WSP05706

• File Number: 8272.500
• Description: Colorado River Basin Salinity Control - Colo Dept of Public Health - WQCC and WQCD
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 7/21/1980
• Author: Kenneth Rennard
• Title: Estimating Erosion and Sediment Yield from Rangeland
• Water Supply Pro - Doc Type: Report/Study

166

WATERSHED MANAGEMENT

(7) Predictive equations based -on watershed parameters such as
drai nage area, runoff, temperature, slope; soils. and 'cover.
Even though such equat ions apply to a limited range' of condi'-
tions~ they are frequently u'sed. Such predictive equations can
be grouped into two categories~ statistical and parametric.
This latter method was studied. and the results are reported in
this paper.
The fallowing sediment yield prediction equations Or techniques
were tested. .
Pacific Southwest Interagency Committee Method (PSIAC):
The method <level oped by the Water Management COl\lllittee of the
PSIAC (9) was intended for, broad planning rather than for specific pro-
ject formulation where more- intensi~~ investigations are required. Al-
though this method was intended for use in areas larger than 10 mi2,
I tested it here to demonstrate a method that might be- readtly used
withln a land resource area (1) to provide realistic answers for plan-
ners. Testing the method improves the confidence of the user in select-
ing parameter values that reproduce observed data.
Nine.factors were recommended for consideration in determining the
sediment yield classification for a watershed. The factors are (A) geo-
logy, (B) soils, (e) climate, (0) runoff, (E) topography, (F) ground
cover, (G) land use, (H) upland erosion and (I) channel erosion/sediment
transport. Each factor is assigned a 1lJ:merical value from a rating
chart (9) 'Which is too long to reproduce here. Descriptive terms for
three sediment yield levels (high. moderate. low) far each factor are
used to select the JlJmerical value., SUlTllring the rating chart values for
t~e nine factors defines a sediment yield rating classification, which
in2tu~n can be converted to the average annual sediment yield in .ac-ftl
mi /yr using Table I. .

4.0

3.0

2.0

0:
'"
.'
21.0
,
~_O.8
. .
o
.. 0.6
o
..J
"'
>= 0.4
>-
2:
~ 0.3
o
"'
U)

TABLE 1.--SEOIMENT YIELD CLASSIFICATION

RATING

ANNUAL
SEDIMENT YIELD
AC-FT /M12

> 3.0
1.0 to 3.0
0.5 to 1.0
0.2 to 0.5
< 0.2

CLASSIFICATION

> 100
75 to 100
50 to 75
25 to 50
o to 25

I
2
3
4
5

FIG. 1.- SEDIMENT YIELD FACTOR RELATIONSHIP FOR PSIAC SEDIMENT YIELD
ESTlMATlffO METHOD

ESTIMATING EROSION

167

0.2

0.10

20 40 60 80
PSIAC FACTOR TOTALS

100

Dendy/Bolton Method:
Dendy and Bolton (2) derived sediment yield equations having wi?e-
spread applicability because they used data ~rom ov,:r 800 reservoTrs
throughout the country to obtain measured sedlment 'y1e1d values. They
segregated the data into areas where runoff was e~ ther less than. or
greater than 2 in. per yr. In areas where runoff 15 less than 2 In.,
they derived the equation:

Numerical values for each of the nine factors -range from 25 to
minus 10. Although only three levels are suggested for general use in
the rating chart) a footnote states that if experience so dictates, in-
terpolation between the three sediment yield levels may be made. Such
interpolation was used in the study. ~
Figure 1 was developed from the data in Table 1 to assist -in in-
terpolation between the classifications of the table. Although such
precision was rot intended for the original method. I felt that such a
scheme could provide additional insight 'into the capacity of the tech-
nique to reflect differences in the observed data.

2909

,

S . 1280 00.46(1.43 - 0.26 log A)

(1)