Optimisation of Pump / Storage to Improve Cultural, Environmental and Economic Outcomes

Christchurch City Council is currently implementing the design and construction of new pumping, storage and pipeline infrastructure to replace existing wastewater treatment plants (WWTP’s) at Lyttelton, Governor’s Bay and Diamond Harbour, which will see all wastewater conveyed across to Christchurch City to the Bromley WWTP.

The flows from each of these locations are relatively small however include high levels of inflow and infiltration and reasonably significant projected population growth. Importantly they have flow records of variable quality. The existing WWTPs are alongside and discharge to the harbour coastline, such that the sites are constrained with difficult access. The conveyance distances from each of the WWTP’s are significant.

This combination of factors made the determination of pump rate and storage volumes a challenge, let alone determining how they would be optimised to improve cultural, environmental and economic outcomes.

This paper outlines the technical evaluation and project decision making processes adopted to increase confidence in the input information and evaluation method used to decide upon the final size of pump rates and storage volumes. The paper highlights where emphasis was placed in the decision making process in order to achieve the cultural, environmental and economic outcomes sought.