Land and Watershed Management - Practices of Irrigation and On-farm Water Management - page 220

require less energy to detach soil particles. Soil erodibility for disturbed soils is high.
On the other hand, permanent stable soils have low erodibility.
6.5.4.3 Topography
Slope length, steepness, and shape are the topographic characteristics that most
affect rill and interrill erosion. Agriculture on slopes greater than 3% increases the
risk of soil erosion. Steeper and longer slopes generate runoff with more velocity
and energy to erode and transport more sediment.
6.5.4.4 Land Use
Land use is the single most important factor affecting rill and interrill erosion
because the type of land use and land condition are features that can be most easily
changed to reduce excessive erosion.
6.5.4.5 Vegetative Cover
Vegetation shields soils from the impact of raindrops and traps suspended sediment
from runoff.
6.5.4.6 Soil Cover Management/Cultural Practices
Cover management practices affect both the forces applied to the soil by erosive
agents and the susceptibility of the soil to detachment. For a given land use like
cropland, important features include the crops that are grown, the type of tillage
system such as clean, reduced, or no till. Important features on a construction site
are as follows: whether or not the land is bare, the soil material is a cut or fill,
mulch has been applied, or the slope has been recently reseeded. Important features
on range and reclaimed land include the native or seeded vegetation, and degree of
ecological maturity.
6.5.4.7 Other Management Practices
Other support practices include ridging (e.g., contouring), vegetative strips and
barriers (e.g., buffer strips, strip cropping, fabric fence, gravel bags), runoff inter-
ceptors (e.g., terraces, diversions), and small impoundments (e.g., sediment basins,
impoundment terraces). These practices reduce erosion primarily by reducing the
erosivity of surface runoff and by causing deposition.
Soil erosion is usually caused by the impact force of raindrops and by the sheer
force of runoff flowing in rills and streams. Raindrops falling on bare or sparsely
vegetated soil detach soil particles, runoff in the form of sheet flow along the ground,
picks up and carries these particles to surface waters. As the runoff gains velocity
and concentration, it detaches more soil particles, cuts deeper rills and gullies into