HomeMy WebLinkAboutControlling Erosion on Construction Sitescontrolli.ng e.rosioo.
on constrL~on sdes
CONSERVATION SERVICE
SOIL
127 E MAIN ST. ROOM lOi.
RIVERHF. AD, N.Y. 11901
U.S. DEPARTMENT OF AGRICULTURE · 5Oll CONSERVATION SERVICE ' AGRICULTURE INFORMAT]ON BULLETIN 347
contrcdli .ng .erpsbn..
on constCzscbon s tes
Each year more than a million acres
of land in the United States are converted
from agricultural use to urban use. These
changing acres are the sites for the new
houses, shopping centers, schools, indus-
trial parks, highways, and airports needed
by our growing population.
These changing acres also are the
source of much of the sediment that pol-
lutes streams and rivers and fills lakes and
reservoirs. Studies show that erosion on
land going into use for highways, houses,
or shopping centers is about 10 times
greater than on land in cultivated row
crops, 200 times greater than on land in
pasture, and 2,000 times greater than on
land in timber.
The amount of erosion that occurs is
determined by the kind of soil, the slope,
the intensity of rainfall, and the construc-
tion methods. Much of the erosion occurs
during the construction period, but areas
below a construction site may erode more
after construction is completed because of
the rapid runoff from impervious pave-
ment, parking lots, or compacted soil.
Improvements in earth-moving equip-
ment have made reshaping of land easier
and have brought steeper and rougher
land into use. Also, the trend toward large
subdivisions and developments to meet
housing needs has left large cleared and
graded areas exposed to erosion for long
periods. Because of these factors, an ever-
increasing amount of land is undergoing
development each year and erosion is be-
coming a more serious problem in urban
areas than ever before.
Damage to the land does not come
from erosion alone. The increased runoff
erodes stream banks and channels and
causes flooding below the construction
site. And the sediment pollutes streams,
lakes, and reservoirs and damages the
area where it comes to rest.
damage to the
construction site
Erosion damage to the construction site
includes rilled and gullied slopes, gullied
waterways and channels, washed-out
roads and streets, undercut pavements
and pipelines, clogged storm sewers,
flooded basements, and debris-laden work
areas. Damage of this kind must be re-
paired. It increases the cost of construc-
tion and causes delays in work schedules.
A construction site also can lose fertile
topsoil through erosion. This loss could
mean that lawns and gardens will be dif-
ficult to establish.
Left, Uncontrolled runoff damages the con-
struction site and carries the sediment that
damages a~-eas downstream,
Right. Grading more land than needed for
immediate construction can result in severe
erosion and sedimentation.
Cutting, filling, excavating, and grading
leave a site highly susceptible to erosion.
damage to stream channels
Stream chaonels below a construction
site can become filled with sedimeot nod
then flood when the volume of runoff
creases during heavy rains. A sediment-
filled stream chaonel can cause stream-
bank erosion and can f{~rce the stream to
meander. Land along the stream may be
damaged by sediment, floodh~g, and
sion, and the esthetic wdue of the stream
may be seriously impaired.
Clearing removes trees and other
plant cover that protects the soil.
damage to water
Sediment is the greatest single pollutant
of streams, lakes, ponds, and reservoirs.
Sediment lowers the quality of water for
municipal and industrial uses and for
boating, fishing, swimming, and other
water-based recreation; it increases the
wear on equipment, such as turbines,
pumps, and sprinkler irrigation systems.
Sediment carries with it pesticides, phos-
phates, and other chercfical pollutants.
damage to property,
public and private
Sediment almost always damages the
areas where it is deposited. It buries
lawns, fills ditches, and clogs storm sew-
ers, culverts, and drains. It can make an
area unsuitable for use as a park or play-
ground. Sediment reduces the storage
capacity of reservoirs and may fill small
ponds and lakes. It is injurious to both
game fish and shell fish. The sediment that
reaches major waterways blocks naviga-
tion channels, fills harbors, and silts
estuaries.
The nationwide damage caused annu-
ally by sediment has been estimated at
more than $500 rrdllion. Much sediment
comes from agricultural land, but the
amount contributed by land undergoing
urban development is high in proportion
to the acreage. Some areas may be getting
sediment from construction sites only, and
the damage may be catastrophic.
public concern
People today want better houses, bet-
ter shopping centers, and better roads.
But they also want pure water, clean air,
more open space, and other improvements
in the environment that make for pleasant
living. People are demanding that natural
resources be developed, protected, and
improved for use now and in the future.
If our population doubles in the next
50 years as predicted, the acreage of land
needed for urban use will increase. And
the hazards of erosion and sedimentation
will be greater if effective and practical
measures for controlling erosion are not
adopted and used widely.
the solution:
self-help and
Many organizations and federal, state,
and local agencies can provide leadership
and assistance in a program for erosion
control. The Soil Conservation Service
(SCS) of the Department of Agriculture
gives technical help through conservation
districts and in cooperation with many
other agencies. But programs for erosion
control need to be initiated by developers,
builders, engineers, planners, architects,
public officials--the people responsible
This storm sewer proved too small, and the
overflow undercut the pipeline. Sediment
from hisher lying construction sites is de-
stroying the lake.
cooperation
for controlling erosion in their com-
nmnity.
