and in the matter applications resource consent by ... · 6. in the council’s application...

Evidence D Peacock

IN THE MATTER of the Resource Management Act 1991

AND

IN THE MATTER Applications resource consent by Gisborne District Council for the Waipaoa Flood Control Scheme Upgrade

STATEMENT OF EVIDENCE OF DAVID HENRY PEACOCK

FOR WI PERE TRUST

28 NOVEMBER 2017

Counsel Instructed Trevor Robinson Barrister Level 6 Harbour City Tower 29 Brandon Street PO Box 8018 Wellington 6143 [email protected]

Evidence D Peacock

Executive Summary

i. The effect of the Waipaoa River Flood Control Scheme is to exacerbate

flooding on the Wi Pere Trust land at Tangihanga.

ii. The proposed upgrade of the scheme will cause an increase in the depth and

extent of flooding at Tangihanga for floods with a magnitude greater than the

Cyclone Bola flood, compared to the status quo.

iii. Unlike previous scheme upgrade proposals, this proposal includes no

enhancements of flood protection at Tangihanga to compensate for the

additional adverse effect.

iv. The Council’s application documents did not acknowledge or assess the

nature and scale of the adverse effect on Tangihanga.

v. The recently completed modelling presented by Mr Goodier suggests the

upgrade will increase flood levels in the upper terrace area where the Trust

has workers living, and on which it has concentrated its investment by around

20% in a design flood (6625m³/s). I regard that as significant.

vi. I also believe that modelled effect is a better case than most other scenarios,

because:

a. A shorter duration – flood (which would be more usual) will have

greater effects if the upgrade proceeds than the reference flood used

in the model scenario presented by Mr Goodier;

b. The upgraded stopbanks will enclose more water than the design

flood:

Neither of those scenarios have been modelled by Council.

vii. If Council took the same approach to its own works as it took to the Trust’s

construction of stopbanks around its irrigation storage reservoir, it would

ensure its upgrade of The Flood Control Scheme had a neutral effect on the

Trust’s lands at Tangihanga.

Introduction:

1. My name is David Henry Peacock. I am a semi-retired consulting engineer. My

qualifications are BE (Civil), University of Auckland; and I am a Chartered Member

of Engineers New Zealand (CMEngNZ). I have practised hydraulic and river

control engineering for over 40 years and have had a close association with the

Waipaoa River for 24 years, first as Deputy Chief Engineer of the East Cape

Evidence D Peacock

Catchment Board then as Asset Manager Rivers and Land Drainage with the

Gisborne District Council. During this time, I observed the Cyclone Bola flood in

the Waipaoa River in 1988 and subsequently directed the repair works for the

Waipaoa River Flood Control Scheme (WRFCS). As a consultant in 2009, I was

co-author of a detailed report recommending an upgrade proposal for the GDC.

2. I am giving this evidence as an independent expert. Although this is a first

instance hearing, I have read and agree to comply with the code of practice

applying to experts in the Environment Court. I note that I have filed a submission

in my personal capacity. My personal submission expresses support in principle

for the proposed upgrade and seeks answers to questions/explanations regarding

aspects of its design not related to its effect on the Wi Pere Trust land. I do not

therefore consider it disqualifies me from giving independent expert evidence for

Wi Pere Trust.

Background

3. The Waipaoa River Flood Control Scheme (WRFCS) comprises some 63

kilometres of stopbanks and protects the intensively farmed Poverty Bay Flats. In

the lower to middle reaches of the WRFCS (from the sea up to about Waituhi) the

stopbanks are 1000 feet (305m) apart and the land between the stopbanks is

publicly owned. However, upstream of this, the scheme banks are built on

privately owned land. In this area, viz; the Ormond loop and upper and lower

Tangihanga, private banking systems have been built to provide a (lower) level of

flood protection for the respective land owners.

4. The Wi Pere Trust land at Tangihanga east of Lavenham Road is an area of

approximately 300 hectares – bounded on three sides by the river with the

Lovelock Loop to the north and the Ormond Loop to the south. It is flat land made

up of a number of flat terraces. The Hawke’s Bay Regional Council letter of 25

September supplying information and commentary on the Council’s applications

refers (like me), to an Upper and Lower Terrace. In this case ‘Upper’ and ‘Lower’

refer to location with reference to the river, and not to their elevation. Between

them there is a higher terrace approximately 3 metres above the ‘Upper‘ and

‘Lower’ terraces bisected by an access road, on which the Trust has a packhouse,

sheep yards, workers accommodation and areas of horticulture development

(formerly vineyards). Within this area, the Trust has also constructed a water

storage reservoir utilising an old river ‘ox-bow’. There is also a higher area in the

north-west corner that Mr Haronga identifies in his evidence.

