By Ryan Ciolfi
From the August 2024 Issue

 

Today, the amount of rain falling per hour is increasing — and with it, effects like dangerous flash floods and erosion are becoming more common. We know this anecdotally, but the data backs it up as well.

According to Climate Central, 136 of 150 U.S. locations analyzed have experienced increasing hourly rainfall intensity since 1970. Rainfall “hours” became 13% wetter on average across all 150 stations from 1970 to 2022. Though hourly rainfall intensity has increased in every US region, the largest increases have been seen in the Central and Southwest. The largest average increase in hourly rainfall intensity was in: East North Central (+19%); West North Central (+18%); Central (+16%); Southwest (+14%); and Northeast (+13%).

The Environmental Protection Agency (EPA) also reports that in recent years, a larger percentage of precipitation has come in the form of intense single-day events. Nine of the top 10 years for extreme one-day precipitation events have occurred since 1996.

While the statistics above relate to data as of 2021, recent years seem to follow the trend. On April 11, 2024, Pittsburgh received 2.77″ of rain in one day, smashing the record of 1.46″ that had lasted since 1933, according to the National Weather Service.

(Photo: Finn Corporation)

 

Heavy Rainfall’s Effect On Soil

Such heavier rainfall events can cause a variety of adverse effects to land and soil, especially its ability to retain water and nutrients. When soil is impacted this way, land also becomes more susceptible to flooding and further soil degradation.

The Oklahoma State University Cooperative Extension reports that rain falls at velocities of 30′ per second, causing destruction of the topography of a dirt site. A single drop of rain can cause soil material to rise as high as 3′ in the air and move nearly 5′ from the site of impact. The Science Society of America estimates 26.4 billion tons of soil are lost each year to erosion globally.

Studies suggest the total cost of soil erosion could be as much as $44 billion annually. For landscape contractors, learning how to prevent water erosion can be one of the most beneficial things you do to not only provide solutions for clients, but ensure the longevity of your design.

Additional issues are caused when eroded topsoil sweeps into water bodies. This can cause problems, such as:

Degraded water quality
Discolored water, reducing enjoyment of recreational activities
Decreased depth of lakes and reservoirs, causing shallower water, susceptible to increased evaporation
Obstruction of hydroelectric turbines and increased cost of purifying water.

Studies suggest the total cost of soil erosion could be as much as $44 billion annually. For landscape contractors, learning how to prevent water erosion can be one of the most beneficial things you do to not only provide solutions for clients, but ensure the longevity of your design.

Types Of Erosion

Water erosion is categorized into four types: Splash, Sheet, Rill and Gully erosion.

Splash erosion occurs when rain strikes the soil surface. The impact of the droplet causes soil to be displaced.
Sheet erosion refers to water runoff moving soil particles. During sheet erosion, water moves around dirt clods and through the path of least resistance.
Rill erosion occurs when thin layers of water move downhill. This typically happens in tiny channels called “rills.” As water builds more momentum down a steeper hill, it is likely to cause greater erosion.
Gully erosion is the advancement of rill erosion. When a rill becomes a channel too large for equipment to correct the problem, it is labeled a gully.

Controlling and preventing erosion is best done by covering soil with either growing vegetation or another natural material. Grass, plants, straw, and other cover materials absorb the energy produced by falling rain and slow the movement of water. Reducing the water flow rate on the surface prevents water from carrying topsoil to another location and allows more time for the soil to absorb the water for vegetation growth.

Preventing Erosion

Planting & Hydroseeding. One of the most important steps to prevent water erosion is to plant in the areas experiencing the most erosion. There are many kinds of plants to choose from, with trees and shrubs outperforming the rest.

Tree roots help stabilize the soil by holding it in place during heavy rains, preventing a lot of runoff. Shrubs with extensive root systems can also help prevent soil degradation and runoff in a similar way.

Planting vegetation will typically help preserve and retain moisture levels in the soil. Hydroseeding is a great way to plant quickly and effectively.

Mulching. Mulching is another effective water erosion solution. Most mulches are generally absorbent, though how much depends on the type. Finely shredded, hard bark mulches are some of the most absorbent. Wood chips can be effective at retaining rainwater and preventing erosion.

Straw mulches also prevent erosion and assist in the revegetation of the landscape. Straw provides an erosion control blanket to protect the ground and freshly sown seeds. Not only does it protect the ground from erosion and seeds from washing away, it also absorbs water and provides additional moisture to promote germination.

Mannering and Meyer conducted research evaluating erosion levels compared to the thickness of the straw blanket. Using a test site with a 5% slope, they simulated rainfall totaling 6.25″ at a rate of 2.5″ per hour. When no straw mulch treatment was applied, they observed 12 tons of soil loss per acre. Applications of one ton of straw mulch per acre or more resulted in virtually no erosion.

A study published in 2019 in the Science of The Total Environment found straw mulch is “efficient management in recent fire-affected mountainous terrains to control soil loss immediately after wildfire.” Erosion is a major concern after wildfires in mountainous regions since the ground, devoid of vegetation, is left without protection from the elements. Fast, even application in such areas can be achieved with a straw blower.

Straw blowers assist in areas torn up by various factors to provide a 95% reduction in erosion, significantly reducing sediment loss that would otherwise end up in streams and wetlands.

Compost Socks & Erosion Control Berms. Compost socks and erosion control berms can serve a variety of uses, including effectively preventing erosion. They are especially well suited to direct or concentrate the flow of rainwater in and around surfaces. These compost-filled mesh tubes can be placed anywhere runoff is heavy to help disperse water and filter any runoff. Flexible and easy to use, compost socks provide direct prevention for erosion-prone areas.

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These devices are used in lieu of silt fence or other fence barriers that use plastic and/or steel components. Erosion or filter socks utilize organic material in a mesh tube that is a much “greener” approach. Compost socks and berms can also help support areas where planting needs to be done— helping to hold the soil in place and provide stabilization while plant roots establish.

Retaining Walls. If other steps taken to prevent water erosion haven’t provided the amount of soil stabilization and water retention required, a retaining wall can generally do the trick. The most permanent of solutions, retaining walls can be especially useful in sloped areas to establish a soil foundation that’s protected from water erosion and runoff.

Diversions & Drainage Ditches. Managing rainwater erosion and runoff effectively can also be accomplished by creating pathways for water to divert or drain from areas such as steep slopes or embankments. Digging a ditch, shallow trench, or even a French drain may be a useful way to create a water diversion, while gutters and piping can provide a streamlined solution if space is tight. When choosing this BMP or best management practice, be sure to choose products whose installation will reduce and capture sediment leaving the site.

While there are many erosion control methods, no two solutions will work the same way for each project or parcel of land. For more information about water erosion prevention solutions and tools, contact an expert.

Ciolfi is the Eastern Regional Sales Manager for Finn Corporation, an international manufacturer of hydroseeders, bark blowers, and straw blowers. He has been in the Green Industry since 1999 and is a Certified Professional in Erosion & Sediment Control (CPESC). Prior to being employed by Finn, Ciolfi worked at an equipment dealer that not only sold Finn equipment but also specialized in erosion control supplies and materials. During his more than 20 years in the industry, Ciolfi has been able to learn different erosion control techniques from his colleagues and customers and enjoys sharing that wealth of knowledge to help make his customers successful. For more information on Finn, visit FinnCorp.com. This article was adapted from an original on the Finn website. More informative articles from Ciolfi are available here.

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