Linwood residential red zone: Summary of Technical Information as at October
2016
Area ID: 16
Purpose of this document:
The following information provides a summary of the local environmental values, conditions and potential
hazards. The information has been gathered using the best available technical data held by a number of
agencies and organisations. It does not identify or assess land use options or the feasibility of land uses.
The information in this document is not, and should not be interpreted as, a pre-determination,
recommendation or decision about future use. No decisions regarding the future use of this land have
been made.
Overview of Linwood residential red zone (Area 16):
Area 16 is approximately 3.4 hectares in area located on the south side of the Ōtākaro/Avon River and
Avonside Drive between Stanmore Road and Woodham Road. The eastern portion of Area 16 immediately
adjoins the grounds of Avonside Girls High School to the north. The school grounds are a large area of
publicly owned space connecting Area 14 with Area 16.
Area 16 is susceptible to a number of natural hazards, which can potentially occur either in isolation or
collectively leading to a number of adverse cascading effects. The risk from many of these hazards will
increase over time due to the accelerating effects of sea level rise. Land contamination may be an issue for
much of the site.
Location Map
1
Natural Environment and Cultural Setting and Features
Natural
Environment
Adjacent to Ōtākaro/Avon River and Tributaries identified as Site of Ecological
Significance (Site ID no. SES/LP/24) in Chapter 9 (Natural and Cultural Heritage)
Appendix 9.1.4.1 of the notified version of the proposed Christchurch Replacement
District Plan1. This site is significant because it 'supports at-risk fish species
including their migration routes, and supports indigenous vegetation and avifauna
that is representative of the Low Plains Ecological District'.
The adjacent Ōtākaro/Avon River mainstem has a significant yellow flag iris (Iris
pseudacorus) infestation. This plant is a weed that forms dense tuberous mats
excluding native wetland plants, choking wetlands, waterways and may degrade
whitebait spawning areas. The plant is designated an “unwanted organism” under
the Biosecurity Act and is identified as a pest by ECan.
Waterways
Adjacent to the Ōtākaro/Avon River, which is classified as a Downstream River with
a 30m setback2 as per Chapter 6 (General Rules and Procedures) of the notified
version of the proposed Christchurch Replacement District Plan3. Christchurch City
Council’s vision for the Ōtākaro/Avon River catchment is set out in the following
document:
http://ccc.govt.nz/assets/Documents/Environment/Water/Avon-River-CatchmentVision-and-Values.pdf
Groundwater –
depth below surface
Current median groundwater depth is predominantly deeper than 1.5m below
surface.
Median groundwater depth with 1m sea level rise is anticipated is to be
predominantly deeper than 1m below surface, except for the lower-lying area at
Linwood Ave (0.5 – 1.0m depth).
Coastal Marine Area
Outside the Coastal Marine Area.
Public Facilities
No public facilities mapped in Area 16.
Reserves
There is a narrow reserve strip running alongside the Ōtākaro/Avon River providing
access for walking and cycling.
A large local community park – Beverly Park, is located west of Area 16 on the
corner of Stanmore Road and Avonside Drive (25,462m2).
Mana Whenua /
Ngāi Tahu Interests
The whole of Area 16 is shown as a culturally significant zone and within the wider
Ngāi Tūāhuriri takiwā area of interest.
Mana Whenua and Ngāi Tahu strongly recognise the relationship of this area with
Te Ao Tūroa (Natural Environment), ecological values and the water. This area also
has significant Mahinga Kai values.
1
The Independent Hearings Panel is yet to issue its decision on Chapter 9 hence the provisions and related maps are subject to change.
A consent is required form the Christchurch City Council to build, fill or excavate within these setbacks
3 The Independent Hearings Panel is yet to issue its decision on Chapter 6 hence the provisions and related maps are subject to change.
2
2
Registered Wāhi Tapu – Tautahi Pā is in close proximity of Area 16.
Archaeology and
Heritage
Chapter 9 (Natural and Cultural Heritage) of the notified version of the Proposed
Christchurch Replacement District Plan4: A site within Area 16 forms part of a
larger heritage setting and feature (heritage item no. 45). The heritage setting and
feature relate to the Holy Trinity Church (now demolished) and graveyard located
to the south of Area 16.
New Zealand Archaeological Association: There is one recorded European
archaeological site, being the remnant of previous residential occupation.
Although there are no recorded sites of archaeological significance to Māori, this
area is known to have been occupied by Māori and accordingly, there is potential
for items or sites of archaeological value to be discovered.
Special or Other
Features
Fitzgerald Retirement Complex (Harper Gardens, Fitzgerald and Holdsworth rest
homes) located to the south of the Trinity church site is noted.
