By Ryan Flaming, County Extension Agent, Agriculture & Natural Resources
Coming into spring is a good time to evaluate and perform maintenance on terraces if fields are in wheat stubble, especially since it has been dry lately this year. In Kansas, over 9 million acres of land is protected by more than 290,000 miles of terraces, making Kansas No. 2 in the U.S. for this soil and water conservation practice. To accomplish their purpose for erosion control and water savings, terraces must have adequate capacity, ridge height and channel width.
Without adequate capacity to carry water, terraces will be overtopped by runoff in a heavy storm. Overtopping causes erosion of the terrace ridge, terrace back slope, and lower terraces and may result in severe gullies. Terraces are typically designed to handle runoff from a 1-in-10-year storm. The rainfall amounts for such a storm are approximately 5 inches for eastern Kansas, 4 inches for central, and 3 inches for western Kansas during a 24-hour period.
Terraces need regular maintenance to function for a long life. Erosion by water, wind, and tillage wears the ridge down and deposits sediment in the channel, decreasing the effective ridge height, and channel capacity. The amount of capacity loss depends on the type and number of tillage operations, topography, soil properties, crop residue, and precipitation. Terrace maintenance restores capacity by removing sediment from the channel and rebuilding ridge height.
Typically, more frequent maintenance is required for steep slopes and/or highly erodible soils. Annual maintenance is necessary for intense tillage operations and heavy rainfall runoff. Less frequent maintenance is often adequate with high residue levels or where lower rainfall occurs and runoff intensity is low.