Erode no more

Features - Design/Build

Lawn & Landscape gets to the bottom of how to mitigate erosion by controlling water runoff.

April 5, 2013
Lyndsey Frey

Jason Miller understands firsthand the devastating effects that April’s nasty mix of snow melt and gully washers can cause. After the 2011 record snow melt and rainfall overflowed the Missouri River levees in Omaha, Neb., for months, Miller was one of hundreds called out by the U.S. Army Corps of Engineers to help reconstruct the levees and protect the more than 25,000 acres from being destroyed by future flooding and erosion.

Hydroseeders were employed to promote early germination and root development to quickly revegetate the levees. Rapid revegetation on the levees’ steep slopes was imperative because the grass roots would help hold the soil in place, while the top growth would protect the soil from rain droplets’ impact during the spring gully washers. Overall, hydroseeding offered a lower-cost alternative than erosion-control blankets due to less manual labor, and delivered faster results in a tight time frame.

“The biggest concern was sediment control … to prevent erosion into waterways,” says Miller, a Finn products specialist at RoadBuilders Machinery & Supply Co. in Kansas City, Kan. “Hydroseeding was a guaranteed fix. Every time the material gets wet, it holds moisture like a sponge so it helps the germination process. (Plus), hydromulching protects the soil … from rainfall because it helps disperse the water droplets.”

Miller was charged with training a group of local landscape contractors on-site to use a 1,200-gallon hydroseeder, and apply the proper formula on the more than 120 acres he was responsible for revegetating.

The best formula for the job included hyrdromulch and a tackifier to help materials hold firm on the steep slopes built along the Missouri River shores. With the warmer, sunnier spring days, the hydromulch’s dark green color and wood fiber acted as an insulator to protect against the cold evening temperatures. “They built up the levees, but they also made them stronger, taller, wider,” says James Loneman, Finn distribution sales manager in Fairfield, Ohio.

Erosion can occur in any landscape – big or small – especially where there are steep slopes, exposed soil due to construction, or areas where there is excessive storm runoff. It not only damages landscapes, but it adversely can affect soil conditions, creating a negative growth environment for plants, and can contaminate waterways. In severe cases due to neglect, erosion can take out whole root systems or even sections of plants, and damage sidewalks, roads and structures.

Alternative solutions. Revegetation and hydroseeding are just one way to impede landscape erosion via controlling water runoff. In fact, there are an abundance of solutions landscape contractors implement, such as incorporating rocks or other aggregates into landscape designs, using groundcover plants, and adding mulch or soil amendments. But, there is no cookie-cutter approach; each solution is site-specific. Erosion control experts share a handful of common solutions landscape contractors are implementing to impede – and prevent – erosion by controlling water runoff.

Erosion Red Flags

FINN Corp. Distribution Sales Manager James Loneman shares common signs a landscape may be suffering from erosion due to water runoff.

  • Gullies or rills in landscapes or on slopes after a hard rain
  • Muddy or murky water in creeks or retention ponds
  • Contaminated water in water features
  • Tree roots or rocks becoming exposed
  • Sediment collecting on sidewalks, driveways or other pavement

“Proper and adequate planning and layout (of landscape design) can certainly mitigate that,” says Brigg Abercrombie, product development/technical manager at Jackson, Miss.-based Forestry Suppliers. “Implementing the necessary precautions initially to minimize erosion is going to maximize the effect. Erosion is kind of like a knock in your car. It ain’t going to get any better; it’s just going to get worse.”

Abercrombie points to one solution many landscapers are using: the company’s erosion control granules. It’s a new soil stabilizing amendment, which is made up of water-soluble polymers. When wet, these granules bond soil particles together, therefore reducing the effects of water runoff.

“It’s a treatment that is truly more geared towards minimizing the effect of stormwater or surface water,” he says. “One other benefit … because it is a polyacrylamide, it has water retention capabilities … and minimizes the amount of irrigation that is required.”

Instead of silt fences, Loneman is seeing more landscape contractors implement sediment socks or logs for perimeter control. Using 9- to 18-inch sediment logs can help keep sediment on-site and filter any contaminants to discharge off clean water.

“The main thing you want to do with water is control it, but also isolate it and slow down the velocity,” Loneman says. “The slope is like a roller coaster, as rain hits the top of the slope, it picks up speed as it goes down. So, we’ll put on these sediment logs every 50-70 feet to break up a slope. It kind of makes a speed bump for erosion control.”

Groundcovers also help mitigate erosion by reducing the amount and speed of water runoff. Groundcover does just that – it covers the ground surface so soil cannot be seen from above.

Not only does it add beauty to landscapes, but it can absorb the impact from rain droplets and reduce the amount (due to the plants absorbing some of the water) and speed of water runoff, while holding the soil in place.

Groundcovers range from turfgrass or ornamental grasses to evergreen groundcovers to flowering ones like lily of the valley and the traditional pachysandra.

Lastly, landscape structures, such as retaining walls, are useful erosion tools in uneven topography and can prevent the sliding or washing away of soil caused by insufficient water drainage. If a slope’s gradient is greater than two feet, use retaining walls as a solution to slow the flow of water by stepping it down from one level to another, says Gary Steinhardt, an International Erosion Control Association member and a professor of agronomy at Purdue University.

“In an agricultural field, sediment may end up at the bottom of the hill, but in urban settings, it may end up in a storm drain and (ultimately), our waterways.” Steinhardt says.

Loneman says landscapers must consider slope conditions, soil conditions, environmental factors and the time of year, among other factors, before any solution is devised.

What’s more, it’s important to realize more than one erosion-control method may be necessary.

“As budgets get tighter and tighter, I see a lot of landscapers using other methods to save money, but then the solution isn’t effective,” Loneman says. “It’s about having the right tool in the right toolbox and always being prepared.”

The author is a freelance writer based in Cleveland.