The presence of a significant grouping of mature trees in the grounds of the former
Avonside Girls’ High School is noted.
Nearby Woodham Park has a playground and aviary.
Hazards
Coastal Hazard
Coastal inundation
Coastal Erosion
Tsunami
SLR = Sea Level Rise
assumed to be 0.4m
over the next 50
years and 1m over
the next 100 years.
None of Area 16 is considered to be prone to coastal inundation or erosion when
considering a one in 50 year storm taking into account sea level rise within the
next 50 years.
The existing average ground elevation above perigean high tide level is 1.6m on
the lower terrace and 2.7m on the upper terrace. Most of the land is within ±0.5m
of these average levels.
For more information on coastal hazards, Christchurch City Council have a web
page dedicated to coastal hazards which can be accessed at:
http://www.ccc.govt.nz/environment/land/coast/coastalhazards/
Information on tsunami risk is available at:
http://ecan.govt.nz/advice/emergencies-and-hazard/tsunami/Pages/southamerican-tsunami-modelling.aspx
4
The Independent Hearings Panel is yet to issue its decision on Chapter 9 hence the provisions and related maps are subject to change.
3
Flooding
Flood modelling shows major flowpaths exist within 40m of the river edge.
Therefore fill should not be placed near the river edge, to avoid exacerbating
flooding elsewhere.
Lower terrace areas fall within the proposed Christchurch Replacement District
Plan Flood Management Area (200 year flood).
If it was proposed to raise the land above flood level in areas away from the main
flooding flowpaths, the average fill height needed would be about 0.3m. Any filling
would need to provide drainage to prevent damming of run-off from the green
zone to the south and east.
The higher terrace areas are above 200-year flood level, so no fill would be
required for flood mitigation purposes.
A 50 year flood event with 1m sea level rise may be 0.5 to 1.0m deep on the lower
terrace levels.
A 200 year flood event with 1m sea level rise may be 0.5 to over 1m deep on the
lower terrace levels.
For further information on flood hazards refer to the: ‘Flooding’ and ‘District Plan’
pages on the Regenerate Christchurch webpage.
Geotechnical
Earthquake induced
Liquefaction, lateral
spreading
Subsidence
(consolidation)
In Area 16 the main geotechnical constraint is the potential for major area-wide
lateral spreading towards the river. The most severe lateral spreading during the
Canterbury Earthquake Sequence was localised to a narrow strip along the edge of
the river.
For further information on geotechnical issues in this area refer to the following
geotechnical summary:
http://ceraarchive.dpmc.govt.nz/documents/flat-land-geotechnical-summaries
Contamination
LLUR Listed Land Use
Register
No known Hazardous Activities and Industries List (HAIL) sites, but the age of
dwellings means that soil contamination from asbestos is possible.
Infrastructure
Wastewater
There are no wastewater mains crossing or within Area 16.
Water supply
There are two water supply mains. One crossing on the Stanmore Road alignment,
connecting to Richmond, and one connecting at the Woodham Road /Linwood
Avenue junction at the red zone. There is a pumping station to the south of the red
zone on Linwood Avenue.
Stormwater
management
There are two stormwater mains crossing Area 16 north/south from Stanmore
Road and Linwood Avenue, discharging into the Ōtākaro/Avon River.
4
In June 2015, Christchurch City Council lodged a resource consent application with
Environment Canterbury for the discharge of water and contaminants to land and
water, including coastal water, from the existing and future reticulated
stormwater network. The proposal includes all reticulated networks within
Christchurch City and Banks Peninsula.
Parts of the residential red zone have been identified under the Ōtākaro/Avon
Stormwater Management Plan (appended to the resource consent application) as
being potentially developed as a detention storage basin, first flush basins and
wetland to service the adjacent existing urban area. The construction of such
facilities will depend on the outcome of decisions relating to the future use of the
residential red zone.
Submissions have closed on the application and a hearing is expected to proceed
after February 2017. Further details can be found at:
http://ecan.govt.nz/get-involved/consent-projects/cccstormwater/pages/notification.aspx
Transport
Under the new Christchurch District Plan, Avonside Drive is described as a Minor
Arterial. It travels the length of Area 16 alongside the river (noted as an area
subject to severe lateral spread above). It is noted that the length of Avonside
Drive in front of the Avonside Girls High School land is not critical for connectivity
with the wider transport network. The intersection of Woodham Road and
Avonside Drive is however critical for continuing network function and efficiency.
Avonside Drive also intersects with Linwood Avenue, a Minor Arterial at the
eastern end of the Area.
Stanmore Road is described as a Collector Road, crossing Area 16 north/south
connecting Linwood and Richmond. The alignment of the Stanmore Road bridge is
important due to the location of stormwater mains which discharge here.
5