Evidence D Peacock

5. In the reach past the Wi Pere Trustees’ land, viz; upper and lower Tangihanga,

there is no true right bank for the WRFCS, floodwaters being effectively confined

by the hill toe west of Lavenham Road. However, there is a WRFCS stopbank on

the true left bank which protects land to the east, including the township of

Ormond. The Wi Pere Trustees have constructed a stopbank to protect most of

the upper Tangihanga river flat, and in 2009, I estimated that as providing about a

“1 in 20 year” (5% AEP) level of flood protection; however there is no stopbank

protecting the lower Tangihanga terrace. I estimate that the lower Tangihanga

terrace would be overtopped by a 3 to 4 year flood. As I discuss shortly, the higher

terrace was flooded during Cyclone Bola, but as far as I am aware, that is the only

occasion it has been flooded in recent times.

6. In the Council’s application documents (at paragraph 3.1), the Wi Pere Trust Land

is described as “part of the flood plain”. This is factually correct, but fails to

acknowledge that the presence of the stopbanks on the opposite (eastern) side of

the river increases the extent and depth of flooding across the Wi Pere Trust land.

The Scheme stopbanks between the foot of Kaitaratahi hill and Ormond prevent

flooding of the Muhunga basin, an area of some 400 hectares. This denies flood

storage which was originally available (pre-WRFCS), and would increase the depth

and duration of flooding of the Wi Pere Tangihanga land. Even more importantly,

the Scheme stopbanks between Ford Road and Ormond have cut off the historic

natural Waipaoa river overflow path via the “Ormond dip” to the Taruheru River. I

estimate that pre-WRFCS a flood equal to the “Bola” event would have been at

least a metre lower than the Bola flood levels over upper and lower Tangihanga,

and would definitely not have flooded the higher terrace between them. Put

simply, the stopbanks divert flood water that would otherwise have flowed east

over the Poverty Bay flats onto the Trust’s land.

7. During the Cyclone Bola flood in March 1988, both upper and lower Tangihanga

were under metres of floodwaters, and even the high terrace between the two had

floodwaters flow over it. Mr Haronga gives evidence of a line painted on an inside

wall of the packhouse on Tangihanga. I measured that line as being 250mm from

the floor up the wall and calculated from that that the water would have been

around 130mm deep on average on the access road. Bola flood waters deposited

deep layers of sand and silt over both the upper and lower terraces.

Subsequently, upper and lower Tangihanga terraces and the high terrace between

them have been designated as “High Hazard” zones in the District Plan and certain

rules apply as to the further development of this land.

Evidence D Peacock

8. Following the Cyclone Bola flood, in 1992 a resource consent was applied for and

granted for a minor raising of the WRFCS stopbanks at ten low spots, to contain a

flood equal in discharge to the Bola event, plus 300mm freeboard. This stopbank

raising was only intended as an interim measure until a full review could be carried

out. This review (by independent consultants) commenced in 1993. In October

1995, this review recommended in principle “Option 3B” as the long-term plan for

the Waipaoa River Flood Control Scheme, to be constructed in two stages, each

stage subject to funding. Stage 1 of Option 3B (also referred to as “Scheme 3A”),

was to reposition the existing inner (private banks) and remove existing transverse

banks across the neck of Lovelock and Ormond Loops to make an unobstructed

floodway a nominal 300m wide (see Figure 1 attached).

9. Following endorsement of Scheme 3B by Council, an application for a resource

consent for Stage I of Scheme 3B (aka Scheme 3A), was made in November 1996

and was subsequently granted in February 1998. However, an appeal was lodged

by Mr Thomas Smiler (Junior) in his own capacity and as a Trustee of the Wi Pere

Trust. Protracted discussions between Council staff and the Wi Pere Trust

resulted in a “side agreement” that Mr Haronga produces which was subsequently

adopted by Council on 24 August 2000 as the basis of settling the resource

consent appeals for the proposed Stage I works that would potentially affect land

belonging to the Wi Pere Trust.

10. Scheme 3A would have meant that Wi Pere Trust would have had a reduced level

of protection on some land to achieve a significantly greater level of flood

protection (assessed at the time as 1/35 AEP) for the balance of both the Upper

and Lower Terraces; as well as the option of raising these banks to a higher level

at their own expense.

