Roadside Revegetation

IMPLEMENTATION GUIDES
10-45). Microcatchments include a storage basin and berm. Berms are typically
4- to 8-inch high obstacles placed on the contour. They are formed from soil or
woody debris (logs), or manufactured products such as straw waddles (Figure
10-45) or compost berms. Manufactured products and woody debris are “keyed”
(partially buried) into the soil surface to prevent water from eroding under the
structure. Compost berms are continuous mounds of compost that can slow water
and filter sediments. Seedlings can be planted on, or immediately above, berms or
obstacles to access captured water. Unless species that propagate vegetatively are
used in these structures (see Section 10.2.2, Collecting Wild Cuttings), care must
be taken to avoid planting where sediment will bury the seedling. The storage
basin, created by terraces or berms, can be improved for plant growth with soil
tillage and incorporation of soil amendments.
Runoff Strips and Constructed Wetlands
A
B
Runoff strips are catchment structures constructed in areas where intermittent
concentrated road drainage occurs. These are typically at the outlets of culverts
or in road drainage dips. Runoff strips capture concentrated runoff into small
ponds or catchment basins. These areas can be planted with riparian species, such as willows
(Salix spp.) and cottonwoods (Populus spp.), or wetland species, such as rushes (Juncus spp.)
and sedges (Carex spp.). Runoff strips are placed in draws or concave topography and are
composed of engineered impoundment barriers, using riprap, logs, or gabion baskets, which
store water from runoff events. The barrier must have a spillway (a low point in the structure)
and be keyed into the sides to assure that concentrated water does not erode around its
sides. Where runoff strips are on gentle gradients, constructed wetlands may possibly be
developed (Figure 10-46).
Planting Islands
Planting islands are used where deep-rooted tree and shrub species are desired, but topsoil,
soil amendments, or soil depth are limiting. They are designed into such revegetation projects
as obliterated roads, view corridors, waste areas, and other highly disturbed sites. The strategy
behind planting islands is to create an ideal growing environment for tree and shrub seedlings
that replicates the natural patterns or features observed in the surrounding landscape and
plant communities (Figure 10-47).
Islands can be created by excavating an appropriate area to a depth of several feet and backfilling
with either topsoil or compost-amended material (Figure 10-48). Alternatively, compost and other
soil amendments (including lime and fertilizers) can be spread over planting islands at the depth
needed to amend the soil profile and mixed thoroughly through the islands with an excavator
or backhoe. Soil compaction must be avoided in these operations or during any subsequent
operation. After planting, mulch can be applied across the surface of the entire island.
Figure 10-45 | Microcatchments are
effective at capturing runoff water
Fill slope microcatchments take advantage
of the low infiltration rates of compacted
fill slopes (A) by capturing the
runoff from road drainage at the bottom
of the fill into topsoil or amended subsoil
favorable for plant growth (B). The extra
water from these surfaces can support
trees and shrubs. Straw waddles, as
shown in the picture on the right, can
be used in fill slope microcatchments to
collect water and sediment. Straw waddles
must be installed on the contour
and keyed into the soil to be effective.
Figure 10-46 | Constructed
wetlands are effective at
capturing runoff water
Constructed wetlands capture water
from roadside runoff and filter sediments
before water enters perennial
streams. Constructed wetlands can
create favorable habitat for unique flora
and fauna.
Figure 10-47 | Planting islands
mimic natural surroundings
Most planting islands are designed to
mimic the natural surrounding environment
of the project site. In this
photograph, seedlings were planted
in clumps to mimic the small islands of
trees that grew in this geographic area.
The inter-island areas were planted with
lower growing grasses, forbs, and shrubs.
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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