WSP01538

• File Number: 8210.470
• Description: Pacific Southwest Interagency Committee
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1974
• Author: Unknown
• Title: Report of the Water Management Technical Subcommittee - Erosion and Sediment Yield Methods - April 1974
• Water Supply Pro - Doc Type: Report/Study

methods with actual field data where suitable data are available.

EVALUATION OF METHODS

Table 1 was prepared to provide the field investigator with a rapid
means of selecting a method for estimating erosion and sediment yield
rates. The table compares each method relative to the factors formulating
all methods considered so that during the planning process all the
methods can be considered for applicability to a particular problem.
By use of the table, the investigator can determine the data necessary
to solve the selected method within the constraints of accuracy needed,
time available, and financial resources. Although Table 1 provides
a convenient guide in selecting an appropriate method for field use,
it should be pointed out that the listed factors are quite general,
and should not be used as a substitute for a detailed study of the
specific characteristics of each factor.

The task force prepared summaries of the 12 methods selected. The objec-
tive of the summaries is to present a brief description of each method
in a format that will allow comparison among the methods. The summaries
in Appendix I show the essential elements of each method including
the location of study, physical characteristics of the research area,
methods of analysis, predictive equations, and tests and limitations of
the method. The summaries are divided into two groups: (1) methods
for estimating erosion, and (2) methods of sediment yield prediction.

SOME APPLICATIONS OF ON-SITE EROSION AND SEDIMENT YIELD
METHODS USING FIELD DATA

As stated in the Introduction of the report, the Task Force intended
to test many of the selected methods in areas of the Pacific Southwest
region where adequate field data were available. This has not been
possible to complete but some applications are presented here for one
on-site erosion method--the universal soil loss equation (Wischmeier and
Smith, 1965), and one sediment yield method--the predictive equation
of Flaxman (1972), as revised (1974).

As a test of the possible utility of the Universal Soil Loss Equation
for rangeland applications, limited data were used from the Walnut
Gulch Experimental Watershed operated by the Agricultural Research
Service in southeastern Arizona (Renard and Simanton, 1973). The utility
of the soil loss method for prediction purposes is predicated by the
need to evaluate the soil, cover and land treatment factors from some
known locations for arid and semiarid rangeland conditions.

The Universal Soil Loss Equation as presented by Wischmeier and
Smith (1965) is

A = RKLSCP
where A is the computed soil loss per unit area.
R, the rainfall factor, is the number of erosion-index units in a
normal year's rain. The erosion index is a measure of the
erosive force of specific rainfall.

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