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Moutoa Floodgates

The Moutoa Floodgates, located between Foxton and Shannon on the Manawatū River, provide vital flood protection for land in the lower reaches of the Manawatū River.

The curving reinforced concrete structure contains nine steel radial gates, each 15 m wide by 4.5 m high and weighing 15 tonnes. The gates are raised by a pulley system attached to the concrete piers and are operated by a series of electric motors. Each gate can be operated independently and standby power is available in case of electricity failure.

The gates were built in response to a 1941 flood, and were completed in 1962. When operated at full capacity, they redirect approximately 2,500m³/s of floodwater through a specially designed, 10km long floodway channel. This diversion of floodwaters protects approximately 280km2 of land in the lower Manawatū Plain from flood damage.

After more than 60 years of operation, the gates were upgraded between 2024 and 2025 to ensure they provide flood protection for decades to come. Read more about these upgrades further down this page.

Watch the video below to learn more about the Moutoa Floodgates.

Upgrade works

After over six decades of service with minimal upgrades, an investigation into the condition of the gates revealed some electrical, mechanical and structural upgrades were required to ensure effective and successful operation of the floodgates.

Upgrades began with the successful installation and switch-over to a new electrical system in October 2024. The remaining upgrades were undertaken in stages to maintain service levels as close to regular operation as possible. Flood modelling was also completed to assess potential impacts of more severe flooding and determine necessary flood contingency plans should adverse weather hit the area while upgrades are underway.

The contract for construction was awarded for $2.5 million, with 75% of that from Kānoa, central government’s Regional Economic Development & Investment Unit.
 

One of the new H-structure poles.

Above: One of the new H-structure poles.

Electrical

The overhead lines, previously spanning across the gate piers, were relocated downstream of the gates. New H-structure poles were installed by Electra on both sides of the floodway to support the approximately 200m span of conductors. This allows easier access to the piers for routine maintenance and for the installation of the upgraded motor and winch sets, which was completed in 2025.
 

Electrical System Upgrade

The motor control system has been upgraded to allow for a smoother and more resilient gate control. This upgrade also included the installation of an automatic switchover between mains and generator in the event of a power failure. 
 

Mechanical upgrade

The old mechanical components were more than 60 years old and had exceeded their design life. The new motors, winch sets and sheaves were installed in 2025, and have a 50 year design life, providing many more decades of flood resilience. The contract included detailed design and fabrication of custom parts, and was awarded by Council in August 2024.

Sheave component on floodgate.

Above: Close up of an old sheave on one of the gates, which forms part of the winch set that lifts and lowers each gate. These have since been replaced.

Above: A newly installed sheave. The wooden beams are temporarily used to stabilise the component during install, and are later removed.

Close up of winch drum, motor and gear box.

Above: Close up of an old winch drum, motor and gear box that forms part of the winch set. These components have since been replaced.

Above: Newly installed winch drum, motor and gear box.

The Manawatū River

The Manawatū River originates north of Norsewood in Tararua District, to the west of the Ruahine Range. It drains 6000 square km on its way through the Manawatū Gorge to the sea at Foxton. On this circuitous route it is joined by several major, fast flowing tributaries, both above and below the Gorge, including the Mangatainoka, Tiraumea and Mangahao Rivers and the streams of the South East Ruahines above the Gorge, together with the Ōroua, Pohangina and Tokomaru below the Gorge. 

On reaching the wide Manawatū Plain the river adjusts to a shallower gradient and meanders over the last 48 km of its journey, with a fall of just 18 cm per km. The Manawatū Plain was formed from silt carried downstream by the river. Much of this flat expanse of land is at sea level or below and consequently the area can flood easily.

Horizons continues to further climate resilience throughout the region through construction of new flood protection infrastructure and upgrades to existing infrastructure.
 

Moutoa floodway

Located on Foxton-Shannon Road, south of Ōpiki and just above Moutoa, the gates divert water from the main river into a specially designed 10km floodway that rejoins the river at Whirokino, just before Foxton Loop.

The floodway bypasses the 30 km of slow-flowing, meandering channel that can easily flood and pour water over many hectares of valuable land. It is 600m wide and is bounded on both sides by 5.5m high stopbanks.

Several features of the design prevent the floodway from being damaged by flood flows:
  • energy dissipation blocks immediately adjacent to the gates reduce the speed of the water as it comes under the gates;
  • the curved shape of the structure enables the water to fan out and spread evenly across the floodway; and
  • the floodway rises slightly away from the gates so the water has room to pool and does not gouge out a channel.