Water Erosion 

Prediction Project 

(WEPP) 

Forest Applications

William J. Elliot and David E. Hall

Forestry Sciences Laboratory

1221 S. Main St.

Moscow, ID 83843

OFE 1 : Road

OFE 2 : Fillslope

OFE 3 : Forest

Length of Plume

United States

Department

of Agriculture

Forest Service

Intermountain

Research Station

General Technical

Report Draft

March, 1997
Obtaining a Copy of the WEPP Forest Files

The WEPP forest files can be obtained on a 3.5 inch diskette from the authors at:

 1221 South Main Street 

Moscow, ID 83843

Tel 208 882 3557 

DG WEPP:S22L04A or Internet wepp@forest.moscowfsl.wsu.edu

The files forest.exe, forestap.dat and forestap.txt can also be obtained by 

anonymous ftp in directory /water/wepp at: 

forest.moscowfsl.wsu.edu

or point your browser to:

ftp://forest.moscowfsl.wsu.edu/water/wepp

Intermountain Research Station

324 25th Street

Ogden, UT 84401

The Authors

William J. Elliot is a Supervisory Research Engineer 

investigating soil erosion processes and modeling in forests. 

He is also the Project Leader of the Engineering Technology for 

Improved Forest Access Research Work Unit of the 

Intermountain Research Station, located at the Forestry 

Sciences Laboratory in Moscow, ID.

David Hall is a computer programmer/analyst for the 

Engineering Technology for Improved Forest Access Research 

Work Unit of the USDA Forest Service Forestry Sciences 

Laboratory in Moscow, ID. He helped develop a series of slope 

stability modeling software for the Forest Service and others. 

He is currently developing improved interface and network 

technology for natural resource models.

Research Summary

The Water Erosion Prediction Project (WEPP) soil erosion model 

is a process-based computer model to predict runoff, soil erosion, 

and sediment delivery. From our field research in forest soil 

erosion and literature reviews on forest physiology, input files 

have been developed for WEPP to predict soil erosion from forest 

roads, harvest areas, and burned areas. This report describes 

input files to run the hillslope version of WEPP for these disturbed 

forest conditions.

Acknowledgments

The authors wish to acknowledge Patty Liu, a seasonal employee 

from the Biological Engineering Department at the University of 

California, Davis, for her assistance in developing the forest growth 

files and in writing first draft of this document. We would also like 

to acknowledge Dr. Randy Foltz, Pete Robichaud, and Charles 

Luce, scientists within our Research Work Unit for providing 

research results to determine forest soil erosion processes and soil 

erodibility.

Key Words

Hydrology, Soil Erosion, Water Quality

Contents

Introduction ........................................................................... 2

Running the WEPP Model .................................................... 2

Input File Description ........................................................... 4

 Roads ........................................................................ 5

 Forests ...................................................................... 8

References .......................................................................... 10

Appendix A. Forest Parameter Values ............................... 11

Appendix B. Deleting Unwanted Files ................................. 14

Appendix C. Source of WEPP Hard Copy .......................... 14

Appendix D. Useful Conversions ........................................ 15
2

Water Erosion Prediction Project (WEPP) Forest Applications

William J. Elliot David Hall

Introduction

The Water Erosion Prediction Project (WEPP) model consists of a physically based soil erosion 

model with a number of output options, numerous typical cropland and rangeland input files, a 

climate generator, and a user-friendly shell with complementary file builders. The WEPP model is a 

public domain model developed by federal agencies that includes an MS DOS computer program and 

user documentation. The sidebar on this page provides instructions for obtaining the WEPP model 

and documentation. This publication describes input files that have been developed by Forest Service 

scientists and engineers to model some typical forest conditions. These files are part of a growing 

database of information to assist in running WEPP for forest conditions.

Obtaining the WEPP Model

The WEPP model, data for over 1,000 soils and climate 

files for over 1,300 stations across the U.S. are on the 

WEPP CD ROM available by contacting :

laflen@ecn.purdue.edu

The same information can be obtained from the internet 

from the USDA-ARS National Soil Erosion Research 

Laboratory (NSERL), located at Purdue University, West 

Lafayette, IN. Instructions for downloading the WEPP 

model and any of the desired databases by anonymous 

FTP can be obtained from 

ftp://soils.ecn.purdue.edu/pub/wepp 

The readme.txt file in this directory provides instructions 

for downloading and installing the model.

The information is also available through the World 

Wide Web at

 http://soils.ecn.purdue.edu:20002/~wepp/nserl.html 

This address will place the user on the NSERL home 

page, and from there, the user can access the required 

information for downloading either databases, 

documentation or the WEPP model. 

