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Diversion vs. Terraces

Diversion vs. Terraces

by John E. Vavroch, Civil Engineering Technician
Natural Resources Conservation Service
Colby, Kansas

Sometimes it rains. Sometimes it doesn’t. Usually, when you need it most, it doesn’t. When it does rain, it often comes too quickly and in too much volume. The result is erosion—the loss of precious top soil. Even with the high residue amounts in our fields today, it is necessary to have structural practices in some fields to control the loss of soil.

When the decision is made to install structural practices, this question often comes up: “Should I terrace the field or could I install a diversion?” Every field is different, but all fields need the foreign drainage controlled and work must begin at the top of the field.

Terraces are designed to handle the runoff only from the terrace above. Usually, 1.5 feet—1.7 feet terrace height is adequate. Diversions are designed to handle the total drainage acres above the diversion. Like a terrace, a diversion can be level which stores water, or gradient which runs water to a suitable outlet. Storage is the critical factor in level diversions. The storage area can be long and shallow or short and deep.  Cost is another factor. Diversions are paid by the cubic yard while terraces are paid by the linear foot. Huge diversions quickly become expensive and are not cost effective.

Diversions should not be installed in lieu of terraces. If a diversion is installed too far down the slope in the field, it may become overloaded with silt causing a maintenance problem. A good rule of thumb–if the diversion channel has any gullies or evidence of concentrated flow above it, it is too far down the slope.

For more information about diversions and terraces, please contact your local Natural Resources Conservation Service (NRCS) office or conservation district office located at your local county USDA Service Center. To learn more about NRCS, visit the Kansas NRCS Web site at www.ks.nrcs.usda.gov.

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