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HYDROLOGICAL PROCESSES

Hydrol. Process. 19, 851–854 (2005)

Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hyp.5816

INVITED COMMENTARY

Why the universal soil loss equation and the revised

version of it do not predict event erosion well

P. I. A. Kinnell*

School of Resource, Environmental

and Heritage Sciences, University

of Canberra, Canberra ACT

2601 Australia

*Correspondence to:

P. I. A. Kinnell, School of

Resource, Environmental and

Heritage Sciences, University of

Canberra, Canberra ACT 2601,

Australia.

E-mail:

peter.kinnell@canberra.edu.au

Introduction

The universal soil loss equation (USLE; Wischmeier and Smith,

1978) and its revised version (RUSLE; Renard et al., 1997) were

developed to predict the long-term average annual erosion A from

field-sized areas from six factors: R the rainfall-runoff (erosivity)

factor, K the soil (erodibility) factor, L the slope length factor, S

the slope gradient factor, C the crop and management factor and P

the conservation support practice factor. The USLE/RUSLE model

is often represented by the equation

A = RKLSCP(1)

where R is the average annual sum of the event rainfall-runoff

(erosivity) factor when this factor is given by the product of the

kinetic energy of the rainstorm E and the maximum 30 min rainfall

intensity I30, L = S = C = P = 1·0 when the area is bare fallow on

a 9% slope that is 22·13 m long with cultivation up and down the

slope, and K is the average annual soil loss per unit of R when

L = S = C = P = 1·0.

Although the USLE/RUSLE model was not designed to predict

event erosion, it can be suggested that erosion for a rainfall event

Aeis given by

Ae= EI30KeLSCePe

(2)

where the subscript ‘e’ indicates parameter values that vary between

rainfall events. For a bare fallow plot with cultivation up and

down the slope, Ce= Pe= 1·0. Also, Keis, in the case of the USLE,

considered not to vary with time, so that Ke= K. As a result, the

relationship between Aeand EI30can be expected to be to be given

by

Ae= bEI30

(3)

a linear equation that passes though the origin with b being a

coefficient. This expectation is not achieved in, for example, the case

of a bare fallow plot at Morris, MN (Figure 1), which is part of the

USLE/RUSLE database.

The Runoff Problem

One problem with the USLE/RUSLE model is that there is no direct

consideration of runoff even though erosion depends on sediment

Received 01 November 2004

Accepted 18 November 2004

Copyright 2005 John Wiley & Sons, Ltd.

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