Feeding the Irrigation Demand - The Ruataniwha Water Storage Scheme

The Hawkes Bay Regional Council has been the initiator for this project which is to regulate and redefine minimum environmental flows in the Makaroro, Waipawa and Tukituki Rivers. As part of the project, irrigation water will be supplied to the Ruataniwha Plains from dam storage. The project is being led by Hawkes Bay Regional Investment Company Ltd (HBRIC), a Council Controlled Trading Organisation (CCTO). HBRIC are responsible for the 4 main work streams as follows:

• Consenting Phase. The Board of Inquiry final decision, determined via the Environmental Protection Authority (EPA), is currently subject to appeals before the High Court.
• Finance,
• Uptake - Sales of Water to irrigators, and
• Design and Build Process.

A target irrigation area in excess of 60,000 hectares on the Ruataniwha Plains is a mixture of dry alluvial river terraces and recently deposited silt loams. The scheme will be capable of servicing between 20,000 – 30,000 hectares. There are approximately 6,000 ha of existing land irrigated from a mixture of groundwater/ surface water sources.

The project includes a dam on the Makaroro River (tributary of Waipawa and Tukituki Rivers) whereby flow is captured over the winter period and released back into the river during the irrigation season. The scheme includes a river intake 20 km downstream from the dam and a distribution network of canals, pipes and pumps to provide water to farm gate. In addition the scheme allows for release of environmental flows and flushing flows.

This paper looks at the river intake, canals, pipes and mechanisms to deliver irrigation water to the farm gate. Downstream of the dam the Makaroro River joins the Waipawa River and a further 10 Km downstream of the confluence, a proposed river intake will draw allocated water from the river to feed the main distribution feed canal. The Waipawa River has significant flow variation from a mere few cumecs in summer to over 1,000 cumecs in flood. This paper looks at the considerations involved in obtaining a stable river intake and the design considerations in conveying and controlling this flow in near flat canals along the distribution network.

The author was part of the design team for a design and build consortia who are now the preferred tenderer on this significant irrigation project. The paper addresses the design carried out for the D&B tender phase and the interactions between designers, constructors and the Principal.