Roadside Revegetation

PLANNING PHASE TWO: ASSESS SITE
Tillage
Infiltration rates can be increased through soil tillage, including subsoiling, ripping, and
disking (see Section 10.1.2, Tillage). In most cases, tillage will reduce compaction and increase
macro-pore space in the surface soil, as well as create surface roughness that further increases
infiltration rates. Depending on the stability of the surface material and the level of organic
matter, the effects of tillage on infiltration might only be effective for a short time. Under
some conditions, tillage needs to be planned into the design of the road. Concentrated water
from poorly designed road drainage or inadequate road maintenance has the potential to
create deep gullies on tilled soils. Steep slopes in areas of high precipitation have a higher risk
of slope failure if tilled slopes are not designed appropriately (see Section 5.7.2, Restrictive
Layer). Deeper tillage and sculpting the subsoil are some methods to reduce these risks (see
Section 10.1.2, Tillage).
Organic Amendments and Tillage
Incorporating organic amendments into the soil surface using a bucket of an excavator
can create large, stable pores. However, unless the pores are interconnecting, they will not
drain well (Claassen 2006). One method for creating continuous pores is to use long, slender
organic material, such as shredded bark or wood, composted yard waste, straw, or hay (see
Section 10.1.5, Organic Matter Amendments). Compared to short A organic materials such as B C
wood chips, longer materials can increase infiltration rates. Incorporating higher quantities
of organic matter in the soil will also increase porosity because of the potential of the organic
material to overlap and interconnect.
Mulch and Tillage
Applying mulch by itself does not necessarily increase infiltration rates, although it can reduce
sediment yields (Hogan and Grismer 2007). However, combined with surface tillage in the form
of subsoiling or ripping prior to application of mulch, infiltration rates can be significantly
increased. Mulch fills in the micro-basins left from the tillage operation (Figure 5-8).
Establish Vegetation
Ultimately, the best method to increase infiltration is to create conditions for a healthy vegetative
cover. Good vegetative cover will produce soils with extensive root channels, aggregated soil
particles, and good litter layers.
5.2.4 ROAD DRAINAGE
Depending on how the road is designed, surface road water from precipitation events is either
dispersed or concentrated. Dispersed water is often seen on outslope or crowned roads, where
water moves in sheets over the road surface during rainstorms and into the fill slopes. This
water can be captured by water harvesting methods, as discussed in Section 5.2.1.2, Mitigating
for Low Precipitation. Concentrated water occurs where runoff from the road surface and
cut slopes, as well as intercepted water from seeps and streams, is collected in ditches that
flow into culverts or other road drainage structures. When designed into the road drainage
system, this water can be available for plant growth. Live silt fences, bio-retention swales,
and constructed wetlands are some structures that take advantage of this additional water.
Road Drainage – How to Assess
Road drainage is assessed by identifying drainage patterns on the road plans. Often the Storm
Water Pollution Prevention Plans will show the detailed direction of surface road water. Culvert
outlets are the areas most likely to have concentrated water that can be considered for use
for plant establishment and standing water for pollinator habitat.
A
Figure 5-8 | Surfaceapplied
compost
Surface-applied compost has greater
surface area contact with the soil when
it is applied to roughened surfaces
(B), compared to smooth surfaces (A).
Creating a rough surface prior to the
application of compost creates better
rooting, greater surface stability, and
faster organic matter decomposition.
Tilling the soil, through subsoiling and
ripping, to depths of 1 to 2 feet (C)
will break up compaction and create
channels for compost to move into the
soil, increasing soil contact and creating
greater infiltration rates.
A
B
Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat
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