Petaluma spends $115,000 on underwater weed harvester

It’s a machine equally agile on land or sea. It’s armed with mechanical blades that whir tirelessly as they reduce huge swaths of reedy obstacles to mere chaff. It moves like a tank, turns on a dime and, like the fellow plant-rendering specialists at Husqvarna, hails from Sweden.

It’s the Truxor DM 5000 amphibious aquatic plant harvester, and it’s Petaluma’s latest weapon against the mosquito-spawning habitat that has caused a headache in the wetlands around the Ellis Creek wastewater plant.

The Petaluma City Council on Monday authorized the purchase of the $115,158 machine to clear excess vegetation growing in the 214 acres of ponds and wetlands around the plant, areas that provide another layer of treatment on top of the mechanisms of Ellis Creek. The amphibious vehicle will be able to navigate the varying depths of those areas, using a long, flat blade that can operate underwater to slice through unwanted brush.

The harvester is anticipated to be significantly more effective than contractors who have worked to remove bulrush around the perimeter levees of some of the wetlands, and will offset the associated costs, which have amounted to $81,000 since 2013, according to information from the city of Petaluma. It is also expected to lower mosquito abatement costs, which average $82,000 per year.

“The amphibious nature is really the selling point,” said Leah Walker, environmental services manager for the city of Petaluma.

Excess vegetation in the wetlands around the plant can negatively impact the treatment process by both impeding the flow of water and reducing dissolved oxygen levels in the wetlands due to decomposition. The overgrowth also complicates mosquito abatement, an ominous challenge given the discovery of West Nile virus in those mosquitoes twice in the past two years.

Petaluma’s Public Works and Utilities Department ruled out chemical and manual weed removal, along with controlled burning due to the proximity to the adjacent Kaiser Permanente campus and nearby business park. Mechanical removal was considered the best route, yet a contractor who spent several weeks on a boat-based harvester in 2010 was unable to effectively remove the plants in the more shallow areas.

Enter the DM 5000, a purpose-built machine that can both paddle through deep water and crawl through the shallows. Petaluma will purchase four attachments for the harvester - front and side blades, a rake to collect and transport cuttings and special plates to collect finer materials, Walker said.

The versatility of the apparatus could broaden its usefulness in Petaluma, Walker told the city council on Monday. The machine should arrive in Petaluma within two or three months, and will be used for three or four months per year, she said.

(Contact Eric Gneckow at eric.gneckow@arguscourier.com. On Twitter @Eric_Reports.)