Use of Earthen Berms For Erosion
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Table of Contents
- Design Considerations
- Construction Considerations
Earthen berms are frequently required as an integral
component in many erosion control systems. They can be used as a dam to
temporarily hold back water (floodwater storage) or they can be used to
deflect or collect water.
- Earthen berms used as a component of a floodwater storage system
- achieve the same objective as a grassed waterway, however, do not
require the land area or associated problems related to the grassed
- work as a slope length reducer. This can reduce sheet erosion problems
yet allow the farmer to continue intensive farming practices;
- reduce the size of outlet pipe required. By storing the water for
a period of time the outlet pipe can be reduced in size and be used
at full capacity for a longer period of time;
- reduce the peak flow occurring further down in the watershed;
- reduce the plugging potential at the drop inlet grate. The ponding
will slow down the flow of water allowing debris to settle out before
it reaches the grate.
- An earthen berm used as a deflector or collector can;
- divert water flow to a less erodible location;
- collect water from many locations and move it to one large drop structure;
- dam water high enough to create sufficient head on a drop structure
to allow it to operate at maximum capacity.
- Any overtopping of the berm can have disastrous effects both on the
immediate project and the environment and structures further down the
watershed. Provisions should be made to handle any overtopping in an
erosion resistant manner.
- Berms (especially narrow based) are vulnerable to rodent damage which
could cause failure of the berm.
- Tillable berms normally can only be cultivated in a direction parallel
to the top of the berm.
- Capital costs of an erosion control system utilizing a berm can sometimes
exceed the cost of a comparative system such as a grassed waterway.
- The ponding of water behind the berm can cause some crop damage especially
in the vicinity of the drop structure.
- When designing an earthen berm for use in a floodwater storage system
the following steps are required.
- The total incoming volume and peak flow rate of water must be determined.
These values depend on the watershed's characteristics
- The maximum available water storage area and volume should be determined
by initially performing a grid survey of the proposed impoundment area.
Once this is completed, the volume of impounded water can be determined
by using charts or mathematical calculations. Any earth to be excavated
within the storage area will increase the overall holding capacity.
- Based on the above, the outlet size and/or spillway dimensions can
be determined. Under most conditions the outlet should be sized to ensure
that the ponding time is limited to less than 24 hours which is the
maximum flood time tolerable to most crops.
- When designing an earthen berm for use as a deflector or collector
the following steps should be taken.
- With this type of structure, the drop structure or spillway will be
large enough to handle the peak flow expected. Normally the maximum
head of water required over a drop structure or spillway should dictate
the maximum height of the berm.
- Necessary reinforcement of the berm should take place at locations
where high water velocities may erode the berm. This reinforcement could
consist of rock riprap or a vegetative lining.
- The following design considerations are required for both types of
- Protection for the potential overtopping of the berm must be installed.
This protection can be as simple as making sure that the crest of the
berm is completely level to ensure that this flow will be distributed
over a wide area. However, in larger or more vulnerable structures an
emergency spillway should be constructed. This could consist of a grassed
waterway or a rock chute underlain by proper filter material.
- Side slopes of the berm should be determined. If farm equipment is
to cross, the slope should not exceed 1:10. If no equipment is expected
to cross, the slope should not exceed 1:3 in sandy soils and 1:2 in
- Access for maintenance operations such as mowing of the berm and maintenance
of other structures must be considered.
- The area from which the soil for the berm construction is obtained,
normally known as the borrow area, should be as close to the site of
the proposed berm as possible. Depth of existing field tile can be a
limiting factor. Location of the borrow excavation should be chosen
to prevent any unwanted changes in surface drainage direction.
- Top soil should be scraped and stockpiled at the sites of both the
borrow area and the area of the proposed berm and should be replaced
after removing and forming subsoil. Grades should be taken during construction
to ensure that the necessary berm height is achieved and to ensure that
it is level.
- If sufficient clay content is not available in the subsoil, fill should
be brought in from off-site. Technical expertise will often be required
for such decisions.
- Where rodents are a potential problem, wire mesh should be installed
below the soil surface to prevent burrowing, especially in narrow-based
- The berm should never be placed on potentially unstable soils. An
example of this is a berm located at the top of an existing gully. This
berm should be located far enough back from the crest of the gully to
not be affected by any future settlement.
- Differential settlement must be controlled. This can happen when a
tile is installed under the berm. Settlement in this trench may cause
a void or an uneven crest in the berm.
An alternative is to install the tile at least 1 year before the berm
is completed. Any settling over the tile will have time to take place
before the berm is installed.
- A tillable berm should not be plowed. However, if significant settlement
occurs, they may be plowed, starting at the base of each side and turning
the furrows upward to build up the berm.
- Non-tilled narrow-based berms should be left in permanent sod
- Regular checks for cracks, settlement and outlet obstructions should
be made especially before major runoff events occur. It is much easier
and more economical to alleviate potential problems at an early stage
than to suffer the consequences and potentially be required to rebuild
the entire berm. This holds true for most erosion control measures.
- An emergency spillway often has to be repaired after an extremely
large storm has taken place. If this repair is frequent, consideration
should be given to major improvement to the capacity of the system.
Qualified erosion control contractors and consulting engineers are available
for the design and construction of erosion control structures. Conservation
Authorities may offer technical assistance and construction supervision
in some areas of the province. Other erosion control factsheets and information
are available by calling 1-888-466-2372.
All erosion control projects must comply with existing legislation, for
example the Lakes and Rivers Improvement Act, and the Fisheries
For more information:
Toll Free: 1-877-424-1300