Erosion Control

General short- and long-term erosion control techniques are outlined below. The erosion control industry has many useful websites with up-to-date technical specifications and guidelines. A list is provided at the end of the chapter. Take advantage of these resources and other educational opportunities to stay abreast of this rapidly evolving industry.

Soil Preparation

Strike a balance between an ideal seedbed and maximum erosion control. Firm, friable soil surfaces — recommended for seeding — can be susceptible to erosion. Loose, rough soil surfaces provide better infiltration and slow runoff.

Surface roughening practices, such as directional tracking and grooving, slow runoff by creating depressions or grooves perpendicular to the flow. On steep slopes, these practices must be used in conjunction with other methods, preferably hydroseeding. 

Directional Tracking

Driving a bulldozer or other tracked vehicle up and down a slope leaves depressions perpendicular to the slope. (Driving a tracked vehicle across the slope can increase erosion.) Tracking may not be appropriate on clayey soil since compaction can inhibit vegetation establishment, and severe compaction can even prevent no-till drills from penetrating the soil. Concerns regarding compaction decrease when hydroseeding or broadcasting during the dormant season, since freezing and thawing will loosen the soil.

Grooving

Pulling a disk or ripper behind a tractor or dozer, or back-dragging a toothed bucket with a loader across a slope creates a series of ridges and grooves. Grooving can be more effective than tracking because the depressions are usually deeper and the soil is left in a looser state. Many implements can be used.

SUDAS (Statewide Urban Design and Specifications) specifies grooves be no more than 15 in. apart and 3 in. deep, though groove depth is subject to debate. Deep grooves improve erosion control, but increase the likelihood of seed becoming buried too deeply to germinate. Seeding method will help determine the appropriate groove depth. One-step hydroseeding is best over deeper grooves since mulch keeps seed near the surface. If seed is not incorporated in a slurry when planted, lighter grooving is recommended.

Mulch

Mulch helps prevent splash erosion and holds seed in place by absorbing rainfall impact and binding soil particles together. Mulching is accomplished by blowing on straw or by hydromulching.

Straw

Dry cereal straw — free of noxious weed seed — can be applied alone or on top of seed to provide short-term erosion protection, conserve moisture and suppress weeds. Typically oats or wheat straw is used — blown on at a rate of 1 to 1½ tons per acre. Straw applied evenly at the correct rate will allow approximately 50% of the soil to be visible. If applied too heavily, seed germination may be affected. Some bale processors can be adjusted to make shorter or longer mulch — longer is better.

To keep straw mulch on site, it must be crimped or tacked in place. Areas accessible to ground-driven equipment can be crimped. Crimpers (a.k.a. mulch tuckers or mulch discs) are mounted on a 3-point and pulled with a front-wheel assist tractor. Test runs are necessary to ensure the crimper wheels go into the soil at least three inches — enough to anchor the straw. Properly anchored straw mulch will stand up straight and look similar to oats mowed high.

Tacking is accomplished by adding tackifier to water in a hydroseeder and applying evenly until the straw is wet, but not running off. This dries and acts as a glue to hold the straw in place. Tackifier rates vary with brand and are provided on the bottle in lbs. per acre. If too much tack is added, the mixture will get slimy and prevent the pump from priming. 

Some IRVM programs use prairie hay — harvested from plots or plantings — in place of straw mulch. Application method and rates are similar to straw, though rates may vary depending on the dominant species in the hay. Fewer bales will be necessary because the hay weighs more than straw.

Roadside Manager Insights

We use wheat straw. It seems to be longer than oats straw and is typically the same price. I have worked with a local contractor who brings up Kansas wheat straw. We have also used Iowa Certified weed seed free straw. 

-Wes Gibbs, Jones County, 2024

With oats or wheat straw, I’ve used seed-bearing stalks to my advantage; it can work as a good cover crop. 

