Hauraki Gulf current hindcast now available

MetOcean Solutions recently completed a 26-year hindcast detailing currents and water elevation of the Hauraki Gulf. The hindcast was created using a 2-dimensional Regional Ocean Modeling System (ROMS) model run at 250 m resolution, delivering detailed depth-averaged currents and water elevation data from 1989 to 2016.

Oceanographer Phellipe Couto carried out the modelling. He explains: “The model resolves barotropic tides - the depth-averaged velocity component of the tide - as well as water levels. The Hauraki Gulf is subject to storm surges, which are driven by wind setup and atmospheric pressure. Low-pressure systems sweeping across New Zealand result in surge, which can act to amplify the tides, causing very low or high water levels."

Snapshots of modelled atmospheric and oceanic fields during a meteorological event. Upper panels show mean sea level pressure contours and non-tidal sea surface elevation provided by the New Zealand-wide grid. The animation at the bottom illustrates the depth-averaged current flow field inside the Hauraki Gulf reproduced in the high-resolution grid.

“To accurately resolve the tides and water levels inside the Gulf, we had to get the forcings right. We used high-resolution tidal constituents at the boundaries combined to fine resolution bathymetry constructed from available data, including data from nautical charts and independent surveys. We also ran a New Zealand-scale ROMS model at 5 km resolution to provide boundary conditions, allowing us to properly downscale energy and associated sea surface perturbations from the larger scales into the 250 m grid of the Hauraki Gulf model. For atmospheric forcing, we used the Hau-Moana data set - the 12 km resolution atmospheric hindcast for the New Zealand-wide domain, and the 4 km resolution Hauraki Gulf data for our higher resolution grid.”

The hindcast data was validated against water elevation data from a tide gauge at Tiritiri Matangi Island.  

“The validation shows good agreement between modelled and measured water elevation levels,” continues Phellipe. “The hindcast provides a robust baseline tide and water elevation data set for the area, outlining the prevailing conditions for use by people who operate within or manage the Gulf. The data can also be used as boundary conditions for higher resolution modelling of local areas within the Gulf, e.g. for the hydrodynamic modelling of estuaries or embayments. This study forms the foundation for developing a full 3-dimensional hydrodynamic model which will help with the management of water quality, and gain insight into transport (e.g. of larvae or sediments), dispersion, and flushing timescales in the Hauraki Gulf.”

For further information about the Hauraki Gulf ROMS hindcast, please contact enquiries@metocean.co.nz.