Restoration and Management of Lakes and Reservoirs - Hydro-Environmental Analysis: Freshwater Environments - page 480

17.5.4 M ecHanIcaL r eMoVaL
Mechanical removal can include (Holdren et al. 2001):

• Hand pulling

• Cutting without collection

• Harvesting with collection

• Rototilling

• Hydroraking

Hand pulling, as the name applies, is the removal of plants by hand. It can be effective particu-
larly for removing pioneer infestations and can be coupled with diver dredging to increase eficiency.
Cutting without collection can be likened to cutting grass without a bagger. It is a temporary
measure, since the grass will regrow. In addition, the cut biomass is left in the water, which may
result in increased nutrient additions and oxygen depletions.
Harvesting is cutting and removal of the material, and includes traditional barge-type harvesters
with both vertical and horizontal cutting blades, and a conveyor belt that gathers the cut material for
later ofloading or shredding (Chilton 2004; Figure 17.10).
Rototilling (also called rotovation, Figure 17.11) is equivalent to tilling a garden (Holdren et al.
2001), where a “tiller” is lowered into the water to till the sediments and the plants are typically
removed using a rake. Hydroraking is similar to a “loating backhoe” (Holdren et al. 2001), which
is used to remove roots, sediments, and other debris.

17.5.5 w ater L eVeL c ontroL
Water level drawdown is a commonly used practice in multipurpose lakes with an outlet control,
where the plants, and in particular their root systems, are exposed to conditions (hot, dry, freezing,
etc.) for a period suficient to kill them (Cooke et al. 2005). The effectiveness of this practice varies,
and Holdren et al. (2001) and Cooke et al. (2005) listed the response of a variety of aquatic plants to
drawdown. Drawdown is effective for a number of species; however, for a number of other species,
biomass increased in response to drawdown. For example, hydrilla and alligator weed were rarely
controlled by drawdown (Cooke et al. 2005) and since it is tolerant to a wide range of conditions,
drawdown may actually give hydrilla a competitive advantage over desirable native plants (Chilton

FIGURE 17.10 Example of mechanical harvesters. (From ERDC, Harvesting, USACE Environmental Research
and Development Center, Noxious and Nuisance Plant Management Information System, 2005. Available at
http://el.erdc.usace.army.mil/pmis/MechanicalControls/MechanicalControlInfo.aspx?mechID=10.)