-Ben Hoskinson, Mahaska County, 2011

We use an agricultural-type bale processor (no cannon). I use the rate of 1.5 T/acre as a minimum when planning. Just be sure you aren’t blanketing over your seed. You should be able to barely see the ground through the mulch before it is crimped. 

-Wes Gibbs, Jones County, 2024

To apply straw mulch, I use a small bale blower with a gas motor. It does a nice job of shredding up the bales. The process is labor intensive and, so I usually only tackle small projects with it. The big round bale blowers/shredders (I don’t have one) are less labor intensive and can cover a lot more area in less time.  This method requires mobilization for the bales and a large tractor to run it .  I generally mulch at 1000 to 1500 lbs. per acre. 

-Ben Hoskinson, Mahaska County, 2011

Our mulch tucker / cultipacker combo is 8 ft. wide and weighs 1600 lbs. We pull it with a 95 HP tractor – you might be able to go a little smaller as long as you have sufficient weight in front to balance it when in the “up” position. 

-Wes Gibbs, Jones County, 2024

We always use 1.5 tons/acre of straw mulch.

-Ole Skaar, Roadside Development, Iowa DOT, 2011

We have a couple organic farmers in the county. When I need straw, I buy it from them. They usually have a field in their rotational plan that will be in oats. I support the concept and like to help them in this small way.

-Linn Reece, Hardin County, 2011

If harvested in the fall just after the seed heads have matured, prairie hay bales will carry enough seed to plant a new site. Some seed supplement may need to be used. I think prairie hay works better than straw. It is just reedy enough that it lays out and kind of locks together.  Straw is a lot lighter and doesn’t lay down as well. 

-Ben Hoskinson, Mahaska County, 2011

Hydromulch

Hydromulches are applied with or on top of seed to conserve soil moisture and, depending on type, prevent splash, sheet or rill erosion.  None are suitable to withstand the shear stress of concentrated-flow situations.

Common Types of Hydromulch

Cellulose (Paper)

Made from recycled newspaper, magazines and corrugated cardboard, cellulose is the least expensive hydromulch. Its advantages over wood fiber mulch include: greater water retention, quicker mixing and better pumpability. Cellulose may be the least effective at controlling erosion since it does not have long, interlocking fibers. Be aware of the “paper mache” effect which reduces moisture and airflow to seed, and occurs when cellulose is applied too heavily or with too much tackifier.

Wood Fiber

Wood fiber mulch is produced from milled wood, typically aspen. It is more expensive than cellulose and does not hold as much moisture, but it has more loft and the interlocking fibers provide greater erosion control.

Wood/Cellulose Blend

Blended  mulch usually consists of 50-70% wood fiber and 30-50% paper products. It falls in the middle of the two previous mulches in terms of cost, water retention, pumpability and erosion protection.

BFM (Bonded Fiber Matrix)

BFM is a wood fiber mulch — usually with elongated fibers — containing various adhesives, binders and synthetic fibers. BFM mulches retain their strength much longer than traditional mulches.

MBFM (Mechanically Bonded Fiber Matrix) and FGM (Flexible Growth Media)

These mulches contain elongated wood fibers and crimped synthetic fibers along with various adhesives and binders. The crimped fibers provide a strong, mechanical, fiber-fiber-soil bond. No cure time is required to provide erosion protection.

Hydromulch Application

Hydromulch is mixed with water and often a tackifier in a truck- or trailer-mounted tank. Spraying the slurry on to the site is called “hydromulching.” When “hydroseeding,” seed and amendments are added to the slurry. The terms are often used interchangeably. Recommended hydromulching rates are shown in Table 1 and discussed in "Seeding Methods."

Tackifiers bind mulch fibers to each other and to the soil, enhancing erosion protection. Tackifiers can be purchased separately or be pre-blended in the mulch. Organic and synthetic tackifiers are available. All products have different recommended rates. See manufacturer recommendations before application.

