The weeks between harvest and when snow flies can be a good time to evaluate and perform maintenance on terraces. In Kansas, over 9 million acres of land is protected by more than 290,000 miles of terraces, making Kansas second in the U.S. for this soil and water conservation practice. To accomplish the goal of 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 one-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.
Check for needed repairs - terraces degrade naturally by erosion and sediment, and can be damaged by machinery, animals, settling, and erosion. Check terraces and terrace outlets regularly (at least annually) for needed repairs. The best time to check is after rains, when erosion, sedimentation, and unevenness in elevation are easiest to spot. Specific items to note are overtopping, low or narrow terrace ridges, water ponding in the channel, terrace outlets, erosion, and sediment clogging near waterway or pipe outlets.
Terraces should be considered only a part of an overall erosion control plan. Use of conservation farming methods, especially residue maintenance, compliments erosion control structures and has been shown to be both economically and environmentally sound.
Information provided by DeAnn Presley, K-State Soil Management Specialist. Additional sources for technical information include local USDA-Natural Resources Conservation Service and County Conservation District offices.
Stacy Campbell is an agriculture and natural resources agent for Cottonwood Extension District. Email him at scampbel@ksu.edu or call the Hays office, 785-628-9430.