11. Although the appeal to the Environment Court against the Scheme 3A proposal

was resolved before the hearing, further hydraulic modelling showed a need to

investigate further the scheme capacity upstream of Kaitaratahi hill. Hence, in

2003, a further review was initiated. This review was not completed by the time I

retired from Council in 2007, but was completed by myself and John Philpott (a

River engineer specialising in Scheme rating systems) and presented to Council in

October 2009.

12. Our 2009 report “Waipaoa River Flood Control Scheme Review - Proposals for an

upgrade of the WRFCS”, costed in detail two major options of which “Option B”

was recommended to Council. Option B was for an upgraded scheme to convey a

Evidence D Peacock

“1 in 150 year” (0.67% AEP) event, then estimated as 5200 m³/s with 0.5m

freeboard over and above that. I note that the 5200 m3/s figure is based on an

earlier assessment of the Bola peak discharge as being 4100 m³/s. an earlier figure

used for this study. This higher level of protection (than Bola) was recommended

as an allowance for climate change. In addition to major stop bank raising, Option

B included the floodway improvements of Scheme 3A, as well as relocating the

existing Scheme banks at Mulloolys bend and soil conservation works on erosion

prone land in the upper catchment (for which there was no incentive package at

that time).

13. Including Scheme 3A had the benefits of:

• Improving the hydraulic efficiency between Ormond and Kaitaratahi, and

• Allowing the development of a net 254 hectares of land at Tangihanga outside

the 305m floodway to a higher level of protection.

14. However, Scheme 3A had the disadvantages of:

• Being more costly than achieving the same level of protection to areas already

protected by the Scheme as by raising the stopbanks.

15. A subsequent peer review (by Beca in 2010) concluded that: “The Review

recommends that Option B be adopted with a design standard of 1 in 150 years.

On the information provided and the assumptions made in the Review, this is a

valid recommendation. However, it should be reviewed in light of any changes

resulting from the recommendations of this peer review”.

16. Subsequently, in December 2011, NIWA reassessed the Bola flow rate and flood

frequency; summarised in their report as follows:

“Various flow estimates have been made for the Cyclone Bola peak flow. Our

analysis suggests that scour is a significant factor, and that allowing for this would

give a peak flow figure of 5300 m3/s ± 15 %.

The Cyclone Bola event on the Waipaoa River in March 1988 is clearly the largest

event in the instrumental record and possibly in the last 80 to 130 years. We first

point out that the real return period of Bola is unknown. If only the instrumental

record is considered then we are reasonably confident that the return period of this

flood is 90 years ± 10 %. With inclusion of historic information we would revise this

estimate to 100 years ± 20 %.

Evidence D Peacock

Given that there is considerable uncertainty in the exact size of the Bola flow, and

given the continuing aggradation of the Waipaoa River bed, there must be a large

allowance for freeboard on downstream flood protection works”.

17. Following the NIWA flood review, a report to Council on the 26th January 2012

questioned the need to proceed with the proposed WRFCS upgrade and

recommended:

• withdrawing the upgrade of the WRFCS from the draft 2012-2022 ten year

plan; and

• reconvening the WRFCS Steering Committee to consider (over the next

three years) possible actions to improve the hydraulic capacity of the existing

Scheme.

18. The current proposal, as described in clause 1.1 of the resource consent

application, is for a design flow of a 1% AEP (6625m3/s) flood allowing for climate

change up to the year 2090, including 0.6-0.9m freeboard. This will involve raising

and widening the existing stopbanks. However, there does not appear to be any

“hydraulic efficiency improvements” included as part of this application.

19. Council has adopted the NIWA assessment of flood frequencies for the purposes

of its current application. That means that different discharges were assigned to

the Bola flood in the 2009 report compared to the flood discharges in the

application. The 5200 m3/s flood is approximately 27% greater than the Bola peak

discharge, and therefore slightly larger than the 6625 m3/s design flood in the

application, which is 25% greater than Bola. The end result is that the current

application seeks approval for a similar level of protection for the areas already

protected by the Scheme, but omits the hydraulic efficiency and other floodway

improvements we had recommended.

20. The extent to which the stopbanks will be raised in the vicinity of Tangihanga is not

clearly stated in the application documents although it will clearly be substantial.

The stopbanks were sufficient to contain the Bola Flood (just), apart from in the

area upstream of Ford Road where there was a low point in the stopbanks. That

area is currently a designated 400 metre long preferential overflow spillway – an

area where water will flow over the stopbanks in a controlled manner during very

high floods rather than risk uncontrolled breaches of stopbanks elsewhere. As I

understand it, the proposal is to ‘equalise’ the extent of the flood protection

provided by the Scheme to the areas currently protected.

