for

initial filling of the reservoir and subsequent operation, and for the

provision of emergency action plans.

(e) Where the NZSOLD Dam Safety Guidelines do not cover specific

design details, the design is based on international guidelines and

practice documents. The International Commission on Large Dams

(ICOLD) publications provide a wide range of guidelines that reflect

current international practice. Specific to the CFRD detailed in the

Application Design ICOLD Bulletin 141 (2010) is a primary reference for

dam design and construction. Other sources include appropriate

guidelines and standards from the US Federal Energy Regulatory

Commission (FERC), the US Bureau of Reclamation (USBR), the US

Army Corps of Engineers (USACE) and the Australian National

Committee on Large Dams (ANCOLD).

(f) These organisations are recognised both internationally and in New

Zealand as producing authoritative standards and guidelines that

represent current best practice.

3.2 Dam Design in General

(a) The primary consideration for the embankment was the ability to handle

high earthquake loadings and possible secondary movement on rock

mass weaknesses within the embankment footprint. The CFRD

embankment was adopted on the basis that it provided the best solution

for the site’s geotechnical issues with the materials available.

3.3 Seismic Design Loadings

(a) The dam site is located around 750 m from the primary active Mohaka

Fault which has an average recurrence of fault movement of around

1300 years and this together with other active faults in the vicinity, pose

a credible shaking hazard to the dam site. GNS has recommended a

maximum credible earthquake (MCE) of magnitude Mw 7.5, equivalent

to 7.1 on the Richter scale. This would produce an estimated 84th

percentile peak ground acceleration at the dam site of 0.77 g.

(b) The MCE is defined as the largest earthquake that can reasonably be

expected to be generated by a specific source on the basis of the

available seismological and geological evidence. It represents the

earthquake hazard level used for design and evaluation of critical

features of high hazard projects.

(c) Modern dam design guidelines, including the New Zealand Society on

Large Dams (NZSOLD), adopt a two level design approach. A dam must

be able to withstand the effects of earthquake shaking that could

reasonably be expected to occur in the life of the dam with none or

minimal, easily repairable damage. This level is known as the

Operational Basis Earthquake (OBE) and is taken equal to earthquake

shaking with an average return period of 150 years. The dam must also

be able to withstand, without uncontrolled release of the reservoir,

earthquake shaking associated with the earthquake source capable of

generating the highest level of ground shaking at the site (in this case

the Mohaka Fault). This is known as the Maximum Design Earthquake

(MDE). This design standard is assessed applying inputs from the MCE

scenario advised by GNS. The Ruataniwha Dam will have a high

potential impact classification (PIC) and therefore the design ground

motion is required to be taken equal to the 84th percentile level of the

ground shaking associated with rupture of the Mohaka fault. This

standard is also applied to other high risk projects like nuclear power

plants.

3.4 Concrete Face Rockfill Dam

(a) The Ruataniwha Dam is a rockfill dam constructed on a hard rock

foundation. Reviews of embankment dam performance during major

earthquakes show that there have been no complete failures of

embankment dams constructed on clay or rock foundations. Well

constructed earth dams can suffer very severe cracking but have

withstood extremely strong shaking from earthquakes of up to

magnitude 8.25 with peak ground accelerations ranging from 0.35 to

0.8 g.

(b) Dams which have suffered complete failure have been constructed with

saturated silt and/or sand materials or on saturated silt/sand

foundations, neither of which apply at Ruataniwha.

(c) The CFRD embankment was adopted on the basis that it provided the

best solution for the site’s geotechnical issues with the materials

available. J Barry Cooke (Cooke & Sherard, 1987), who was the driving

force behind the development of CFRD’s notes:

The CFRD embankment is considered to have the highest

fundamental conservatism against earthquakes

(d) This view that CFRD is inherently resistant to seismic loading is widely

supported by dam engineering specialists (Fell et al, 2005 and Materon

& Fernandez, 2011) and by organisations such as the International

Committee on Large Dams (ICOLD, 2010).

(e) The main factors supporting this view are that the CFRD embankment is

dry, preventing the development of significant water pressures within the

voids in the rockfill embankment (known as pore pressures) that would

adversely affect the embankment stability, it has a rock foundation that

does not magnify the incoming acceleration force, and the rockfill is

compacted in thin layers to a dense state with vibrating rollers.

(f) In addition, the construction has the very significant advantage that it is

stable even without the concrete face. The rockfill embankment can

handle ‘flow through’ conditions without instability issues. By that I mean

that the rate of water flow through the dam will be controlled by the

upstream zones, such that the dam will not suffer from internal erosion

as water flows through the embankment and the downstream rockfill

batter slopes will not fail. These embankments are designed to

accommodate large flood inflows that may fill the dam prior to

construction of the concrete face.

