Moutoa Sluice Gates

Category
Engineering Work (eg road, bridge, sawmill, dam)

Description
The sluice gates form a major component of the lower Manawatu River Control Scheme, giving flood protection to 300 square kilometers of valuable rural and commercial property.

These gates, (5km from Shannon on the road to Foxton) which can divert more flood water than any similar structure in New Zealand, form part of the country’s first major river control scheme.

The Lower Manawatu River Control Scheme gives flood protection to 300km of valuable rural land, and to large parts of Palmerston North and Feilding, which could otherwise be flooded by the Manawatu River and its tributaries. The scheme includes 100 km of stopbanking on the Manawatu between the sea and the gorge, and another 120 km of stopbanking on the tributaries.

The function of the sluice-gates, completed in 1962, is to divert floodwater from the Manawatu River down a floodway 10 km long that bypasses 30km of river channel which is very winding and has too flat a gradient to carry the necessary discharge. About a third of the land protected by the scheme is dependent on the gates.

During the design event (a 100-year flood), these gates can divert 3000 m3 second which is 70% of the design flow. They have been operated at an average frequency of once in 18 months to two years for period of up to 60 hours.

The gates were subject to intensive model testing to optimize hydraulic performance and to check for possible problems with seepage, piping and uplift.

Features of construction included wellpointing on a large scale to permit the 210 m by 37 m structure to be built in dry conditions. The groundwater level was lowered 5 m, down to 2.5 m below mean sea level.

The road bridge running along the top of the structure included one of the early uses of precast post-tensioned beams.

IPENZ “Engineering to 1990” project
This item of New Zealand’s engineering heritage was recognised as part of the IPENZ “Engineering to 1990” project which the Institution organised to help celebrate the country’s sesquicentenary in 1990. A plaque was unveiled to mark the significance of this power station as part of the development of the nation.

Owner: Manawatu-Wanganui Regional Council
Engineers: Newton-King O’Dea
Contractors: Wilkins & Davies Construction Ltd

Location
5km from Shannon on road to Foxton

Region/s
Wanganui / Manawatu

Access Info
The sluice gate structure can be viewed at all times.

Nature of Engineering
Natural Hazard Protection, Infrastructure (incl. Road, water, ports)