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CANALISATION OF THE CHRISTCHURCH RED RESIDENTIAL ZONE

By declaring the Red Zone the Government is going to end up as a major Christchurch landowner . It was a brave and laudable move to do what it has done. If there is a way of getting some $ back, it is worth investigating.

Canalisation offers a way of doing this....think Lake Hood, Whitianga Waterways and the Gold Coast. Lake Hood is probably the most relevant example, for the canalisation has been developed on relatively low cost land by a private trust, and not targeted at the super rich for holiday homes. The Dutch are also world authorities on working with waterways, and we can learn from them as well.

The short video adjacent by Designshop Architecture shows how canalisation can be achieved. Some of the video material has been reproduced from Koee  Olthuis of WaterStudio.nl to illustrate how one foundation can have many houses styles.

Here are some thoughts to consider:

1. Red Zone land has little commercial value as it stands. Some will be converted to green parks of various sorts or restored to wetland, but profit generated from the sale of allotments in this area can help cover the cost of canalisation and development. The physical development cost will be around the cost of conventional sub-division, but there is no or low initial land cost. A trial should be looked at.

2. Where possible the existing Avon river frontage can be left with trees and walk/cycle ways...Avonside Drive is an example. Some revetting may be necessary. The stone embankments above the Wainoni Rd bridge have come through all the quakes unscathed.

3. Some of the land in Bexley/Anzac Ave area is of little use except for wetlands and park as it is too low lying and soft.for redevelopment..

4. There is a major problem with the Avon bed being raised and narrowed in places, shrinking the flood storage capacity, and increasing flooding in the lower part of the river.  It makes sense to dredge the Avon to increase flood capacity and lessen risk from flooding and sea level rise. This can be done by a simple machine like a dredge (electric power from overhead lines) that deposits spoil in appropriate places via a moveable conveyor, from whence it can be spread further and compacted. There is already a gold dredge like this in Otago, and they have a long history on the West Coast. We aren't looking for gold, we want the tailings for fill. Avoid diesel powered excavators if possible to reduce capital cost of works and they don't work that well in water. Excavated material can be used layered and compacted on the cleared land to build up ground level. A figure of 2.0m has been mentioned by geotechnics experts. That would provide a thick enough "crust" of "good ground" that meets building codes.

5. Creating canals will assist 4 above as well as providing a new lifestyle that is not present in Christchurch. That lifestyle is "niche" but likely to appeal....a boat at your back door and a car at the front door. Pre-quake locals used to fish and whitebait the Avon at their back door. Provided boats do not have motor residues discharging to the water the Avon can actually be used a transport link and water recreation for these lucky people. Lake Hood is a template. Over a period of years Bottle Lake and Kerrs reach could become a rowing and sailing venue like Lake Hood.

6. The issue of lateral spread can be addressed by many geotechnic measures, which can be as simple as cable and geotex cloth in some circumstances. Making banks convex using this system helps to reduce lateral spreading under earthquake because the bank is in tension.

7. Canal edge allotments can be sold like Lake Hood, the inner areas reserved for conventional sub-division. Allotments do not need to be large. Parks provide local supervised recreation areas if designed properly.

8. The use of concrete caisson foundations as the Dutch construct means water's edge houses can rise and fall with tides (simple hoop mooring) and in worst case scenario of rising sea level can be moved. Services connections can be designed to be flexible, and there is an opportunity for houses to be largely independent of central grid services.

9. Roadways only need to be light construction, designed with swale drainage not stormwater drains to reduce cost and allow easier surface soakage.