3.5 Effect of Earthquakes on Rockfill Dams

(a) The effect of earthquakes on concrete faced rockfill dams is to deform

the embankment with flattening of the slopes due to ravelling and sliding

of shallow materials. This produces a permanent slumping and

spreading of the dam rather than a failure along a distinct surface, i.e. a

large crack or rupture. Analyses are required to ensure that this

slumping of the dam is not excessive and that sufficient embankment

height above the normal water surface level (freeboard) is provided to

retain the storage.

(b) The magnitude of an earthquake and the peak ground acceleration

produced are often combined to give the Earthquake Severity Index

(ESI). The Mw 7.5 magnitude and the 0.77 g ground acceleration for

Ruataniwha give an ESI of 20.8. This index is used to estimate the likely

crest settlement of rockfill dams as outlined in ICOLD (2010). The higher

the ESI, the greater the crest settlement.

(c) As an example of rockfill dam stability under earthquake loading, ICOLD

(2010) provides data to demonstrate that a 200 m high CFRD subjected

to a MCE of 7.8 on a fault located 26 km from the dam site is stable.

This has an ESI of 21.6 and ICOLD predict a crest settlement of around

2 m.

(d) The capability of rockfill dams to safely handle extreme earthquakes

was demonstrated by the performance of the 156 m Zipingpu CFRD in

the May 2008 Sichuan earthquake (Xu Zeping, 2008). The Zipingpu

Dam is located 17 km from the epicentre of the magnitude 8.0

earthquake and was subjected to very severe shaking with a peak

ground acceleration of 0.5 g to 0.6 g and acceleration at the dam crest

of 2.0 g. The corresponding ESI ranges between 21 and 26. The dam

crest settled about 730 mm and the maximum lateral displacement was

reported to be close to 200 mm at the crest. The estimated crest

settlement using the ICOLD method is 2.0 m, much larger than the

actual settlement of 0.73 m.

(e) As would be expected, the dam suffered extensive spalling of concrete

at face slab joints but performance was considered adequate for an

extreme earthquake with no indication of a major failure.

(f) Ruataniwha has a similar ESI to these two examples but at 83 m is only

a fraction of the height. The estimated settlement using the ICOLD

method is 0.7 m, much less than predicted for the other two examples

and similar to that which occurred at Zipingpu.

(g) The above data indicates only moderate deformations under the MCE

are expected for the Ruataniwha Dam. A conservative freeboard is

provided to accommodate this settlement with a factor of safety of 2

applied to the assumed settlement of 0.8 m, giving a total of 1.6 m.

(h) It is noted that this movement would be expected to cause considerable

damage to the concrete face and result in substantial leakage. This

damage is not a dam safety issue and the embankment would remain

stable. The concrete face and toe slab is accessible for post-earthquake

repairs.

3.6 Detailed Analysis for Earthquake Loadings

(a) Preliminary theoretically based analyses of the expected effects of

earthquake ground motion on the dam have been undertaken by Tonkin

& Taylor. The analyses allow estimation of the permanent deformation

that may occur. Under the OBE minor deformations (<10 mm) are

estimated. These deformations would result in no damage or easily

repairable damage. Under the MDE estimates of permanent

deformations, using methodologies considered to be the most reliable,

are up to about 1 m. In making the latter comment, I am relying on

information sourced from Dr. Matuschka. These estimates are in line

with the estimates discussed above. Damage would be expected but

would not be expected to result in breach of the dam.

(b) The above data provides only a general assessment of the expected

earthquake effects on the dam. The PD notes that detailed dynamic

analysis of the dam will be required during detail design. This is an

expensive exercise that takes some time and is beyond the scope of the

feasibility studies that form the basis for the PD.

(c) This analysis will determine whether the design provisions proposed are

adequate or whether additional provisions such as reinforcement with

geogrids are required. As such, this is an appropriate level of analysis to

leave to detailed design.

3.7 Potential for Secondary Movement

(a) Given the close proximity of the Mohaka Fault to the dam site, there is a

possibility of secondary or sympathetic movement on pre-existing

shears or secondary faults within the footprint of the embankment itself.

The geotechnical investigations located a zone of rock mass weakness,

referred to as SZ1, on the left abutment of the dam running roughly

parallel to the river and described in Paragraph 4.2 of the PD. GNS have

investigated this weakness and have confirmed that there is no

evidence of movement along this weakness in the last 10,000 years.

(b) Notwithstanding this, GNS consider that the possibility of secondary

movement of 0.1 m to 0.5 m here or elsewhere in the foundation

remains. While construction across such a feature is an unusual

procedure with limited international precedent, there is general

agreement on the types of defensive measures that should be provided

to handle such a movement.

