Last Updated: May 2005
The Aquatic Vegetation Cutter (AVC) is a unique workboat that uses twin bow mounted blades to shred densely matted plant material. The first AVC, known as the Cookie Cutter, was developed in Florida in the early 1970’s to deal with emergent aquatic vegetation, floating islands of vegetation and sediment, and to cut openings in shoreline and wetland areas through emergent wetland plants. A more powerful type of AVC, called the Swamp Devil, was introduced in the early 1990’s and included several engineering improvements over the earlier units.
Description
The AVC is an unusual weed control system. It is a boat with two five foot-diameter, hydraulically driven knifelike blades on the front of the hull. The blades provide propulsion through the water as well as cut and clear the vegetation. These blades spin rapidly at the direction of the operator and cut everything in the path of the vessel. Shredded vegetation is cast off to the sides by the action of the blades. The blades can be raised and lowered hydraulically, either independently or together, to give the operator flexibility when treating an area. The blades are available in a variety of configurations to best suit the application.
The boat houses a powerful diesel engine and hydraulic system, an operator's control station, and the drive blades mounted on the bow. The operator controls the flow of hydraulic fluid to the blades with simple controls. The operator can direct the blades to spin in a forward or reverse motion. The forward motion cuts anything the blades touch.
The AVC has the power to move sediment as well. This vessel can move from open water into wetland soils that support various emergent aquatic or wetland. In this way, operators can create open channels into infested areas.
Uses
This system has some application against invasive aquatic plant species in certain circumstances and has been successfully used in a variety of projects. A few of these include marsh restoration, fire protection, mosquito control, wild rice cultivation, melaleuca removal, drainage and irrigation, storm water retention pond maintenance, water hyacinth chopping, tussock removal, etc. An AVC can also cut into the hydric soil and create a channel from six to eight feet wide by three feet deep. The Swamp Devil can shred brush and chop down trees up to five inches in diameter.
The AVC can cut channels into wetland areas on lake shoreline that are infested with noxious weeds. A major problem with some species of aquatic invasive species is the loss of wetland habitat for waterfowl and fur bearing animals. These species form a dense vertical wall along infested shorelines that these animals cannot penetrate. Such plant beds cannot be used for nesting by many species of ducks that would use native wetland plant communities in these locations. The AVC is one system that can cut channels into this weed mass and open up areas for nesting and bird access.
Operational Considerations
The AVC has application against some invasive species when there are extensive infestations that need to be reduced very rapidly in an aquatic or wetland area. It is often used to open areas in heavily infested wetlands and shoreline to improve nesting habitat and waterfowl access. The AVC’s ability to penetrate thick growth and remove both the plant material and the underlying sediments allows the system to open channels into areas that would not otherwise be accessible to birds. It can also cut and remove root systems in hydric soils near the shoreline as it cuts into the banks.
The AVC does not have any type of harvesting capability; it merely cuts the mats of vegetation. There is a tendency for the plant material to be thrown by the cutting action further into the weed beds. How this spoil is handled depends on the situation. If it is a large or open water body, or if there is a reasonable flow, in-situ disposal may be acceptable. If the work is primarily parallel to the shoreline, a harvesting system may be required to support the operation by collecting and removing the chopped material.
The AVC can suspend sediments if it is working among plants in shallow water or against a shoreline. This could affect the environment and some states may require a permit. While the action may improve the habitat, the removal of hydric soils as the blades cast the material aside might be considered dredging. This activity may be subject to wetland dredge and fill regulations as a result. The operator should check with the local agencies to determine if permits are required.
AVC operations should take place well before the flower forms to ensure that this management method does not assist in the distribution of plant seeds. If the equipment is cutting plants during periods of seed production, spread of the plant can occur. The equipment should also be cleaned to ensure that the weed is not spread to the next site where work will be conducted.
Expected Results
The AVC works at an average speed of one mile per hour. It can chop over one acre per hour of heavy growth at this rate. On softer plant material, like water hyacinth, the AVC can shred more than two acres per hour. The use of containment devices, like lightweight oil spill control boom, can help improve the cutting efficiency of floating vegetation in some cases.
When clearing extensive areas of densely matted floating vegetation, some managers increase efficiency by cutting free large sections of the floating island and towing them to shore with another workboat. These manageable size mats are then extracted from the water with a clam shell.
The AVC is a very effective tool for cutting up and dispersing large mats of aquatic vegetation. It can move rapidly through these weed mats and dramatically reduce them. It is most effectively used to open established weed beds to clear areas of the plants and root systems and to cut channels into the weed beds to improve nesting opportunities.
The system will efficiently clear all vegetation that it contacts. It can also create channels up to three feet deep in shoreline hydric soils. The AVC is a useful tool for restoring an overgrown body of water back into a waterway again.
It should be noted that many invasive aquatic plants can eventually recolonize the treated areas if an ongoing weed maintenance control program of some kind is not implemented. Managers should plan accordingly for best success.
This section was prepared by Jane Daffenbach of Aquarius-System.
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