ISU Extension News

Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915

6/11/99

FOR IMMEDIATE RELEASE

Contacts:
Gerald A. Miller, College of Agriculture, (515) 294-4333, soil@iastate.edu
Elaine Edwards, Extension Communications Specialist,(515) 294-5168, eedwards@iastate.edu

Maintaining Grass Waterways

AMES, Iowa -- It seems that we've already seen more than our fair share of gully-washers and steady, heavy rainfall this season. When the weather turns wet, it's especially important to prevent erosion by having permanent grass waterways ready to handle runoff, according to Jerry Miller, agronomist at Iowa State University.

Wide, shallow, sod-lined waterways reduce the flow speed of water, and provide a cushion of grass for the water to "ride," which prevents the formation of gullies. Waterways also can be used as outlets for concentrated water coming from terraces, diversions, or adjacent properties. Grass waterways also can act as a filter, settling out sediments. But be careful--settling out too much sediment will build up the middle of a waterway, and will direct runoff back onto the field, Miller said.

Most farm conservation plans integrate waterways as part of their design. Miller said grass waterways are most effective when used in combination with other conservation strategies, such as crop residue management, terraces, buffer strips, and other erosion control practices and structures.

So how do waterways get in good shape and stay that way? Rainfall and runoff result in a constant cut and fill process in waterways, so it takes planning, inspection and maintenance. There are several strategies to keeping a waterway in optimum order.

Manage the general shape of a waterway. A parabolic shape is preferred because it is the shape found most often in natural waterways, it is the most crossing-friendly shape to farm equipment, and the flow of water is less likely to meander.

To avoid causing gullies alongside the waterway, don't plant endrows that run parallel to the waterway. Try to keep crop rows perpendicular to the waterway, using the contour method. When operating tillage equipment, enter a couple feet into the waterway before lifting the implement; cross the waterway and enter the field on the contour on the other side. By doing that, the cultivation patterns will direct runoff into the waterway.

Miller said waterways should carry water off the field at a slow speed. Keeping adequate grass cover is the key to maintaining good flow velocity. If the grass cover degenerates, small channels will form inside the waterway. One way to keep good grass cover is to shut the sprayer off before crossing the waterway. Emphasize to commercial applicators that they must do so as well. If the grass cover is diminished for any reason, be sure those areas are reseeded quickly.

Choosing a grass is also important. Allow for the characteristics of the species when seeding a waterway. Consider the following: bromegrass is hardy and aggressive, and is popular for protecting waterway channels. Kentucky bluegrass is also used extensively in waterways. It thrives in Iowa, but lacks the root depth of other grasses. Reed canarygrass grows equally well in dry and wet areas and works well in waterways that are too wet for other grasses. Timothy is not as deep-rooted as other grasses, requires more fertile soil, and does not thrive on wet soil or during hot, dry weather.

Once a grass is established, mowing waterways is important, Miller said. Allowing the grass to mature will allow too much sediment to be trapped. The waterway could lose its shape, or the water will simply circumvent the waterway altogether. Also, to allow for bird nesting, be sure that any mowing occurs before May 10 and after July 15.

If sediment does settle into the center of the waterway, or if the bottom of the waterway becomes flat or even slightly humped in the middle, it will be impossible for water to run down the center. To avoid that, use sound conservation strategies on the land above the waterway. At the first sign of a filled-in waterway, reshape and reseed the area to ensure proper function.

Also, inspect the waterway outlets. Little gullies can evolve into a gulch in a single rainstorm. Install a waterway outlet structure where runoff falls into the road ditch or other outlet. Structures are especially important where when water falls from one level to another. Get help from the local conservationist in designing an outlet structure that will prevent gullies and gulches from cutting back into the waterway.

There are more tips for keeping a waterway healthy. If the grass stand is poor, try to fertilize the grass periodically and evaluate the results. Be sure to always maintain proper waterway width when performing any tillage operations near the waterway--don't "nibble" away at the edges. Inspect the area frequently and repair minor rills or gullies by reshaping and reseeding.

Remember that the waterway is not a thoroughfare--tire tracks will lead to the formation of a gully. And minimize or eliminate livestock traffic through a waterway--hoof prints are natural erosion starters. If there are burrowing animals (badgers, groundhogs or moles) they'll have to be controlled as well. Also, running water tends to swirl around obstructions, so keep the waterway clear--no rocks, tree stumps, or debris and junk.

Wet seasons can dramatically point out the necessity for sufficient waterways, Miller said. Make sure your farm's conservation plan uses grass waterways as needed to protect the soil. Some years, they are all that stand between the soil and severe erosion.

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