(c) These defensive measures have been provided at SZ1 as a

precautionary measure despite there being no evidence of movement at

this feature. The dam alignment has been carefully selected to ensure

the SZ1 zone passes through the dam abutment at terrace level rather

than on the steep face of the gorge. This allows a more economical

detail for toe slab construction across the SZ1 zone. Upstream of the toe

slab the zone is exposed on the left wall of the gorge and will be

covered by a zone of fine silty material (Zone 1A) held in place by

random fill (Zone 1B). This material will feed into any cracks that

develop in the zone during earthquake activity and provide a seal.

Downstream of the toe slab the zone will be covered by filter compatible

material that will allow any leakage through the lineament to emerge in

the rockfill in a controlled manner without piping (i.e. internal erosion) of

foundation material.

(d) Other measures nominated in the Technical Feasibility Study Report1 for

this area to address potential secondary movement include a

substantially longer toe slab, additional grouting, wider filter zones, half

width face slabs that will better adapt to movement, additional toe and

face slab seals and instrumentation to monitor any movement. I note

these measures are in addition to those described in the PD (Section

4.4.3) and applied relative to seismic loadings generally, i.e. flatter dam

slopes, greater crest width, and freeboard measures addressed below in

my evidence .

(e) There is some possibility that a weakness will exist somewhere else in

the foundation that has not been identified by geotechnical

investigations. Full geological mapping of the exposed foundation during

construction is normal practice. Any similar weakness to SZ1 found

during the construction phase would be investigated and similar

defensive measures provided, as is achievable during the construction

phase within the parameters of the Application Design.

3.8 Other Earthquake Related Issues

(a) In addition to shaking at the dam site, major earthquakes at this site

have a number of other impacts that need to be considered.

(b) Seiche effects from potential rupture of the Mohaka Fault where it

crosses the reservoir would be expected. GNS have advised that a

single event vertical displacement of 0.4 m to 1.0 m should be

considered as possible. This has been allowed for by providing

adequate freeboard that includes a factor of safety of 2 for the GNS

upper limit of 1.0 m.

( c ) Investigations have located a 90 m high landslide on the right bank of

the reservoir approximately 0.5 km upstream of the dam that could

remobilise during reservoir filling or be triggered by a major earthquake.

(d) Based on the information currently available, this is expected to involve

a volume in the order of 360,000 m3. The key concern is the impact that

a further landslide failure would have on the storage water, particularly

associated with the probability of the landslide failure occurring at the

1 Tonkin & Taylor, (August 2012)

same time as a nearby rupture of the Mohaka fault. This could cause a

seiche capable of overtopping the dam.

(e) The Application Design assumes the landslide would be stabilised to

eliminate this problem. If it is left in situ, additional freeboard would need

to be considered.

(f) An area of dilated, potentially unstable rock has been identified on the

left bank wall of the gorge extending from the downstream toe of the

embankment a further 200 to 250 m downstream. Part of this area has

failed sometime in the past, most likely as a result of earthquake

shaking. There is an expectation, based on visual inspection that the

remaining area of dilated rock mass could mobilise during the maximum

design earthquake.

(g) While failure of the rock mass does not directly affect the dam, it may

contain sufficient material to partially block the gorge. If operational and

spillway flows were released upstream of the fallen rock mass, water

would build up behind the blockage, submerging the outlet works and

substantially reducing outlet capacity at a time that emergency storage

drawdown is required. It would also submerge the embankment rockfill

roughly up to half the height of the embankment at a time when after-

shocks would be expected.

(h) The Application Design ensures that the spillway and outlet works return

flow to the Makaroro River downstream of this potential rockfall area.

This will allow normal operation of the spillway and outlet works during

such an event.

3.9 Freeboard Requirements for Flood and Earthquake

(a) Freeboard requirements have been determined to cater for three

separate scenarios, an extreme flood event, an extreme earthquake

event and a post-earthquake condition with a 1 in 20 AEP flood.

(b) The extreme flood event assumes a flood inflow equal to the Probable

Maximum Flood (PMF) occurring on a full storage. The PMF is the

largest flood that may reasonably be expected to occur from the most

severe combination of critical meteorological and hydrologic conditions

that are reasonably possible. By definition, the PMF does not have a

probability associated with it. However, a conservative approximation

can be obtained by extrapolating flood frequency distributions as a linear

relationship and if climate change is assumed this gives a nominal AEP

of 4x10-6 (1 in 250,000 years). The corresponding AEP without climate

change is 6.8x10-7 (1 in 1,500,000 years).