Tackifying agents are preblended in BFM, MBFM and FGM products and undergo a chemical process known as “cross-linking” which prevents rainfall from rewetting and dissolving the tackifier after it is applied.

Amendments are added to the slurry to accelerate seed germination and establishment and improve poor soils. Amendments include water soluble fertilizer, water-storing polymers and plant growth stimulants. Refer to the manufacturer for recommended rates. Peat moss and compost screenings can also be added as a soil amendment, though little research exists on rates.

Synthetic fibers can be added as an amendment to increase the mechanical bond of traditional wood fiber and blended mulches.

Hydromulch Profile

Courtesy of landandwater.com.

Roadside Manager Insights

An important factor that can get overlooked when dealing with sheet erosion is the additional overland flow that may be coming from the roadway. This can really affect hydroseeded areas, and increased rates of hydromulch may be needed. This doesn’t seem to be an issue when using blankets – which makes sense since blankets are appropriate for protection against channelized flow.

-Jim Uthe/James Devig, Dallas County, 2024

SUDAS section 7E-5 deals with mulching to prevent sheet erosion, but I feel they are overly cautious. For instance they don’t recommend hydromulching on slopes steeper than 6:1. I recommend looking at manufacturer specs for available products.

-Jim Uthe, James Devig, Dallas County, 2024

I use a wood/paper blend which I think works the best. The wood I’ve used by itself doesn’t have enough substance. I also use FGMs or BFMs as a supplement to the wood/paper or as a stand alone.

-Ben Hoskinson, Mahaska County, 2011

Compost Blanket

Typically used on poor soil, a compost blanket is a 1–4 inch layer of compost applied with a blower truck. The compost is a blend of coarse and fine material. If seed is applied with the blanket, the layer should not exceed 2 inches; establishing roots may not penetrate the underlying soil if the blanket is deeper. Be sure the compost is well-cured; if applied while still “hot,” vegetation may not establish.

A compost blanket should not be used where overland flow is expected. The blanket will absorb rainfall, but overland flow can erode the compost. If the blanket must be used in areas with overland flow, till in the compost.

When applied correctly, compost blankets are very effective at preventing erosion and promoting seed growth. Specialized equipment is necessary to properly apply compost blankets, so a contractor is typically hired. Due to the expense, a guarantee should be requested to ensure the job is done correctly.

Rolled Erosion Control Products (RECPs)

RECPs are arguably the best way to stabilize most channel areas. They are also used to stabilize slopes. Because RECPs need vegetation to function properly, site conditions must be conducive to vegetation establishment. In extremely poor soils or deep shade, riprap or erosion stone may be the best option. Temporary and permanent rolled products are available.

Manufacturers of RECPs provide specs for their products online. Most manufacturers also provide software to help determine the appropriate product for a given site. A list of virtually all RECPs on the market and their specifications is in the Geosynthetics Specifier’s Guide.

Types of RECPs

Erosion Control Blankets (ECBs)

Erosion control blankets are temporary, degradable rolled products made of natural or polymer fibers mechanically, structurally or chemically bound together to form a continuous matrix. Blankets are usually classified as netless, single-net or double-net.

Netless blankets consist of fibers stitched together with a biodegradable thread. Because there is no net, this product is typically used in intensively mowed areas and areas where animals could become entangled in netted products.

Single- and double-net blankets consist of one or two polymer or jute nettings interwoven with natural fibers — typically straw, coir (coconut) and/or excelsior. In general, netless and single-net are used on slopes or in low-flow channels. Double-net can be used on slopes and in higher-flow channels.

Turf Reinforcement Mat (TRMs)

TRMs are permanent, non-degradable, rolled products made of synthetic materials. These three-dimensional mats provide immediate erosion protection, enhance vegetation establishment and offer long-term functionality by permanently reinforcing vegetation. TRMs are typically used in high-flow ditch channels and on very steep slopes where unreinforced vegetation may not provide adequate erosion protection.

