A trial of an unmanned aerial vehicle (UAV) is being undertaken by Seqwater for the management of aquatic weeds on its lakes.

The innovative approach to treating floating aquatic weeds was initially trialled at Somerset Dam last month.

Seqwater Chief Executive Officer, Peter Dennis, said the trial sites were selected based on difficulty to access the weed infestations by boat or shore.

“Some aquatic weeds are notoriously difficult to access, located either in between dead trees, under paperbark swamps or in shallow water. The location of these weeds has meant traditional treatment methods, such as boat-based or land-based spraying, could not be readily used.

“Managing difficult infestations requires more effort – staff may have to wade through water or use canoes to reach the weeds. In comparison, the UAV can be operated from the shoreline or a boat. It is flown remotely by a licensed pilot who is assisted by a spotter.

“The craft can carry up to 23kg, or 16 litres of herbicide at a time, and deliver a swath of herbicide 3.2m wide. Depending on the density of weed infestation and required coverage rates, a single tank of herbicide can last up to an hour,” said Mr Dennis.

Mr Dennis said there were three main species of floating aquatic weed infestations found in Seqwater drinking water storages, Salvinia, Water Lettuce and Water Hyacinth.

“The type of weed and abundance of infestation is predominantly dependent on seasonal influences and inflows following rain. The rate of growth increases over summer, while floodwaters can bring new weeds into the dam.

“Under favourable conditions, some species of aquatic weeds can double in size every four to five days. Floating aquatic weeds can have a number of negative impacts on water quality, including depleting dissolved oxygen levels and increasing nutrient loads within the lake.

“We are monitoring treated infestations to determine the success of the spraying. Based on the results, we will look to trial the drone again in September or October when the weather is warmer and the plants are actively growing.

“There is a great potential for the use of drones for herbicide application for both aquatic and terrestrial spraying. I look forward to learning more about their benefits for Seqwater,” said Mr Dennis.

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