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Ask the Indiana NRCS Expert: Grassed Waterways

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Grassed waterway

Do you have eroded channels on your farmland due to intense rainfall and water runoff? To help you learn more about what can be done and how Indiana NRCS can help, Agricultural Engineer Scott Wagner has stopped by Ask the Expert to answer frequently asked questions about grassed waterways.

The last few years we’ve been experiencing higher than normal intense rainfalls. These rainfalls have been causing a lot of issues from eroded channels to flooding in many fields across Indiana. What can be done to fix these issues?

This is a complex answer that includes cover crops, soil health, better subsurface drainage, among other management considerations. If you have severe erosion issue one possible way to address them is constructing a grassed waterway on your land. Grassed waterways are one of the oldest conservation practices in Indiana and they have been shown to manage eroded channels and more efficiently direct large rainfall events across the landscape. Ultimately, they save the producer time and money by keeping nutrients onsite and allowing for an efficient planting and harvest season by not having to slow down to cross these eroded and flooded channels.

What is a Grassed Waterway?

USDA’s Natural Resources Conservation Service’s Field Office Technical Guide (FOTG) definition is a shaped or graded channel that is established with suitable vegetation to convey surface water at a nonerosive velocity using a broad and shallow cross section to a stable outlet. To put it into layman’s terms, it’s a vegetated lined channel which slows down runoff water and conveys it to a stable outlet at a slower speed. The slower speed reduces erosion in the channel, while improving water quality.

What factors determine if a grassed waterway is the right solution for my land? 

There are many factors that are used to determine if a grassed waterway is the right solution. The most important is if there are concentrated flows in a field. Many soil health management systems have reduced, if not eliminated, some of these concentrated flows across a landscape. However, are these concentrated flows causing residue movement and erosion which isn’t being eliminated by a temporary cover? If you answered yes, the grassed waterway is the best solution to capture sediment and nutrients while controlling erosion in these channels. 

Where are Grassed Waterways typically installed?

Grassed waterways are commonly installed in erosion prone areas, draws between two hills and other low-lying areas in crop fields or outlets for other conservation practices. They are typically installed as part of a conservation management system. 

What type of vegetation is planted in a Grassed Waterway?

A mix of perennial plant species (native species are encouraged). This includes grasses, legumes and sometimes native forb species. These plants are excellent at forming sod and with their stiff upright stems act as a nutrient filter. A nurse crop and temporary cover are established immediately after the grassed waterway’s construction to provide rapid vegetation establishment and prevent erosion before  permanent vegetation can become established. The temporary cover may be as simple as straw mulching or as complicated as installed erosion control netting to protect against erosion.

How big does a Grassed Waterway need to be?

There are a couple of factors used to determine the size of the waterway. The first is the capacity of the grassed waterway. They are designed to handle the peak runoff expected from a 10-year, 24-hour duration storm event. In Indiana, a 10-year, 24-hour storm event from northeast to southwest will produce 3.7 to 4.7 inches of rainfall.  Depending on the cover, landuse and soils in the drainage area, this could equate to 2 to 3 inches of rainfall running off the landscape that will need to be controlled with the grassed waterway. Another factor determining the size is the stability of the soils and vegetation to the velocity of the runoff during a storm event. An easily eroded soil and low vegetation density would require a greater area than a non-erosive soil and thick vegetation density. An easy way to think about this is sandpaper. A higher grit sandpaper is not very rough and can be easily ran across a piece of wood. While a lower grit sandpaper is rough, and it takes a lot more energy to run it over the wood. This energy transfer is relatable to vegetation density. The thicker and taller the grass stand, the better job it will do at resisting and slowing down water. In Indiana grassed waterway’s can be as small as 20 feet wide to as wide as 60 feet or more depending on the factors mentioned above.  

What kind of operation and maintenance can be expected with a Grassed Waterway?

Proper operation and maintenance are very important at protecting your investment in the grassed waterway. One of the first and often overlooked is associated with the farming practices outside the grassed waterway. Minimizing tillage or no-till along with cover crops can go a long way toward extending the life of the grassed waterway. Heavy tillage and no cover can lead to increased runoff not only of rainfall, but of sediment and nutrients. Also, don’t plant end rows along the sides of the waterway. Crossing the waterway during planting/harvest is acceptable if the ground conditions allow.  Inspect the waterway frequently and repair areas of erosion and limited vegetation. Mowing is very important for maintaining a heathy vegetated stand and preventing brush/trees from becoming established which could reduce the capacity of the grassed waterway. Mowing should not take place between April 1 and August 15, to prevent interfering with wildlife nesting.  

Where can I go to get more information on Grassed Waterways?

Your local USDA Service Center would be the best place to start. There is an office that services every county in Indiana.  Go to Farmers.gov/service-locator to find your nearest office. These offices are staffed by Farm Service Agency and Natural Resources Conservation Service employees. They will be able to assist you with getting more information on technical and financial assistance programs.

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