SUDAS classifies TRMs by material and by their performance in channel and slope applications. Refer to Table 1 for more information.

Selecting the Appropriate RECP

Slope Applications

Manufacturers’ general application guidelines are the easiest way to select a product. A link to an example of these guidelines is provided here. Slope length and grade are used as criteria. Product longevity (determined primarily by material weight) must also be considered when using degradable products. Time of year, soil fertility, aspect, seed mix and other factors affect how quickly vegetation establishes. A product may be appropriate for a specific slope length and grade, but if installed over a seeding in poor soil, it may deteriorate before vegetation establishment.

Manufacturer software is also used to select products for slope protection. Links to examples are provided below. Slope length and grade, surface condition of the soil and the soil erodibility (K) factor for the soil type (found in the NRCS soil survey for each county) are entered in the program which then suggests multiple appropriate products. Growing conditions and seed mixes determine the appropriate functional longevity.

Software Examples

Channel Applications

When stabilizing a concentrated flow area with temporary RECPs, estimate the amount of flow and time it will take for vegetation to establish. Then use manufacturer specs to select a blanket with the appropriate strength and longevity.

For large-scale projects, especially in high-flow situations, further analysis may be necessary:

Courtesy of landandwater.com.

Installing RECPs

Erosion Control Blanket Installation

RECPs are often maintenance-free after vegetation has established. Until then, inspect after every runoff event, adding staples where erosion has occurred. Routine maintenance is easier than repairing and reseeding the large ruts and gullies that can form under improperly installed or maintained RECPs.

TRM Installation

Roadside Manager Insights

I had heard at one time that forbs germinate better under straw than excelsior, but I’m starting to become a skeptic on that claim. For instance, I just inspected a project where we used Curlex-2 and there were just as many partridge pea seedlings in the blanketed areas.

-Jim Uthe, James Devig, Dallas County, 2024

TRMS can stabilize very steep slopes, but in a typical county roadside setting it may be cheaper to buy more right-of-way, grade it to a generally slope, and stabilize by hydroseeding or seeding/mulching.

-Jim Uthe, James Devig, Dallas County, 2024

We used double-net, straw/coconut blankets for concentrated flow areas with success, but due to the cost we’re switching to double-net straw. They seem to allow just as good germination as the straw/coconut blend and are almost $20 cheaper per 100 ft. roll. They seem to provide adequate protection in a typical ditch bottom, but don’t last as long.

Single-net straw blankets are available, but they only work in low-flow channels and are much more difficult to unroll than double-net. Double-nets are only about $7-10 more.

-Jim Uthe, James Devig, Dallas County, 2024

If you’re doing a lot of RECP installations, get a staple gun. It’s worth the money! And if you need to cover a lot of surface area, I suggest the 16 ft. rolls (vs. the more common 8 ft. rolls). They’re still fairly easy to handle and they cut your installation time and labor almost in half. 

-Wes Gibbs, Jones County, 2024

We do not use straw or straw/coir blankets in channels. Those materials don’t absorb water like excelsior, so the blankets float if rain causes any flow. You might get them to work with sediment logs or lots of staples, but that isn’t cost effective. Nothing beats good wood excelsior.

-Ole Skaar, Roadside Development, Iowa DOT, 2011

Other

Flow Transition Mats

Flow transition mats are a “green” alternative for riprap or concrete in the transition area between flow outlets and channel flow. The semi-rigid, plastic mats – approximately 4 ft. x 4 ft. x ½ in. – are designed with holes which allow vegetation to grow. The mats are installed on top of a TRM in areas of high scour, such as culvert outlets. Flow transition mats can provide better protection than riprap and installation is an easy, one-man job.

Roadside Manager Insights

ScourStop can be used as a riprap alternative for channel protection if flow occurs only during larger rain events. The channel needs to dry out at times so vegetation can establish.

-Ole Skaar, Roadside Development, Iowa DOT, 2011