Avonside Residential Red Zone: Summary of Technical Information As at September Area ID: 14A, 2016 14B
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Avonside residential red zone: Summary of Technical Information as at September Area ID: 14A, 2016 14B 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 Avonside residential red zone (Area 14): Area 14 is approximately 49 hectares in area and is surrounded by the loop of the Ōtākaro/Avon River to the west, north and east. To the south the area is bounded by existing urban areas across Retreat Road and Patten Street, and the site of the former Avonside Girls High School. Across the Avon River, the majority of Area 14 is surrounded by Areas 15 and 12. Area 14 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 Adjacent to the Ōtākaro/Avon River and Tributaries identified as Site of Ecological Environment 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 Ōtākaro/Avon River main stem adjacent to Area 14A 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, 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. The 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-Catchment- Vision-and-Values.pdf Three waterways are located near Bowie Place and Bracken Street, and discharge into the Ōtākaro/Avon River (Adams Invert, Cowlishaw Street Invert and Lewingtons Drain). These waterways are subject to minimum setback requirements (refer to Chapter 6 of the notified version of the proposed Christchurch Replacement District Plan)4. Groundwater – Median groundwater depth is typically between 1.0m and 2.5m below the ground depth below surface surface at present. Median groundwater depth with 1m sea level rise is predominantly 0.5 – 1.0m below the ground surface on lower terrace, and 1.5 – 2.0m below the ground surface on the upper terrace. Coastal Marine Area Outside the Coastal Marine Area. Public Facilities There are no schools, community facilities or libraries mapped within Area 14. The Area immediately adjoins the grounds of the former Avonside Girls High School to the south (note that the school is planned to be re-established on a new site). Whilst the school grounds are not red zoned, it is a large area of publicly owned space connecting Area 14 with Area 16. 1 The Independent Hearings Panel is yet to issue its decision on Chapter 9 hence the provisions and related maps are subject to change. 2 A resource consent is required from the Christchurch City Council to fill, excavate or build within this setback. 3 The Independent Hearings Panel is yet to issue its decision on Chapter 6 hence the provisions and related maps are subject to change. 4 A resource consent is required from the Christchurch City Council to fill, excavate or build within this setback. Furthermore, the Independent Hearings Panel is yet to issue its decision on Chapter 6 hence the provisions and related maps are subject to change. 2 Reserves Road Reserve runs along the Ōtākaro/Avon River bank. There are 2 local/community parks. Retreat Reserve is on the corner of Retreat Road and Patten Terrace (1304m2) and the larger Sullivan Park (10334m2) to the north of the Area with frontage to Galbraith Avenue. Retreat Reserve contains a grove of mature trees. Mana Whenua / The riparian corridor of Area 14 is identified as a culturally significant zone, whilst Ngāi Tahu Interests the whole of Area 14 is part of a 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. Archaeology and Chapter 9 (Natural and Cultural Heritage) of the notified version of the Proposed Heritage Christchurch Replacement District Plan5: There is one listed feature located on the corner of Retreat Road and Avonside Drive. This is a pump station. New Zealand Archaeological Association: The majority of the area north of Morris Street and bounded by the river banks in Area 14A is a known archaeological area being M35/615. This is the site of a 19th Century wool scour with associated rubbish dump. There are 14 recorded European archaeological sites, predominantly in Area 14A (in bend in the river). The majority of these are artefacts or remnants of previous residential occupation. Although there are no recorded archaeological sites of Māori origin, 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 No additional features other than as identified above. Features Hazards Coastal Hazard Lowest-lying parts of Area 14A (mostly around rivers edge will be subject to coastal inundation in a one in 50 year storm taking into account sea level rise within the Coastal inundation next 50 years. Coastal Erosion Riverbank edge in north-eastern part of Area 14A will be susceptible to daily tidal Tsunami influence within the next 50 years. Area 14 represents the western extent of coastal erosion due to future sea level rise in the Ōtākaro/Avon catchment. SLR = Sea Level Rise assumed to be 0.4m Combined Coastal Hazards and Impact of sea level rise: – within area impacted by over the next 50 a 1 percent annual exceedance probability inundation event with future 1.0m sea years and 1m over level rise (assuming no mitigation). Area 14, indicates approximately 60 per cent of the next 100 years. Area 14A and 30 per cent of Area 14B affected by inundation by 2115. 5 The Independent Hearings Panel is yet to issue its decision on Chapter 9 hence the provisions and related maps are subject to change. 3 The existing average ground elevation above perigean high tide level is 1.3m in Area 14A and 2.0m in Area 14B. Most of the land is within ±0.8m 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/south- american-tsunami-modelling.aspx Flooding Lower terrace areas fall within the proposed Christchurch Replacement District Plan Floor Level Fill Management Area (200 year flood). These cover a significant ARI = Average proportion of Area 14. Recurrence Interval Some small areas at the river edge and Bracken St fall within the High Flood Hazard Management Area (500 year flood and more than 1m depth). Flood models show major flowpaths exist within approximately 60 to 80m of the river’s edge for most of Area 14A. It is therefore an area of flood conveyance. Raising the land near the river edge would likely worsen flooding elsewhere. 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 0.5m. The depth of flooding for a 50 year flood event with 1m sea level rise may be 0.5 to 0.7m deep over the lower terrace. The depth of flooding for a 200 year flood event with 1m sea level rise may be 0.5m to over 1m with a greater extent of deeper water. It is noted that the higher terrace between Retreat Road and Morris Street creates higher ground influencing land drainage patterns. For further information on flood hazards refer to the: ‘Flooding’ and ‘District Plan’ pages on the Regenerate Christchurch webpage. Geotechnical Most of Area 14A is prone to severe lateral spreading, Earthquake induced For further information on geotechnical issues in this area refer to the following Liquefaction, lateral geotechnical summary: spreading http://ceraarchive.dpmc.govt.nz/documents/flat-land-geotechnical-summaries Subsidence For Area 14B this area is generally set back about 100 to 150m from the river, (consolidation) lateral spreading is less severe and the main geotechnical issue is severe liquefaction. Contamination Area 14A - Six Hazardous Activities and Industries List (HAIL) sites (landfill, concrete, dry cleaning, skin/wool processing (note reference to wool scour under LLUR Listed Land Use Archaeology above), storage tank, scrap yard, workshop, pesticide), however the Register affected area is only small.