21 March 2024
File Ref: OIAPR1274023063-25734
J Thurston
By email: [FYI request #25891 email]
Tēnā koe
Request for information 2024-027
I refer to your request for information dated 26 February 2024, which was received by Greater
Wellington Regional Council (Greater Wellington) on 26 February 2024. You have requested the
following:
“
Information Requested:
I would like to request information on stopbanks in the Lower Hutt area, along the Hutt River. The
Riverlink project is apparently going to provide protection between Kennedy Good and Ewen
bridges for a one in 440 year flood, compared to the current state (as best as I can tell the current
state is one in 100 year flood protection: https://www.gw.govt.nz/your-region/emergency-and-
hazard-management/flood-protection/our-work/rivers-and-schemes/hutt-river/flood-protection-
hutt-central-from-just-north-of-ewen-bridge-to-kennedy-good-bridge/ but please correct me if I am
wrong about the status quo or the plan.
I would like to request:
1) the current stopbank height and flood protection measure (i.e protection from X in X years
flooding) for the stopbanks south of Ewen bridge on both the western (Ava/Petone) and eastern
(Moera) sides of the river from Ewen bridge through to Waione St overbridge. Please indicate
whether these are at different levels of protection at different points i.e. if the western side from
Ewen to Ava bridges is different from that of the western side from Ava to Waione overbridge. I am
asking here about sections of stopbank that I understand are not within scope of the Riverlink
project; please correct me if I am wrong.
2) information on when the Council last considered the suitability and efficacy of the stopbanks
south of the Ewen bridge as described above, and the results of any such consideration
3) any plans the Council (or any related party that the council knows about) to re-assess or
otherwise consider improvements to the stopbanks described above
Wellington office
Upper Hutt
Masterton office
0800 496 734
PO Box 11646
PO Box 40847
PO Box 41
www.gw.govt.nz
Manners St, Wellington 6142
1056 Fergusson Drive
Masterton 5840
[Wellington Regional Council request email]
4) whether the Council has any information on potential costs and benefits of improvements to the
stopbanks outlined above
5) I note that the stopbanks in question protect the Gear Island Water Treatment plant. Has the
council or wellington water considered the efficacy of the protection of the Gear Island water
treatment plant, or put any plans in place to improve protection from flood surges? I also note that
Gear Island is between Te Mome Stream and the Hutt River, so flooding could come from either
direction.”
Greater Wellington’s response follows:
On 14 March 2024
Part 5 of your request was transferred to Hutt City Council. Further
correspondence on this request will come directly from Hutt City Council.
Clarifications:
I would like to request information on stopbanks in the Lower Hutt area, along the Hutt River. The
Riverlink project is apparently going to provide protection between Kennedy Good and Ewen bridges
for a one in 440 year flood, compared to the current state (as best as I can tell the current state is
one in 100 year flood protection: https://www.gw.govt.nz/your-region/emergency-and-hazard-
management/flood-protection/our-work/rivers-and-schemes/hutt-river/flood-protection-hutt-
central-from-just-north-of-ewen-bridge-to-kennedy-good-bridge/ but please correct me if I am
wrong about the status quo or the plan.
The existing stopbank between the Melling Link Bridge and Mills Street currently has the lowest level of
flood protection in the area, for a 1 in 65-year flood event protection (in any year there’s a 1.5% chance
of a flood that size happening).
When all of the works under Te Awa Kairangi programme are completed, the Hutt Valley will be protected
from a 2,800m3/s (cumecs) flood or a 1 in 440-year flood event including for future climate change (with
a 0.2% chance of a flood that size in any year).
Request:
1) the current stopbank height and flood protection measure (i.e protection from X in X years
flooding) for the stopbanks south of Ewen bridge on both the western (Ava/Petone) and eastern
(Moera) sides of the river from Ewen bridge through to Waione St overbridge. Please indicate
whether these are at different levels of protection at different points i.e. if the western side from
Ewen to Ava bridges is different from that of the western side from Ava to Waione overbridge. I am
Page 2 of 6
asking here about sections of stopbank that I understand are not within scope of the Riverlink project;
please correct me if I am wrong.
