Pollution in coastal waters is a growing concern, affecting marine ecosystems, fisheries, and local communities. To better understand the current conditions in Wellington Harbour, we have developed an interactive map showing the distribution and movement of pollutants in near-real-time.

The map is based on hydrodynamic simulations using our 3D SCHISM model, which accounts for tides, currents, and water mixing, combined with a Lagrangian model that tracks water masses over time.

Using the slider below, you can explore the spread of the wastewater plume at different times of the day. Click on the map to view a timeseries for a specific location. The values range from 0 to 1, where 1 represents the maximum concentration at the pipe, and 0.5 indicates the plume has been diluted by half.

Using this tool, residents, researchers, and decision-makers can:

• Track the movement of pollutants hour by hour
• Identify areas of high concentration and potential environmental impact
• Support planning for mitigation or monitoring activities

Below, you can explore the map interactively. Use the time slider to move through the day and see how pollutant levels change across the harbour.

About the Data
Our model is updated daily using data from the Oceanum Datamesh platform. The map shows surface pollution concentrations. 

Lagrangian Coherent Structures ?

Have you ever noticed swirling, billowing, or circular patterns in the ocean, rivers, or sky, like these shown images below (Figure 1) ?

At first glance, these features may seem chaotic, ephemeral and unpredictable and they are indeed difficult to study with traditional modelling and observation approaches. The main reason is that trajectories of fluid parcels can be very sensitive to their initial conditions (e.g. starting on either side of an eddy), and studying individual tracers may provide unreliable estimates of the overall transport.

However, behind the complexity of individual tracer patterns, there are robust skeletons of fluid flows, termed “Lagrangian Coherent Structures" (LCS) which shape these patterns. The LCS are free from the uncertainties of single trajectories and provide a valuable framework to identify, quantify, and forecast the key transport features, in the ocean, atmosphere or any fluid. More specifically, LCS identifies regions within a fluid that exhibit the strongest attraction, repulsion, or shearing behavior over a given location and  time interval. These structures act as invisible barriers and fronts, organizing the flow into distinct regions and influencing how material, such as pollutants (plastic, oil, debris), marine organisms, or geophysical quantities (heat, salt, nutrient) move through the ocean.

LCS provides a powerful new way of looking at ocean circulation, transport and connectivity. A useful analogy is they inform on the “weather” of the oceans; identifying independent transport regions, locating dynamical fronts between them, and how they interact.