What is currently proposed?

The proposed site for the development is located approximately 20km from the coast and 7km above the railway viaduct. Any development would be outside the area of the river protected by the Water Conservation Order.

Hydro dams use the power of water to generate electricity. If constructed, the dam would create a relatively small lake approximately 13km in length in a remote area of the river. The purpose of the dam is to provide a ?head? of water 40 to 50m above current ground level. The ?head? and the flow of water through the dam would then provide the force required to generate electricity. Based on the current available information the dam would provide enough energy to power up to 27,000 average houses (approximately equivalent to the Gisborne region).

The dam would have limited storage and would generate energy generally from the river flow. Therefore, on any given day the flow out of the reservoir would be about the same as the flow into the lake. This means that no significant change would occur to the river flows currently passing the Raupunga and Mohaka townships.

How would the dam be built?

Historically most dams in New Zealand were built using earth excavated and compacted to form the main structure. A few dams, such as Clyde, were built from poured concrete using formwork. In the past two decades many dams around the world have been built using a new technology called Roller Compacted Concrete (RCC). This uses locally excavated materials ? such as gravels ? mixed with cement to form the main part of the dam. The mixed material is laid down and compacted in layers, much like you would build a road.

The proposed method of construction for the Mohaka dam is a variation of RCC. This has a number of advantages over earth or concrete dams including:

Safety during construction. Flood events during construction would be allowed to pass over the partly constructed dam without the risk of failure. This is not possible with earth dams.

Simple operation. Once built, the dam would not need large gates or a separate spillway to control flood events. Flood water would be passed over the crest of the dam along with floating debris such as wood.

Safety. The Hawke?s Bay is a seismically active area with active faults off shore from Mohaka/Raupunga and in the mountains to the west of the Mohaka River. No active faults are located anywhere near the dam or lake. However, it will be subject to shaking during earthquake events. The RCC dam proposed for the site is very stable under earthquake shaking.

Dams have been looked at for a long time on the Mohaka so what has changed?

The ability to generate electricity on the Mohaka River has been recognised since the early 1900s. Serious investigations occurred during the 1970s and late 1980s for up to three dams along the river. The initiation of the Water Conservation Order in the late 1980s resulted in these investigations being put on hold. The Water Conservation Order was finally put in place in November 2004 and allows for the possibility of a hydro dam in the area Meridian Energy is now investigating.

There are a number of reasons why Meridian Energy became interested in this project. We believe that renewable generation (hydro and wind) is the sustainable answer for New Zealand?s current and future energy needs.

The Hawke?s Bay region relies on some of its electricity being generated in other parts of the country. It therefore has a risk to its security of power supply if transmission problems occur in the region. This proposed development would improve the security of supply for Hawke?s Bay.

The Water Conservation Order allows for hydro development to be considered in the lower river and furthermore, the changes in dam construction technology described above mean that it is much more likely that this project can now be developed safely and cost effectively.

Meridian Energy also recognises that in today?s world, in addition to satisfying environmental concerns, any hydro development must offer benefits to the directly affected landowners and the local community. We have a strong track record of working with local communities including iwi. Recent initiatives in the Manawatu, the Waitaki Valley and Southland have seen the establishment of community funds to undertake projects in the local area.