Harbour health on the improve
A new scientific survey of Porirua Harbour shows much lower sedimentation rates than those estimated five years ago.
The first comprehensive survey of the sea floor of the harbour was done in 2009 as part of the research work towards its restoration.
Last November Porirua City Council and Wellington Regional Council commissioned a five-year follow-up survey, which has been completed.
‘‘The findings are very encouraging – the survey found sedimentation rates over the past five years much lower than expected,’’ said councillor and Te Awarua-o-Porirua Harbour and catchment joint committee chairwoman Bronwyn Kropp.
The study found the sedimentation rate for the Onepoto and Pauatahanui arms of the harbour was 2mm per year on average.
That is significantly lower than those calculated for the 1974-2009 period, but consistent with other sedimentation observations by Wellington Regional Council.
‘‘While this is good news for the past five years, caution is required when interpreting these rates,’’ Kropp said.
‘‘These new rates will be a combination of natural variations and a lack of major storms over the past five years that would normally deliver more sediment to the harbour. ‘‘But the result is heartening.’’ The Porirua Harbour Trust recently released a positive annual scorecard for the harbour and last year’s Guardians of Pauatahanui Inlet cockle survey was also encouraging.