Average Annual Soil Erosion by Water on Cropland and CRP Land, 1982
Description
This is a shaded polygon map where soil erosion
by water on cropland and Conservation Reserve
Program (CRP) land is displayed in five shaded
classes of tons per acre per year using these
ranges: Less than 1, 1 to 3, 3 to 5, 5 to 8, and
8 or more. The Universal Soil Loss Equation
(USLE) is used to determine the values. The
shaded polygons represent 8-digit hydrologic
units. Areas where cropland and CRP land occupy
less than 5% of the total area in 1982 are
hatched. Areas with 95% or more Federal area are
shaded gray. 111 million acres are eroding at a
rate above 5 tons per acre per year due to
water. The national erosion rate averages 4.0
tons per acre per year. Total water erosion
equals 1,688 million tons annually.
Cautions for this Product:
Erosion by water includes sheet and rill erosion
and excludes gully erosion. Since cropland and
CRP land may occupy only a small percentage of
the total area of some of the polygons, the map
may leave a misleading impression as to the
significance of higher erosion rates in some
areas where there is little cropland. Data are
not shown where cropland and CRP are less than
5% of the total area. Data are not collected on
Federal land. Data are not available for Alaska
or the Pacific Basin. Data for Puerto Rico and
the U.S. Virgin Islands is shown by 6-digit
hydrologic unit.
Sources
Source:
National Resources Inventory, 1997
Distributor:
USDA-NRCS-RIAD
Reliability:
NRI sample data are generally reliable at the
95% confidence interval for state and certain
broad substate area analyses. Generally,
analyses that aggregate data points by smaller
geographic areas and/or more specific criteria
result in fewer data points for each aggregation
and therefore less reliable estimates. NRI maps
reflect national patterns rather than site-
specific information.
Layers
Aggregate Layer:
8 Digit Hydrologic Unit Areas with Federal Land
Other Layers Displayed:
States, Rivers
Definitions
Conservation Reserve Program (CRP):
A Federal program established under the Food
Security Act of 1985 to assist private
landowners to convert highly erodible cropland
to vegetative cover for 10 years. [NMCSP]
Cropland:
A Land cover/use category that includes areas
used for the production of adapted crops for
harvest. Two subcategories of cropland are
recognized: cultivated and noncultivated.
Cultivated cropland comprises land in row crops
or close-grown crops and also other cultivated
cropland, for example, hayland or pastureland
that is in a rotation with row or close-grown
crops. Noncultivated cropland includes permanent
hayland and horticultural cropland. [NRI-97]
Erosion:
The wearing away of the land surface by running
water, waves, or moving ice and wind, or by such
processes as mass wasting and corrosion
(solution and other chemical processes). The
term "geologic
erosion" refers to natural erosion processes
occurring over long (geologic) time spans.
"Accelerated
erosion" generically refers to erosion that
exceeds what is presumed or estimated to be
naturally occurring
levels, and which is a direct result of human
activities (e.g., cultivation and logging).
[NSSH-96]
Gully erosion:
The erosion process whereby water concentrates
in narrow channels and, over short periods,
removes the soil from this narrow area to
considerable depths, ranging from 1 to 2 feet to
as much as 75 to 100 feet. [NRI-97]
Sheet and rill erosion:
Removal by runoff water of a fairly uniform,
usually imperceptible, thin layer of soil often
accompanied by formation of many small eroding
channels. Rills are only a few inches deep and
do not hinder farm machinery. Tillage erases
them, but they tend to recur after heavy rain
during the growing season, especially where
cover is limited. [SSM]
Universal soil loss equation (USLE):
This equation estimates average annual soil loss
from sheet and rill erosion. Location specific
data for the field in which the NRI point falls
or that portion of the field surrounding the
point that would be considered in conservation
planning are used in the NRI calculations. The
equation is: A = RKLSCP, where A is the
computed soil loss per unit area, R is a
rainfall factor, K is a soil erodibility factor,
L is a slope length factor, S is a slope-
steepness factor, C is a cover and management
factor, and P is a conservation practice
factor. [NAM]
Water Erosion:
The process of detachment, transport and
deposition of soil in which the primary agent is
water. This may include sheet, rill and gully
erosion; however, for the purposes of this
analysis, unless otherwise stated, water erosion
refers only to sheet and rill erosion and
excludes gully erosion.
Product Information
Product ID:
5055
Production Date:
12/7/00
Product Type:
Map
For additional information
contact the Resources Inventory and Assessment Division.
Please include the Product ID you are inquiring about.
nri@wdc.usda.gov
or 1400 Independence Avenue SW - P.O. Box 2890 -
Washington D.C. 20013. If you use our analysis products,
please be aware of our disclaimer.
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