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J.C. Ritchie
determine spatial patterns of soil erosion. Others techniques involve measuring
sediment loads at the outlet of catchments and relating these measured sediment loads
to soil erosion on the catchment using sediment delivery ratios (Walling 1983).
However, estimating soil erosion rates from sediment loads by sediment delivery
ratios has long been recognized as a problem (Roehl 1962; Walling 1983) and
provides no information on spatial patterns. Radioactive fallout (I37Cesium) and
naturally occurring radioactive elements (i.e., 21Opb) have also been used to measure
soil erosion and sediment deposition (Ritchie and McHenry 1990). The use of
radionuclides allows the measurement of both eroding and depositing sites within a
field and thus provides better information on actual soil loss from a field and the
spatial patterns of erosion and deposition within a field. Detailed information on
classical field techniques for measuring soil erosion can be found in a field manual
of methods for agricultural hydrology (Brakensiek et al. 1979) and a recent review of
soil erosion measurement techniques is presented by La} (l994a).
In addition to field measurements of soil erosion, empirical and process-based
mathematical equations/models have been developed to estimate soil erosion (Foster
1991; Lane et al. 1992). The most widely used soil erosion model is the Universal
Soil Loss Equation (USLE) which is an empirically based equation developed from
data collected from standard soil erosion plots on "typical" soils of the United States
east of the Rocky Mountains (Wischmeier and Smith 1978). The USLE has been
extensively used and ,,misused" in the United States and around the World. Even with
its limitations, the USLE is the most widely used, powerful and practical management
tool for estimating sheet and rill erosion on agricultural landscapes. A Revised
Universal Soil Loss Equation (RUSLE) using the same form and factors with revised
coefficients is available with applications to a wider range of conditions and locations
than the original USLE but is still based on empirical relationships (Renard et al.
1991, 1997). The form of the equation for the RUSLE (and USLE) is:
A=RKLSCP
Where A is the average annual soil loss per unit area; R, the rainfall factor; K, the
soil erodability factor; L, the slope length factor; S, the slope steepness factor; C, the
crop management factor; and P, the soil erosion control practice factor. Numerical
coefficients for these factors were determined empirically from field and laboratory
data (Wischmeier and Smith 1978; Renard et al. 1997). Many other efforts to develop
empirical and physically-based models of soil erosion and its off-site effects have
been made that have had varying degrees of success and applications in management
and research. A general discussion of soil erosion models with a more in depth view
of their applications and limitations is given by Foster (1991), Lane et al. (1992) and
Lal (1994a).
The limitations of current measurement techniques and models to provide information on the spatial and temporal distribution of soil erosion across catchments and on
the movement of eroded particles into streams limit our ability to develop costeffective land management strategies for erosion control. Such limitations point to the
need to investigate other techniques to supplement current techniques for monitoring
J.C. Ritchie
determine spatial patterns of soil erosion. Others techniques involve measuring
sediment loads at the outlet of catchments and relating these measured sediment loads
to soil erosion on the catchment using sediment delivery ratios (Walling 1983).
However, estimating soil erosion rates from sediment loads by sediment delivery
ratios has long been recognized as a problem (Roehl 1962; Walling 1983) and
provides no information on spatial patterns. Radioactive fallout (I37Cesium) and
naturally occurring radioactive elements (i.e., 21Opb) have also been used to measure
soil erosion and sediment deposition (Ritchie and McHenry 1990). The use of
radionuclides allows the measurement of both eroding and depositing sites within a
field and thus provides better information on actual soil loss from a field and the
spatial patterns of erosion and deposition within a field. Detailed information on
classical field techniques for measuring soil erosion can be found in a field manual
of methods for agricultural hydrology (Brakensiek et al. 1979) and a recent review of
soil erosion measurement techniques is presented by La} (l994a).
In addition to field measurements of soil erosion, empirical and process-based
mathematical equations/models have been developed to estimate soil erosion (Foster
1991; Lane et al. 1992). The most widely used soil erosion model is the Universal
Soil Loss Equation (USLE) which is an empirically based equation developed from
data collected from standard soil erosion plots on "typical" soils of the United States
east of the Rocky Mountains (Wischmeier and Smith 1978). The USLE has been
extensively used and ,,misused" in the United States and around the World. Even with
its limitations, the USLE is the most widely used, powerful and practical management
tool for estimating sheet and rill erosion on agricultural landscapes. A Revised
Universal Soil Loss Equation (RUSLE) using the same form and factors with revised
coefficients is available with applications to a wider range of conditions and locations
than the original USLE but is still based on empirical relationships (Renard et al.
1991, 1997). The form of the equation for the RUSLE (and USLE) is:
A=RKLSCP
Where A is the average annual soil loss per unit area; R, the rainfall factor; K, the
soil erodability factor; L, the slope length factor; S, the slope steepness factor; C, the
crop management factor; and P, the soil erosion control practice factor. Numerical
coefficients for these factors were determined empirically from field and laboratory
data (Wischmeier and Smith 1978; Renard et al. 1997). Many other efforts to develop
empirical and physically-based models of soil erosion and its off-site effects have
been made that have had varying degrees of success and applications in management
and research. A general discussion of soil erosion models with a more in depth view
of their applications and limitations is given by Foster (1991), Lane et al. (1992) and
Lal (1994a).
The limitations of current measurement techniques and models to provide information on the spatial and temporal distribution of soil erosion across catchments and on
the movement of eroded particles into streams limit our ability to develop costeffective land management strategies for erosion control. Such limitations point to the
need to investigate other techniques to supplement current techniques for monitoring