ASR - A Global Partner for the Sustainable Management of Coastal and Marine Resources

Raglan Research

Location: Raglan, New Zealand

Type of Project: Research / Community Outreach

ASR Projects- Raglan Research

The sewage outfall pipe and snapshots from the "licensed release strategy" effluent dispersal simulation.

Project Overview:

Several outfall dispersals were simulated using the Raglan Tidal Model (RTM). Simulations were run to highlight the differences of downstream effluent fate between licensed release strategies and those employed during storms and high traffic holiday seasons at Raglan.

Project Outcomes:

Simulations reveal the effectiveness of the Environment Waikato licensed release strategy for flushing treated wastewater discharge from the harbour. This entails releasing intermittently, timed to correspond to the evacuative abilities of an ebb tide. However, during high rainfall and/or during high-traffic holiday seasons the wastewater plant becomes overloaded and the load must be released despite tidal state. The results show that if the official discharge guidelines are adhered to (i.e. on the outgoing tide), very little of the effluent remains in the harbour. However, if discharge continues into the flood phase of the tide, sewage effluent can be widely dispersed throughout the harbour.

Additional dispersal simulations were run to replicate accidental pumping station failures. Model output reveals the downstream fate of contaminated water and provides a more detailed picture of potentially impacted bathing beaches and food-gathering beds.

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