Today's conservation problems on /and
undergoing development for urban use
follow by nearly three decades the initia~
tion of soil and water conservation work
on farmland. Most of what we know
about erosion and sediment control has
been learned from research, demonstra-
tion, and action programs on farmland.
This wealth of information and experi-
ence can serve urban areas equally well
if properly interpreted. The basic prin-
ciples of soil and water conservation and
resource development can be applied any-
where.
principles of erosion and
Erosion is a process of detachment and
transportation of soil particles. Rain fall-
ing oll bare soil or on soil with sparse
cover detaches soil particles, and the run-
off carries the detached particles down
the slope. Rills and g,allies are cut by tile
force of the moving water. The soil parti-
cles are deposited as the water slows down
and spreads out. Water moving over the
land and in downstream channels carries
soil material in proportion to the volume
and velocity of the water.
Top. The sediment in this storm drain,
which is less than a year old, is more than
2 feet deep in places. The sediment came
from a nearby construction site.
Right, The capacity of this culvert is no
8 longer adequate because of sediment.
sediment control
Erosion and sedimentation can be con-
trolled effectively, and at reasonable cost,
if certain principles are followed in the
use and treatment of land. These prin-
ciples are: (1) using soils that are suited
for development, (2) leaving the soil bare
for the shortest time possible, (3) reduc-
ing the velocity and controlling the flow
of runoff, (4) detaining runoff on the site
to trap sediment, and (5) releasing run-
off safely to downstream areas.
In applying these principles various
combinations of the following practices
have proved effective:
1. Selecting land where drainage pat-
terns, topography, and soils are favorable
for the intended use.
2. Fitting the development to the site
and providing for erosion control in the
site development plan.
3. Using for open space and recrea-
tion those areas not well suited for urban
development.
4. Developing large tracts in small
workable units on which construction can
be completed rapidly so that large areas
are not left bare and exposed for long
periods.
5. Grading at a minimum and re-
moving only undesirable trees wherever
possible.
6. Controlling runoff and conveying
it to storm sewers or other outlets so it
will not erode the land or cause offsite
damage.
7. Protecting critical areas during
construction with mulch or temporary
cover crops and with mechanical mea-
sures such as diversions and prepared
outlets.
8. Constructing sediment basins to
detain runoff and trap sediment during
construction.
Sediment from construction sites in the
watershed has almost filled this lake.
Choked to death by sediment.
10
9. Providing for safe offsite disposal
of runoff, including the increased runoff
resulting from construction.
10. Establishing permanent vegeta-
tion and installing erosion control struc-
tures as soon as possible.
select the right land
Builders and developers can minimize
erosion, sedimentation, and other conser-
vation problems by selecting the best site
for an intended use. Tracts of land vary in
suitability for different uses, so knowing
the kind of soil, the topography, and the
drainage pattern of the area will help in
identifying and evaluating potential prob-
lems.
Regional and community planning is
guiding land development in much of the
rapidly urbanizing areas. Community
planners, using information about the
soils and about the geology, hydrology,
and topography of the area, determine
how the different kinds of land in a com-
munity can best be used. They make
studies to determine future land needs
for urban, agricultural, recreational, and
other purposes. Other studies project pop-
ulation growth and trends and determine
the land needs for schools, transporta-
A pond or reservoir in the right place can bring many benefits to the landowner or the community.
tion, utilities, and other public services.
The studies are based on community ob-
jectives to meet all necessary needs for
land in ways that can protect natural re-
sources, enhance the environment, and
provide for both efficient and pleasant
communities.
soil surveys can help
Soil surveys can be used iri community
planning to determine land use suitability.
Soil surveys include soil maps, soil de-
scriptions, and soil interpretations. The
interpretations serve to point out the haz-
ards and ]imitations in nsing the soils for
different pnrposes. With this kind of in-
formation developers and builders can
select sites that have the fewest limitations
for a certain use and know that their se-
lection will be compatible with the com-
munity's plans and interests.
Left. The soil data that a soil surveyor re-
cords can help bring about better land-use
planning and urban development.
Right. Planning results in orderly develop-
ment of land.
More and more developers and build-
ers are making use of soil and other
resource data in selecting land for devel-
opment and in preparing site development
plans.
Soil surveys were first used by farmers
and agricultural scientists. They have
guided the use and treatment of farmland
and rangeland for years. Highway engi-
neers have found soil surveys useful as an
aid in designing highways as well as in
determining the best routes. Sometimes
adjustments in locating the right-of-way to
avoid highly erodible soils or steep
topography can reduce erosion problems
greatly. Bankers are using soil surveys in
land appraisal for making loans. Land as-
sessors are using them as one criterion in
determining a fair tax base. And land-
planning agencies in increasing numbers
are using them. The same soil survey can
serve many different uses. To date soil
surveys have been completed for more
than 2,000 counties or other areas and
additional surveys are being completed
each year.
