Terrace POLLUTANTS ADDRESSED: Nutrients and Organics, Sediments, Salinity
DESCRIPTION: A terrace is an earth embankment, channel, or a combination ridge and channel constructed across the slope to intercept runoff water. A terrace provides level surfaces within sloping fields thus increasing irrigation efficiencies and reducing surface sheet flows. LOAD REDUCTION MECHANISM: Nutrients/Organics Management- Vegetated strips between terraces provide a filter for nutrients carried down-slope by runoff Salinity Reduction- Vegetated strips between terraces provide a filter for salinity carried down slope by runoff Sediment Reduction – Vegetated strips between terraces provide a filter for sediment carried down slope by runoff ADDITIONAL BENEFITS: Increases crop-growing area Prevents loss of soil from erosion
Arid Southwest BMP
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LAND USE CLASSIFICATION: Agricultural lands POTENTIAL TREATMENT AREAS: Agricultural Lands ALTERNATIVE MANAGEMENT MEASURES: Cover Crop Filter Strip Irrigation Land Leveling PERMITTING REQUIREMENTS: None
Terrace POLLUTANTS ADDRESSED: Nutrients and Organics, Sediments, Salinity
Level 300: MILD ENGINEERING LOAD REDUCTION POTENTIAL: LOW
MEDIUM
HIGH
ESTIMATED TIME FOR LOAD REDUCTION: IMMEDIATE
MONTHS2 YEARS
> 2 YEARS
EXPECTED MAINTENANCE: LOW
MEDIUM
HIGH
ESTIMATED COST: LOW
MEDIUM
HIGH
PLANNING AND IMPLEMENTATION: This practice generally applies to cropland but may also be used on other areas where field crops are grown such as wildlife or recreation lands. 1. Terraces are installed for one or more of the following purposes: a. Reduce slope length for erosion control b. Reduce sediment content in runoff water c. Improve water quality d. Intercept and conduct runoff to a safe outlet e. Retain runoff for moisture conservation f. Prevent gully development g. Reform the land surface for better farm ability h. Reduce flooding 2. A variety of terrace configurations have developed as a result of research and field experience. Four common types of terraces
Arid Southwest BMP
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include broad-based which are farmed on both sides and used on more uniform gently sloping fields; flat channel which are used to conserve moisture; steep back slope which result in a benching effect; and narrow based which have permanent cover planted on both sides of the ridge. 3. Terraces may be parallel on fairly uniform terrain or vary from parallel when the terrain is undulating. Since parallel terraces are more acceptable, designs often provide for cuts and fills to improve terrace alignment and farm ability. 4. Channel grades may be uniform or variable as long as the water velocity is non-erosive and meet other design criteria. The runoff from terraces may be handled by grassed waterways or underground pipe outlets depending on site conditions and economics. Soil infiltration may also be utilized for disposal of runoff when level terraces are installed and the soil is sufficiently permeable to remove the water stored in the channel before crop damage occurs. 5. Terraces require careful design, layout and construction. Additional information including standards and specifications are on file in the local NRCS Field office Technical Guide. Riparian Planting Zone: Upland Zone and Flood flows.
SOURCES OF ADDITIONAL INFORMATION: TMDL Water Quality Study of the Virgin River Watershed, submitted to Utah Department of Environmental Quality, Division of Water Quality. http://www.waterquality.utah.gov/TMDL/Duchesne_River _Watershed_TMDL.pdf