This consultation covers bank stabilisation along Ashgrove Terrace to Palatine Terrace / Eastern Terrace
We received 27 submissions during the consultation period.
A report will be presented to the Spreydon-Cashmere Community Board for approval at the Community Board meeting of Friday 8 December 2017. The agenda with this report will be available on the Council website(external link) from 5pm, Tuesday 5 December 2017.
Feedback received on Ōpāwaho/Heathcote River Bank Stabilisation - Stage 1 [PDF, 384 KB]
Come and meet the team
Wednesday 15 November, anytime from 4pm to 7pm.
Boardroom, Beckenham Service Centre, 66 Colombo Street, Christchurch
Christchurch City Council (CCC) has been undertaking the Land Drainage Recovery Programme (LDRP) to reduce the risk of flooding and to fix waterways that were affected by the earthquakes. As part of the LDRP, investigations into earthquake damage along the Ōpāwaho / Heathcote River upstream of Radley Street have been undertaken.
The inspections identified a number of areas where the banks are unstable and eroding. While slumping and other instabilities have been a feature of the river for a long time, the earthquakes have accelerated this process and caused more widespread instability than would usually be present. A number of areas were identified as high priority, requiring work within the next 5 years to maintain waterway capacity or prevent further bank failure.
Funding has been obtained to address these high priority areas. The work will proceed in two stages. This first stage is currently being consulted on. The second stage are those areas which may be affected by low stop banks if these are selected to manage frequent flooding. As further approval and consultation is required for the low stop banks, work on the second stage will not take place until later in 2018.
The stabilisation works need to ensure that the drainage function of the river is improved (through additional capacity and preventing further slumping), while also ensuring that cultural, recreational, ecological, landscape and heritage values are taken into consideration. Therefore, wherever possible, waterway area has been increased by widening the channel. This enables bank stabilisation through a ‘naturalised’ bank profile (rather than hard engineering structures), and increases the capacity of the river. The work will be in keeping with the Mid Heathcote/Ōpāwaho Linear Park Masterplan, which was approved in 2009.
Different types of bank instability require different methods to address the issue. The different designs to be used along the waterway are described in detail in pages 12 to 20, and these designs are then referenced on each plan. To see what is in your area you will need to refer first to the plan, and then look for the detailed description and cross-section of each design type.
There are a number of common features throughout most
designs:
In some areas it is proposed to narrow the road and remove some bankside carparks. This allows drainage capacity
to be increased, setting aside space for footpaths and still considering the other community values.
Trees provide significant landscape and ecological values to the waterway, and many of the existing trees are providing benefits to bank stability through their roots. The intention is to retain and protect as many healthy and structurally sound trees as possible and increase the existing tree cover within the area, while maintaining stability of the river banks and not impeding water conveyance.
The potential effects of the bank stabilisation works on trees has been quantified as much as possible during the design phase of the project. As part of this, a tree survey has been undertaken to confirm the condition of existing trees and inform the project design.
Amendments to the design may be required due to unforeseen circumstances, especially during construction, which may result in additional tree removals or changes to the proposed tree planting being required.
For new tree planting, final species selection will be dependent on potential variations in site conditions, and availability of tree stock.
The key design principles are:
Extensive tree planting and landscaping is proposed as part of this project, with the intention of improving the landscape and ecology values of the area in the long term. The new plantings have been designed in alignment with the MidHeathcote River/Opawaho Linear Park Masterplan (2009) and Council’s Streamside Planting Guide, with the following aims:
The approximate number of trees to be removed, relocated and new trees to be planted include the following:
Arboricultural report - 1 November 2017 [PDF, 5.4 MB]
T1 is the most preferred bank profile, but can only be applied where there is sufficient space to cut the bank back to provide a more stable slope and also increase the waterway area. It features:
T2 is similar to T1, but due to various constraints (such as the road, or to preserve space for other assets or recreational use) the batter is steeper and so needs to be planted. It also features:
T3 is used where space constraints mean that a steeper bank is needed. It includes a small rock wall above a lower bench. This allows the waterway area to be increased (to improve flows) and the profile to be varied to match the space available. It features:
E1 is used to preserve an existing mature tree in good health, or where the bank is stable enough currently and does not require cutting back. This type is used to minimise the trees needing removal, but includes succession planting of a new tree further away from the bank to facilitate future bank stabilisation works when stability or the existing tree deteriorates. It also includes:
The following types of bank treatment are specifically designed for each location and so a typical cross-section is not able to be provided for each site. This includes gabion walls (structured rock filled baskets) and the treatment around bridge abutments.
A general description is provided of each below.
Gabion walls are proposed where there are severe space limitations due to existing assets (e.g. roads) or very steep and high waterway banks. They are also used where there are deep slope failures that extend below the river bed.
These include:
Image of Gabion Wall
Refer above for visualisations of bank stabilisation treatments and further information
Ashgrove Terrace: 77 to 85 Ashgrove Terrace
Ashgrove Terrace: 167 to 191 Ashgrove Terrace
Ashgrove Terrace: 193 Ashgrove Terrace to Barrington Street
Ashgrove Terrace: 327 Ashgrove Terrace to Colombo Street
Waimea Terrace/Hunter Terrace: Colombo Street to 25 Waimea Terrace
Waimea Terrace/Hunter Terrace: 25 to 51 Waimea Terrace
Waimea Terrace/Hunter Terrace: Tuscany Place to 79 Waimea Terrace
Sloan Terrace and Centaurus Road
Centaurus Road: 32 to 46 Centaurus Road
Centaurus Road: 48 to 60 Centaurus Road
Centaurus Road: 60 to 84 Centaurus Road
Centaurus Road: 65 Centaurus Road to Palatine Terrace
Eastern Terrace: Corson Avenue to Malcolm Avenue and Palatine Terrace
Eastern Terrace: 119 to 153 Eastern Terrace and Palatine Terrace: 24 to 42 Palatine Terrace
Eastern Terrace: 155 Eastern Terrace to Beckenham Park and Palatine Terrace: 44 to 58 Palatine Terrace
Palatine Terrace: 60 to 76 Palatine Terrace