Roadside Revegetation

IMPLEMENTATION GUIDES
seeds. Poorly applied seeds, where the applicator either misses spots or applies over seeded
areas, will also results in an uneven application.
Seed densities can be monitored indirectly by measuring the area where a known weight
of seed has been applied and matching it to the estimated acreage it was targeted to cover.
For example, on a project where a seed mix is split into a quarter-acre bags, the area seeded
with one bag of seed mix would be measured. If a quarter-acre bag covered only 0.2 acres,
the seed was sown more thickly and the density was increased by 25 percent (0.5/0.2). If the
seed bag had been applied over 0.30 acre, the seeds would have been spread across more
area and the seed density would have decreased by 17 percent (0.5/0.3). These measurements
should be done as each seed mix is being applied. If there is a significant change in density,
adjustments to the seeding operations can be made.
Measuring a seeding area unit is important not only for determining if seeding rates are
being applied correctly, but also for accurately paying the seeding contractors. Contract
administrators should be measuring the area that each seed bag or known seed quantity is
being sown during, or immediately after, seed application. Figure 9.2 in Chapter 9 describes
a method to measure area by measuring the slope length that has been seeded at each road
station marker and multiplying it by the distance between markers.
Proper seed handling should also be monitored. Seed bags should stored in suiTable conditions
and always handled with care. Seed bags should not be thrown or dropped or left in
unsuitable conditions.
10.3.2 HYDROSEEDING
Introduction
Hydroseeding is a method of hydraulically applying seeds, stabilizers, and soil amendments
to the surface of the soil for the primary objective of revegetation. The term hydromulching
is often used interchangeably with hydroseeding, there is an important distinction; hydromulching
is the application of hydraulic mulch and surface stabilizers for the primary purpose
of erosion control. Hydromulching is typically conducted on multi-year construction projects,
when surface soils need to be temporarily stabilized for soil erosion or dust abatement. While
hydromulching and hydroseeding operations both must stabilize the soil surface, hydroseeding
has the additional and overriding goal of placing viable seeds in a surface environment to
germinate and grow into healthy plants. Meeting the dual objectives of erosion control and
plant establishment in one operation is often a balancing act. The best methods for soil
stabilization are not always optimal for seed germination and plant growth. In this section,
we will focus on hydroseeding, not hydromulching. We will discuss how to best meet the
needs of early plant establishment using hydraulic sowing methods and leave the discussion
of stabilizing the surface through hydromulching to the many articles on this subject and to
the manufacturers of these products.
Hydroseeding equipment is composed of (1) a tank that holds a slurry of water, seeds, soil
amendments, and stabilizing products; (2) paddles or agitation jets in the tank to mix the
slurry; (3) a high pressure pumping system; and (4) a hose and nozzle (Figure 10-97).
Tanks come in a variety of sizes, from a few hundred to over 3,000 gallons. As the size of the
tank increases, the speed and efficiency of the operation improves. Because the travel time is
the same for any size hydroseeding unit, the farther the water source is from the project site,
the more efficient larger tanks become.
The hydroseeding tank is analogous to a large mixing bowl filled with various ingredients
and blended together with water to make a slurry. Typical hydroseeding ingredients fall into
these categories:
Figure 10-97 | Hydraulic seeder
The hydraulic seeder is composed of a
tank that holds and mixes a slurry, and
a pump system that moves the slurry
through a nozzle for application to the
soil surface.
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