Dredging Activities
The Whanganui River naturally carries sediment downstream. Over time, sand and silt build up in parts of the river channel and around port infrastructure, reducing water depth and making navigation more difficult.
Dredging removes this build-up to maintain safe access for vessels, support port operations, and ensure key infrastructure remains usable.
While decisions about the long-term future of the port are being considered, there remains an ongoing need for targeted dredging to keep critical areas operational and safe.
One current priority is maintaining access at the boat ramp. This work helps ensure the Coastguard can continue to launch in an emergency and that recreational users can safely launch and retrieve vessels.
Dredging is carried out in specific areas where sediment accumulation affects navigation, access, or operational requirements.
Current dredging activities are focused on:
- The boat ramp area, to maintain safe access for Coastguard and other vessel users.
- The navigation channel around Wharf 3, to maintain navigable depths.
- Areas around existing marine infrastructure where sediment build-up affects vessel access and operations.
All dredging is undertaken within the requirements of the port’s resource consents.
The material removed during dredging is primarily sand and silt that has naturally accumulated within the river.
Depending on river conditions, tides, location, and operational requirements, dredged material may be managed in different ways.
In some circumstances, material is transported and placed at designated consented disposal locations. When placed during suitable tidal conditions, the material is carried by natural river and tidal flows towards the river mouth and out to sea.
Where practical, our preference is to move dredged material to the designated disposal area, where the material is dispersed by natural river and tidal processes. In some situations, this is not possible or practical because of the location, tide, river conditions, urgency, available equipment or operational constraints.
Sidecasting is a dredging method where sediment is removed from one location and placed nearby rather than being transported to a separate disposal site. This is because sometimes sand or silt builds up in a location where it affect access, vessel movement, or use of port infrastructure. Where the issue is urgent, moving the material a short distance can quickly restore safe depth at a boat ramp, berth, slipway, channel or other marine infrastructure.
It is one of several recognised dredging techniques used in ports and waterways throughout New Zealand and internationally.
Sidecasting may be used:
- To clear a navigation channel.
- To maintain access around marine infrastructure.
- When tidal conditions make transport to another disposal location impractical.
- When urgent access needs to be restored quickly.
The method used for dredging depends on a range of factors including safety, urgency, tidal conditions, river flows, location, and operational requirements.
For example, maintaining safe access at the boat ramp can require a rapid response so that Coastguard vessels can continue to launch during emergencies and users can safely access the water.
In these situations, sidecasting can be the most practical and efficient method available.
In other locations, sidecasting may be used to reshape or maintain a navigation channel by relocating sediment a short distance away from the area requiring clearance.
Whanganui Port works with a range of river users including commercial operators, recreational boaties, emergency services, and marine businesses.
Dredging helps ensure that key infrastructure remains accessible and that vessels can continue to operate safely within the river environment.
The port recognises that dredging activity can raise questions within the community and is committed to providing information about why dredging occurs and how decisions are made.
- Follow us on Facebook for regular updates
- Email the project team – portproject@whanganui.govt.nz
