Reef Programme System Repair – Water Treatment Train Case Study

Mackay sugarcane grower, Shane Cowley, has been able to improve the water quality flowing into a wetland on his property by installing a treatment train’ before the water reaches the wetland and ultimately flows into Bakers Creek and the Great Barrier Reef lagoon. This project has also increased Shane’s farm water capacity for irrigation and improved aquatic connectivity for native fish species.

The treatment train approach for improving water quality requires water to pass through multiple chambers to reduce nutrients, sediments, and pesticides before the water exits into waterways. The number, size and arrangement of the basins can be specific to the land area available which allows landholders to easily retrofit a treatment train to their existing farm layout. They also provide additional benefits such as increasing irrigation capacity. A typical treatment train would include a primary sediment detention basin, a shallow Macrophyte zone and a larger basin such as a wetland to increase the detention time of the water before exiting to the waterway.

With assistance from the Australian Government System Repair Reef Programme, Shane was able to build a treatment train on his property, which drains approximately 700 ha of land. Working with Reef Catchments to design a system to fit into the available area, a 1 ML first flush detention basin was constructed to capture the first flush event. This structure is large enough to capture a 25 mm runoff event. A second flush chamber was also created, consisting of a long deep marsh (Macrophyte) zone for filtering nutrients and fine sediment from the water. A second detention chamber features a 3 ML waterhole at its end to supply irrigation water. The water then flows over a rock weir at the end of the waterhole into a wetland, ensuring cleaner re-oxygenated water entering the wetland. Additional to the treatment train, a fishway was constructed at the bottom of the wetland to improve the movement of fish between Bakers Creek and the wetland.

Monitoring at the inlet and outlet of the treatment train was undertaken in 2015 and 2016. The monitoring tested for sediment, nutrients and herbicides entering and exiting the treatment train. Water quality improvement was shown across most of the tested pollutants. Some results showed herbicide concentrations being reduced by 50 %. The most significant water quality improvement was seen when rainfall events were captured in the system and retention times were longer.

Reef Catchments worked together with Shane on this project to provide help with the system design and funding up to 50 % of the costs. The wetland has also been revegetated with native plants to restore habitat and connectivity. The project is complete however Reef Catchments will continue to monitor and assess the effectiveness of the treatment train.

Early results after the first flush wet season have showed some herbicide concentrations being reduced by 50 %. In addition to delivering significant environmental and ecosystem benefits, the ‘treatment train’ provides good operation and production outcomes. This extra water means that Shane can irrigate nearby cane blocks several more times each year and significantly increase their production, as well as improving the water quality for my wetland and the Great Barrier Reef lagoon.