In making a soil map, the boundaries of
the different kinds of soil occurring on a
tract of land are delineated on an aerial
photograph. The delineations show the
location and extent of the different kinds
of soil in relation to streams, roads, build-
ings, and other features of the landscape.
Soil surveys describe the characteristics
and properties of each kind of soil-its
texture, slope, depth, erodibility, perme-
ability, degree of wetness, presence of im-
pervious or porous layers, and other
information useful in construction. The
soil descriptions are the basis for inter-
preting soil suitability for different uses.
Many soils are well suited to many uses;
others, because of limitations, are suited
to only a few uses.
Soil limitations are expressed as slight,
moderate, and severe. A severe limitation
does not mean that the soil cannot be
used for a specific purpose, but rather that
the cost of overcoming the limitation for
that purpose may be prohibitive.
Soils vary in permeability and in their
suitability for use as septic-tank absorp-
tion fields. Some soils have impervious
layers that cause them to slip when satu-
rated. Wide shrink-swell ratios, flood
hazards, and seepage problems impose
limitations on other soils for use as con-
struction sites.
Soil surveys published in recent years
are useful in urban planning and construc-
tion. Older surveys have interpretations
only for farming uses of the land. But the
soil descriptions in the older surveys con-
tain basic information from which inter-
pretations for urban use can be made.
Anyone needing such interpretations usu-
ally can get help from the local conserva-
tion district or the Agricultural Extension
Service.
Soil surveys do not lessen the need for
onsite investigation.
include erosion control
in the development plan
If a program for erosion control is
worked out during the planning and de-
sign stages, before plans become fixed and
construction begins, the problems brought
on by soil erosion, runoff, and sedimenta-
tion can usually be avoided or lessened.
Detailed information on the soils, topog-
raphy, and geologic and hydrologic con-
ditions should be obtained during field ex-
amination of the site. Particular attention
should be given to identifying and evaluat-
ing problems that may cause serious ero-
sion during construction. For example,
will disposing of runoff be a problem?
Runoff originating on the site and runoff
13
14
A well-planned site
will include open-space
areas. This one is used as
an outdoor laboratory.
from the watershed above must be con-
trolled and disposed of safely. Considera-
tion should also be given to offsite
measures that may be needed to prevent
damage to downstream land and property
by either erosion or sediment.
Special consideration should be given
to fitting developments to the site and the
landscape. Street, lot, and building layout
can minimize or encourage erosion during
construction and complement or detract
from the natural environment. Steep
slopes and areas of highly erodible soils
can be protected or left exposed; clearing
and grading can save or destroy trees and
can result in limited or excessive soil dis-
turbance; cut-and-fill slopes can be stable
or unstable, protected by cover or left
bare for long periods. These are the kinds
of considerations that need to be weighed
and resolved during planning and design
to get erosion control into the site devel-
opment plan.
On sites where the cost of controlling
erosion may be high because of the mea-
sures needed to overcome the site limita-
tions, alternative uses or a layout that is
more compatible with the land should be
considered. The cluster method of devel-
oping residential areas, for example, fits
the buildings and streets to the natural
characteristics of the land. In using tfie
cluster method on sloping land, houses
can be built only on the more level areas
and the steep, more erodible land is left
undisturbed. Erosion hazards have been
minimized and costs have not been in-
creased.
The problems presented by small areas
where erodible soils or steep slopes im-
pose severe limitations may be solved best
by using these areas as open space. Per-
haps they can be added to public parks or
to areas managed by community associa-
tions. In some places, schools make good
use of them as nature areas or outdoor
laboratories for class study.
There are always alternative ways of
effectively controlling erosion and sedi-
ment production on most sites. The final
plan generally is based on such factors as
the time of year that construction will take
place, the extent of grading, the amount
of cover on the land, and the builder's
preferences. On most sites a combination
of fitting the development to the land,
limiting grading, limiting the exposure of
bare soil, and applying appropriate ero-
sion control practices will prove the most
practical.
erosion
and
sediment
control
measures
]'here are two kinds of erosion and
sediment control measures--mechanical
and vegetative. The most widely used of
these measures are discnssed here from
the standpoint of their general use and pur-
pose. Detailed information and standards
and specifications developed for local
conditions can be obtained from the local
office of the Soil Conservation Service or
from conservation districts. SCS can also
give technical advice. Erosion control
measures must be properly designed, in-
stalled, and maintained if they are to
accomplish their intended purpose.
mechanical measures
Mechanical measures are used to re-
shape the land to intercept, divert, con-
vey, retard, or otherwise control runoff.
land grading
Grading only those areas going into
immediate construction, as opposed to
grading the entire site, helps immensely in
controlling erosion. On large tracts, to
avoid leaving a large area bare and un-
protected, milts of workable size can be
graded one at a time--as construction is
completed on one, grading proceeds to
another.
On some sites, until storm sewers are
installed, only the street rights-of-way are
graded. This leaves only linfited areas ex-
posed to erosion and usually the adjacent
undistnrbed areas can be used as tempo-
rary outlets for diversions, or berms, built
to protect the graded street rights-of-way.
