Mahurangi harbour under threat

A decade of harbour monitoring shows that the Mahurangi is filling up with sediment but Auckland Regional and Rodney District Councils are determined to halt the trend.

At Rodney District Council’s Strategy and Policy Committee meeting yesterday the Auckland Regional Council (ARC) released its most recent State of the Environment monitoring information. This shows that the harbour’s environment is under stress, and that sediment is thought to be the cause.

Historical research shows sediment has been entering the harbour at a fast rate for 150 years, since the original forest cover was removed. The inner Mahurangi harbour is full of silt and the outer harbour is silting up rapidly.

“If this rate continues, in a few years the Mahurangi will lose its water clarity, shellfish will die, oyster farming will be less viable, fishing and boating will be affected and it will be harder to find the clear blue water we enjoy swimming in now. Mangrove areas are likely to expand and the harbour will become more shallow and muddy,” said Eddie Grogan, ARC’s Manager Land and Water Quality.

“The good news is that the scientists also predict that the trend can be halted and even reversed, if – and it’s a big if – sediment can be stopped from running off the land at the current rate,” said Mr Grogan.

Rain can wash soil off any surface where the land is bare, including urban areas, farms, forests and roadsides. The bigger the storm, the worse the run-off and the Mahurangi area gets hit with more intense storms than the rest of Auckland region.

There are ways of significantly reducing sediment run-off, which is basically to keep vegetation on land as much as possible and to block sediment from reaching waterways, such as fencing off and planting buffers along stream sides.

“While we can’t stop the rain, we can control what happens on the land. We are deeply concerned about the Mahurangi, but we are also hopeful. We hope that the community will sit up and take notice, and that we can all work together to do everything we can to turn this situation around. The Mahurangi harbour is beautiful, and we want to keep it that way,” said Mr Grogan.

Rodney District Council’s Manager of Environmental Policy and Planning Peter Vari said the District Council was committed to addressing the issue in partnership with the ARC and the Mahurangi communities.

“We are appointing a Natural and Coastal Environment Advisor who will become our key contact person and we will be distributing information on the issue to assist people’s understanding of the issues.”

The ARC will also shortly be appointing a dedicated officer for Mahurangi. The two councils will be establishing a joint project team to co-ordinate various activities with the community.

The ARC and Rodney District Council intend to jointly develop an action plan in the coming months to work together, in partnership with the local community, to save the Mahurangi. The action plan will address not only environmental goals, but also social, cultural and economic goals for the Mahurangi community.

It is also considered that the ‘window’ for obtaining the benefits from improved catchment management is relatively short (a few years) before the situation becomes irreversible in parts of the harbour. The benefits of remedial actions may take some time to deliver the required large scale improvements, so remedial action needs to be taken as an urgent priority.

In its draft regional community plan, the ARC is proposing to put about $600,000 into kicking the project off, from July.

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