Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
during plant establishment. This can take an active form, such as irrigation, or a passive form,
such as redirecting surface water to planted seedlings.
Irrigation
Irrigation can be expensive, and it is generally used only on projects with high visibility or when
rapid establishment is necessary for slope stability. These are projects where revegetation
objectives include minimizing the risk of seedling failure or enhancing vegetation growth.
Several basic types of irrigation systems are used in roadside revegetation. They are grouped
into fixed systems, such as overhead sprinkler and drip irrigation, and manually applied systems.
Fixed systems are discussed in Section 10.4.5.2 Drip Irrigation. Manual systems require water
to be delivered directly to each plant, either from a hose or water container.
If only a few applications are necessary, the entire project can be irrigated by hand. Personnel
can water each seedling or seeded area using a water truck or hydroseeding equipment (with
water only), although care must be taken to avoid pulling hoses over establishing plants.
Creating basins around seedlings will pond the surface-applied water and keep it concentrated
in the seedling root zone. However, a better way to be certain that water will be delivered
directly to the roots is to integrate the deep pot irrigation system into drip or manually applied
irrigation methods (Bainbridge and others 2001). Pipes made from polyvinyl chloride (PVC) or
other materials are placed at depths of 1 to 2 feet beside the seedling at the time of planting.
The pipes are then filled with water when the soils dry out in summer. The advantage of deep
pipe irrigation is that water is delivered directly to the root system and, because the water is
placed deeper in the soil, roots are forced to extend farther into the soil for moisture. Refer
to Section 10.4.5.1 Deep Pot Irrigation, for how to install this system.
For any irrigation method, it is important to monitor the wetting pattern of each irrigation.
This will ensure that water is applied at the appropriate rates. Digging a hole where the water
has been applied at least several hours after irrigation will show how far the water has moved
into the soil profile. Duration of irrigations can be adjusted accordingly.
Water Harvesting
Water harvesting is the alteration of local topography to capture runoff water and concentrate
it in areas where it can be used by plants. Water harvesting designs can be applied to roadside
revegetation in several ways. They include, but are not limited to, contour bench terraces, runoff
strips, and fill slope microcatchments. Fill slope microcatchments take advantage of water
that drains off road surfaces and shoulders during intense rainstorms by capturing runoff in
berms or depressions created at the base of the road shoulder (Figure 5-5). Shrubs and trees
planted in these catchment areas will receive greater soil moisture. Contour bench terraces
are structures carved out of cut and fill slopes that collect and store runoff water. When filled
with topsoil or amended soil, they are referred to as planting pockets. Figure 5-6 shows how
planting pockets collect water. Even very low rainfall events, which would normally be of
insufficient quantity to moisten the soil surface, can recharge soil in planting pockets and fill
slope microcatchments. Sediments will also be deposited on the benches and pockets during
rainstorms, building the soil up over time and reducing soil erosion. Water harvesting not only
supplies additional water to plants but reduces sediment and peak flow water to the stream
system. Road practices that intercept water and sediments from the road surface for water
quality improvement are also a source of additional water for plant growth. These include
amended slopes, filter strips, amended ditches, bio-retention swales, and constructed wetlands.
In addition, some of these structures create surface-water sources for pollinator species.
5.2.2 RAINFALL INTERCEPTION
The amount of water entering the soil profile from a rainfall event can be significantly reduced
by the interception of live or dead vegetation cover. Rainfall is captured through a series of
layers, beginning with the tree and shrub canopy, the ground cover, litter, and duff, and is
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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