Waikato Region Bathymetry and Sediment Habitat Mapping

Abstract from report: Effective management of coastal resources relies on an understanding of the state of, and the impact of pressures on, the coastal marine area. This includes an understanding of the extent and condition of seabed habitat. Waikato Regional Council (WRC) is responsible for managing the coastal marine area (CMA) that extends from Mean High Water Springs (MHWS) to 12 nautical miles offshore. Habitats range from sheltered shallow estuaries to dynamic open coast beaches, intertidal and subtidal rocky reefs, and deeper water offshore marine environments. We have summarised the state of knowledge of the extent of seabed habitats within the Hauraki Gulf and the comparatively sparsely studied Waikato west coast, to provide a single habitat and bathymetry resource for the entire Waikato region CMA. This report also identifies data gaps, and is intended to be used to identify areas that may be ecologically significant, and prioritise future data collection.

This work was originally undertaken for the Waikato region east coast for the Sea Change Tai Timu Tai Pari Hauraki Gulf Marine Spatial Plan (2017) and was then extended to include the west coast of the region. The study collated available bathymetric and habitat data.

Waikato Region

Varied.

Bathymetric data collected from multiple sources, including sounding sheets, electronic navigation charts, LIDAR (WRC, 2007/8 and 2017), multibeam surveys and single beam surveys. Open source software GERRIS used to manage multiple datasets, and stored using a 2D kd-tree heirarchical database system. Rocky reef extent was mapped where possible using high resolution bathymetry and a slope analysis method. Where high resolution data not available, sounding sheets, existing habitat maps and local interviews were used to identify potential areas. Also used DOC and MFish 2011 reef layer. Intertidal rocky reefs were mapped using aerial photography. A confidence level was applied to each reef identified, depending on the certainty of the approach. Soft sediments were identified using existing quantitative sediment information including NZOI sediment charts (Bardsley, 2008), and New Zealand Regional Sediments (Mitchell et al., 1989). Also local study by NIWA provided data in Kawhia and the WRC Regional Estuary Monitoring Programme provided data for Waingaroa Harbour. Also digitised raster navigation charts. Used folk scale to classify sediment grain size. Then interpolated within GIS to create continuous sediment dataset. .

The data is incomplete, and habitats are identified using a range of data. A confidence level was applied to each reef identified, depending on the certainty of the approach.

Bathymetric data has been converted to New Zealand Transverse Mercator/New Zealand Geodetic Datum 2000, and both local vertical datums, and New Zealand Vertical Datum 2016.

Data was gathered for the Sea Change Tai Timu Tai Pari Hauraki Gulf Marine Spatial Plan (2017), and since extended to include the entire region.

Report available for download (see link below). For data contact Waikato Regional Council.

Data collection is ongoing.