Our Ideas
Reliable irrigation would allow Hurunui’s community and farmland to become more sustainable as an agricultural district. While the Hurunui River carries a lot of water to the sea, low flows are common in summer restricting irrigation and impacting on productivity. Unless excess flows can be stored in winter and drawn upon in dry periods, Hurunui farmers will continue to struggle and the community will fail to thrive.
We hope to develop a community irrigation scheme with hydro power generation based on Lake Sumner and the South Branch of the Hurunui River. The proposed scheme would irrigate approximately 42,000 hectares of land in the Hurunui and Upper Waipara catchments (see map top right).
Land which may be irrigated includes the Hawarden area, Scargill Valley, North Waipara, Masons Valley and Omihi. The project would also be able to boost irrigation currently supplied by the Amuri Irrigation Company's Balmoral Scheme, via the Hurunui River and areas adjacent to the Balmoral Scheme.
Storage is proposed in two areas:
Lake Sumner
Lake Sumner has a natural lake level variation of 3.2 metres. By installing a low, underwater weir near the outlet, we propose to use half of this variability to hold back water for storage in the months prior to irrigation, and then let it return to normal variation in winter. The lake will be held at a height that is within its natural range, but at a slightly higher average than normal during summer months. It is important to note that the lake level will not be outside its normal operating range, which will still leave some beach uncovered, and most of the lake margins unchanged.
South Branch
The proposed dam in the South Branch is NOT in the main stem of the Hurunui River, allowing the vast majority of water to flow from source to sea in the North Branch. We propose to store 111 cubic metres of water in the South Branch reservoir which will effectively create a new 7km high country lake. The maximum dam height would be 75metres above the bottom of the gorge, but only 35metres of this will be seen above ground. The sides will be an earth dam construction and will be planted to reflect the vegetation of the area. Given the remoteness of the location (35km from the nearest village and 19km from the confluence with the main stem), the dam will be unobtrusive to all but a few high country trampers.
If we are able to hold back some (not all) of the freshes that flow through the Hurunui River in spring, we expect to keep flows at normal levels, and may even boost low flows in summer. Asa result, Maori Gully will continue to see the full range of fluctuations in flow, and kayakers will still be able to enjoy their recreational pursuits.
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“The best way to ensure sustainability is to harvest water from the Hurunui River when river flows allow, and to access water from a water storage system when river flows are required for the river’s ecological needs.” Amanda Loeffen, Project Manager, Hurunui Water Project
“Farming under the current conditions isn’t that profitable. We haven’t really moved forward in the past 30 or 40 years, compared to other areas. But with irrigation we could be a highly productive area. We will have decent production rather than playing catch up all the time.” Tom Costello - Hawarden Farmer (click here for Tom's full story)
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Map showing storage sites and irrigable area- This map shows the relationship between the location of the proposed storage sites, and the potential irrigable area in Hurunui District.