Phragmites removal improves Hamilton Water facilities

In 2020, Hamilton Water documented that approximately 60 of its 135 stormwater management facilities (SWMFs) were being infested by Phragmites.

Phragmites, also known as European Common Reed (Phragmites australis), is an invasive perennial grass species that poses a significant threat to the functionality of SWMFs. They can grow up to five meters tall and form dense stands with up to 200 stems per square meter.

These dense stands can significantly reduce the water capacity of ponds and clog inlet and outlet drainage channels, increasing the potential for flooding during heavy rain events. Their presence in SWMFs impedes sediments from settling properly, which can degrade water quality and overall effectiveness of stormwater management.

Phragmites compete with native plant species, which can lead to a loss of biodiversity. Hamilton Water focused on the eradication of the species to restore functionality to their SWMFs and protect downstream water sources.

Hamilton Water ran into different challenges with removing Phragmites. They started with the herbicide WeatherMax (glyphosate) combined with a rolling practice to flatten the plants. Glyphosate is not approved for use over water, so the water had to be pumped out of SWMFs before application.

In 2021 an herbicide approved for use over water was introduced called Habitat Aqua (imazapyr). This provided a more effective solution with updated best management practices. Rolling and flattening the plants was found to be counterproductive as it broke the stems of the live plants and prevented the herbicide from reaching the roots. The greatest challenge of the project was the resilience and reproductive capacity of Phragmites.

The initial treatments carried out proved to be highly effective, significantly reducing the Phragmites infestation across the SWMFs.