(c) The PMF with a peak inflow of 795 m3/sec produces outflow discharges

of 585 m3/sec in the primary spillway and 167 m3/sec in the secondary

spillway. The storage level rises 4.9 m from the full supply level (FSL) of

RL 469.5. An additional 1.0 m freeboard is provided for potential wave

action, giving a total requirement of 5.9 m above FSL.

(d) The extreme earthquake event has the potential to produce settlement

in the rockfill dam, a seiche generated by vertical or horizontal

displacement across the Mohaka Fault and a vertical displacement

within the embankment due to secondary movement on SZ1 zone or

other zone of weakness in the left abutment. The seismic parameters

used for the MDE have an AEP of approximately 2x10-4 (1 in 5,000).

Note that this is the probability of the event the dam is designed for, not

the probability of failure.

(e) As noted above, settlement of the rockfill dam has been estimated at 0.8

m and a factor of safety of 2 has been applied to this estimate. The

upper bound displacements produced by GNS of 1.0 m for the Mohaka

Fault vertical displacement and 0.5 m for secondary movement have

been adopted with a factor of safety of 2 for calculation of the freeboard

requirement , giving a total freeboard requirement of 4.6 m.

(f) The post-earthquake scenario requires provision for settlement of the

rockfill embankment (0.8 m as above with the safety factor of 2) and

displacement due to secondary movement (0.5 m as above with the

safety factor of 2). It also provides for a 2.5 m flood rise due to the 1 in

20 AEP inflow giving a total freeboard requirement of 5.1 m.

(g) The extreme flood event proved to be the critical scenario with a greater

freeboard of 5.9 m. This has been rounded off to 6.0 m and the parapet

crest on the embankment is set at RL 475.5 m, 6.0 m above the FSL of

RL 469.5 m.

3.10 Other New Zealand Dams

(a) Four NZ dams have been referred to in relation to RWSS (including by

submitters), Opuha, Matahina, Marlborough (Haldon Ranges Dam), and

Clyde. Brief descriptions of the issues involved and comparisons with

the RWSS are provided below together with comment on other relevant

NZ dams.

Opuha Dam

(b) Opuha Dam is a zoned earthfill dam located at the entry to the Opuha

George, about 12 km upstream from the township of Fairlie (Pickens &

Grimston, 2001 and Lees & Thompson, 2003). The dam was partly

constructed to a height of 29 m in February 1997 when it was filled by

flood flows. River diversion flows were provided by a 1.8 m diameter

pipe through the embankment and it is understood this was designed for

a flood with an AEP of 1 in 10.

(c) As the dam was being overtopped, the contractor cut a channel in one

side of the dam to prevent overtopping but this channel eroded rapidly

and the dam failed with one-third to half of the embankment fill being

lost.

(d) The flood was estimated to have an AEP of 1 in 12 to 1 in 14. There

were no injuries or fatalities but the breach caused substantial stock

losses and damage to farms adjacent the river. River protection works

were extensively damaged and about 200 residents were evacuated.

(e) The dam was reconstructed with much greater diversion capacity. A

series of open channels cut through the left abutment provided the

ability to cope with an AEP of 1 in 100 at lower embankment levels to 1

in 300 at higher embankment levels.

(f) The Ruataniwha river diversion proposal is described at Paragraph 3.13.

The dam is provided with a 4.0 m diameter diversion tunnel and the

embankment rockfill is protected with steel reinforcement to pass

extreme flood inflows over the embankment. The river diversion capacity

equivalent to a flood with an AEP of 1 in 1,000 compares with an AEP of

1 in 10 for the Opuha Dam prior to failure.

Matahina Dam

(g) The original 82 m high Matahina Dam is a zoned rockfill dam with a

sloping earth core flanked by transition zones. The core and inner

transition zones are founded on rock while the outer transitions and

rockfill zones are founded on a 20 m thick deposit of dense, coarse

alluvium. The core material is a sandy, clayey silt that is stiff and

susceptible to cracking and readily erodible. The inner and outer

transitions zones and the core material were not filter compatible and

the dam did not meet modern design standards. Any crack in the core

material could allow seepage to erode the core and inner transition

material through the rockfill and potentially fail the dam.

(h) Investigations had shown that this process had occurred to some extent

on two previous occasions, one of which was associated with the 1987

Edgecumbe earthquake. The basic problem with Matahina was a lack of

filter compatibility between adjacent zones and the dam was at risk

under normal operating conditions. Being subjected to strong

earthquake ground motion increased this risk.

(i) The maximum credible earthquake for Matahina is a magnitude Mw 7.2

event with peak horizontal and vertical ground accelerations of 1.25g

and 1.3 g respectively. There are several fault traces through the dam

site and the possible fault displacement is 3 m.

