Southshore residential red zone: Summary of Technical Information as at October
2016
Area ID: 1
Purpose of this document
The following information is 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 does not, and should not, be interpreted as pre-determining,
recommending or making any decisions about future uses. No decisions about the future use of this land
have been made.
Overview of Southshore residential red zone (Area 1)
Area 1 is located along the western margin of Southshore and faces the Ihutai/Avon-Heathcote Estuary. It
is approximately 15 hectares in area and is typically flat and low lying. The western margin of the area is
bounded by the eastern shore of the Ihutai/Avon-Heathcote Estuary while the residential properties adjoin
the area to the east.
Area 1 is highly 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.
Location Map
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Natural Environment and Cultural Setting and Features
Natural
Environment
Area 1 adjoins the Ihutai/Avon Heathcote Estuary and Environs Significant
Ecological Site identified as Sites of Ecological Significance (Site ID no. SES/LP/14) in
Chapter 9 (Natural and Cultural Heritage) Appendix 9.1.4.1 of the notified version
of the proposed Christchurch Replacement District Plan. This site is significant
because the estuary 'is an originally rare ecosystem that contains indigenous
vegetation communities that have been greatly reduced within the Low Plains
Ecological District, and is also of local, national and international importance in
terms of it supporting a representative assemblage of indigenous and migratory
birdlife, including 23 threatened species'.
The area is also adjacent to the Christchurch Coastal Strip (Site ID no. SES/LP/6),
although there is green zone land between the sub-area and this SES. This site is
significant because it 'supports both remnant and planted indigenous plant
communities that are representative of the Low Plains Ecological District, and
supports several species of flora and fauna that are either nationally threatened, at
risk or uncommon'.
Waterways
The site is adjacent to the Ihutai/Avon Heathcote Estuary.
Groundwater –
depth below surface
Median groundwater depth is typically between 0.9m and 1.7m below surface
level at present.
m = metres
Median groundwater depth with 1m sea level rise is shallower than 0.5m across
much of the area, and shallower than 1m across the remainder.
Coastal Marine Area
Immediately adjoining the proposed Coastal Marine Area to the west and south,
except where there is legal, unformed road between the residential red zone and
the coast.
Public Facilities
No public facilities mapped in Area 1. There is a playground at the eastern end of
Plover Street.
Reserves
Whilst there are no reserves within Area 1, it has a close relationship to the reserve
land which follows the coastline of the Spit. This includes the Spit Reserve (which is
a Scenic Reserve under the Reserves Act) Southshore Beach Park (a regional park),
South New Brighton Park and the Ihutai/Avon Heathcote Estuary Regional Park.
Mana Whenua /
Ngāi Tahu Interests
This area is recognised to have strong cultural significance with the connection to
Ihutai and the former Māori Reserve.
The whole of Area 1 falls within a culturally significant zone specifically covering
Southshore as well as being part of a wider Ngāi Tūāhuriri takiwā area of interest.It
is also part of a Statutory Acknowledgement Area - a statutory recognition defined
under the Ngāi Tahu Claims Settlement Act 1998 and applied to areas of cultural,
spiritual, historical and traditional association.
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.
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Archaeology and
Heritage
Chapter 9 (Natural and Cultural Heritage) of the notified version of the Proposed
Christchurch Replacement District Plan: No listed features.
NZ Archaeological Association: There are six listed archaeological sites within the
boundary of Area 1, with several more listed sites and one known archaeological
area in the immediate vicinity. The sites all relate to Māori occupation and more
specifically are described as containing archaeological remnants of horticulture
and middens.
The area is known to be of archaeological significance and accordingly, there is
potential for items or sites of archaeological value to be discovered.
Special or Other
Features
A legal, unformed road is present in some places along the estuary edge adjacent
to the red zone properties.
Hazards
Coastal Hazards
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.
All of Area 1 will be subject to coastal inundation in a one in 50-year storm taking
into account sea level rise within the next 50 years. Area 1A is slightly higher in this
location (this is assumed to be fill) and will be less affected by coastal inundation.
Areas 1B and 1C will be susceptible to daily tidal influence, due to sea level rise,
within the next 50 years.
It is noted that this is an area of active wave erosion and wave set-up (compared
with areas further up-stream where the erosion may be more related to the
changing water level in the river channel and salinity as a result of the tidal
influence).
Private property owners along the western side of the residential red zone have in
the past filled the land and constructed retaining walls along the estuary edge of
varying permanence.
The existing average ground elevation above perigean high tide level is 0.9m in
Area 1A, 0.6m in Area 1B and 0.4m in Area 1C. Most of the land is within ±0.2m of
these average levels.
This area has been identified as being within an evacuation sector, given its risk
from future possible tsunamis (most likely being one generated off the coast of
South America or Alaska).
The area has also been mapped as being in a tsunami inundation zone. ECan has
tsunami factual and emergency evacuation information located at:
http://ecan.govt.nz/advice/emergencies-and-hazard/tsunami/Pages/southamerican-tsunami-modelling.aspx
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Flooding
Flooding has historically occurred in this locality due to the very low land levels and
ineffective drainage after significant rain events. Under the proposed Christchurch
Replacement District Plan, all Area 1 falls within the Flood Management Area (200
year flood event). Areas 1B and 1C fall within the High Flood Hazard Management
Area (more than 1m depth in 500 year flood). Depth of flooding for 200 year flood
event with 1m SLR may be over 1m across much of the area.
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 1, the main geotechnical constraint is the potential for major area-wide
lateral spreading towards the estuary. The most severe lateral spreading during
the Canterbury Earthquake Sequence was localised to a narrow strip along the
edge of the estuary. If groundwater levels rise in future (due to sea level rise) then
this will reduce the thickness of the non-liquefying ground surface crust, increasing
the potential for liquefaction-induced subsidence in future earthquakes.
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
Area 1A = Minor ground contamination constraints exist. Rocking Horse Road
Landfill noted on the LLUR however the actual landfill area is smaller than mapped.
Landfill contents are known to be relatively inert from post-earthquake
investigations in this locality. Area 1A is noted on Christchurch City Council shallow
fill records. Review of borelogs within the vicinity shows evidence of waste in the
fill on some adjacent properties (Mermaid Place and south end of Rocking Horse
Road). There are no bore logs available for this specific area.
Areas 1B and 1C = No known pre-earthquake ground contamination concerns. Age
of dwellings means that soil contamination from asbestos is possible.
Infrastructure
Wastewater
A wastewater main travels along the boundary of Area 1 on Estuary Road, with a
further short wastewater main at the Pumping Station on Rocking Horse Road
(approximately at the mid-point of the Area 1B). This is to be replaced by a
pressure sewer system.
Water supply
The water supply main similarly, follows the alignment of Estuary Road, north of
Ebbtide Street.
Stormwater
management
There is a stormwater main on Estuary Road, with several stormwater mains
crossing the area to discharge into the Estuary between Caspian and Plover
Streets, and at the very southern end from Pūkeko Place. Stormwater discharge
points are not effectively draining after significant rain events, causing ponding
elsewhere.
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Transport
This Area is accessed from either Estuary Road or Marine Parade and then from
Rockinghorse Road. Estuary Road, at the northern end of Area 1, is classified as a
Collector Road under the new Christchurch District Plan.
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