Calypso Science and OCEANUM.IO operate a national scale hydrodynamical ocean model that produces hindcasts and forecasts for all New Zealand. Those data are used to drive the OpenDrift particle model, which allows realistic simulations of bodies, objects, oil spills and in this case - sewage, to be made. Here, a constant release of numerical ‘sewage particles’ occurs at 5-min time steps, from the original start of the spill. Since 7 February, releases have been made from the long outfall pipe, several kilometres offshore, reflecting temporary restoration of the discharge system. These particles have a half life of 2.5 days, which mimics the marine degradation of the bacteria and virus load over time. All the key processes are included - advection by wind, effects on tidal and non-tidal currents, diffusion and mixing into the surrounding water.
Note: This app is made freely available for public use. It is provided for visualisation purposes only and does not replace any official guidance from the public health authorities. Please refer to https://wellington.govt.nz/ for the latest advice.