(j) The dam underwent a major upgrade in 1998 that provided a leak

resistant downstream buttress that would prevent any internal erosion of

the core and inner transition zones from leading to uncontrolled erosion

and failure of the dam. In addition, the dam freeboard was increased by

3 m to 6 m.

(k) The Ruataniwha proposal requires the various rockfill zones to be filter

compatible in accordance with modern engineering practice to prevent

occurrence of the internal erosion problem that occurred at Matahina.

The impervious element of the CFRD is an upstream concrete face

rather than the erodible clay core used at Matahina. The CFRD can

withstand large leakage through the dam without any concerns as to the

long term stability. Like the upgraded Matahina Dam, the Ruataniwha

proposal has generous freeboard to accommodate possible effects of an

earthquake on the Mohaka Fault.

(l) The other critical difference between the two dams is that Matahina Dam

is constructed across an active fault with potential fault displacement

estimated to be 3 m. Ruataniwha is not constructed across an active

fault although there is a possibility that secondary movement may occur

on a weak zone passing through the embankment. The only such weak

zone located to date is stable with no movement in the last 10,000

years. If secondary movement does occur, the maximum displacement

is estimated by GNS to be up to 0.5 m and similar defensive

mechanisms to those adopted at the SZ1 feature mentioned above

would be required to cater for this level of movement.

Haldon Ranges Dam

(m) The Haldon Ranges Dam is a water storage dam (capacity of about

250,000m3) located near Seddon in Marlborough. The embankment is

approximately 17 m high and is a zoned earthfill embankment. A

magnitude ML6.5 earthquake on 21 July 2013, located in Cook Strait,

resulted in some cracking along the upstream side of the crest of the

dam. A MW6.6 earthquake on 16 August 2013, located beneath Lake

Grassmere and much closer to the dam, resulted in additional

deformation and cracking on the upstream shoulder and crest. Although

the risk of a breach was assessed as unlikely the reservoir was lowered

as a precaution and to allow inspection and assessment of repairs. The

observed behaviour is not outside the range of possibilities for an

earthfill embankment when subjected to strong earthquake ground

motion. There were a number of other dams in the area that

experienced no damage. In making these comments, I am relying on

information sourced from Dr. Matuschka.

Clyde Dam

(n) The Clyde Dam is a 102 m high concrete gravity dam on the Clutha

River. It is located approximately 3 km from the active Dunstan Fault.

There is a possibility that rupture of Dunstan Fault could result in

sympathetic movement on a river channel fault that was encountered in

the dam foundations during construction. As a consequence the dam

design incorporates a special slip joint that can accommodate up to 2 m

of movement. This is a similar situation to Ruataniwha, except that the

Clyde Dam is a different type of dam (not CFRD) and in the Ruataniwha

case, the potential for sympathetic secondary movement has been

anticipated.

Other NZ Dams

(o) In addition to the Matahina and Clyde Dams, there are other existing

large dams in New Zealand that either overlie active faults or are very

close to active faults where secondary faulting is expected. Dr.

Matuschka provided the following examples and comment:

Aviemore Hydropower Dam (Waitaki River). The Waitangi Fault

underlies one side of the dam. Strengthening works have been

undertaken and analyses have been undertaken that provide

confidence that the dam will not fail due to rupture of the fault.

Ohakuri Hydropower Dam (Waikato River). The Maleme Fault Zone

is an active fault and is evident immediately north and south of the

dam

Aratiatia Dam (Waikato River). The Aratiatia Fault is inferred to pass

very close or under this dam.

Ruataniwha Dam (Upper Waitaki), located close to Ostler fault

(p) In the last 15-20 years more detailed studies have been undertaken to

assess the potential for fault displacement hazards for the design of new

dams as well as for safety assessments of existing dams. It is now not

uncommon to have to consider the potential for secondary faulting as a

result of movement on nearby active faults.

3.11 Spillways

(a) Two spillways are provided to pass flood flows. A concrete lined chute

spillway controlled by a 25 m wide arc-crested concrete ogee crest is

located on the right abutment. This spillway terminates in a hydraulic

jump dissipator located within the rockfill quarry for the embankment. An

outlet channel excavated into the quarry floor takes flows back to the

river. This channel is located well away from any rockfall that may result

from earthquake induced damage to the area of dilated, potentially

unstable rock on the left bank wall of the gorge.

(b) A secondary (auxiliary) spillway consisting of a simple 50 m wide

unlined excavated channel is located on the left abutment. This spillway

has a crest level that is 3.25 m above the primary spillway and does not

operate for normal flood inflows. Discharges commence for floods that

exceed the 1 in 200AEP inflow with a full storage. For a 1 in 1,000 AEP

inflow the discharge through this spillway is limited to 21 m3/sec. The

maximum discharge of 167 m3/sec occurs for the PMF inflow on a full

storage.

