Concerns about increasing mud, poor water quality in Porirua Harbour

News from Porirua Harbour Trust
The Porirua Harbour Trust has completed the third comprehensive “State of the Harbour” scorecard which reports on progress toward arresting the decline in harbour condition and returning it to a healthy and resilient state.

It is clear that the joint councils in the last few years have worked hard to put in place strategic and operational plans to arrest the state of decline in the catchment, and they should be applauded for their effort. Whether the tide has turned for the better for the harbour is still to be proven. The annual monitoring results indicate that it may take longer than thought to halt the decline.

In releasing the third annual scorecard the Chairperson of the Porirua Harbour Trust, Grant Baker stated that the key concerns are the increased level of mud in the Pauatahanui Arm, the ecological health of the harbour and streams, particularly the Porirua Stream and water quality of our swimming beaches.

Mr Baker said that the scorecard maps and assesses five indicators related to the harbour and catchment. The scores are designed to highlight changes in key aspects of harbour and catchment quality and to give an indication each year of progress against the Porirua Harbour and Catchment Strategy and Action Plan.

The five indicators reported on in the “State of the Harbour” scorecard are: Agency Action; Sedimentation; Education and Recreational Usage; Ecological Health and Waste

Mr Baker said it was pleasing to see a rating of Excellent for the rate of Sedimentation of the Onepoto Arm (subtidal), Pauatahanui Inlet (intertidal and subtidal) and the harbour overall. The ongoing work as Transmission Gully is built and the significant land development planned across the catchment will be the big test in the next few years.

Agency Action has improved in the scorecard to Good as a result of affirmative actions for the harbour and its catchment by Porirua City and Greater Wellington Regional Councils and this is to be applauded said Mr Baker.

The Annual Scorecard is extremely important said Mr Baker; over the last 20 years the harbour has become increasingly recognised for the wide range of values it has. The harbour is beautiful and more and more people want to live on its edges, or have views across the water to the surrounding hills. Many drive, cycle, and walk around the harbour while others enjoy recreational activities on the water as well as in the surrounding hills. The historic development and use of land around the harbour has however resulted in the steady degradation of values that make the harbour special.

Overall, when considering the longer term data available to the review team, the results show generally positive and progressive actions and improvement in harbour quality and condition over the last decade – with three notable exceptions:

• significantly increasing amounts of soft mud in the subtidal areas particularly in the Kakaho and Horikiri stream area where deep soft mud in the shallow sub tidal area has extended 20 – 30 metres closer to shore in the last 12 months. (Mud causes problems for harbour life as it creates conditions where oxygen and nutrients are reduced. The result is a smelly, unhealthy layer that reduces diversity of plants and sea life).

• generally poor water quality for swimming at the beaches and shellfish gathering areas and for the first time the Paremata Bridge area has been downgraded to fair.

• the recent readings across the three key streams in the catchment may indicate a decline in stream health and this is of concern longer term.

The Trust uses a review panel to consider data available from the Councils as well as the Trust’s own surveys and projects comprising Grant Baker, Chairperson of the Porirua Harbour Trust; Lindsay Gow, Trustee of the Porirua Harbour Trust; Dr John McKoy, Marine Scientist and Clive Anstey, Landscape and Resource Planner.

Overall the third “State of the Harbour” report is encouraging in respect of the plans that are in place but it may be some years before we can really say that the tide has turned for the better in restoring the harbour to a healthy state.

The full report is available on the Porirua Harbour website www.poriruaharbourtrust.org.nz

 

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