Filter Berms: All You Need To Know About

Erosion control and water conservation are two major concerns for environmental sustainability.

Every year, thousands of acres of fertile land are lost due to soil erosion. As a result of this process, the land becomes barren and useless for anything else, including grazing.

To cope with this issue, there is a growing effort to find ways to control erosion. Governments and environmental organizations have been constantly looking for better ways to fix these problems.

That said, the responsibility of preventing erosion, and protecting water resources falls on everyone. Therefore, it is important to know about the different types of erosion control methods and how they work.

Although there are various methods for controlling erosion, one of the most low-cost and efficient ways is to use a filter berm. Filter berms allow us to control erosion while using the land’s natural features to our advantage.

In this post, we’ll look at what filter berms are, how they work, and how effective they are at reducing erosion.

What is a filter berm?

A filter berm is a man-made feature used to control erosion and runoff. It is a ridge of soil or rock that is placed along the edge of a channel or waterway to prevent sediment from entering the water.

What are the uses of Filter Berms?

The main purpose of a filter berm is to act as a filter, trapping sediment and other materials before they can enter the water. By doing so, it preserves both fertile land and water resources.

filter berm

Filter berms are versatile structures that can be used for a variety of purposes. However, there are a few specific places where they are commonly used.

High sheet erosion areas

High sheet erosion area is a term used to describe an area where the soil is eroding at a high rate. This usually happens on the slopes that have little or no vegetation.

Filter berms are effective at controlling sediment in high sheet erosion areas, and steep slopes up to a 2:1 slope, and other disturbed construction site areas. 

Roadsides

Roadside filter berms reduce sedimentation on roadsides and in road drainage systems, helping to prevent soil erosion.

They help to keep sediment from entering the roadway and causing accidents or damaging the road surface. As a bonus, by using these berms on the roadside, we can also prevent dirt and other debris from entering waterways like creeks and rivers.

Construction Sites

Construction sites are another area where filter berms can be used to great effect. The construction process creates a lot of disturbed soil, which is prone to erosion.

By installing a filter berm around the perimeter of the site, we can reduce the amount of sediment that enters the water. This helps to protect both the land and the water from being polluted by sediment and other materials.

Farmers’ fields

Filter berms are often installed around farmlands as well. By doing this, farmers can reduce runoff that might cause water erosion and soil loss.

The berms also help to keep the soil moist, which is beneficial for crops. As an added bonus, the mulch from the berm can be used as a natural fertilizer for the crops.

Water Conservation

Filter berms around farmlands help to conserve water by preventing water loss. They help us to better retain water in the soil, which is beneficial for crops.

This means more of the water can be used by plants and crops rather than wasted down a storm drain or stream.

Helping migration of aquatic animals

Filter berms can also help in the migration of aquatic animals. This is because they provide a safe passage for them to cross without being injured by passing cars or boats.

For example, turtles and salamanders tend to relocate to different habitats as they grow. A filter berm can provide a safe passage for them to cross without being injured.

By understanding the benefits of filter berms, we can see why they are such an important tool in controlling erosion.

They are versatile, low-cost, and effective at reducing sedimentation. They can be used in a variety of places to great effect, helping us to protect our land and water resources.

What are the primary design considerations for Filter Berms?

Despite their simplicity, there are a few considerations that need to be made when designing filter berms. Here are the most important ones:

Intended use

A filter berm is not a one-size-fits-all solution. It needs to be designed specifically for the intended use. For example, a roadside berm will need to be designed differently than a berm used in agricultural fields.

This is where the intended use comes into play. The designer will need to take into account the specific conditions of the area where the berm will be used. We have covered a few of the most common uses, but there are many other possibilities.

Location

Another consideration to take into account is the location. The berm should be located where it will do the most good. For example, a filter berm used on a roadside should be located where the slope is greatest.

Similarly, if we are trying to control sediment runoff from a construction site, the berm should be installed around the outermost edge of the disturbance. The location of each berm will depend on its intended use and other site-specific parameters.

To the greatest extent possible, build berms away from the toe of a slope and on the flattest accessible surface to allow sheet flow energy to disperse and give more sediment storage.

Install berms perpendicular to the sheet flow contour with the ends turned upslope to avoid runoff from circumventing the berm.

Elevation

The elevation of the berm is also important. It needs to be high enough so that it is effective in controlling sediment.

However, the berm also needs to be low enough that water can pass through it easily when there’s a storm.

Slope

The slope of the land is another important consideration. The berm installed on a farm field will require different parameters than a berm installed on a steep hillside.