(c) The secondary spillway channel discharges into a steep gully and

through a large stand of trees before returning to the river. Considerable

scour would be expected in the gully during such an extreme event and

damage to the stand of trees. There has been no sub-surficial

investigation in this area but a preliminary estimate of scour has been

made and is shown in Figure 200 (Appendix C) of the PD.

(d) The auxiliary spillway does not operate until inflows exceed the 1 in 200

AEP flood event and little damage is anticipated for inflows up to the 1 in

300 AEP flood. The PD notes (page 52) that a rainstorm and

consequent flood event of this magnitude would be expected to mobilise

massive amounts of debris upstream of the dam, much of which would

be trapped by the dam. Detritus eroded from the auxiliary spillway area

would be expected to be a small proportion of that trapped by the dam.

(e) Further geotechnical investigation is required in the spillway channel

area to confirm that the spillway channel will not erode back through the

spillway crest. Further geotechnical investigation is also required in the

gully to provide better estimates of potential downstream scour in an

extreme flood event. If geotechnical investigations predict excessive

erosion, the auxiliary spillway dimensions can be reduced or the spillway

eliminated and the primary spillway enlarged to compensate.

3.12 Outlet Works

(a) The outlet works are located in the diversion tunnel and comprise:

A low level submerged intake structure at the upstream portal of the

diversion tunnel controlled by a vertical slide gate to provide an outlet

at low storage levels.

A free standing high level wet intake tower founded at RL 440m at a

high point above the tunnel. The tower is connected to the tunnel

with a steel lined raised bore shaft. Intake ports are provided at two

levels operated by a baulk and trashrack system. Access to the

tower is by boat and a system of ladders and platforms.

A 2100 mm diameter steel pipe liner within the tunnel lining is

provided as the main outlet from the grout curtain to the downstream

portal.

A 600 mm diameter bypass pipe located within the tunnel lining

provides an independent discharge facility. This allows flow

maintenance releases during construction of the main penstock and

during subsequent maintenance of the main outlet.

A bifurcation of the main 2100 mm diameter outlet at the

downstream tunnel portal with one 1500 mm diameter penstock

leading to the main outlet and a second 1500 mm diameter penstock

leading to the hydro power plant.

(b) The main outlet has been proportioned to allow dewatering of the

reservoir within a 3 month period based on the criteria developed by the

USBR (ACER, 1990). This sizing also limits head losses to an

acceptable level for the power station operation and provides for

irrigation releases and environmental flushing releases.

3.13 River Diversion during Construction

(a) International practice for river diversion is to provide a relatively simple

and low cost diversion capacity during the early stages of construction

where work mainly consists of river bed excavation and low level

embankment construction. At this stage of the project there is no risk to

downstream interests and failure of the river diversion system is a

business risk to the contractor.

(b) As the embankment construction continues, the dam stores increasing

volumes of water during a large flood event and failure can cause major

damages at the construction site and in the river downstream. This

requires an increasing degree of conservatism in the provision of

diversion flood handling capacity.

(c) The diversion works provide a 4.0 m diameter diversion tunnel in the

right abutment and a 10.5 m high upstream cofferdam for the initial

diversion works. The cofferdam controls the river during river bed

excavation and initial embankment construction. Once the main

embankment rises above cofferdam level (RL 408 m), the cofferdam is

no longer relevant to the diversion works and the main embankment

with a steel reinforced downstream face controls the river. This provides

a diversion capacity of at least 1 in 1000 AEP at any stage where public

safety and major damage are at risk. Simply put, the dam crest can be

safely overtopped (without failure) by the greater water depths than will

occur at 1 in 1000 AEP at any stage of construction before the crest

height is above the flood level (at RL 439 m). As construction levels rise

above RL 439 m the tunnel outlet capacity and the dam storage capacity

progressively increase and the dam is capable of handling progressively

larger inflows greater than the 1 in 1,000 AEP event.

3.14 Initial Filling of the Storage

(a) As noted at Paragraph 3.12, the outlet works is constructed in the

diversion tunnel. This requires the diversion tunnel to be closed off after

completion of the embankment and spillway for outlet construction. The

maintenance of river flows during this construction period is provided by

a 600 mm bypass pipe that is located in the tunnel lining and is not

affected by outlet construction activities. It has a limited discharge

capacity and only a marginal impact on the rate at which the storage

fills. Should the dam fill during this period, the spillway can safely pass

excess inflows.

(b) As part of the Feasibility Study, a probabilistic assessment was

completed on the length of time needed for the reservoir to fill from the

time the diversion tunnel is closed. The time is heavily dependent on the

month that filling commences. If filling commences in August to

December it would likely take between 7 and 12 months. If filling begins

in April to July it would likely take 3 to 5 months. Commencement in

January to March would take an intermediate duration.

