Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
Mitigating for High Rainfall and Wind
Minimize Disturbance
In areas of high rainfall or sites where water quality values are high (near streams or rivers), the
best engineering design is to keep the footprint of the construction project disturbance to a
minimum. Not only does this reduce the risk of delivering sediment to the aquatic system, it
can reduce project costs by reducing the amount of area needing revegetation.
Integrate Erosion Practices
On disturbed sites, especially those near streams, the integration of erosion practices with
plant establishment techniques offers the best approach to stabilizing the soil surface. These
include practices such as increasing soil cover, shortening slopes, reducing slope gradients,
leaving roughened surfaces, increasing infiltration rates, and quickly establishing native
vegetative cover. These will be covered in the following sections.
Use Appropriate Mulching Practices
A surface mulch is one of the best practices for controlling surface erosion (see Section 5.6.3,
Soil Cover); however, mulches can blow off the soil surface under strong winds. Some materials,
such as wood strand mulches (see Section 10.1.3.10, Wood Strands), have been tested under
high wind conditions and, because of higher weights and interlocking particles, these materials
are more resistant to high winds. Lighter mulch materials, such as straw and hay, are more
susceptible to removal by winds.
On windy sites, straw and hay are often crimped into the soil, but this operation can also cause
soil compaction. Tackifiers used with hydromulches are used effectively to stabilize straw and
hay mulches. Mulches placed on roughened soil surfaces can also reduce the potential that
the mulches will be lost by wind.
Install Windbreaks
Windbreaks or a shelterbelt is a line of trees that reduce the wind velocity and reduce the
potential for erosion on the downward side of the trees.
Place Large Woody Material
Down woody material, such as trees and large branches, can block the soil surface from wind
and rainfall.
5.6.2 FREEZE-THAW
Freeze-thaw is the process of ice formation and ice melting that occurs in a 24-hour cycle
within the surface of the soil. At night, temperatures drop at the soil surface and water begins
to freeze within the soil pores, creating ice crystals. As ice crystals continue to form, water
is drawn from the soil below through capillary action to replace the water that created the
ice crystals. During freezing, ice crystals expand in the soil and push soil aggregates apart
(Ferrick and Gatto 2004), weakening the internal structure of the soil. When soils thaw the
following day, soil strength is greatly reduced (Gatto and others 2004), leaving the soil surface
significantly less resistant to erosional forces. Freeze-thaw is considered one of the least
understood aspects of soil erosion (Ferrick and Gatto 2004) and yet accounts for significant
annual soil losses (Froese and others 1999).
The formation of ice crystals will destabilize the seed germination environment. Freeze-thaw
cycles affect germinating seeds by creating ice crystals that physically push the new seedlings
above the soil surface, exposing the emerging roots to extremely harsh conditions for seedling
establishment, including low humidity, high temperatures, and sunlight. On steeper slopes,
soil particles and germinating seeds move downslope after each freeze-thaw cycle, further
destabilizing the seed germination environment. Freeze-thaw processes can also affect
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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