After the storm sewers are installed, other
areas can be graded and the runoff can be
directed to the streets and storm sewers.
As a general rule, grading should be
held to the minimum that makes the site
suitable for its intended purpose without
appreciably increasing runoff. Only unde-
sirable trees should be removed wherever
possible.
In some areas heavy cutting, filling, or
reshaping of the natural topography is
needed to increase the percentage of us-
able land. Heavy grading almost always
increases erosion hazards and should be
accompanied by the maximum use of ap-
propriate erosion control measures.
15
The conservation measures applied
here have stabilized this critical area.
The grading plan should show location,
slope, and elevation of the areas to be
graded and the measnres to be used for
disposing of runoff and for erosion con-
trol. Constructed slopes should be limited
to a degree of steepness that will provide
stability and allow easy maintenance. Re-
taining walls may be required.
Stumps and other decayable material
should not be used in fills. Soft, mushy
soil material is not suitable for fills that
are to be nsed to support buildings nr
other structures.
bench terraces
Bench terraces constructed across the
slope of the land and fitted to the natural
terrain are used to break long slopes and
slow the flow of runoff. In some areas the
terraces are constructed wide enough to
be nsed as residential sites. The cut-and-
fill slopes of the bench terraces are always
steeper than the natural slope of the land,
so land slides may be a threat. Engineer-
ing studies should always be made to
guide the design of the slopes and insure
a reasonable degree of slope stability and
safety.
Small bench terraces are sometimes
used on the face of cut-and-fill slopes to
help control runoff and erosion and estab-
lish vegetation.
subsurface drains
Subsurface drains are sometimes
required at the base of fill slopes to
remove excess gronnd water. In heavy
grading, it may be necessary to fill natural
drainage channels; subsurface drains may
have to be installed below the newly filled
areas to prevent accumulation of ground
water.
Subsurface drains may be needed in
vegetated channels to lower a high water
table that prevents establishing an effec-
tive plant cover.
diversions
Diversions intercept and divert runoff
so it will not cause damage; they consist
of a channel and a ridge constructed
across the slope. Diversions need a stable
outlet to dispose of water safely.
In many places diversions are placed
above critical slopes to divert runoff. Run-
off over such slopes would cause serious
erosion. Diversions can be used in this
same way to protect construction areas.
Also, they can be used on long slopes, in
a series if needed.
17
A diversion protects a steep cut slope
by diverting runoff to a safe outlet.
Permanent diversions should be seeded
to the same grasses that cover the sur-
rounding areas. If built to protect open
spaces, they should blend into the land-
scape for both better appearance and ease
of maintenance.
Berms are a type of diversion. They are
compacted earth ridges on a slight grade
and have no channels. They may be per-
Berms can be used to protect newly
constructed slopes until the slopes are
stabilized with permanent vegetation.
They can be constructed across graded
rights-of-way in a series and at intervals
needed to intercept runoff. The side slopes
of the berms are made fiat enough to
Berms too must have stable outlets.
Well-stabilized ungraded areas adjacent to
the street rights-of-way are often used as
temporary outlets. In many places half-
channel flumes, sod, or other material can
be used to make temporary outlets.
Storm sewers dispose of runoff from the
streets and adjacent lots. Temporary dj-
versions may be needed to control runoff
on the lots and convey it safely to the
streets and storm sewers.
The use of storm sewers for runoff dis-
posal does not prevent sediment from
being deposited downstream. To reduce
the sediment load carried by runoff
through storm sewers during construction,
some developers have improvised small
sediment basins adjacent to sewer inlets.
The sediment collected in the basins is
removed following each runoff-producing
rain.
Storm sewers should discharge where
the grade is stable. Generally an energy
dissipator is needed to slow the force of
the flow at the point of discharge.
outlets
Most outlets are grassed waterways,
either natural or mamnade, and serve to
dispose safely of water from diversions
and from parking lots, highways, and
other areas.
Natural waterways, or swales, can be
improved by grading, reshaping, and re-
vegetating. Manmade outlets should have
fiat side slopes and a wide bottom so they
can be easily maintained. They should
have adequate capacity.
This concrete-lined channel will carry runoff
from the road su~ace and road shoulders,
The shoulders have been mulched and
seeded.
have preferred permanent basins that can
be used later to protect downstream areas
from accidentally released materials that
would cause pollution.
The location, design, and construction
of a sediment basin should be such that
serious damage to areas downstream
would be avoided should the basin fail.
If the minimum storage requirement can-
not be met, excavation to enlarge the
basin and periodic cleanout may be nec-
essary.
Sediment basins are constructed to dis-
charge on stable ground below the dam.
Emergency spillways should be added to
increase safety. Exposed areas of the em-
bankment and the emergency spillway
should be protected by mulching and
seeding.
stream channel and bank
stabilization
The increased runoff from coestruction
sites may make it necessary to stabilize
the stream channel below.
