Ashburton Lyndhurst Irrigation Scheme

WSP provided detailed regular reports to funding providers, the Ministry of Primary Industries (for the Irrigation Acceleration Fund) during design phases, and to financier BNZ during construction.

CLIENT BRIEF/PROJECT CHALLENGES

ALIL wanted to convert their aging race-based irrigation scheme to a gravity-fed pressure pipe network. The wanted to use water more efficiently, by reducing the need for on-farm pumping from races and flood irrigation to pasture.

ALIL required a trusted advisor to work with them through an extensive upgrade project over several years. ALIL is a farmer owned cooperative, so full confidence in the technical  recommendations made by WSP was essential.

Also key for ALIL was WSP's expertise in preparing and presenting regular reports to the scheme's funders to assure them that capital was being managed and spent wisely.

OUR SOLUTION

ALIL tasked WSP to:

• Investigate various possible solutions, each with different mixes of pumping, gravity-fed pipe, power generation and existing races to quantify relative costs and benefits associated with each. A key part of the investigation process was to clearly define what each shareholder required, particularly around daily precipitation requirements and type of irrigation (flood pressure).
• Manage a performance-based design and build tender. WSP advised ALIL on contractor attributes to allow them to decide on an appointment based on the proposed solution, technical design ability and their construction ability. WSP then worked closely with ALIL and the preferred contractor to find the optimised solution. We played a key role in in working collaboratively with ALIL and the contractor to ensure the combined knowledge and skills of all parties produced the best result.
• Finalise the final contract. This involved the commercial and legal review of the contract documentation as well as undertaking technical reviews of the final contractor design solution.
• Project manage the NEC3 design and build construction contract and provide onsite construction supervision.

OUTCOME/CLIENT BENEFITS

The completed scheme has allowed farmers to significantly increase their pastoral production and financial returns, with added community benefit of on-farm and downstream employment.

The pressurised water delivery has reduced reliance on pumps and the cost of expensive electricity to run them. With the increased pressure available to operate efficient pivot irrigators, wasteful flood irrigation has been discontinued. In addition, the scheme has provided improved irrigation scheduling flexibility that allows water availability to crops when they most need it.

ALIL was able to take collective responsibility for the Farm Environment Plans for the scheme's irrigators and so better manage limited available water at a catchment level during summer. The
significant capital investment has delivered a scheme with 50+ years of design life and provides a real advantage to the next generation of farmers.

LIST OF PRIMARY SERVICES

• Project management
• Concept and feasibility studies
• Economic assessments and valuations
• Scheme specimen design
• Civil and structural engineering design
• Tendering and procurement
• Construction supervision
• Integrated infrastructure commissioning

KEY FACTS

• The original scheme was constructed in the 1940s and delivered water through a race system for pasture flood irrigation.
• The new scheme covers an area of 28,000 ha and serves around 250 individual properties with a total scheme flow of 12.5 cubic metres/sec.
• 5 No. x 900mm dia. mainline pressure reducing valves installed to control pressure and flow.
• 12km of concrete lined steel (CLS) pipe of diameters 1,145mm and 1,283mm.
• 220km of high-density polyethylene (HDPE) pipe of diameters from 110mm to 1,200mm and pressures between PN4 and PN10. 
• 750,000m3 of water storage in ponds
• Hydraulic inlet structures at 4No ponds and outlets provided with mechanical brushed screens with capacities up to 3m3/sec.
• Remotely controlled SCADA system installed to measure and control flows and pressures throughout the system and at the 250 property offtakes.