Action Civil

CATEGORY 1A: Projects with a value of less than $5 million (Company turnover less than $10 million)

PROJECT: Stormwater Upgrade Otaki Beach. CONTRACTOR: Action Civil

Flood water mitigation

The Otaki Beach Stormwater project was constructed to mitigate a significant flooding issue for low-lying properties in and around Moana Street, Otaki Beach. Inundation regularly affected the area and residential properties were at risk of significant damage from large flooding events.

This upgrade contract was awarded to Action Civil in July 2015 following a tender process, and was finished in January 2017.

The stormwater network upgrade consisted mainly of a new 1200 dia RCRRJ gravity stormwater line; 900 dia GRP rising stormwater main; all inclusive of manholes; sumps carriageway and berm reinstatement and reinstatement of other associated civil works; together with the outlet into the Otaki Beach dune area.

Also included was the construction of an in-situ concrete pump station to six metres deep complete with pumps, valves, draft tubes and all other associated works. A precast concrete electrical switchroom was also required to house the complete electrical works associated with the three pumps. This pumping station has been designed to mitigate a Q100 (one-in-100-year) flood risk. Each pump is capable of pumping 1034 litres per second. This equates to over three cubic metres of water being moved per second if all three pumps are activated at once.

At the highest draw times, up to 1,555,200 litres of ground water was extracted per day to get the water tables low enough for the pump station and pipe laying excavations to be carried out and construction take place.

Over 600 metres of gravity 300mm to 1200mm concrete stormwater pipe was laid along Moana Street. This pipework contributed to the storage retention of the overall pump station.

A further 185 metres of 900mm GRP pumped rising main pipe was laid along Moana Street and up Koromiko Street to the pump station outlet.

In addition, the contract included, but was not limited to – setting out of all works, temporary trench shields, sheet piling, off-site/on-site cartage and carriageway reinstatement, together with concrete driveways and footpaths, berm reinstatement and works within protected sand dunes. Action Civil’s total contract value was $3,146,000 – undertaken over 17 months. l