Currently, the stopbanks and flood protection measures along the Hutt River, downriver of Ewen
Bridge and outside the scope of the RiverLink project are as shown in
Table 1, with the stopbank
reaches given in
Figure 1 (from Living with the River1; note that the capacity has been updated to
reflect work carried out):
Table 1: Hutt River Flood Mitigation Scheme - Security of Flood Defences
Stopbank Name
Capacity (m3/s)
WEST BANK
Estuary Bridge to Ava Railway Bridge
Shandon (875m)
2100
Sladden Park (400m)
2100
Ava Railway Bridge to Ewen Bridge
Alicetown (950m)
2300
EAST BANK
Seaview Marina to Estuary Bridge
Port Road (450m)
1600
Estuary Bridge to Ava Railway Bridge
Moera (1250m)
2100
Ava Railway Bridge to Ewen Bridge
Strand Park (1070m)
2300
The Hutt River Floodplain Management Plan (HRFMP) specifies that the agreed design standard for
the Hutt River is a risk-based 2300 m3/s standard (1 in 440-year return period flood). The risk-based
approach also applies varying protection standards to different areas in the floodplain, depending
on how flood-prone they are. This includes, among other things:
•
a requirement to upgrade all major stopbanks (i.e. those protecting the main urban areas
of Lower & Upper Hutt cities) to a 2800 m3/s capacity with all remaining stopbanks to a
2300 m3/s capacity;
1
https://www.gw.govt.nz/assets/Documents/2022/08/1440_HuttLivingwithth_s2818.pdf
Page 3 of 6
•
a requirement for bank-edge and berm protection to a 2300 m3/s capacity in main urban
areas, with a 1900 m3/s (1 in 100-year return period flood) capacity for isolated and small
urban areas;
•
a requirement for all new bridges and their floodways to pass a 2800 m3/s flood.
This is the standard to which all new works are constructed and maintained. It is reflected in Greater
Wellington's capital works programmes and asset management plan.
Figure 1. Hutt River Flood Mitigation Scheme defences and reaches.
Page 4 of 6
2) information on when the Council last considered the suitability and efficacy of the stopbanks south
of the Ewen bridge as described above, and the results of any such consideration.
Refer to the link for latest annual report to Council covering the stopbanks requested:
https://www.gw.govt.nz/assets/Documents/2023/11/Environment-Committee-23-November-
2023-order-paper-v4.pdf.
For annual asset management condition report, refer page 9.
For annual Floodplain Management Plan implementation report, refer page 358.
3) any plans the Council (or any related party that the council knows about) to re-assess or otherwise
consider improvements to the stopbanks described above.
The Hutt River Floodplain Management Plan (HRFMP) is still the guiding document for flood risk
management projects on the Hutt River. Stopbank upgrades on both sides of the Hutt River and the
River Channel improvements between Ava Rail bridge and Ewen bridge were completed in 2009, as
per the implementation plan for the HRFMP.
Refer to Section 8.4, page 161 for information on reviewing the HRFMP.
Hydraulic modelling of the Hutt River flood risk is underway; when completed Greater Wellington
will be reviewing the priority of initiatives identified in the HRFMP in 2001.
4) whether the Council has any information on potential costs and benefits of improvements to the
stopbanks outlined above.
Greater Wellington has no specific information on potential costs and benefits of improvements
for
stopbanks downstream of Ava Rail bridge, other than that contained within the Hutt River Floodplain
Management Plan and associated reports.
5) I note that the stopbanks in question protect the Gear Island Water Treatment plant. Has the
council or wellington water considered the efficacy of the protection of the Gear Island water
treatment plant, or put any plans in place to improve protection from flood surges? I also note that
Gear Island is between Te Mome Stream and the Hutt River, so flooding could come from either
direction.”
The efficacy of the protection to the Gear Island Water Treatment Plant was considered, along with
other key infrastructure and private property, as part of the Hutt River Floodplain Management Plan
completed in 2001. Gear Island Water Treatment Plant is within the area protected by the stopbanks
on the true right bank of the Hutt River with the design standard of 2300 m3/s level of protection
being selected for that area.
This part of your request has been transferred to Hutt City Council, as the Water Treatment Plan is
their asset. They will be responding directly within statutory timeframes.
Page 5 of 6
If you have any concerns with the decision(s) referred to in this letter, you have the right to request
an investigation and review by the Ombudsman under section 27(3) of the Local Government Official
Information and Meetings Act 1987.
Please note that it is our policy to proactively release our responses to official information requests
where possible. Our response to your request will be published shortly on Greater Wellington’s
website with your personal information removed.
Nāku iti noa, nā
Lian Butcher
Kaiwhakahaere Matua Taiao | Group Manager Environment
Page 6 of 6
