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Stump Removal and Sprout Prevention
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The establishment and control of proper vegetation is an important part of dam maintenance. Properly maintained vegetation can help prevent erosion of embankment and earth channel surfaces and aid in the control of groundhogs and muskrats. The uncontrolled growth of vegetation can damage embankments and concrete structures and make close inspection difficult.
Tree and Brush Hazards
Trees and brush should not be permitted on embankment surfaces or in vegetated earth spillways. Extensive root systems can provide seepage paths for water. Trees that blow down or fall over can leave large holes in the embankment surface that will weaken the embankment and can lead to increased erosion, as is the case in the failed earth embankment dam shown here. Brush obscures the surface limiting visual inspection, providing a haven for burrowing animals, and inhibiting the growth of grass vegetation. Tree and brush growth adjacent to concrete walls and structures may eventually cause damage to the concrete and should be removed.
Stump Removal and Sprout Prevention
Stumps of cut trees should be removed so vegetation can be established and the surface mowed. Small stumps may be entirely removed if removal does not require extensive excavation into the embankment which could compromise the structural integrity of the dam. If the stump is of sufficient size where complete removal would require significant excavation into the embankment, then the stump should be ground down to about 6 inches below the surface. All other woody material should also be removed or ground down to about 6 inches below the ground surface. The cavity should be filled with well-compacted clay soil with a surface dressing of top soil to promote a vigorous grass cover.
Stumps of trees in riprap should be cut as close to the rock layer as possible and then chemically treated so they will not form new sprouts. Certain herbicides are effective for this purpose and can even be used at water supply reservoirs if applied by licensed personnel. These products should be applied in strict coherence with local and state herbicide regulations. Other instructions found on the label should be strictly followed when handling and applying these materials. Only a few commercially available chemicals can be used along shorelines or near water.
Embankment Maintenance
Embankments, areas adjacent to spillway structures, vegetated channels, and other areas associated with a dam require continual maintenance of the vegetal cover. Grass mowing, brush cutting, and removal of woody vegetation (including trees) are necessary for the proper maintenance of a dam, dike, or levee. All embankment slopes and vegetated earth spillways should be mowed at least twice per year: once in the late spring and then during fall when the growing season subsides. Aesthetics, unobstructed viewing during inspections, maintenance of a non-erodible surface, and discouragement of burrowing animal habitation are reasons for proper maintenance of the vegetal cover. The embankment shown here is an excellent example of properly maintained embankment vegetation.
Methods used in the past for control of vegetation but now are considered unacceptable include chemical spraying and burning. Acceptable methods include the use of weed whips or power brush-cutters and mowers. Chemical spraying to first kill small trees and brush is acceptable if precautions are taken to protect the local environment. It may also be necessary to use a dedicated slope mower such as the one shown here.
It is important to remember not to mow when the embankment is wet. It is also important to use proper equipment for the slope and type of vegetation to be cut. Also, always follow the manufacturer’s recommended safe operation procedures.
Resources
ASDSO Resources
Free Webinar
Introduction to Inspecting Dams for Owners and Operators-2013
Sample Inspection Forms I
Sample Inspection Forms II
Sample Inspection Forms III
The ASDSO website houses national guidelines on dams. Go to:
DamSafety.Org/ManualsandGuidelines
For more information, videos and tools for dam owners go to:
DamOwner.Org
Watch for training in your area sponsored by ASDSO or your State Dam Safety Office. Access your state’s Dam Safety Program by clicking your state at:
DamSafety.Org/States
DHS/FEMA Resources
Pocket Safety Guide for Dams and Impoundments (FEMA National Dam Safety Program)
Impacts of Animals on Earthen Dams (FEMA National Dam Safety Program)
Animal Impacts on Earthen Dams - Owner Intro (FEMA National Dam Safety Program)
Impacts of Plants on Earthen Dams (FEMA National Dam Safety Program)
Plant Impacts on Earthen Dams-Owner Intro (FEMA National Dam Safety Program)
Dam Safety: An Owners Guidance Manual (FEMA National Dam Safety Program)
Identification of Visual Dam Safety Deficiencies (FEMA Training Aids for Dam Safety [TADS])
The Department of Homeland Security and FEMA make several publications and videos available through their websites. Visit their websites below and search "dam safety" for more information.
FEMA.gov
DHS.gov
Videos
Perfect to Imperfect Dam - Maintenance (YouTube, Download)
Slope Failure (Youtube, Download)
Identification of Visual Dam Safety Deficiencies (FEMA Training Aids for Dam Safety [TADS])
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