Avondale Residential Red Zone: Summary of Technical Information As at September Area ID: 8A, 8B 2016
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Avondale residential red zone: Summary of Technical Information as at September Area ID: 8A, 8B 2016 Purpose of this document: The following information summarises 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 Avondale residential red zone (Area 8): Area 8 (including 8A and 8B) is approximately 51 hectares in area and is located east and south of the Ōtākaro/Avon River. The area is bounded by Avonside Drive to the west, Hulverstone Drive to the north. Avondale Road and Mervyn Drive, as well as existing residential areas, define Area 8 to the east and south. Area 8 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'. Area 8 adjoins the Porritt Park Loop at its southern end, a remnant ox-bow of the Ōtākaro/Avon River. Inanga spawning sites are present in the adjoining section of the Ōtākaro/Avon River (CCC spawning site locations “Reach ID 3 and 5”). The Ōtākaro/Avon River mainstem adjacent to Area 8A 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 Has a long frontage running parallel to the Ōtākaro/Avon River from north of Porritt Park to Orrick Cres, just south of ANZAC Drive. The Ōtākaro/Avon River is a Downstream River with a 30m setback2 under 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-Catchment- Vision-and-Values.pdf In addition, Area 8 has proximity and frontage to the Porritt Park Loop of the Ōtākaro/Avon River, which is an Environmental Asset with a 7m setback. Groundwater – Median groundwater depth is typically between 0.8m and 1.6m below surface depth below surface level at present. Median groundwater depth with 1m sea level rise is predominantly shallower than 1m, and shallower than 0.5m across much of Area 8. Coastal Marine Area Outside the Coastal Marine Area. Public Facilities There are no public facilities mapped within Area 8. Avondale School and Chisnallwood Intermediate are both located to the east of Area 8. Avondale School is to be closed in 2017. 1 The Independent Hearings Panel is yet to issue a decision on Chapter 9 hence the provisions and related maps are subject to change. 2 Consent is required form the Christchurch City Council to fill, excavate or build within these setbacks. 3 The Independent Hearings Panel is yet to issue a decision on Chapter 6 hence the provisions and related maps are subject to change. 2 Reserves Area 8 adjoins Porritt Park at its southern end as well as Avondale Park to the east. Avondale Park contains a tennis court and facilities for organised sports. Porritt Park contains facilities for rowing. A smaller local/community park, Cedarwood Reserve sits just north of Area 8. A reserve following the Ōtākaro/Avon River immediately adjoins the residential red zone, along Avonside and Hulverstone Drives. Mana Whenua / A wide corridor of land running parallel to the Ōtākaro/Avon River is shown as a Ngāi Tahu Interests culturally significant zone and covers the majority of Area 8. The whole of Area 8 is also 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 Plan: No listed features. New Zealand Archaeological Association: No recorded sites. Although there are no recorded archaeological sites of Māori origin, this area is known to have been occupied by Māori and material evidence of Māori occupation has been found in this area in the past. Accordingly, there is potential for items or sites of archaeological value to be discovered. Special or Other No additional other than listed above. Features Hazards Coastal Hazard Almost all of Area 8 (with the exception of a couple of small pockets of higher land) is mapped as being subject to coastal inundation in a 1-in-50-year storm taking Coastal inundation into account sea level rise within the next 50 years. Coastal erosion is expected to Coastal Erosion be confined to the water edge. Tsunami The existing average ground elevation above perigean high tide level is 0.5m. Most of the land is within ±0.4m of these average levels. SLR = Sea Level Rise assumed to be 0.4m For more information on coastal hazards, Christchurch City Council have a web over the next 50 page dedicated to coastal hazards which can be accessed at: years and 1m over http://www.ccc.govt.nz/environment/land/coast/coastalhazards/ the next 100 years. Information on tsunami risk is available at: http://ecan.govt.nz/advice/emergencies-and-hazard/tsunami/Pages/south- american-tsunami-modelling.aspx Flooding All of Area 8 is within the proposed Christchurch Replacement District Plan Flood Management Area (200 year flood event), and approximately half of Area 8 is 3 within the High Flood Hazard Management Area (more than 1m depth in 500 year flood). Land within Area 8A contributes significantly to flood conveyance, and loss of this conveyance could exacerbate flooding elsewhere. Filling should be avoided in the flowpath between Ardossan Street / Hulverstone Drive and the river. The depth of flooding (applying a 50 year flood event model with 1m of sea level rise) indicates a depth of 0.5 to over 1.0m across most of Area 8. In a 200 year flood event, the extent of flooding over 1.0m increases across the whole area. For further information on flood hazards refer to the: ‘Flooding’ and ‘District Plan’ pages on the Regenerate Christchurch webpage. Geotechnical In Area 8 the main geotechnical constraints are thin and weak surface crust, plus in Area 8A the potential for severe area-wide lateral spreading due to its proximity to Earthquake induced the water edge. Liquefaction, lateral spreading For further information on geotechnical issues in this area refer to the following geotechnical summary: Subsidence (consolidation) http://ceraarchive.dpmc.govt.nz/documents/flat-land-geotechnical-summaries Contamination The area has mapped Hazardous Activities and Industries List (HAIL) sites for pesticides associated with horticultural land use. These activities are mapped over a large area, however much of this is expected to be relatively low-level, with some small localised areas of greater contamination. Several small HAIL sites are associated with storage tanks and workshops. The age of dwellings means that soil contamination from asbestos is possible. The area is noted on Chrsitchurch City Council shallow fill records. Eight borelogs available from within the residential red zone show no evidence of waste within the fill. Borelogs from adjacent properties (Waratah Street, Thorness Street, Cowes Street) show evidence of waste within the fill. Infrastructure Wastewater Wastewater mains are limited to a small length at the intersection of Breezes Road and Avondale Road. There are no pumping stations within Area 8, although a wastewater pumping station sits immediately east of the red zone boundary on Niven Street. Water supply A water supply main travels along part of Avondale Road and crosses over the Ōtākaro/Avon River to supply the green zone in that location. Stormwater A stormwater main travels along part of Avondale Road. There are additional management stormwater mains from Breezes Road discharging into the Ōtākaro/Avon River at the southern end of Area 8, with further stormwater mains on Mervyn Drive, Baladin Street, Chardale Street, Briarmont Street and Orrick Crescent (on the 4 residential red zone boundary) at the north eastern end of Area 8. All discharge to the Ōtākaro/Avon River. 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. Part 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.