Stream channels can be stabilized by
installing grade control structures or
by paving. Undercutting of banks can be
controlled by measures that withstand the
flow, such as concrete structures or rock
riprap built along the toe and lower facing
of the bank, or by measures that dissi-
pate the energy of the flow, such as jetties,
piling, and fencing built into or along the
channel. Realining the channel may be
desirable or necessary in many places,
but it creates the risk of starting a new
erosion cycle.
Stabilizing stream channels and stream-
banks is usually complex and costly. Con-
trol measures should be undertaken only
on the basis of thorough engineering
studies and plans. If a stream runs along
or through a flood plain that is to be de-
veloped for parks and recreation, for ex-
ample, esthetic values may determine the
methods of improvemeet.
vegetative measures
Vegetative measures provide tempo-
rary cover to help control erosion during
construction and permanent cover to sta-
bilize the site after construction is com-
pleted. The measures include the use of
mulches and temporary and permanent
cover crops.
Erosion can be controlled with less dif-
ficulty on some sites than on others during
construction, and permanent cover is easy
This newly sodded channel will dispose of
runoff safely. The slope has been planted
to honeysuckle and mulched with tanbark.
Note riprapping at critical points.
Grass protects a channel against ero-
sion by reducing the velocity of flow. The
most suitable grass species are those that
produce a dense uniform cover near tile
soil surface, are long lived, tire able to
withstand small amounts of sedimenta-
tion, and provide protection during all
seasons of the year. The species selected
should be adapted to the locality and the
site.
Jute netting or fiber glass can be used
as channeI liners to protect the channel
from erosion until vegetation becomes
established. Liners may not be needed if
runoff can be diverted from the channel
during the establishment period.
waterway stabilization
structures
A waterway needs a stabilizing struc-
ture if its slope is so steep that the velocity
of runoff exceeds the limit of protection
that the vegetation alone gives. Grade
stabilization structures, special culverts,
and various kinds of pipe can be used in
combination with vegetation. Energy dis-
sipaters may be required. The structures
should be designed and constructed to
provide permanent stabilization.
lined channels
The alternative to using vegetated wa-
terways with grade stabilization structures
is using lined channels. Such channels,
paved ditches and valley gutters for ex-
ample, have many uses in urban areas
where slopes are too steep or soils too
unstable for control by vegetation alone.
Fiber-glass mats can be used as tempo-
rary lining for ditches and channels.
sediment basins
The function of a sediment basin is to
detain runoff and trap sediment, thus, pre-
venting damage to areas downstream. By
detaining runoff, sediment basins also
duce peak flows. Basins can be excavated
or formed by a combination of dam mid
excavation. Earth dains can be con-
structed across waterways to form basins.
Under some conditions a highway em-
bankment can serve as a dam. Sediment
basins are almost always temporary struc-
tures. They are graded into the surround-
ing landscape after construction bas been
completed and the :~rea has been
stabilized. But they can be designed as
permanent structures il' there is a perma-
nent need for them. Some industrial firms
19
to establish on some sites and di¢icult on
others. Establishing and maintaining good
plant cover is easy in areas of fertile soil
and moderate slopes. Usually such areas
can be stabilized by using the plants and
cultural methods that are common in the
community.
Sites that are difficult to stabilize, be-
cause of exposed subsoil, steep slopes, a
droughty exposure, and other conditions,
require special treatment. Such sites are
called critical areas because they erode
This vegetated channel and drop structure
dispose of runoff safely.
severely and are the source of much sedi-
ment if they are not well stabilized.
mulch
Straw mulch can be used to protect
constructed slopes and other areas
brought to final grade at an unfavorable
time for seeding. The areas can be seeded
when the time is favorable without
moving the mulch.
Mulch is essential in establishing good
stands of grasses and legumes on steep
cut-and-fill slopes and other areas where
it is difficult to establish plants. By
ducing runoff, mulch allows more water to
infiltrate the soil. It also reduces the loss
of soil moisture by evaporation; holds
seed, lime, and fertilizer in place; and re-
duces seedling damage from heaving of
the soil caused by freezing and thawing.
The materials most widely used in
mulching are small-grain straw, hay, and
certain processed materials. Grain straw
is easily applied and generally is more
readily available than hay, and it costs
less. in some places, certain hays are pre-
ferred because they are a source of seed
of plants that can be used for stabilization.
Straw and hay mulches are usually
applied at the rate of I~A tons per acre.
Paper netting helps secure straw mulch on
a newly seeded waterway.
A number of processed mulches are
available, and some show promise of
greater use under specific conditions.
Hydromulching, in which seed, fertilizer,
and mulch are applied as a slurry, is a
fast, all-in-one operation that requires
little labor. Hydromulching may not be
successful if done during a period of high-
intensity storms.
Straw and hay mulches must be an-
chored to keep them from blowing or
washing away. Anchoring methods in-
clude spraying the mulch with asphalt,
tucking the mulch into the soil with a
straight-blade disk, stapling netting over
the mulch, and driving pegs into the
mulched area at intervals of about 4 feet
and interlacing them with twine.
