What is the proposed Waitohi storage?

Waitohi is an alternative storage site to the South Branch and Lake Sumner. It is more expensive but it has been recommended by the Hurunui-Waiau Zone Committee as a location that will not cause environmental, cultural or recreational problems. If HWP can find a way to make Waitohi affordable then it will fast-track water storage for irrigation to the Hurunui-Waiau Zone.

What will Waitohi look like?

HWP is proposing a large dam in the Hurricane Gully top section of the Waitohi Valley, avoiding the inundation of farmland and homesteads on the lower terraces. This water would have to be pumped or tunnelled through the hills to the storage site from the Hurunui River below Surveyors Stream. We are investigating ways to use hydro generation to reduce the costs.

What do we mean by affordable?  

HWP wants the scheme to be affordable for all kinds of farmers, not just the ones that can afford to convert to intensive dairying. It is important from a water quality perspective that we keep nitrate loading to a minimum. It is also important to the local community that traditional ways of living can be maintained. We are currently working through the costs to the farm gae. Previous estimates of around $5000 to $6000 may need to be revisited.

What happens if it is not affordable?

The Hurunui-Waiau Zone Committee has already endorsed water storage as a necessity. If the scheme is too expensive, we will not be able to sell the water and the scheme will fail. That is not an option. The Government funding is designed to support a commercial scheme for uptake risk in the early years and is not seen as a subsidy. We therefore see it as crucial that we keep South Branch and Lake Sumner available as fall-back options in case we cannot find a way to make the Waitohi scheme work. This is also endorsed by the Zone Committee.

What is happening now?

HWP is going through extensive investigations and engineering work to optimise the scheme on Waitohi. We have hydro and geotechnical engineers testing various options to determine the most promising solution. We are also testing the ecological effects to make sure that there are no surprises. We should have a firmer idea of the costs by October 2011. We are planning to visit landowners in the Waitohi by this date to share our information.

Are dairying interests behind the project?

Dairying is not driving the project. Less than 25% of Hurunui farmers surveyed say they would consider converting to dairy, with another 20% indicating they may use irrigation to grow crops to support dairying. It is likely that only a part of the Hurunui District will be suitable for dairy farming due to topography and soil types. It is more likely that farmers will use the ability to irrigate to diversify their operations. We are investigating the optimal range of crops that are suitable for the various soil types in the area.

What about the impact of intensive farming?

There is no doubt that we need strict controls on practices for all kinds of farming. The advantage of a global scheme like the HWP proposes is that all the water will be metered, measured and monitored. If farmers do not follow the “Best Practices Agreement” then HWP will have the ability to shut off the water. The idea of measurement and soil moisture balance monitoring is going to make the application of water as efficient as possible, and the adoption of sustainable practices paramount. Whether the land is used for dairying or higher value crops, the principles are the same.

What volume of water from South Branch and Lake Sumner is needed to irrigate the proposed 42,000 hectares?

Originally we looked at storing around 27million cubic metres of water for part of the year in Lake Sumner. Lake Sumner has a natural variation in lake level which could be controlled by use of a control gate at the outlet. Storage in Lake Sumner would be supplemented by a dam on the South Branch of the Hurunui River, holding 111 million cubic metres of water. How much water we need depends on several factors, including how much we are able to store, the river's minimum flows and the minimum size of reservoir needed to meet demand. If we are able to hold back some (not all) of the freshes that flow through the Hurunui River in the spring, it is possible the Hurunui's flow will be maintained at close to normal flows, and we may even be able to supplement some of the adjacent rivers that are currently struggling. Storing water in Lake Sumner and South Branch is now being considered alongside another HWP proposal based on the Waitohi River.

Why the combination of Lake Sumner and South Branch?

Neither South Branch nor Lake Sumner alone could irrigate the 42,000 hectares of land that has been identified in the irrigable area. The combination of the two is greater than the sum of each as they are supplied by water from two different sources and therefore give greater reliability. It was hoped that a combination of the two sites effectively reduces the environmental effects on both as we are able to reduce the total volume stored at each. For example, incorporating Lake Sumner storage means that the South Branch reservoir is full at least 50% of the time, minimising the effects of draw down. Even at its lowest point, reached once every ten years, the South branch reservoir maintains a full 5km length of water. Likewise, the addition of South Branch enables us to reduce the volume of storage on Lake Sumner so that lake levels are kept within normal ranges and its margins are minimally affected. Feasibility research into the Waitohi River storage site is much less advanced, but is progressing quickly to meet the Hurunui-Waiau Zone Committee's requirements.

How will fishing in the Hurunui River be affected under the South Branch/Lake Sumner option?

Flows in the lower stretches of the river, even after the intake, will be increased by several cumecs in the summer months. Depending on the final Environment Canterbury recommendation for Variation 8 of the NRRP, the use of storage allows flows to be at least the same as today, and up to 3 cumecs higher in January and April. This will encourage fish passage when the river is low.

Will there be fish passage on Lake Sumner to allow fish to spawn?

The weir on Lake Sumner is only going to be held at a maximum of 1.5 metres during the summer, and when the weir is at its highest, flows will be at least 9 cumecs. In addition to this, a narrow channel will run alongside the weir to enable fish passage at all times. The ecologists are not concerned that there will be any limitation of fish passage with the addition of the weir. Given that many of the salmonids spawn on this branch of the river, it is hoped that salmon and trout will continue to live along the whole stretch of the Hurunui River, from source to sea. Boat passage between Lake Sumner and the North Branch will be maintained at all times for kayakers, jet boats and other small boats.

How big is the proposed South Branch dam? Will it prevent fish passage?

Many people are concerned about the size of the dam on the South Branch. It is true that fish cannot climb a dam over a few metres high, and the proposed dam is 75 metres in total. However trout will naturally stock the new recreational lake above the dam, and will find spawning gravels around the Lake Mason area. They may be smaller than before, but there will be plenty of lake trout. Salmon found their way into the Hurunui River originally from other rivers in New Zealand when they were introduced into the country many years ago. It is clear that they need to live in the sea for part of their life-cycle and they usually spawn where they were introduced. However, there is more than 150km of available river for spawning either below the dam, or in the North Branch, so it is not known how many fish will be affected by the loss of the South Branch for spawning. Fish and Game have some partial data on salmon numbers, but given the small population of salmon in the Hurunui compared to other rivers, and the gaps in information about spawning in other reaches, it is not known how many fish will survive without some form of supplementation. For comparison, it is worth looking at the success that Fish & Game have had with stocking salmon at Opuha Dam and the health of the river after storage was completed.
See http://www.country-wide.co.nz/article/7717.html for the Opuha Dam story.

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