Background to
the Morphum Layer 2022
Under the National
Policy Statement for Freshwater Management 2020 all regional councils are
required to map Natural Inland Wetlands in their region. Gisborne District
Council engaged Morphum Environmental Ltd to undertake an initial desktop-based
mapping assessment of Tairāwhiti wetlands. This assessment, undertaken between
2021 and 2022, is Council’s first step toward satisfying NPS-FM wetland
requirements, which include the creation of a geospatial inventory of all
Natural Inland Wetlands in Tairāwhiti.Methodology
The Morphum
Layer used Aerial imagery and LiDAR elevation data, as well as existing wetland
geometry databases and other geospatial data to determine indicative wetland
sites.
The wetland
assessment considered definitions and classification from the National Policy
Statement for Freshwater Management (NPS-FM) and the Wetland Types in New
Zealand document (Johnson and Gerbeaux, 2004).
Mapping effort was
focused on identifying natural wetlands rather than artificial or improved
pasture type wetlands. Wetland polygons were smoothed using the Polynomial
Approximation with Exponential Kernel (PAEK) method with a smoothing tolerance
of 20 m.
Farm ponds smaller
than 1,000 m² were not mapped, and some wetlands highly likely to fall under
the pasture exclusion criteria or former wetlands were excluded.
Approximately
3500 individual wetlands were delineated and
classified across the Motū, Waipaoa, Waiapu,
Hangaroa-Ruakituri, Uawa, Waimata, and Wharekahika-Waikura catchments.ResultsRemotely delineating and classifying wetlands is challenging due to the ecological variability and transitional nature of these ecosystems. Wetland boundaries fluctuate both seasonally and annually as changing weather conditions affect the water table and vegetation present.
As this is a
provisional assessment, not all of these sites will be wetlands under the
NPS-FM. The Morphum Layer should be viewed as showing indicative wetland
sites—a starting point for further investigation and discussion of wetland
extent, class, and wetland values. The next step is to determine which
sites meet that definition.
Data delivered by
Morphum Environmental August 2022
