Excessive Erosion on Cropland, 1997
Description
This dot density map shows acres where excessive
erosion from wind and water is occurring on
cropland. Each red dot represent 5,000 acres of
highly erodible land eroding excessively (57.3
million acres). Each yellow dots represent
5,000 acres of non-highly erodible land eroding
excessively (50.5 million acres). Data are
aggregated by 8-digit hydrologic units.
Excessive erosion is defined as erosion greater
than the tolerable rate (T). Highly Erodible
Land is defined as land where the erodibility
index is greater than or equal to 8. The
Universal Soil Loss Equation (USLE) is used to
calculate water erosion. The Average Annual Wind
Erosion Equation (AAWEQ) is used to calculate
wind erosion. A total of 108 million acres are
eroding excessively resulting in 1.3 billion
tons of erosion. In instances where both sheet
and rill and wind erosion were classified as
excessive, acreage was counted only once to
avoid double counting. Therefore, acreage
comparisons with tables for sheet and rill and
wind erosion with regard to T will be greater
than the 108 million acres in this analysis.
Areas with 95% or more Federal area are shaded
gray. Excess erosion leads to water quality
concerns from sediments, nutrients, and
pesticides as well as air quality in wind
erosion areas of the West, Midwest, Northern
Plains, and Southern Plains. Excess erosion is
also an indicator of forgone opportunities for
improving soil, water, and air quality,
sequestering carbon dioxide, and helping in
goals to reduce greenhouse gases in the
atmosphere.
Cautions for this Product:
Erosion by water includes sheet and rill erosion
and excludes gully erosion. Within an 8-digit
hydrologic unit, dot counts represent acreage
totals correctly plus or minus one dot to
account for remainders. This map does not show
rates of erosion or how much erosion has
occurred. 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 are aggregated 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:
Cross of States with 8 Digit Hydrologic Units and Federal Land
Other Layers Displayed:
Rivers, States
Definitions
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]
Erodibility Index (EI):
The soil erodibility index (EI) provides a
numerical expression of the potential for a soil
to erode considering the physical and chemical
properties of the soil and the climatic
conditions where it is located. The higher the
index, the greater the investment needed to
maintain the sustainability of the soil resource
base if intensively cropped. It is defined to
be the maximum of (RxKxLS)/T (from the Universal
Soil Loss Equation) and (CxI)/T (from the Wind
Erosion Equation), where R is a measure of
rainfall and runoff, K is a factor of the
susceptability of the soil to water erosion, LS
is a measure of the combined effects of slope
length and steepness, C is a climatic
characterization of windspeed and surface soil
moisture and I is a measure of the
susceptability of the soil to wind erosion.
Erodibility Index scores equal to or greater
than 8 are considered highly erodible land.
(NRI, 1992)
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]
Highly Erodible Land (HEL):
Land that has an erodibility index of eight or
more (NFSAM).
Hydrologic units:
A hierarchical system developed by the U.S.
Geological Survey that divides the United States
and the Caribbean into 21 major regions, 222
subregions, 352 accounting units, and further
subdivided into 2,150 cataloging units that
delineate river basins having drainage areas
usually greater than 700 square miles. [USGS]
Non-Highly Erodible Land:
Land that has an erodibility index of less than
eight. NRI, 1997
T-Factor:
The soil loss tolerance which can be used with
the USLE or the WEQ. It is the maximum rate of
annual soil erosion that will permit crop
productivity to be sustained economically and
indefinitely. [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.
Wind erosion:
The process of detachment, transport, and
deposition of soil by wind. [NAM]
Wind erosion equation (WEQ):
An erosion model designed to predict long-term
average annual soil losses from a field having
specific characteristics (NAM). E= f(IKCLV)
where E is the estimated average annual soil
loss expressed in tons per acre per year; I is
the soil erodibility; K is the soil ridge
roughness factor; C is the climatic factor; L is
the equivalent unsheltered distance across the
field along the prevailing wind erosion
direction; and V is the equivalent vegetative
cover. [NAM]
Product Information
Product ID:
5083
Production Date:
12/7/2000
Product Type:
Map
For additional information
contact the Resources Inventory and Assessment Division.
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