A Wai-Inu Blueprint

Hugh Blake-Manson, Infrstructure Advisor, Waugh Infrastructure Management Ltd

Murray England, Asset Manager – Water Services, Selwyn District Council

Background Selwyn District sits in the heart of the Canterbury Plains, with a deep understanding of its ki uta ki tai “mountains to sea” Arthurs Pass to Te Waihora guardianship responsibilities. Bounded by the alpine sourced Waimakariri and Rakaia Rivers, wai sustains Councils 27 rural and urban water supplies, providing over 77% of the population with over 8.8x106 m3 of potable water per annum. With 8 stream/river and 45 ground water sources, asset management practice supported by targeted capacity and renewals modelling is essential.

Research has shown Selwyn’s drinking water source reliability and quality is steadily declining (nitrate levels in 11 wells is >=3 mg/L), while demand is increasing through annual 4% population increases – particularly in Lincoln and Rolleston. Previous assessments have established that $322M is required for nitrate removal (OPEX $25.6M per annum) and $10M for fluoridation (OPEX $1M per annum). These challenges require a different approach – one that was consistent, auditable, and repeatable. A fit for future framework to capture and assess these and emerging factors is needed.