2I
22
temporar~ cover
Temporary cover crops can be used
where cover is needed for a few months
or a year or two. If construction is delayed
on a site that has been cleared and graded,
temporary cover crops can be used to pro-
tect the site against erosion. And they can
be planted at a time of year that is unfa-
vorable for seeding and establishing per-
Rapidly growing plauts, such as annual
rye grass, small grain, sudangrass, and
millet, are most often used for temporary
cover. Plants that are adapted to the lo-
cality and the season of the year during
which protection is needed should always
be used.
permanent cover
Special care should be taken in select-
ing plants for permanent cover. There are
many grasses and legumes, trees, shrubs,
vines, and ground covers from which to
choose ill most humid areas of the country
bat only a few in most dry regions. Final
choice should be based on adaptafion of
the plants to the soils and climate, ease of
establishment, suitability for a specific
use, longevity or ability to self-reseed,
The asphalt-paved apron and drop chute will
carry runoff into the sediment basin.
maintenance requirements, esthetic val-
ues, and other special qualities.
The best plants are those that are well
adapted to the site and to the purpose for
which they are to be used. For example,
grasses used for waterway stabilization
must be able to withstand submergence
and provide a dense cover to prevent
scouring of the channel. In playgronnds,
grasses must be able to withstand tram-
piing. In some places, such as south-fac-
lng cut-and-fill slopes, the plauts needed
are those that are adapted to droughty
areas. In olher places, plants must be able
to tolerate shade. Some plants can beau-
tify as well as stabilize an area.
Maintenance may be the most inrpor-
rant factor in selectiug plants for perma-
nent stabilization. Most tame grasses and
legumes require mnch maintenance, and
they gradually give way to native grasses,
shrubs, and weedy phmts if they are not
mowed and fertilized regularly. In some
areas native plants are preferred. On steep
slopes and other inaccessible areas, it is
preferable to select plants that require
little or uo maintenance. Sericea lespe-
deza, crownvetch, and honeysuckle, for
example, are long lived and provide good
erosion control with a minimnm of main-
This temporary sediment basin has a per-
forated riser to make easier the gradual
drawdown of impounded runoff.
tenance. Most native grasses, trees~ and
shrubs grow well with little or no main-
tenance.
fibrous materials
A number of fibrous materials have
special uses in erosion control.
Jute netting, a coarse, open-mesh, web-
like material, can be applied directly on
the soil to protect newly seeded channels
until vegetation becomes established. It
can also be used in repairing outlets and
diversions where gullies have cut the
channel. In some places it can be used to
hold down straw mulch.
Cotton netting and paper netting are
both lightweight; they can hold straw
mulch in place and prevent it from blow-
ing or washing away.
Solid heavy-duty fiber-glass matting
can be used as a temporary channel liner
where water velocity is too high for the
use of vegetation or where vegetation is
not wanted. Impregnating the mat with
asphalt prolongs its life. Perforated fiber-
glass matting can be used in the same way
as jute netting to protect newly seeded
channels. It can be used as a transition
apron, lining the head of a channel to pro-
tect it from runoff, especially that from
road culverts, which tends to cut a gully
down the channel. And used as erosion
stops, perforated matting can check
rilling.
Fiber-glass erosion stops have certain
advantages over rigid stops of masonry
or wood. Soil often settles around rigid
structures causing a turbulent and erosive
flow. The fiber~glass stops are flexible and
conform to the channel. Also, they are
porous--water can seep through them--
so subsurface drainage is improved.
stabilizing
cut-and-fill
slopes
The first requirement in stabilizing cut-
and-fill slopes is to prevent runoff from
flowing over the face of the slopes. Tem-
porary diversions, berms, shoulder dikes,
or other measures should be used to inter-
cept and divert the runoff. Permanent
structures such as brow ditches and valley
gutters are required where the areas con-
tributing to runoff are large, for example,
in areas of highway construction.
23
A temporary cover of annual ryegrass pro-
tects this graded area against erosion until
construction begins,
The cultipacker seeder works exceptionally
well on a well-prepared seedbed.
Small benches, intercepter ditches, or
other measures can be used to protect
long slopes from runoff originating on the
slope itself.
Methods of establishing vegetation vary
for different parts of the country, depend-
ing on the plants used and on soil and
climate. In selecting plants and in getting
them established, it is best to be guided by
the methods commonly used and recom-
mended in the area.
As a general rule, when seeding grasses
and legumes it is advisable to prepare as
good a seedbed as site conditions permit.
Applications of lime and fertilizer should
be based on local standards or on soil
tests.
Usually a good stand can be obtained
by broadcasting, drilling, or hydroseeding
if other conditions are met. Mulching
after seeding and then anchoring the
mulch are essential in most areas. Irriga-
tion is oeeded in many places.
Sodding is more costly than seeding,
but it provides immediate protection. It
should be ased where the concentration of
runoff is such that other methods of stabi-
lizatioo will not be effective. Sod can be
laid anytime the soil is not frozen. Sod
responds to a good seedbed and to lime
and fertilizer. The strips of sod should
always be laid across the slope, anchored
to the soil, and watered. Some grasses can
be established by sprigging and chunk
sodding.
