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Grassed Waterways versus Underground Outlet Tile

By Bill J. Schroter, Engineering Technician (Civil)
Natural Resources Conservation Service
Hays, Kansas

When it comes to cropland, most everyone agrees that we have to control the water erosion in our fields, but with the recent increases in land value over the past several years, many are looking for alternative ways of fixing this problem. Being located in Northcentral Kansas is a unique place in that the terrain is in a transition area going from the rolling hills of Eastern Kansas to the flats of the western part of the state. This leaves producers in the area with a wide variety of options when it comes to conservation on the ground. In particular, I would like to point out some advantages and disadvantages of both grassed waterways and underground outlets (also known as tile terraces).

First, let’s assume that this is going to be an outlet for a terrace system. With more and more producers going to a no-till or minimum till operation, there is getting to be a lot of requests for a terrace that is minimal in height with a bigger channel. This can be achieved with much less expense by using a waterway as opposed to tile terraces. A waterway is designed to drain all terraces immediately as the water is flowing into the terraces whereas underground outlet terraces are designed to hold the water for a period of time no longer than 60 hours. This usually equates to a bigger terrace. However, some ground may be steep enough that this wide channel terrace is unachievable. In this steeper ground, many times a waterway may have to be so wide to keep from eroding that it is the more expensive alternative when figuring in-ground productivity loss. This is where a smaller underground pipe may be the more cost effective route to go.

Now let’s look at some pros and cons of installation and use. Almost all dirt contractors have the equipment to build a grassed waterway, but they may be lacking a big enough backhoe to efficiently dig a 36-inch deep trench to lay pipe for an underground outlet system. You or the contractor may also have to travel to get the necessary materials for an underground system including the pipe, inlets, elbow, rock, etc. The advantage of an underground system is that the terraces can be installed at the same time the underground outlet is installed. With a grassed waterway, a cover crop may need to be planted and then followed up by a grass seeding. Then if the rains come and all goes well, your terraces can be installed to drain into the waterway in two or three years. While both these practices have a life span of at least ten years, there will always be some maintenance. With a waterway, maintenance issues (such as gully erosion or berm damage) are easily seen and can usually be corrected before too much damage has been done. Depending on the amount of work done, you may then have to wait and reseed portions of your waterway. On the other hand, problems with underground pipe can be more difficult to recognize and may get to a point where they are major problems. Once corrected though, you are done and ready to move on to the next project.

These are just a few things to think about in your quest to save your soil. For a site-specific field recommendation, please visit your local Natural Resources Conservation Service (NRCS) office or conservation district office located at your local county U.S. Department of Agriculture (USDA) Service Center (listed in the telephone book under United States Government or on the internet at offices.usda.gov). More information is also available on the Kansas Web site at www.ks.nrcs.usda.gov. Follow us on Twitter @NRCS_Kansas. USDA is an equal opportunity provider and employer.