(c) It is common practice to construct the permanent outlet works in the

diversion tunnel once the dam and spillway construction have been

completed. International practice is to place no restraint on filling rates

and as noted in the project Description there are numerous examples of

fast filling storages. These include:

140 m high Alto Anchicaya Dam, Columbia; 1 week

202 m high Campos Novus Dam, Brazil; 1 week to 90% height

110 m high Cethana Dam, Tasmania, Australia; 10 weeks

85 m high Cogswell Dam, USA; 71 hours

148 m high El-Infiernillo Dam, Mexico; 17 weeks.

125 m high Ita Dam Brazil; 10.4 weeks.

160 m Foz Do Areia Dam, Brazil; 21 weeks

94 m high Murchison Dam, Tasmania, Australia; 2.6 weeks

122 m high Reece Dam, Tasmania, Australia; 7 weeks

(d) In a few cases where there have been problems with extensive face

slab cracking and large leakage volumes at CFRD dams, no action has

been taken to lower the reservoir. The concrete face rockfill dam can

safely handle large leakage through the rockfill and is stable even

without the concrete face in place.

(e) Hold points for reservoir filling are not considered necessary from a dam

stability point of view and rapid filling of the storage is not considered a

dam safety issue.

3.15 Construction Program and Cost Estimate

(a) The total construction time from contract award to project completion is

estimated at 54 months. This includes an 11 month period for

construction of the outlet works and powerhouse which is an unusually

long time for outlet works construction and is largely due to leaving valve

installation until after completion of the powerhouse. A minor adjustment

to the construction schedule would make it possible to have the river

outlet operating within 6 months of tunnel closure.

(b) Construction cost estimates were developed by Tonkin & Taylor

together with Bond Construction Management and with input from the

Regional Council. The process included risk and opportunity workshops

to identify risks that may increase the construction and opportunities that

may exist to reduce the cost. Bond Construction Management

subsequently carried out a simplified risk analysis to determine the

appropriate contingency and then the Target Out Turn Cost.

(c) The cost estimate included allowances for the various defensive

measures mentioned above to provide a structure capable of handling

flood and seismic loads.

3.16 Design and Review Procedures

(a) The Application Design has been peer reviewed by independent

experts. The independent review reports are reproduced at Appendix H

of the Technical Feasibility Study Report produced by Tonkin & Taylor

(August 2012).

(b) The RWSS Conditions Schedule 1 requires that the final design for the

dam structure and related diversion tunnel, spillway and power station

structures be designed by a professionally qualified engineer

experienced in large dam design in areas subject to seismic activity.

This designer is required to certify that any variations to the Application

Design meet or exceed the dam design criteria relevant to dam safety

underpinning the Application Design.

(c) It is also required that a second professionally qualified engineer

experienced in large dam design in areas subject to seismic activity

approved by HBRC and CHBDC certifies agreement with that opinion.

(d) These requirements are in accordance with the requirements of the

NZSOLD Dam Safety Guidelines.

(e) As noted at paragraph 3.6, detailed dynamic analysis of the dam will be

required during detail design. This analysis will determine whether the

design provisions proposed are adequate or whether additional

provisions are required. This analysis will be subject to the peer review.

4. COMMENTS ON SUBMISSIONS

4.1 I have been provided with copies of the submissions received on the RWSS.

Relevant to my area of expertise I address the following issues raised by the

submitters

(a) Submitters Jenny Baker (#216), Ngai Te Upokoiri ki Omahu Marae

(#357), NZ Federation of Freshwater Anglers (#237), Operation Patiki

(#252), Craig Preston Trust (#295), Eugenie Sage (#362), Catherine

Schillinger (#137), Daniel Stabler (#138), Phylis Tichinin (#215) and

Waipatu Marae (#395) all express concern that the dam is to be located

on or near known faults, consider that this poses an unacceptable

hazard to the community and the environment, and are not satisfied this

has (or can be) accounted for in the design.

(b) Arden Properties Ltd. (#118) considers that the project is high risk, to be

constructed on unstable bedrock, that no independent feasibility study

has been done and queries which independent person signed off on

Makaroro as a good place to build a dam.

(c) Andrew Gifford (#297) and Leo-Hylton–Slater (#205) submit that there

has been inadequate consideration, ‘apprehension’ or investigation of

seismic risks,

(d) Brian Chambers (#335) has raised the issue of potential earthquake risk

and the increased costs needed to adequately mitigate these.

(e) The Council of Outdoor Recreation Associates (#396) and Eugenie

Sage (#362), express concern that the dam is to be located adjacent

fault lines and raise the issue of the failed Opuha Dam, which they

suggest the Ruataniwha dam is ‘modelled’ on or would have similar

risks to. NZ Federation of Freshwater Anglers may be referring to this

dam as well.

