SUSTAINABLE
MANGAWHAI
THE SUSTAINABLE MANGAWHAI PROJECT.
The harbour lies at the heart of the Mangawhai community. It underpins the growth of our town, the well-being of its residents and businesses, and its appeal to holidaymakers. It also
supports significant biodiversity, including regionally and nationally important seabird populations.
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The Community Survey undertaken by Mangawhai Matters in 2021 confirmed that for both residents and visitors, the significance of the coastal environment was overwhelming. The character of the town is shaped by the physical environment.
Mangawhai Matters Society Inc looking into the future of Mangawhai Harbour, the threats it faces, and how these might be managed in the future. The first of these are published below.
Stage One - Scoping the Issues
Mangawhai Harbour and Spit
Published October 2023
(Corrected version, 14 November 2023)
The Summary Report sets out the main findings of Stage One of the Sustainable Mangawhai Project. It considers the implications of a more volatile climate and sea level rise for the harbour and spit based on the study of the coastal physical processes acting on them conducted by Dr Terry Hume.
In light of the significance of the recreational services identified with the harbour and coast, outlined in the accompanying Research Notes, the Summary Report also canvases the sorts of policy measures that might mitigate those threats. It suggests that these can be best advanced by the agencies responsible for managing the harbour working together to develop and act on a comprehensive long-term plan.
Coastal physical processes and management
Published August 2023
Mangawhai Matters is pleased to provide a comprehensive report on the coastal processes affecting our harbour and spit prepared by Dr Terry Hume, Environmental Consultant – Coasts. It identifies the threats they face, and management options for responding to them. The report covers the impact of ocean storms and currents, the dynamics of dune development and sand movement, tidal flows, bank erosion, and water quality.
Community and Economy
Visitors and Retail Spending
Published October 2023
This research note outlines retail spending in Mangawhai over the five years to March 2023. It highlights the important contribution of spending in Mangawhai stores by visitors.
July 2024 Update
The arrival of two large format stores (Bunnings and New World) combined with rapid population growth, has resulted in much more local spending. As a result, spending by visitors has dropped from 50% of all retail sales in 2019, to 42% in 2024. However, the holiday and visitors sector still accounted for $50m in turnover in the year ending March 2024, and as such remains critical to sustaining the current level of retail and personal business services available in Mangawhai.
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Read the 2024 update on retail spending here.
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Recreation in Mangawhai
Published October 2023
This research note reports on a survey undertaken in summer and autumn 2023 of visitors in Mangawhai to illustrate why they visit and holiday in Mangawhai.
Quantifying the Benefits of Visiting Mangawhai
Published October 2023
This research note looks at what it costs people visit and stay in Mangawhai as an indication of the value the place on the experience. It includes information on length of stay and size of visiting group organised by type of accommodation. It also identifies the value of second homes and dwellings with immediate access to the shoreline and its views to indicate the residential investment made to access the recreational opportunities available.
Managing our Harbour
Published October 2023
This note identifies what the agencies responsible for managing the Mangawhai Harbour and the distal spit spend on an annual basis to do so.
Stage Two (A): State of the Physical Environment
Stage Two (A) examines the current state of the physical environment and the impacts that a changing climate might have on it. Several independent studies have been commissioned to look more closely into the threats identified in the Stage One report into coastal physical processes and management.
These reports will be posted as they are completed. They cover the topography of the spit, land use and run-off in the catchment, the risks of inundation, and the character of the habitats within the harbour.
In addition, the economic analyses, set out in the Stage One Report, have been updated.
Stage Two (B) will then take the results of these studies and assess the likely consequences of changes in the physical environment for biodiversity and community well-being.
Topographic Mapping of Mangawhai Spit
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The greatest threat to Mangawhai Harbour was identified as degradation or breaching of the spit that defines and protects it. Mangawhai Matters commissioned a team of coastal mapping specialists from Auckland University to prepare a detailed map of the shoreline of the spit and its topography. This was compared with a 2018 aerial survey to identify recent changes and any threats they may impose. The results provide a basis for early management action and for ongoing monitoring.
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You can read the full Auckland University report here.
You can read the report's executive summary here.
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Mangawhai Matters has prepared a presentation based on the report. This summarises the results and identifies actions that those responsible for the spit (DOC, NRC and the MHRS) might take to lower the immediate risks.
You can read the presentation here.
December 2024
Mangawhai catchment contaminant and sediment loading
Major storms in late summer 2023 saw substantial sediment delivered from the catchment into Mangawhai Harbour, possibly a sign of things to come.
A team from the National Institute of Water and Soil (NIWA) estimated current and potential future nutrient and sediment loads delivered to Mangawhai Harbour, to assess eutrophication, E-coli, and sedimentation risks. The study considers the catchment's topography, geology, soils, and land use. It uses scientifically sound models to estimate total nitrogen (N), phosphorus (P), and E-coli loads under current and changing climatic conditions, the latter using Shared Socio-economic Pathways (SSP) scenarios.
The study indicates that current and predicted nutrient loads are unlikely to cause eutrophication in what is a well-flushed harbour. Sediment yield is predicted to be low to moderate, reflecting the catchment's physical character. The Southern and Tara arms account for most sediment load with deposition rates relatively high in Back Bay as a result.
Although nutrient loads are unlikely to be excessive, future climatic conditions and rapid urbanisation are likely to increase sedimentation risk. Even under more benign conditions, effective erosion controls and stormwater management are crucial to mitigate damaging sediment accumulation in some areas of the harbour.
The full report is available here.
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A summary is available here.
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The interactive map of land use and predicted
nutrient and sediment sources can be examined here.
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