The slope of the land should be taken into account when designing and installing filter berms because it will affect how easily water can pass through them. The steeper the slope, the more carefully the berm needs to be designed and installed.

When possible, create berms 1.5m or more away from the slopes’ toes to allow water coming from the slopes to deposit sediment in the most space possible. A second berm may be necessary if this 1.5m distance is not available owing to construction constraints. The goal is to have sediment deposited as close to the toe of the slope as possible.

The maximum slope of the drainage area should be 10%. Place several berms perpendicular to the flow route at regular intervals down steeper (> 6 percent) and/or longer slopes (more than 50-75 feet).

Size and shape

Berms also need to be designed with a certain size and shape. These factors will determine how effective the berm will be in controlling sediment.

A berm that is not of the correct size and shape will not be effective in controlling sediment runoff. It is important to get these factors right in order to maximize the benefits of the berm.

Berm shapes are typically trapezoidal, and the shape must be continuous along the length of the berm.

The berm should be wide enough so that it can effectively trap sediment and debris. It should also be tall enough so that it can control the flow of water.

However, it is important to remember that a berm that is too large will be more difficult to install and may not be cost-effective. Similarly, a berm that is too small will be ineffective at controlling sediment and water flow.

The shape of the berm is also important. It should be designed to fit its intended use and location.

For example, a filter berm used to control sediment from a construction site should be designed as an arc. This will help channel the water away from surrounding areas. While there is no one-size-fits-all shape for a filter berm, these general guidelines can help you get started.

Soil type

Soil type is another important consideration when designing a filter berm. The soil needs to be able to support the construction of the berm, but it also needs to have high infiltration rates in order for it to work effectively.

A variety of different materials can be used as filters including sand, gravel, and crushed stone. However, there are also effective filters are those that are made from natural materials such as compressed straw or wood chips.

Berms made of fiber rolls or other lighter-weight materials must have complete soil contact and be anchored or otherwise secured.

Level Contour

Place berms on level contours to help disperse concentrated flows. Avoid building berms that channel or concentrate runoff. Water should flow perpendicular to the berm at impact and not be concentrated. The goal is to have the water spread evenly over the entire berm.

Flow around ends

To prevent water from running around the berms’ ends, the berms must be built upslope, with the ends elevated. This will help to keep the water on the berm and flowing through it.

Vegetation

Vegetation will help to stabilize the berm and keep it in place. It will also slow down the flow of water, allowing more sediment to drop out. It may also provide wildlife habitat to help mitigate the impacts of construction.

For permanent sites, seeded berms allow plants to grow directly on the berm and 1.5m in front and behind it. Grass on and around the berms will help slow down water flow for filtering.

It is recommended to immediately stabilize soil berms with means such as plants, erosion control blankets, or similar practices. Also, install energy dissipation materials such as riprap where berms may induce scour or erosion.

However, it is not recommended to use soil additives or fertilizers for the seeded berms. Because of the high potential for runoff, these can contaminate water resources.

Drainage area

The berm should be designed to allow for the drainage of water. This will help keep the berm from ponding and to function properly. Design berms to handle peak flows from a two-year, 24-hour storm event.

Maximum Drainage Area of a Filter Berm Based on Slope and Slope Length.

SlopeSlope Length (meter)Berm Size Required
0%-2% (Flatter than 50:1)76.2m0.3 x 0.6m
2%-10% (50:1-10:1)38.1m0.3 x 0.6m
10%-20% (10:1-5:1)30.48m0.3 x 0.6m
20%-33% (3:1-2:1)15.24m0.4 x 0.8m
>50% (>2:1)7.62m0.46 x 0.9m

Dispersing flow

Flow coming off a slope should be dispersed across the width of the berm to decrease erosion. This can be done by angling the berms towards the slope, making them wider at the top than at the bottom, or using multiple berms in series.

In most storm occurrences, sheet flow and runoff should not surpass the height of the berm capacity.

If berm overflow is a possibility, larger berms should be built, or other viable sediment management measures should be used. To keep sediment from spreading vegetation should be seeded on the berm and in front of it.

What are the installation and maintenance considerations for Filter Berms?

Filter berms are installed in a manner that allows runoff to pass through the berm while trapping sediment. However, they are only good as long as they are installed properly and maintained well.

Therefore, filter berms should be inspected regularly and after all rain and snowmelt events to ensure they maintain their form and flow. If the berm becomes saturated, water can flow around the ends of the berms which decreases their effectiveness.

Additionally, sediment should be removed from the filter berms regularly to keep them performing at their best. For long-term sediment control, berms can be seeded during construction to add a vegetative filtering component.

