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Conservation Choices: Terraces

Terrace Header

Terrace PhotoWhat it is

A terrace is an earthen embankment constructed across a field slope. They break long slopes into shorter ones – usually following the contour.

There are two basic types of terraces—storage terraces and gradient terraces. Storage terraces collect water and store it until it can infiltrate into the ground or release through a stable outlet.

Gradient terraces are designed as a channel to slow runoff water and carry it to a stable outlet.

How it helps

  • Help reduce erosion by reducing slope length.
  • Retain runoff for moisture conservation.
  • Provide nesting habitat.

Planning ahead

  • Will other conservation practices be used in conjunction with terraces to prevent sedimentation in the terrace channel?
  • Are soils and topography such that terraces can be constructed and reasonably farmed?

Tech Notes

  • Grassed backslope terraces have a farmable frontslope with a 2:1 backslope (2 feet horizontal to every 1 foot of vertical drop).
  • Narrow base terraces have 2:1 slopes on both the frontslope and backslope.
  • Broadbase terraces should not be built on slopes greater than 6%. Farmable slopes should not be steeper than 5:1.
  • Steep front, farmable backslope terraces should not be built on slopes greater than 6%. The front slope should be built with a 2:1 slope and the backslope should not be steeper than 5:1.
  • Terraces are designed to control runoff from a 10-year storm.

Maintenance

  • Periodically inspect the terrace, especially following significant rain events.
  • Promptly repair or replace damaged terrace components.
  • Maintain terrace ridge height, channel profile, cross-section and outlet.
  • Remove accumulated sediment in the terrace channel to maintain grade and capacity.
  • Regularly clean inlets for underground outlets. Repair or replace inlets damaged by farm equipment. Remove sediment around inlets to ensure they remain the lowest spot in the terrace channel.
  • Control rodents, trees and brush.

Iowa Practice Standard

Iowa Job Sheet

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