eCoast Marine Consulting and Research recently completed a project led by eCoast Director Dougal Greer along with fellow Director Jose Borrero and Rhys McIntosh. Northland Regional Council were looking for a product that can help with decision making around consenting of stormwater discharges into the Whangārei Harbour.

eCoast developed a pollutant dispersal model to simulate stormwater release for a range of outfall scenarios. The model provided long term simulations that can be used to calculate acceptable limits for discharge concentrations for a range of contaminants at various mixing zone limits.

Interestingly, analysis of modelling results showed that the highest pollutant concentrations at the edges of the mixing zones are not simply associated with the largest rain events, rather they are a complex interaction of tidal conditions and hydrographs.

The model now provides a general framework that can be used to simulate other outfalls as the need arises.

The animation shows the dilution of stormwater runoff into Whangārei Harbour.