When the berms reach their expected lifespan, they should be scattered with a loader, rake, bulldozer, or other vehicles to be integrated into the soil, or they can be left on top of the soil for final seeding. There is no need for any other type of disposal.

The responsible engineer should direct the placement of filter berms at the areas indicated on the designs.

Berms should be built along to the slope’s base or in other affected regions, with a 0.3m high by 0.6m broad berm. In extreme cases (e.g., 2:1 slopes), a second berm must be built at the top of the slope.

If the filter media berm is to be left as a permanent filter or as part of the natural environment, it may be seeded at the time of installation to establish permanent vegetation.

Filter berms should not be used in direct flow or runoff channels. If direct water flow is possible, use DitchChexxTM in identical diameters and stake as directed.

The installer must remove sediments gathered at the berm’s base when they reach 1/3 of the berm’s exposed height, or as specified by the Engineer. In order to limit sediment disturbance operations, an additional berm may be built upslope of the existing berm.

Filter berms are not such stable and efficient structures. Therefore, they must be maintained regularly. Here are some steps which must be applied to maintain filter berms, as their efficiency directly depends on their condition.

Filter berms must be checked regularly every week, especially before and after rainfall, because the increased water flow may damage them. Therefore, they need to be resettled to fulfill the purpose.

If the geotextile fiber is used, it needs to be cleaned or changed frequently because of the sediment build-up in its holes. Not changing the geotextile fiber is going to make the filter berm useless. So you must look for a place that will not be affected by this, to dispose of the sediments.

A recommended thing is to change the size of gravels frequently to keep the efficiency of the filter berms.

Filter berms must be removed once they don’t serve the desired goal anymore. Because they are prime structures that may house pests, mosquitos, fungi, and other undesired organisms in the territory.

Is There a Difference Between a Dam and A Filter Berm?

Dams are structures that block the flow of water, while filter berms allow water to flow through them. Dams are typically made out of concrete or other sturdy materials, while filter berms can be made from a variety of materials, including geotextile fabric, soil, and rocks.

A dam is a permanently constructed barrier on a massive scale, whereas a filter berm is a small barrier that is also meant to filter the water while also trapping sediments to allow them to flow away from land.

Finally, a dam is built to control large amounts of water from heavy rainfall or large bodies of water while a filter berm is used to control overland sheet flow.

Which Materials Are Used to Construct Filter Berms?

Berms can be built from soil, rock, wood chips, compost, or compacted soil. The choice of material will depend on the function of the berm and the local soil conditions as well as the budget for the project.

Soil

The most common type of berm is made from soil, which can be easily excavated and does not require specialized equipment to install. In order to improve the strength of soil berms, they are usually compacted to reduce the amount of settlement that will occur over time.

Soil berms that handle erosive flows must be stabilized (e.g., erosion control blanket overseed). Berms that divert flow should send it to a sediment control BMP for muddy flows or a scour-resistant dispersal zone for water that isn’t likely to erode (for clean upland diversion flows).

Soil berms should not be used in places of high flow. To avoid ditch downcutting prior to stabilization, use correctly spaced stone and/or fiber log check dams.

Compost

Compost berm is made from a mixture of soil and compost, which can improve the quality of soils in an area by improving its water retention properties. It works similar to a soil berm but has the added benefit of being able to improve the quality of the soil.

Rock

Rock berms are more expensive to construct than soil berms, but they are very durable and can last for many years with little maintenance. The type and size of rock used will depend on the location and expected lifespan of the berm.

However, projects can use different sizes of rocks in order to grade berms for better water control.

Wood chip

Wood chip berms are made from a mixture of wood chips and soil. The wood chips help to stabilize the berm while the soil helps to hold the shape of the berm. They are typically used in sensitive environmental areas and can be designed to blend in with the surrounding landscape.

It is a great practice to use netting to avoid washouts during storm events and preserve the integrity of the berm system.

Can you walk or drive over a Filter Berm?

Filter berms are designed to slow the flow of water and sediment, so it is not advisable to walk or drive over them.

If for some reason you need to walk or drive across the berm, you should ideally use a bridge or crosswalk. Because the berm’s ability to prevent erosion decreases when it is used as a throughway.

If this is not possible and you need to walk or drive across the berm, try to restore these sections immediately with a rake or shovel. Otherwise, the effectiveness of the berms reduces due to continued driving or food traffic on them.

Conclusion

Filter berms serve a variety of different purposes in order to protect soil from erosion and sedimentation. They are made from a wide range of materials, depending on the location and function they need to fulfill.

Finally, filter berms must be maintained over time with regular grading or scraping in order for them to remain effective. They usually do not require considerable labor or construction costs and can be used in a variety of settings.

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