Knights Drain - proposed wetland and landscape plan

The Knights Drain project is part of the wider Land Drainage Recovery Programme (LDRP) which seeks to restore the flooding risk in Christchurch to 'pre-earthquake' levels.

Consultation has now closed

We received 16 submissions with nine respondents in general support, and five respondents supporting the plan but with some concerns.  Two respondents did not generally support the proposal. 

A report was presented to Council and approved at their meeting on Thursday 27 July 2017.

Comments received

Knights Drain feedback [PDF, 244 KB]

Why are we doing this project?

The Knights Drain project is part of the wider Land Drainage Recovery Programme (LDRP) which seeks to restore the flooding risk in Christchurch to ‘pre-earthquake levels’. The Knights Drain catchment has experienced a greater flood risk since the earthquakes due to land damage. We are proposing a scheme that will deliver the necessary storage upstream of the new pump station but also aims to improve water quality prior to discharge into the Avon River.

One way to reduce the flood risk and deliver an efficient system is to provide more storage. The area to the north west of the Pages Road and Anzac Drive intersection is proposed as a site for new flood storage ponds. The ponds will store flood water in heavy rainfall events and slowly release it back to the stormwater network when there is capacity.  This will reduce the flood risk to properties in the adjacent areas and reduce the demands on the existing pump station.  There will still be flooding of streets and properties in extreme flood events after the basin is constructed, but it will be less than what might happen today.  Overall the proposed scheme will increase the resilience of the community by reducing exposure to a range of natural hazards.

The ponds will also provide water quality treatment to the water discharging from the catchment into the Avon River, reducing sediment and contaminants in the water.

Location map

What does the preferred option look like?

To provide the required stormwater storage and water quality treatment the area will be dug out by approximately one and a half to two metres to form two ponds. Flow will be diverted into the ponds via a new connection from Knights Drain. The water will travel through the ponds where the sediment and some of the contaminants can settle out and back to Knights Drain upstream of the pump station.

The existing timber lined Knights Drain will be realigned further away from the existing properties and remain connected to provide an overflow path to the pump station in extreme events when the capacity of the ponds has been exceeded. Both ponds will remain wet at all times as the base will be below the water table. The banks of the ponds will be stabilised to prevent any increase in lateral spreading risk to the neighbouring properties. The existing Knights Pond at the north of the site will be retained and enhanced.

The proposed landscape concept for the scheme incorporates native coastal forest and floodplain plants surrounding the ponds to provide shading, support birdlife and reflect and enhance the surrounding environment. The space will be accessible to the public with a footpath and viewing platform where the public can observe the wetland and birdlife from.  Some tree removals will be required to enact the works.  A floating wetland will also be considered at the next design stage to further improve water quality.

The combined ponds and wetland will offer a range of advantages for the long-term management of storm water in the area. The design is based on a six-values approach to managing environments in Christchurch:

*  drainage

*  recreation

*  landscape

*  culture

*  ecology

*  heritage

Planting proposed in and around the new wet-pond area will extend the existing adjacent coastal wetland habitat through the addition of native coastal forest species. The forest and shrubland will be dominated by species like kahikatea and totara with an understorey of locally sourced trees and shrubs. In the future the plantings can be expected to support native bush birds like fantail, grey warbler, bellbird and kereru (NZ wood pigeon) and in the long term even some species that have been absent from the city for many years. As well as providing habitat in their own right, these plantings will also help screen the constructed wetland habitats. These habitats can be expected to support species like Australasian bittern, marsh crake, black and little cormorants and
other native wetland birds.

The proposed scheme means the Council need to acquire 13 residential properties to the north west of the intersection of Pages Road and Anzac Drive. Council already owns a number of properties within the footprint of the works. Property owners that could be affected if the proposed scheme is approved are being contacted directly by Council.

Click to enlarge.

Timeline

Construction timing will be dependent on the acquisition of the residential properties and may be staged.

New Pump Station - Anzac Drive

What are we seeking feedback on?

We would like to hear your views on the proposed ponds, landscape concept, and any ideas, feedback or concerns you may have.

This feedback will form part of reports to the Community Board and Council for final approval. The Council meeting is planned for July 2017 and all submitters will be advised of meeting details and the proposed recommendation following consultation. This will be followed at a later date by a Community Board meeting for approval of the landscape plan.