If trees are used to stabilize steep
slopes, they are usually planted in pure
stands. Mulching is important. Vines are
usually established by transplanting in-
dividual plants or crowns.
R~ght, top. Hydroseeding--spraying seed
and fertilizer in a water solution is one way
of establishing grass on a graded area.
Right, bottom. The notched-disk machine is
anchoring the mulch to the soil
Below. This machine spreads a uniform cov,
er of straw mulch to control erosion on the
face of the dam.
26
apply
measures
during
construction
installation of erosion and sediment
control measures should be planned and
scheduled as a part of construction opera-
tions. Construction contracts should
clearly outline the location, scope, and
manner of performing or installing the
measures.
If possible, construction should be
scheduled for that time of year when ero-
sion is less of a hazard. This is particularly
advisable for those sites where limitations
for construction are severe because of
steep slopes and erodible soils. Avoiding
erosion hazards is an inexpensive way of
controlling erosion and sedimentation.
Structures for controlling erosion on
newly graded areas should be written into
the grading contract. All permanent struc-
tures should be installed as early in the
construction schedule as possible. Sedi-
ment basins also, if they are needed,
should be installed early. Newly con-
structed slopes and other areas
susceptible to erosion should be mulched
or seeded to a temporary cover crop as
soon as possible after grading. Finished
grading leaves the soil extremely vulner-
able to erosion. For this reason, it is
advisable to schedule finished grading for
the time of year that is favorable to estab-
lishing vegetation; the site can be seeded
and mulched or sodded immediately fol-
lowing grading.
During construct/on, equipment should
be used in a manner that does not leave
the site more susceptible to erosion. Leav-
ing deep wheel tracks up and down the
slope, for example, should be avoided.
Cultivation and seeding should be across
the slope where possible. Access and work
roads should be located and built so as not
to encourage erosion.
If the construction site borders streams,
lakes, or reservoirs, special measures may
This severely eroded fill was the source of
tons of sediment that were deposited on
parkland below.
The same area 2 years [ater is well stabi-
lized. A shoutder dike prevents runoff from
going over the face of the slope.
be necessary to prevent damage to fish
and wildlife, water supplies, and irrigation
systems. Construction should conform to
regulations of water resource and fish and
wildlife agencies.
Restoring borrow pits and spoil areas
should help control runoff and sedimenta-
tion. Such areas should be drained,
graded, and revegetated so as to blend
into the surrounding landscape~ Diver-
sions, dikes, and sediment basins should
be used where needed to keep sediment
from entering streams or damaging land
and structures.
Responsibility for maintenance of the
permanent structures and plantings should
be clearly understood when ownership or
management of property transfers from
the developer or builder to a private own-
er, a public land administering agency, or
a community management association.
Permanent structures should be
spected soon after installation to locate
and correct any deficiencies. They then
should be inspected annually and after
major storms.
Plantings should be fertilized and
mowed according to a plan if they are in-
tended to be permanent. In some places a
change in cover may be planned or
needed. Reseeding or other appropriate
measures may be necessary in places to
improve the cover before erosion becomes
serious.
working together
Interest in community and area-wide
planning is increasing in both urban and
rural sectors. People want to get the most
beneficial use out of the land, and they
want pure water and clean air. They un-
derstand that these amenities come only
as a result of good planning; welbadmin-
istered ordinances, codes, and regulations;
public understanding and support; team-
work; and dedicated leadership.
SCS through conservation districts can
help engineers~ planners, zoning boards,
builders, and others by providing them
with soil, water, and plant data, interpre-
tations, inventories, and other technical
assistance.
A few local governments have adopted
erosion and sediment control programs
along with appropriate ordinances, build-
ing codes, and regulations to help carry
out their conservation policy. Ordinances,
codes, and regulations can be helpful in
two ways. They establish public policy
and criteria and guides for erosion and
sediment control, and they protect the
people, public property, and natural re-
sources.
Ordinances have sometimes failed to
accomplish their intended purpose be-
cause they were too complicated and
vague. Those that seem to work tie certain
controls into the local code by adding to
or amending existing subdivision regula-
tions. Builders and developers already
complying with the code merely assume
additional responsibilities.
27
Native trees, shrubs, and other plants
have stabilized and beautified this roadside.
In areas where an erosion and sediment
control ordinance has been adopted, the
local conservation district has usually ac~
cepted the responsibility of providing
technical assistance to the local govern-
ment agency that administers the code. A
site development plan then is approved
only if the developer or builder provides
for a level of protection against erosion
that meets the standards set by the con~
servation district.
Some local governments have adopted
ordinances to control flood-plain develop-
ment or encroachment. Flood plains are
the areas adjacent to streams that flood.
This steep cut slope was stabilized with
serioea ]espedeza, a Iow-maintenance cover.
In recent years, some local govern-
merits have modified their zoning and
flood-plaio regulations to provide for
planned unit development, whereby the
upland and the flood plain are considered
as a unit. This makes it possible to avoid
problem areas and to preserve open space
for scenic and recreation purposes.
