Selwyn Rural Water Supply Reservoir 2014

Selwyn Rural Water Supply Reservoir 2014


[mt_lineheader size=’4′]Selwyn Rural Water Supply Reservoir 2014[/mt_lineheader]

Client: Selwyn District Council
CONTRACT VALUE: $385,000.00
Contract period: 1 Oct 2013 – 30 April 2014


The Contract required us to design and build a 490m3(490,000 litres) effective capacity reservoir and the associated pipework to connect in to the existing reticulation. The reservoir could be constructed either in steel or concrete with a minimum life of 50 years and had to be fit for a potable water supply.

Technical Difficulty

The St Johns Ambulance communications aerial that services the central Canterbury region is located on-site and within the corridor where the new pipe connections were to be made. The aerial needed to be protected.

No as-built information was available for the existing underground pipework facility so the location of the pipes had to be determined by pot-holing. This information also allowed us to finalise the positioning of the steel reservoir inlets and outlets as these are made at the time of pre-fabrication.

The ground conditions had low load bearing capacity. The foundations were excavated to clean clays/gravels then tested to ensure the safe bearing capacity exceeded 100 kPa (14.5 lbs per sq inch). A 700mm thick base of imported screened river gravels was constructed on which the concrete foundation pad was poured.

We retained SPIRE New Zealand Limited as structural engineers for the foundation design and Tasman Tanks to design and fabricate the reservoir in colour-steel with a heavy duty PVC liner. Bevan White, Chartered Professional Engineer, from SPIRE New Zealand signed-off the design as complying with the Building Code requirements.

Once the approved design was to hand we prepared and lodged the Building Consent application with the Selwyn District Council. We attempted to resolve several issues around land ownership which precluded the issuing of consent. The regulatory path then led us to applying for an exemption from the Building Code under a clause that allows for the construction of public utilities.

Once the approvals had been gained an order was placed for the reservoir with an 8 week lead-time, ex-Australia, to delivery and assembly. The pre-fabricated reservoir then needed to be accurately set-out on the foundation slab to ensure the inlets and outlets aligned with their respective connection points, and assembled.

The galvanised steel pipework was then fabricated on-site to marry the differing pipe diameters up and to ensure all the flanged joints properly aligned and sealed.

The reservoir and connecting pipework was sterilised in accordance with Safe Drinking Water Guidelines and then commissioned.