Evidence D Peacock

21. Putting that localised Ford Road area aside, if (as stated in the application) the

intent is to raise the stopbanks sufficiently to retain an additional 25% of water

(another 1325m³/s) plus another 600-900mm free board on top of that, the

stopbanks will clearly need to be raised significantly. From Table 3 ( page 16 of

Appendix 4 of the application), the proposed stopbank levels opposite the upper

and lower Tangihanga terraces will need to be about 0.7m higher than the current

design stopbank levels1. Of the 0.7m increase in stopbank height, 0.3 metres is

due to the increase in freeboard from 0.3 to 0.6 metres, hence the rise in flood

levels due to the 25% increase in capacity is 0.4 metres. Whilst the floodway is

very wide here (about 1,500 metres), to me, an increase in flood levels of 0.4m is

less than what I would have expected for an increase in flow capacity of 25% (1325

m3/s). I understand GDC/HBRC were to provide further information. However, at

the time of writing I have still not received the coupled 1D/2D model flood levels for

the Waipaoa River in this area, and so cannot comment further.

22. This is important, because the inevitable result of raising the stopbanks on the true

left bank of the river will be to increase flood risk on the Wi Pere Trust land. The

higher the floodbanks are raised, the greater the effect will be. The Council’s

application documents do not identify or assess the extent of this effect.

Wi Pere Trust Applications – Irrigation Pond

23. In 2014, I was commissioned by the Wi Pere Trust to assist with the consent

application for an irrigation pond in the F2 (High Hazard) overlay in the GDC

Combined Land and Regional District Plan (CRLDP). This pond is located in an old

Waipaoa river oxbow, but in order to provide more storage volume the pond was to

be raised above the high terrace level by construction of stopbanks around the

perimeter, and would therefore require a discretionary resource consent to divert

flood flows.

24. I prepared an analysis of the hydraulic effects of the proposed stopbanking using

empirical methods, and this was checked by the HBRC using a 1D hydraulic

model. The conclusions were that flood levels on the WRFCS stopbanks opposite

the irrigation pond at the 22M bench mark would be raised by up to 200mm, this

effect diminishing to 50mm upstream and downstream of 22M over a total distance

of 1350 metres.

1 The Table suggests the increase will need to be 0.68m at the 21M mark and 0.9 at 22M.

Evidence D Peacock

25. I expressed the view at the time that the effect was minor, but Hawke’s Bay

Regional Council (advising the Council) disagreed.

26. However, I did agree with the GDC requirement that the Wi Pere Trust raise the

stopbanks to standard Scheme specifications over the 1350 metre length identified

– in effect to ensure that its works had a neutral effect on the Scheme. The

resource consent was granted in April 2014, and stopbank raising commenced

shortly afterwards. All surveys, plans and construction costs (including soil testing

and supervision) were funded by the Wi Pere Trust.

Assessing Effects of Proposed Works on Wi Pere Trust

27. As above, raising the stopbanks on the opposite side of the river will increase flood

risk to Tangihanga. However, raising the Scheme banks will only influence the Wi

Pere property for flood events with a discharge equal to or greater than that of the

Cyclone Bola flood. While the Bola flood is rated by NIWA as a “1 in 100

year“ event, with the increased precipitation likely as a result of climate change,

floods of this magnitude will become increasingly more common – one of the

reasons Council is proceeding with the Scheme upgrade. To assess the likely

increase in flood levels on the Wi Pere property a comparison has to be made of

the likely flooding with and without the proposed raised stopbanks for floods

greater than Bola, as follows:

• With the existing stopbanks an over-design flood would overtop the Scheme

banks at the upstream end of the Scheme, cross Mullooly Road and travel

through low lying land, the Waipaoa village and fill the Westmere basin. If

the flood peak was relatively short this may have provided sufficient storage

volume to shave the peak off the hydrograph, so that the discharge further

downstream is less than the Bola peak. In this case flood levels in upper and

lower Tangihanga would not be increased above Bola levels. However, if the

flood magnitude was greater still or the flood peak extended, then

floodwaters would rise to above Bola levels further downstream toward upper

then lower Tangihanga, but at the same time floodwaters would spill over the

Scheme banks and also flood the Muhunga basin and Ormond village. In

this scenario, I would not think that flood levels on the Wi Pere land would

exceed Bola levels by very much, as so much water would be overtopping

the Scheme stopbanks opposite its land.

Evidence D Peacock

• With the Scheme stopbanks raised as proposed, the stopbanks would be

about 0.7 metres higher than the existing banks opposite the upper

Tangihanga terrace. This means that flood levels could theoretically, under

some circumstances, be up to 0.7 metres higher than with the existing banks.

