Canterbury Strategic Water
Study (CSWS) - A Summary
Evaluating storage options . . .
• Group of 15 - 28 including individuals from Fish & Game,
local farmers, Community Development, Ngai Tahu, a
Resource Management consultant, farmers from across
Canterbury, environmentalists, Irrigation New Zealand and
Water Rights Trust, Forest & Bird, and others with an
interest in water.
• People present in personal capacity, not as representatives
• Group identifies additional options to those from Stage 2.
• Evaluate each option against 22 topics covering social,
economic, cultural & environmental impacts on 6-point
scale.
• Evaluation in three bites:
– Hurunui
– South Canterbury
– Rangitata River – Ashley River
• Based on Aqualinc identifying hydrologicallyfeasible storages that increase irrigable
area and improve reliability
• Only considered options based on major
reservoirs (>50,000,000m3) (almost all in-channel)
• Many options considered,
& rejected, by Aqualinc
All options integrate run-of-river takes with
storage:
– Run-of-river water used to meet irrigation
demand whenever possible;
– Releases from storage used to meet run-ofriver shortfall (particularly in late summer &
dry seasons).
Overall . . .
• All options have positive and negatives.
• For some Group participants, all options
are acceptable
• For some, all options are unacceptable
• Overarching concerns about
irrigation leading to
land use intensification
which means adverse
impacts on water quality
CSWS Evaluation groups
• Farmers & irrigators in majority
• Range of other interests (environment,
conservation, angling, kayaking, community
development . .)
• Few women, Maori, or people from small towns
• Limited number of people had on-the-ground
knowledge of proposed sites
CSWS Stage 3 was not
• A process with statutory standing
• A technical evaluation of water quality or
other environmental impacts
• Based on site visits
Evaluation of Hurunui options
• Range of options based on South Branch dam,
Lake Sumner and a dam on a mid-Hurunui
tributary (e.g. Mandamus).
• Group’s thinking changed through the process
with the option of managing Lake Sumner within
historical range becoming more attractive as
concerns increased about a high dam on South
Branch with loss of salmon fishery and other
adverse impacts
• A combination of managing Lake Sumner with
some other “back-up” storage (but not South
Branch dam) may allow much of the land to be
irrigated
• Aqualinc modeling results need to be revised
given proposed Hurunui River Regime Plan
Comments from interest group
discussions on Hurunui options
• Big dams not favoured, particularly on main tributaries.
On-farm storage offered as an alternative.
• Irrigation seen as intensive dairying and leading to N & P
pollution & bad bugs. Skeptical (at best) that best
practice would solve issue.
• How can this be a strategic study if one of the options –
NO DAMS – is not being considered? Some strong
opposition to dams on rivers, more irrigation & dairying.
• Irrigation seen as only benefiting farmers at a cost to the
environment with society (not the farmers) bearing the
consequences of land-use practices.
• Hurunui District mayor & councilors recognise the need
to have a strategy for water and development as part of
their long term plan.
• National Conservation order application for Hurunui
River lodged.
How the group felt about the options . .
South Branch
L. Sumner
(current rules)
(with “natural”
lake variation)
South Branch
L. Sumner
(Mosley rules)
(without var.)
South Branch
& L. Sumner
L. Sumner &
Mandamus
L. Sumner &
South Branch
L. Sumner &
Mandamus
Evaluation scale
Raised Sumner
(with “natural” var.)
(without var.)
Strongly positive
Neutral
Strongly negative
South Canterbury options
• Using only water from within area:
– Raised Opuha dam;
– Opuha dam + Opihi dam (near Fairlie)
– Pareora dam
• With Tekapo water:
– Opuha + Opihi dam (two operating ranges)
– Opuha + Tengawai dam
– Opuha + off-channel storage
– Opuha only
South Canterbury evaluation
• Very water-short area. Storage options constrained by
water availability (Opuha, Opihi, Tengawai, Pareora)
• Opuha scheme is unlikely to be able to meet demand of
its existing irrigators in all years. In very dry times, like in
1988, lake may not refill in winter/autumn & irrigation
restrictions of 3 months or more
• Tekapo water required but significant challenges:
–
–
–
–
Meridian consent;
cultural (water mixing);
environmental;
use of water for electricity generation
versus use for irrigation.
