The area of land that meets the criteria for spray irrigation in Robinsons Bay is 41 hectares and for drip irrigation is 64 hectares. Therefore, there is enough land in Robinsons Bay for a spray or drip irrigation scheme. A 5 kilometre pipeline from the treatment plant to Robinsons Bay would be required, with wastewater flowing by gravity.
Please see page 11 of the booklet [PDF, 15 MB] [PDF 16MB] for a map showing the areas that meet the criteria for spray and drip irrigation and spray irrigation to pasture in Robinsons Bay, and possible storage pond locations.
There are four locations where wastewater storage ponds could be constructed in the valley, and two other locations on the north and south sides of the valley. If the ponds were located in the valley, they would be able to be fed by gravity from the proposed wastewater treatment plant as it is at a higher elevation. A pump station would be needed next to the storage pond(s) to pump the reclaimed water to the irrigation area.
Below are images of the site currently and an artist’s impression of irrigation to trees in upper Robinsons Bay. This is indicative only and has not been prepared in accordance with the NZ Institute of Landscape Architects Best Practice Guide, Visual Simulations.
The current land use compromises of residential lifestyle blocks, tourist accommodation and pastoral farming developed from its rich pioneering history, with associated archaeological areas and several historic cottages. The current landscape reflects this history.
The estimated cost of a scheme for drip irrigation to trees in Robinsons Bay is $6.6 million, which is the least expensive standalone option. It is less expensive than a similar scheme in Takamātua Valley as there are better sites for storage ponds. The estimated cost for of a scheme for spray irrigation to pasture in Robinsons Bay is $7.7 million. This is slightly more expensive than the estimated cost of $7.4 million for a harbour outfall, so additional budget would be required to fund this option.
- Opportunity for beneficial reuse
- Enough suitable land for irrigation, with several potential pond sites
- Fewer land owners with whom to negotiate land acquisition, compared with Takamātua Valley
- A known landowner willing to sell an area suitable for irrigation to trees
- Most favourable soil types of the three irrigation areas being considered
- Low groundwater level, compared with Takamātua Valley
- Suitable distance from treatment plant to allow conveyance by gravity
- Least expensive standalone option – lower capital and whole-life costs; irrigation to trees is within project budget
- Reclaimed water from Akaroa is disposed in an area which is populated and does not have a reticulated wastewater system
- There would be an increased risk of instability of stream banks near the irrigation area
- The valley is prone to flooding; this would be taken into account in the design of the irrigation area and pond(s).