Latest News – Catchment Repair

Phase 2 sites

Tully and Johnstone landholders continue to work closely with the Wet Tropics Major Integrated Project (MIP) team to identify, design and implement treatment systems that may reduce agricultural pollutants entering local waterways.

An additional 10 catchment repair sites are progressing to the detailed design phase, including six bioreactors, two wetlands, one riparian planting, and one High Efficiency Sediment Basin (HES).

Three different bioreactor designs will be implemented:

  • In-drain bed bioreactor: Positioned within an existing cane drain, water passes through the bioreactor system daily. In times of high rainfall water will pass over the bioreactor.
  • Offline bed bioreactor: Water is redirected from an existing sub-drainage pipe into the bioreactor bed. The water passes through the bioreactor before entering the existing farm drainage system.
  • Sub-drainage pipe bioreactor: Where sand is typically placed around sub-drainage pipes to improve paddock drainage, this simple and innovative bioreactor design replaces the sand with woodchip, turning the entire area around the pipe into a bioreactor.

A workshop was held with landholders in the Tully and Johnstone basins to fine tune bioreactor designs before construction begins in August and September. We are focused on finding solutions that work for the landholder – that are not over-designed, and that fit into the farm with minimal disruptions.

The embellished wetlands will enhance or enlarge the treatment area of sites already functioning to some degree as wetlands, by improving the hydrology so that the landscape is better able to process and treat water to remove nutrients.

We rely heavily on local expertise to experiment with designs to suit the landscape and climatic conditions in the area. Landholders know this part of the world best, and the design workshops were an invaluable tool to help get the best systems in place using local knowledge.

The treatment systems will start to be monitored as soon as they are implemented. Monitoring information will help answer key questions about their functionality, value for money and feasibility for future adoption. It’s an exciting time because everything we learn here can inform future projects, and potentially be applied in other sub-catchments.

Site assessment - on the hunt for bioreactor sites

Phase 1 sites

HES Basin

The first HES Basin ever to be trialled in an agricultural setting was installed on a banana farm last year. It needed a few tweaks to get it working correctly, and data now shows it’s doing what we expected.

Monitoring currently consists of the use of in-situ sensors to record turbidity in 5-minute intervals, as well as flow and height data. We also collect fortnightly water samples. The monitoring program is being reviewed and we are investigating event sampling. We expect this will capture additional data to help understand the HES Basin’s performance.


Completion of two treatment wetlands is on hold due to a very drawn out wet season. A constructed wetland on a banana farm is just waiting for planting to be completed, and the landscape wetland on a former grazed paddock needs a considerable period of dry weather before construction can recommence.

We are collecting water samples from all of our wetland sites. From this we can set baselines and gain further understanding of how constructed wetlands establish and function over time in the Wet Tropics.


A “wall” bioreactor was installed late last year. They are challenging to monitor as ground water is extremely complex, so the team has been working hard to get water samples and hydrology data, which will help us get baseline data and to better understand how the groundwater behaves at the site.

Monitoring consists of the use of piezometers to record water levels and take groundwater samples once a week. Literature shows that bioreactors take several months to settle in, so next year’s wet season sampling data will show us how an established bioreactor functions in the Wet Tropics. 

For more information contact Suzette Argent – 0459 996 692

A constructed wetland