• Prefer option based on use of
Tekapo water with current Opuha
• Pareora stand alone option but
more hydrology needed
How the group felt about the options . .
Using local water only
Raised Opuha
With water from Tekapo
Opuha + Opihi 20m range
5m range
Opuha + Tengawai
Opuha + Opihi
Opuha + off-channel storage
(Stoneleigh Rd)
Pareora
Opuha only
Evaluation scale
Strongly positive
Neutral
Strongly negative
Mid-central Canterbury evaluation
• Options – Lees Valley, Wainiwaniwa Valley,
Lake Coleridge water, Stour Valley
• For some of Group all options OK, for others
none are acceptable;
• Participants see storage as critical
– Some believe major storage is only
option (economically)
– Others think smaller storages
require more consideration
• Integrated option worth considering
Lees Valley
• BIG is a positive & a negative:
– Supplies all irrigable area north of Rakaia
• Big economic benefit
• Big environmental risks
– Single solution (no CPW)
– $1 billion +
– Huge dam
• Long time for initial filling
• Significant impacts on
Waimakariri and Ashley Rivers
Waininaniwa Valley
• Option evaluated similar to CPW except
water not restricted to Selwyn area (could
use water north as well)
• Evaluation echoed concerns and
advantages expressed in media and
letters to newspapers
• More immediately “do-able” than Lees
Valley
Lake Coleridge
• Trustpower provided limited information, on a
confidential basis, on an option they are scoping
• Diverts water from Lake Coleridge for new
power generation & water to north & south
(siphon) for irrigation
• Non-compliance with Rakaia WCO a major
hurdle even though
– Operates within consent conditions for Harper,
Wilberforce and Coleridge lake levels
– Likely little impact on Rakaia flows below Gorge
• Requires other storage – Coleridge storage able
to improve short-term reliability of supply but not
dry-year reliability
Stour Valley
• Water diverted from South Ashburton to reservoir in
Stour Valley
• Rakaia and Rangitata River takes
• Utilises RDR & BCI infrastructure (with changes to get
water south of Ashburton River)
• Concerns about impacts on wetlands, iconic lakes &
landscape in/near Stour valley (area recommended for
World Heritage status)
• Adverse impacts on Ashburton River flows (though may
be able to improve flows in lower river)
“No major storage” option
• Group had an initial discussion of the impacts if
there was no new (major) water storage in midcentral Canterbury:
– Irrigation development would stop, probably contract
– Farmers increasingly struggle to meet market
expectations (time- and product-specific)
– Rural economy decline (with flow on impact on rural
towns & Christchurch) and impact on social
infrastructure
– Loss of opportunities to use releases from storage to
improve river ecosystems (as done in Opuha)
– Reduced environmental impacts/risks (stop land
intensification & reduce new run-of-river takes) but
extent debated
How people felt about the options
Lees Valley
Lake Coleridge
No storage
Waianiwaniwa Valley
Stour Valley
Strongly
positive
Neutral
Strongly
negative
An integrated option
• At the last meeting of the mid-central
Group, an integrated option was proposed
to:
– provide new irrigation
– improve low flows and flow variability in most
rivers
– only require one new storage reservoir
– supply water south of Rangitata, if possible
• Aqualinc has modelled initial results
An integrated option
For the area from Ashley River
to Rangitata River an option
that:
– provides water for significant new
irrigation
– improves low flows and flow
variability in most rivers
– only requires one new storage
reservoir
– supplies water south of
Rangitata, if possible
Esk R
L Coleridge
X
X
run-of river takes
Reservoirs/lakes
X
X
X
Lees Vly
Ashley Gorge
Head race – schematic only
RDR + BCI
141,000ha irrigable area
X X
Lake filling time
X
Meeting
water
demand
CRUNCH issues
CHALLENGES to be worked throu
Where to . ..
• Are we close?
• Could we work together to find
innovative solutions for Canterbury’s
future prosperity that use water wisely
for primary production with
environmental gains . . . .