Esthetic values are beiog lost in many
urban areas as parts of streams, creeks,
and runs are replaced by underground
water disposal or drainage systems. But
the loss goes beyond esthetics. Such sys-
tems are costly to install, and they in-
crease the peak flows of runoff down-
stream. Innovations in storm drainage
systems are needed to reduce peak flows,
lower costs, and preserve and enhance
esthetic values. An alternative to an un~
derground water disposal system could be
a stabilized natural stream with multipur-
pose structures for flood storage and
water-based recreation. Alternatives, of
course, need to be tested.
public understanding
and support
There is no substitute for a well-in-
formed public. People must know about
the resource potentials and problems in
their area, aud they must know about the
erosion and sediment control programs
that can help them.
Civic groups are helping in many ways
to inform the public. Some, for example,
make available to other groups speakers
and slide shows on urban erosion and
sedimentation problems.
Builder associations publish technical
material on erosion and sediment control
practices and distribute it to their mem-
bers. Some include conservation items in
their newsletters; others join conservation
districts or local government agencies in
promoting erosion and sediment control.
Conservation councils, watershed as-
sociations, river-basin commissions, com-
mittees for preservation of grcen space,
for protection of stream valleys, or for
acquisition of park land, and many others
influence public opinion and provide
forums for citizen reaction.
Some builders and developers serve on
their local conservation district governing
board. Many builders and developers
have been recognized by conservation
districts for their outstanding conserva-
tion work.
policies need to be
clearly stated
The conservation policy that a com-
munity or local government intends to fol-
low must be clearly outlined and simply
stated. Complexity or vagueness can lead
to misunderstanding on the part of build-
ers and developers, zoning boards, state
or federal government agencies, or one of
the many other groups that may have a
function to perform or have simply an
interest in conservation policy and pro-
cedures.
SCS conservationists working through
conservation districts meet periodically
with policy planning boards or other rep-
resentatives of local government to re-
view and evaluate conservation policy and
operating procedures and to improve, if
possible, coordination among individuals,
groups, and organizations.
conservation districts
provide leadership
Conservation districts are local public
bodies responsible under state law to pro-
mote the conservation of soil and water
and related resources. Districts meet their
objectives through citizen, group, and
community participation.
Crownvetch controls erosion and beautifies
as well
3O
Conservation districts across the coun-
try have broadened their programs to give
needed priority to urban conservation
problems, particularly problems on land
use. Several states have amended their
district enabling legislation to include ur-
ban areas within their district boundaries.
in some states, the nriginal legislation
limited district operations to rural areas,
Many districts have strengthened their
leadership in the community through the
election or appointment of urban leaders
to their governing body. Districts are
managed by local citizens who know local
prnblcms, and districts that take in sub-
stantial areas of urban land or rural land
being converted to urban use need strong
urban leaders on their governing boards.
Conservation tours, workshops, and
seminars have been effectively used by
districts to inform the public in urban
areas about conservation problems. Dis-
trict newsletters, leaflets, and films have
also been effective. A few districts have
employed a public relations specialist to
give leadership to such activities.
Districts are now looking beyond their
own boundaries to form multidistrict re-
source councils to help solve resource
conservation problems affecting large
areas,
Left. The fibrous material will help protect
this newly seeded streambank.
Right, Retaining walls of concrete rubble
have stabilized and improved this storm
channel. Careful planning and construction
have saved the trees.
Below. The fiat slopes along this concrete-
lined storm channel can be easily mowed.
assistance is available
SCS, through local conservation dis~
tricts, gives technical help to builders,
developers, town and county officials, and
others in working out land and water rem
source problems.
SCS can advise builders or developers
concerning conservation problems, pro-
vide technical information, and suggest
alternative solutions~ The builders or de-
velopers decide what they want to do after
considering the alternatives and use their
own planners aod engineers to carry out
the decisions.
Builders and developers are encour-
aged to discuss erosion and other conser-
vation problems with district conserva-
fionists before starting a site development
plan.
Conservation in urban development
means teamwork on the part of many
agencies, organizations, groups, and in-
dividoals. The hub of the program is the
county, town, or other local government
and the local conservation district.
The Focal government establishes land-
development policy and is responsible for
community planning, zoning, approving
site plans, issuing pernfits, and inspecting
constroction. Local government is the
developer when public land is used for
schools, recreation, parks, highways, and
other public purposes.
Conservation districts and the Soil Con-
servation Service are the technical arms of
the team. Districts represent the public
and promote the public interest. SCS pro-
vides the technical information. It a/so
makes soil snrveys and adminislers the
small watershed program.
Other agencies of the Department of
Agriculture contribute to conservation
with research on soil and water conserva-
tion and with educational programs. The
Department of Housing and Urban De-
velopment insures loans for land develop-
ment and through other programs helps
communities and municipalities in many
ways. Other departments and agencies
provide assistance in the fields of hydrol-
ogy and geology, health and sanitation,
transportation, outdoor recreation, and
preservation of scenic and historic areas.
Stone, or rubble, side slopes provide added
protection for this channel in open parkland.
Open-space land for parks and recreation
add beauty and enjoyment to everyday liv-
ing.
December 1970