Due to the location of Sheffield/Springfield, an alternative strategy was developed to provide water to this area and to avoid significant pumping costs. The construction of the Sheffield Irrigation Scheme enables the supply of irrigation and stockwater to approximately 30 farms in the Springfield/Sheffield area with water being delivered for the 2017/18 irrigation season.
This Scheme is physically discrete from the remainder of the CPW Stage 1 and Stage 2 infrastructure and can, therefore, be developed and operated in isolation. The Scheme takes water from both the Waimakariri and Kowai Rivers to irrigate an area of up to approximately 4,300ha.
To access this water, an intake has been constructed at the top of the Scheme and a 2.5Mw pump station transfers up to 2m3/s of water from the Waimakariri River into a 2.08Mm3 Storage Pond on the corner of Cox’s Road and SH73. In addition to this, gravity-fed water is supplied utilising the existing Selwyn District Council (SDC) stockwater network from the Kowai River. This enables, depending on the level of demand and the Storage Pond levels, water to be taken solely from one water source or both simultaneously.
From the Storage Pond, water is reticulated via a HDPE pipe network down the Canterbury Plains in a south-east direction delivering 4mm/day of water at a target minimum pressure of 3.5 bar to individual farms.
CPWL have been working with SDC to increase the efficiency and reliability of the Malvern Stockwater Scheme for all of its customers, year round. Using the CPW infrastructure to supply stockwater rather than the current open channel system will enable the closure, with full landowner consent, of a number of small lateral water races fed by the Kowai River. This frees up water for irrigation use (albeit subject to more restrictive flow conditions) which would otherwise be lost through ground infiltration and evaporation (between 70-95%). No additional water over and above what is already consented from the Kowai River is allowed to be taken from. Under the existing regime, a large amount of water must be taken from the Kowai River to ensure sufficient water reaches the extremities of the stockwater network. Alongside this, opportunities have been identified to provide raw water to the two rural water treatment plants in the area. This would improve the reliability of the existing system and ensure there is sufficient capacity to keep up with a growing town.