It’s a natural process for soil to erode and be transported as sediment through rivers and streams to the coastal environment. It happens gradually every time rain falls, and in large quantities during major weather events.
This happened long before humans came along – but the rate at which sedimentation now occurs in Northland has been accelerated by land being cleared for agriculture, forestry and urban development.
More sediment going into our coastal environment can have several adverse effects on humans, and ecological values. Sediment can reduce light levels in the water, which affects plant growth, and hinder the ability of animals to find prey and avoid predators. It can also smother marine plants and animals, and cause sandy environments to change into shallow, turbid, muddy environments.
Northland Regional Council has investigated sediment accumulation rates and sources of sediment in Whangārei Harbour, Bay of Islands and Kaipara Harbour. These investigations have estimated sediment accumulation rates at those locations of between 2.4mm and 6.4 mm per year, over the past 100 years. This compares with an average sediment accumulation rate of 0.23mm per year during the past 10,000 years, prior to deforestation by humans.
This startling increase in sedimentation is consistent with increased soil erosion following large-scale deforestation. It indicates a major shift in the sedimentary regime of Northland estuaries.
We’ll use the information from these studies to make informed decisions on activities that contribute to sediment erosion, and prioritise land management initiatives to reduce erosion and sediment runoff into Northland's coastal environment.
In-water (and beach) hull cleaning
Hauling out is the preferred option for hull cleaning. In-water hull cleaning may be carried out subject to strict restrictions. You must ensure that no contaminants (marine pests or anti-fouling paint) are discharged into the coastal environment during the cleaning process.
Vessel hull antifouling cleaning and maintenance on the foreshore
Any vessel anti-fouling cleaning or maintenance on the foreshore requires a resource consent.
Hull cleaning on the foreshore can release contaminants from antifouling paint into the coastal environment.
Boat sewage is a serious risk to human and animal health and to the environment. To continue to enjoy Northland's coast and safely gather and eat kaimoana (seafood), our waters must be kept free of sewage. There are strict rules covering sewage discharges from boats in Northland waters – these apply to every type of boat or craft.
Failure to comply with the rules is likely to result in formal enforcement action.
Northland's marine pollution rules
It's illegal to discharge untreated sewage into any coastal waters:
- within all Northland harbours and in the Bay of Islands
- less than 500 metres from the high tide mark
- less than 500 metres from a marine farm
- less than 200 metres from a marine reserve.
If you suspect a boat is illegally discharging sewage, phone the Northland Regional Council's 24/7 Environmental Hotline 0800 504 639.
Stock in the coastal marine area
To help protect our important coastal marine areas, Northland rules require farmers to keep their stock out of the tide.
When stock get into tidal areas, they can pollute the water and cause real damage to important ecological environments.