28. In the further information supplied by Hawkes Bay Regional Council, dated 25th

September, the increase in flood levels are estimated to be +0.16m and +0.4m at

the upper and lower Tangihanga terraces respectively. I understand Council (viz

the applicant) has advised the Trust that this is calculated for the design flood

(6625m³/s). While I would agree that these increases are not likely to materially

increase damage to the upper and lower terraces, it is in my view likely to be

significant for both the irrigation pond and the high terrace land between upper and

lower Tangihanga, where level differences were provided.

29. The Trust requested that the applicant supply levels at a number of key locations,

and floodwater depths for the design flood at seven locations have since been

provided. From the table on page 2 of Attachment 1 of the Goodier evidence, on

the higher terrace between the upper and lower Tangihanga terraces, the average

increase in floodwater depths at 5 locations due to the proposed stopbank raising

has been predicted to be 0.1m. This result however is for just one model run of

part of the long duration design (6625 m3/s) flood. Whilst it may not make much

material difference to the difference in depths between the two modelled scenarios,

it appears to me that the stopbanks around the perimeter of the irrigation pond may

not have been included in the models. The reason for requesting levels at points 5

- 7 inclusive was to ascertain if the banks of the irrigation pond would be

overtopped. Those banks are a consistent elevation (higher than the rest of the

terrace), but the modelled results are not consistent with that. I do not therefore

think they can be relied upon to assess potential effects on the irrigation pond.

30. As regards flood duration, Mr Goodier states on page 4 of Attachment 1 of his

evidence, that: “Model results do show a potential difference in duration of flooding

in the Wi Pere Trust area by the peak flows arriving about 2-3 hours earlier in the

proposed case as compared to the existing case”. This is because there is much

less flood storage volume available upstream of Tangihanga in the proposed

scenario, and I believe that further modelling would show that floods of the same or

lesser magnitude but with short duration flood peaks, would show substantially

greater differences in flood depths than 0.1m.

Evidence D Peacock

31. In addition, I note that the HBRC calculation fails to take account of the potential for

the freeboard provided to contain more water than the design flood. Since this is

what is enabled by the consents sought, I believe this should be the reference

point. The Trust requested Council advise the relevant ‘brim-full’ levels, but has

yet to receive model results.

32. Mr Ruifrok expresses the opinion that the modelled effect of the proposed works

will be less than minor on Wi Pere. I do not understand how he can arrive at that

view. Given the nature of the land uses on the upper terrace, the modelled 20%

increase of water levels at point 3 is in my view likely to be significant. More

importantly, I believe that the modelled effect is a better case than most other

scenarios would show. A shorter duration event would, as above, have a more

significant effect, as would a flood of greater magnitude than the design flood that

did not overtop the raised floodbanks. The velocity of floodwaters could also

increase significantly in an over-design flood. In either event, the damage to the

road and to horticultural crops would be substantial. The packhouse, sheep yards

and nearby house (floor level not far above the Bola peak level), could be

damaged or even swept away by floodwaters in the design flood. If the walls of the

irrigation pond were overtopped, very silty water and debris would be deposited in

the pond. The Waipaoa floodwaters during Cyclone Bola had a sediment

concentration of about 4% by weight, and deposited some 300 to 500mm of silt

and sand over McPhail’s flat not far upstream from Tangihanga. Deposition of silt

in the pond would result in the loss of valuable water storage volume available for

irrigation purposes in the summer.

33. The model outputs presented by Mr Goodier suggest there will be no difference at

points 1 and 2 (the house the Trust owns on Lavenham Road and the former

vineyard on higher ground adjacent to it). However, in other flood scenarios, I

suggest that this may not be the case.

34. In summary, this is the reverse of the situation in 2014 when Wi Pere raised the

banks around its irrigation pond and had to mitigate the adverse hydraulic effects

by raising the Scheme banks at their own expense. Application of the same

principle would require the applicant to take action to mitigate the effects of raising

the WRFCS stopbanks by works that ensure those effects on the Trust are neutral.

35. It appears to me that Council is not prepared to mitigate the adverse effects on the

Wi Pere Trust’s land because it is not part of the WRFCS; refer to Cl 22 in the

Evidence D Peacock

evidence of Mr J Ruifrok. This stance raises planning and legal issues that are

addressed in the evidence of Mr Willis and the submissions of Mr Robinson.

David H Peacock

28 November 2017

and in the matter applications resource consent by ... · 6. in the council’s application...

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