Suction-assisted diving in Cayuga Lake, 2011.

Suction-assisted diving in Cayuga Lake, 2011.

Onion bags from the suction-assisted diving in Cayuga Lake, 2011.

Onion bags from the suction-assisted diving in Cayuga Lake, 2011.

Mechanical Controls

Mechanical controls are the physical removal of the plants (or root). This can be done through the processes of dredging or harvesting. 

Dredging

Dredging is when the bed of a harbor, river, or inlet is cleared by scooping out unnecessary mud, weeds, and other rubbish. In some instances, dredging can be used as a aquatic plant management  tool. It is usually most applicable to shallow waterways that are enclosed or can be contained.  

Important components of dredging that make the difference between it being helpful or harmful to hydrilla eradication are:

  • Length of time to dredge the area
  • Extent of dredging
  • Coordination of dredging components (navigation channel and FCC)
  • Handling of dredged materials (referred to as spoils)

The optimal blend with hydrilla eradication would include a shortened duration (less than 5 years as an initial estimate), bank-to-bank dredging (including bays and contributing streams),  dredging from upstream to downstream, having a large area to hold dredged materials and handing the dredged spoils long term so that the tubers can never be reintroduced to a waterway. 

Herbicides need to be used for at least three years after the dredging operation because dredging can fragment hydrilla plants and redistribute tubers, Dredging in the Cayuga Inlet may inform others considering dredging as one tool in eradicating hydrilla.

Diver-Assisted Suction Harvesting 

Hand harvesting paired with a vacuum hose is a standard removal process for aquatic plants such as Eurasian watermilfoil. The operation involves literally hand-pulling the weeds from the lake bed and feeding them to a suction hose. It requires water pumps to move a large volume of water to maintain adequate suction of materials that the divers are processing. The material placed by the divers into the suction hose along with the water is deposited into onion bags with water leaving through the holes in the bag mesh. The bags must have a large enough 'mesh' size so that silts, clay, leaves and other plant material being collected do not immediately clog the bags and block water movement. 

Diver-assisted suction harvesting has been rejected so far as a tool for removing hydrilla. For a complete assessment of this process and analysis of its effectiveness in the Inlet, see Assessment of Diver-Assisted Dredging (one of the other names for this technique). 

Last updated October 5, 2015