Modern terrace systems

Excerpt

TERRACES are among the oldest and most common soil erosion control practices. Despite the many criticisms of terraces—they cost too much, they are too hard to farm—farmers continue to build them. Why? Because terraces perform a function that no other conservation practice does: They intercept runoff before it becomes erosive and conduct it at a non-erosive velocity to a stable outlet. Terraces fill a niche in cropland conservation systems that no other practice can by controlling sheet, rill, and gully erosion as well as channel erosion caused by concentrated flow on steeper, longer slopes.

A terrace is an earthern embankment, channel, or combination of ridge and channel constructed across a slope. Terraces were used on 31.3 million acres (12.7 million hectares) of land in 1977. An average of 600,000 additional acres (243,000 hectares) were protected in each of the last three years of record, 1976, 1977, and 1978. The significance of these figures is clear when considering that a 1977 inventory estimated that erosion exceeded allowable rates on one-fourth of the 412 million acres (167 million hectares) of cropland in the …