Harvesters

Self-contained modified barges with underwater cutting blades and conveyor belts that remove material from the water column or surface and transport it to another location for disposal.

Considerations:

Water uses and functions

  • No water use restrictions
  • May be only option where herbicides are not effective or immediate removal is required
  • Fast moving water where herbicide concentrations cannot be maintained
  • In areas where herbicides cannot be applied (drinking water intakes, brackish water)
  • For plants that are not susceptible to herbicide control (lyngbya)
  • Remove masses of plants or organics from bridge pilings and flood control structures
  • Removing floating (especially drifting) masses of organic material (peat, muck)

Fish and wildlife

  • Coordinate activities around nesting and foraging activities, especially birds and alligators
  • Non-selective - removes all plant and animal species that cannot escape harvester path
  • May select for invasive plants
  • Removes slow growing native plants mixed with invasive plants like hydrilla
  • Hydrilla recovers faster from harvesting than native plants and shades them out
  • FL study: up to 32% removal of young-of-year sport fish per harvest in hydrilla
  • Studies in other states show similar results of harvesting fish and invertebrates

Control feasibility

  • Harvest rate is generally slow
  • Removes 2-8 acres of aquatic plants per day - removal rate is influenced by:
    • Plant type
      • Submersed plants more difficult to harvest than floating or emergent
      • Cutting blade and belt are well below water surface
      • Submersed plants are more difficult to see
      • Tall emergent plants like cattail are difficult to collect on conveyor
      • Woody species like willow are difficult to cut
    • Weight - aquatic plants are mostly water
      • Hydrilla weighs approximately 20 tons per acre; water hyacinth ranges from 200-800 tons per acre
      • Organic content - floating islands can be composed of peat up to four feet thick
  • Invasive water hyacinth and hydrilla expand faster than harvesters can remove them
  • Not effective in shallow water or in flooded timber reservoirs
  • Cannot reach plants where control may be important (shorelines, among trees or snags)
  • Fragments of invasive plants like water hyacinth are left for immediate recolonization
  • Can spread invasive plants like hydrilla or milfoil by creating numerous viable fragments
  • Turbidity issues possible in shallow water or when hauling muck or peat across lakes and rivers

Other considerations

  • Expenses are generally high
    • Acquisition cost of machinery
    • High maintenance
    • Operating costs
      • Invasive plants like hydrilla may require 2-3 cuts per year
      • Costs can double for each mile material is hauled within a water body
      • In-lake hauling costs can be reduced using higher speed transport barges
      • In-lake disposal sites close to harvest area reduce project cost
      • Sacrifice small area of lake bottom to stack material from large harvest area
      • Large in-lake disposal sites may provide wildlife habitat
      • May be public opposition (unsightly; odor from decaying plants)
      • Costs escalate if harvested material must be hauled to external disposal site
      • Loading and trucking expenses
      • Sealed dump trucks may be required for over-the-road hauling
      • Disposal fees may be required (rent private land, landfill)
      • Disposal site preparation and restoration costs may include:
      • leveling, water containment, spreading, drying, chipping or burning woody material, temporary road preparation and dismantling, reseeding, pave streets or driveways damaged from heavy equipment
  • Few uses for harvested material
    • Aquatic plants are mostly water (90%+)
    • Harvesting and processing costs exceed market value of any product
    • Organic material from floating islands can augment poor soil or be used as fill
  • Cost-effective for small scale projects, especially native plant removal

Examples of Feasible Control:

  • Harvest lyngbya from Crystal River where fast flowing springs and tidal action preclude herbicide use
  • Remove floating islands of herbaceous and woody vegetation and buoyant organic sediments up to four feet thick on Lake Lafayette and Orange Lake
  • Immediate removal of floating masses of plants from bridge pilings on the St Johns River
  • Maintain established trail system through multiple native plant species on Lake Tsala Apopka where several different herbicides would be required to control different plant types.

Shore-based track hoes or draglines

Machinery that lifts aquatic plants and associated organic material directly from the water and piles it along shorelines or into dump trucks for off-site disposal.

Considerations:

Water uses and functions

  • No water use restrictions
  • Usually for emergency removal of debris at bridges or flood control structures
  • More reactive vs. preventive or proactive management

Fish and wildlife

  • Few wildlife restrictions if conducting emergency removal from shore or structures
  • Coordinate activities around nesting and foraging activities, especially birds and alligators

Control feasibility

  • Harvest plant material accumulating in flood control canals and structures or against bridges
  • May need to remove material to disposal site
  • If hoe or crane is on bridge, may need to alter or shut down traffic
  • Harvest rate is generally slow
  • Best suited for emergent and woody species and thick floating masses of organic material
  • Harvest wind-blown floating tussocks, floating islands or debris from lake shorelines
  • Need access to shoreline for removal equipment
  • Harvesters or tugs may need push vegetation or organic material to track hoe or dragline
  • May raise turbidity issues in shallow water
  • Fragments or debris may drift downstream

Other considerations

  • Expenses are generally high
  • Acquisition cost and maintenance of machinery
  • Operating costs - depends on plant type and amount of suspended organic composition
  • Herbaceous vs. woody plants vs. trees
  • No suspended organic material to peat up to four feet thick
  • May need disposal site to:
    • Remove material from private property
    • Prevent material from washing back into water body

Examples of Feasible Control:

  • Floating islands and tussocks that drifted out of Lake Hancock and clogged the Peace River flood control structure were shredded to facilitate removal with a track hoe.
  • Hurricane Wilma blew floating plants and ripped up cattail onto the rim canal on Lake Okeechobee where they were removed via land-based track hoes.

Barge-Mounted Track Hoes or Draglines

Similar to harvesters except that material is lifted out of the water by grappling devices or buckets rather than conveyor belt. Applications and considerations are similar.

Considerations:

Water uses and functions

Fish and wildlife

Control feasibility

Other considerations

  • Generally more cost-effective at removing floating islands than herbaceous plants
  • Pick up woody species or trees that could jam conveyor harvesters
  • Not cost-effective for submersed plant removal

Examples of Feasible Control:

  • Barge-mounted dragline and hoes removed about 35 acres of dense floating island material (peat up to 4 feet thick, trees up to 10 inches in diameter and 50 feet tall) from boat ramps and residential shorelines and docks on Lake Pierce generated by Hurricane Charlie in 2004.

Last updated: 20 March 2012