(f) The Environmental Defence Society (#304) expresses concern that

information on probability of failure is not provided and submitters are

unable to comment on the risk posed by the dam.

(g) Patrick Maloney (#314) expresses concern that the dam is to be located

in an area surrounded by earthquake fault lines and considers that third

party reviews independent of Tonkin & Taylor are required for the

seismic risk and the dam design required to handle this risk.

(h) Angus Robson (#259), expresses concern that the dam is to be built on

or adjacent to 3 known faults, considers that the GNS studies are

inadequate, and that the dam should not be built until it can be proved to

be an order stronger than the Matahina and Marlborough Dams.

4.2 My response is that the issues raised are addressed in my evidence.

(a) The general issues with safety of the dam under seismic load are dealt

with in Paragraphs 3.2 to 3.10 of my evidence. The dam is not located

on known faults but is located close to three known faults. The MDE has

been selected as the MCE in accordance with the NZSOLD Dam Safety

Guidelines. Under and after the MDE level shaking, damage to the dam

is expected but no uncontrolled release of the storage water. The

embankment displacements under the MDE obtained from initial

assessments are not large. The CFRD embankment was adopted on

the basis that it provided the best solution for the site’s geotechnical

issues with the materials available.

(b) The freeboard adopted for earthquake scenarios has been

conservatively estimated, assuming the upper bound values obtained

from initial assessments and those provided by GNS take place in the

most critical direction and then applying a factor of safety of 2.

(c) The Ruataniwha Dam has the potential to undergo a similar degree of

earthquake shaking to other New Zealand Dams such as Matahina,

Clyde and Aviemore Dams. Unlike Matahina and Aviemore dams it is

not constructed across an active fault. There is a possibility of

secondary or sympathetic movement on a pre-existing shear zone or

secondary fault as at the Clyde dam. The only such weakness located to

date has been stable for 10,000 years. Detailed foundation mapping

during construction will locate any other foundation weaknesses and

defensive measures would be provided.

(d) The issues of peer review, an independent study and an independent

person to sign off are addressed at Paragraph 3.15(c) of my evidence.

(e) The issue with the potential for increased costs is addressed at

paragraph 3.15 of my evidence. The various defensive methods and the

provision of adequate freeboard have been included in the cost

estimates.

(f) The issue of the failed Opuha Dam is addressed at paragraph 3.10 of

my evidence. The failure was due to inadequate river diversion capacity

during construction. The Opuha Dam river diversion capacity catered for

an AEP of 1 in 10 years. The corresponding capacity for the Ruataniwha

Dam is a minimum of 1 in 1,000 years at any time where public safety

and major damage are at risk.

(g) The issue of probability of failure is addressed at paragraph 3.9 of my

evidence.

(h) The issue with Matahina and Marlborough (Haldon Ranges) Dams is

addressed in Paragraph 3.10 of my evidence. Dr. Villamor comments

about the adequacy of the GNS studies in her evidence.

Phillip Richard Carter September 2013

5. REFERENCES

Cooke & Sherard

(1987)

Cooke, J.B., Sherard J.L., 1987, Concrete face Rockfill Dams;

Parts I & II , American Society of Civil Engineers, Journal of

Geotechnical Engineering, Vol. 113, No. 10, October 1987.

Fell et al (2005) Fell, R., MacGregor, P., Stapleton, D., Bell, G. Geotechnical

Engineering of Dams, 2005

ICOLD (2010) International Committee on Large Dams, 2010. Bulletin 141,

Concrete Face Rockfill Dams – Concepts for Design and

Construction, ICOLD 2010, Paris, France.

Lees & Thomson

(1997)

Lees, P. and Thomson, D., (2003) Emergency management,

Opuha Dam collapse, Waitangi Day 1997, NZSOLD

Symposium on Dams – Consents and Current Practice,

Proceedings of Technical Groups, Volume 30, Issue 2 (LD),

pp84-89.

Materon &

Fernandez (2011)

Materon, M., Fernandez, G., 2011. Considerations on the

Seismic Design of High Concrete face Rockfill Dams

(CFRD’s), Second International Symposium on Rockfill Dams,

Rio de Janeiro, Brazil, October 27 to 28.

Pickens &

Grimston (2001)

Pickens, G.A. and Grimston, J.D. (2001) The Opuha Dam

Project, Dams –Development, Sustainability and Performance,

Proceedings NZSOLD/ANCOLD 2001 Conference on Dams,

Auckland

before the board of inquiry in the matter of the … · a concrete face rockfill dam (“cfrd”)...

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