Erosion on Crossing Sites:
roots stabilize the soil, and stems and leaves slow the water to give it
time to percolate slowly into the soil profile. The potential for
severe soil erosion exists after any culvert installation or enhancement
project because it displaces or destroys plant material and the layer of
litter on the surface. There are several steps you should take to
reduce the amount of soil erosion at your work site.
surrounding this culvert
has begun to erode away.
step is to protect the work area long before the heavy construction
use of sand bags, silt fences, straw bales and straw wattles have proven
benefits for small construction projects. Then as the project is
progressing, it’s important to leave in place, the greatest amount of
existing vegetation as possible. Assuming the plants/trees
do not threaten personal safety.
After the project is
step is to reseed and protect any disturbed soils. Some good reseeding
tips to protect your work site would include:
If needed roughen
the soil surface to provide a better seedbed by breaking through the
hydrophobic layer. A steel rake works well for this, or,
depending on the slope, a small tractor drawn harrow could be used.
material (top soil or black muck) to ensure nutrients are available
for seed germination. Add organic
- Broadcast the
seed. Seeding rate depends upon the variety of seed used.
Rake or harrow in ¼" to ¾" deep.
If the area is
small enough, roll or tamp the seed down to ensure good soil/seed
weed-free hay straw as a mulch. If the area is small, crimp the
hay into the soil with a shovel. This will help keep both soil
and seed in place during a significant wind and rain event.
Control weeds as
needed by cutting off the flower before it can reseed
Do not use
herbicides for broadleaf weed control until after the grass has
germinated and developed leaves.
step is to stabilize the upland area draining toward the stream crossing. This task can be safely
accomplished by numerous means. The most commonly used methods are
Sand Bags are made of woven polypropylene and work well as a temporary
solution to detour the path of unwanted runoff during the construction
period. Biodegradable products should be used for all long term
There are a variety of products available for erosion control.
Use biodegradable materials that will not interfere
with long term
fences are made of woven wire and a fabric filter cloth. The cloth
traps sediment from runoff. These should be used in areas where
runoff is more dispersed over a broad flat area. Silt fences are
not suitable for concentrated flows occurring in small rills or gullies.
To install a
(pre-assembled) silt fence, simply unroll, stretch and continue to drive
stakes. If possible, each fence should be installed in a 6" deep
trench to prevent sediment flow underneath the fence. Make sure
that all supporting posts are on the downhill side of the fencing.
is a flexible open weave (holes approximately ⅛" x ⅛") geotextile
designed to hold seeds and soil in place until vegetation is
established. The natural looking, high strength polypropylene mesh
protects the soil surface from water and wind erosion while offering
partial shade and heat storage to accelerate vegetative development
allowing uninhibited growth of wood plant species, grass, and ground
is made from curled excelsior, 80% of the fibers are six inches or
longer in length. Fibers expand as they come in contact with moisture.
When water is released into the soil, the drying causes the fibers to
contract. This process helps the fibers dig into the soil. The aspen
fibers are biodegradable and add natural nutrients to the soil. The
product breaks down in 9 - 12 months.
A variety of similar products (generally called Erosion Control Blankets) are also available.
bales placed in small drainages act as a dam – collecting sediments from
upslope and slowing the velocity of water traveling down. Bales
should be carefully placed in rows with overlapping joints (like
building a brick wall). Some excavation is necessary to ensure
bales butt up tightly against one another forming a good seal. Two
rows (or walls) of bales are necessary and should be imbedded below the
ground line at least six inches or held in place by stakes or rebar
driven into the soil.
wattles are extremely effective in controlling hillside erosion and
serving as makeshift dams for blocking sediment into waterways and
channels. They are constructed of long tubes of plastic netting
packed with excelsior, straw, or other material. Wattles are used
in a similar fashion to log terraces. The wattle is flexible
enough to bend to the contour of the slope. Straw wattles last 3 - 5 years and can be left in place.
From a recent
study, the U.S. Fish & Wildlife Service reported that out of 3,300
wattles placed in a particular year, only 10 failed from storm and
animal disturbance. It was also reported that straw wattles
are as effective as hand trenching, and they last much longer.
bars are berms of soil or bedded logs that channel water off roads and
trails to avoid the creation of gullies. Water bars are angled down the
slope to the outlet side. These bars can divert water to a vegetated
slope below or redirect it to a channel that will take it to a culvert.
On-site soil types and the road grade will dictate spacing requirements
for protecting your site.
Water bars can only be used on abandoned roads or
where very light vehicle traffic occurs.
provide a barrier to runoff from heavy rainstorms. Dead trees are
felled, limbed, and placed on the contour perpendicular to the direction
of the slope. Logs are placed in an alternating fashion so the runoff no
longer has a straight down slope path to follow. The water is forced to
meander back and forth between logs, reducing the velocity of the
runoff, and giving water time to percolate into the soil.
Logs should be
6 - 8 inches in diameter (smaller logs can be used) and 10 - 30 feet
long. The logs should be bedded into the soil for the entire log length
and backfilled with soil so water cannot run underneath. The backfill
material should be tamped down.
logs from rolling by driving stakes on the downhill side. It is best to
begin work at the top of the slope and work down. It is easier to see
how the water might flow by looking down on an area to better visualize
the alternating spacing of the logs.
is a method where wood-based fiber products are used to spray on
hillsides with unstable soils. Products of this type contain fiber
mixed with a tacking agent, or binder. The liquid solution can be
formulated to contain specific grass seed species so new vegetation can
help stabilize the hillside.
seeding and mulch cover have done a great job on this site. One
year after installation, a heavy vegetative mat is established and the
bank should continue to be stable.