[Code of Federal Regulations]
[Title 7, Volume 1]
[Revised as of January 1, 2005]
From the U.S. Government Printing Office via GPO Access
[CITE: 7CFR12.21]

[Page 344-345]
 
                          TITLE 7--AGRICULTURE
 
PART 12_HIGHLY ERODIBLE LAND AND WETLAND CONSERVATION--Table of Contents
 
               Subpart B_Highly Erodible Land Conservation
 
Sec. 12.21  Identification of highly erodible lands criteria.

    (a) Basis for identification as highly erodible. Soil map units and 
an erodibility index will be used as the basis for identifying highly 
erodible land. The erodibility index for a soil is determined by 
dividing the potential average annual rate of erosion for each soil by 
its predetermined soil loss tolerance (T) value. The T value represents 
the maximum annual rate of soil erosion that could occur without causing 
a decline in long-term productivity. The equation for measuring erosion 
is described below.
    (1) The potential average annual rate of sheet and rill erosion is 
estimated by multiplying the following factors of the Universal Soil 
Loss Equation (USLE):
    (i) Rainfall and runoff (R);
    (ii) The degree to which the soil resists water erosion (K); and
    (iii) The function (LS), which includes the effects of slope length 
(L) and steepness (S).
    (2) The potential average annual rate of wind erosion is estimated 
by multiplying the following factors of the Wind Erosion Equation (WEQ): 
Climatic characterization of windspeed and surface soil moisture (C) and 
the degree to which soil resists wind erosion (I).
    (3) The USLE is explained in the U.S. Department of Agriculture 
Handbook 537, ``Predicting Rainfall Erosion Losses.'' The WEQ is 
explained in the paper by Woodruff, N.P., and F. H. Siddaway, 1965, ``A 
Wind Erosion Equation,'' Soil Science Society of America Proceedings, 
Vol. 29. No. 5, pages 602-608. Values for all the factors used in these 
equations are contained in the NRCS field office technical guide and the 
references which are a part of the guide. The Universal Soil Loss 
Equation, the Revised Universal Soil Loss Equation, and the Wind Erosion 
Equation and the rules under which NRCS uses the equations are published 
at Sec. Sec. 610.11 through 610.15 of this title.
    (b) Highly erodible. A soil map unit shall be determined to be 
highly erodible if either the RKLS/T or the CI/T value for the map unit 
equals or exceeds 8.
    (c) Potentially highly erodible. Whenever a soil map unit 
description contains a range of a slope length and steepness 
characteristics that produce a range of LS values which result in RKLS/T 
quotients both above and below 8, the soil map unit will be entered on 
the list of highly erodible soil map units as ``potentially highly 
erodible.'' The final determination of

[[Page 345]]

erodibility for an individual field containing these soil map unit 
delineations will be made by an on-site investigation.

[61 FR 47025, Sept. 6, 1996; 61 FR 53491, Oct. 11, 1996]