Pump Station PS205 is Christchurch’s largest storm water pump station with a capacity of 13 m3/s, lifting water from Horseshoe Lake to the Avon River by 3 Archimedes screws. During the Christchurch earthquakes the pump station settled approximately 150 mm, significantly reducing the return period flood event against which the pump station could pump at full capacity and consequently increasing the risk of flooding in the catchment it protects.
Assessing the feasibility of restoring or increasing lift height was challenging due to the hydraulic complexity of a screw pump, old age of equipment and difficulty in sourcing design specifications. Additional challenges in determining a preferred approach include the uncertainty around sea level rise and the future use of the Residential Red Zone surrounding the pump station.
In response to this complexity the study adopted a multi-layered approach utilizing a range of information sources and evaluation methods including:
- computation fluid dynamics modelling (CFD) to assess the hydraulic limitations and determine increase in loading with screw extension
- specialist market suppliers and Contractors to draw upon specialist industry experience and to validate CFD modelling outputs
- data research to source historical drive train component specifications
- Council operatives to gain historical knowledge
The study confirmed a lift upgrade of 0.45 m (0.3 m above pre-earthquake levels) was technically feasible. This upgrade would enable pumping at full capacity during flooding up to a 50-year return period event. It further identified that additional lift, possibly as much as 0.6 m (0.45 m above pre-earthquake levels) is likely to be feasible.
The paper outlines the assessment method, outputs, value gained from the study process and the resulting confidence gained by Council to make an informed decision on the retention and upgrading of this asset.