Forest Road Engineering Guidebook - Ministry of Forests

an outflow location that will not destabilize the gully sidewalls and so create
a larger sediment source.
Ditch stabilization
In addition to armouring ditches with shot rock or lining them with a geosynthetic,
other options are available to minimize ditch erosion.
• In erodible soils, the ditchline can be seeded or an anti-wash vegetation
fabric installed. This can be very effective under low-velocity flow conditions
and on soils that are erodible, and it usually helps to establish grasses.
In erodible soils, it may be necessary to widen the ditch, as well as slope
the sides more gently than normal.
• In some cases, polymer stabilizers (soil binders) can be sprayed within
the ditchline. The manufacturer’s assurance should first be obtained that
use of the stabilizer will not result in adverse impacts, such as leaching,
on stream water quality.
• If soils upslope of the ditchline are sensitive, then ditchline erosion treatments
can be incorporated at the same time. The prescriptions may or
may not be identical.
• In rare situations where the stabilization options described above do not
work, consideration could be given to armouring.
• It is important that grader or other machine operations do not disturb the
ditchline stabilization measures. Should this occur, the ditch should be restabilized
as soon as practicable.
Alternatives to ditching
Forest Road Engineering Guidebook
In some instances, ditches may be inappropriate:
• on sites where there is a need to minimize bench cuts for stability or economic
concerns (e.g., to reduce the volume of blasted rock)
• on sites where there is a need to minimize the amount of site degradation
• on ridge or hilltop roads where natural drainage occurs
• along one-season winter roads.
Nevertheless, cut slope and roadway drainage should still be accommodated
in the above situations, with the use of:
• subdrains (such as French drains) in place of ditches
• French drains in place of ditch relief culverts
• road surface drains such as dips and swales
• road insloping or outsloping
• open-top ditch relief culverts
• erosion-resistant surfacing.
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