In an undisturbed forest, soil erosion is 

generally negligible. Disturbances such as 

roads, harvesting activities, or fires will lead to 

soil erosion. We have provided seven forest 

profiles that describe both roads and harvest 

areas in the forest. The road files are for 

insloped roads, outsloped roads, insloped roads 

with a sediment plume, and rutted roads. The 

harvest area scenarios are for a 100-year forest 

regeneration sequence, a forest with a burn in 

year 2, and a forest skid trail with a skid 

operation in year 2. This document 

supplements the WEPP User Summary

(Flanagan and Livingston 1995). 

All of the management files are in the 

cropland format. Although cropland is an 

‘‘agricultural’’ format, this format was used 

instead of the rangeland format because 

cropland allows for ‘‘tillage’’ operations which 

are necessary to describe blading or traffic on 

roads, skidding in forests, and other operations 

that mechanically disturb the soil.

Running the WEPP Model

Instructions for running the WEPP model are given in the WEPP User Summary (Flanagan and 

Livingston 1995). To run the hillslope version of the model, management (*.man), slope (*.slp), soil 

(*.sol), and climate (*.cli) files are required (WEPP User Summary page 8). File builders are 

provided with the model to assist the user in building and running WEPP files (pages 90-115). When 

using forest files, we recommend that the user run the WEPP program for 30 years, once he/she has 
3

confirmed that the files will run a single year. If additional years are required, then the management 

and climate file builders may be used to build longer files. 

The WEPP interface directly accesses a file 

editor, DOS EDIT by default, or the file can be 

edited with any word processor or text editor and 

saved as a text file.

The WEPP model can be run through either 

the Hillslope interface or the Watershed interface. 

The files described in this document are all for the 

Hillslope file builder. Once a hillslope has been 

successfully built and run, it can be incorporated 

into a watershed along with other hillslope and 

channel elements.

Reviewing WEPP Forest Files

 The WEPP input files are ASCII format and 

can be viewed or edited with any word processor or 

file editor, or the text editor specified in the WEPP 

WEPP Forest Files Installation

The WEPP Forest Files can be obtained on a 3.5 

inch diskette from the authors for installation on a 

computer capable of running the WEPP program. 

WEPP version 95.7 must be installed on your 

computer before you can install the WEPP Forest 

Files. Refer to page ii of the WEPP User Summary

Quick Start Guide to install WEPP. 

Place the diskette labeled WEPP Forest Files into 

your floppy drive, move to the floppy drive, and 

type forest Z: (where "Z" is the letter of the drive 

on which WEPP is installed). Forest will look for 

WEPP on the drive you have specified. If it 

cannot find WEPP there, it will look for WEPP on 

drive C and then on drive D. When forest has 

found WEPP, it will ask you to confirm 

installation to that WEPP directory. Press Q to 

quit the forest files installation, or any other key to 

continue. 

interface. The files described in this document are summarized in table 1. The management file 

builder will not show the correct input values for the trees100.man file, because the 100 year 

simulation period is too long for the current file builder and it will truncate the file. The file is not 

too long for the WEPP model, however. The WEPP program will generally run if the input files are 

correctly modified in the DOS editor, even though they may be beyond the file builder’s capability. 

If viewing the input files with an editor refer to pages 10 to 13 in the WEPP User Summary for a line 

by line description of the slope and soil input parameters. A description of the management input 

parameters is found on pages 30 to 54 of the User Summary.

Running WEPP

Complete instructions to run WEPP are presented in the 

User Summary. To run the model, the user must change 

to the WEPP Directory (cd\WEPP). From the WEPP 

directory, enter HILL, and the WEPP hillslope interface 

will be started. Once the hillslope interface is running, 

the user may begin to select or modify files, or may load 

all of the forest files described in this document by 

loading the FOREST table using the LOAD command 

under the FILE menu in the interface menu bar. The 

menu bar can be accessed with the mouse, or by hitting 

the <Alt> key.

Modifying the WEPP Forest Files

The files in the Forest WEPP database can 

be modified to describe many situations. Most 

new users will prefer to use the file builders 

until they become comfortable with the WEPP 

program. Experienced users, particularly when 

carrying out sensitivity analyses, or studies 

looking at a range of options, may find it faster 

and more convenient to modify a single value 

with the text editor.

The management file includes a 

description of the vegetation, and the timing 

and effects of ‘‘tillage’’ operations on soil 

erodibility properties.
Table 1−Files provided with this document.

Condition Soil File Slope File Management 

File

Inslope bladed road inslope.sol inslope.slp inslope.man

Outslope bladed road outslop3.sol outslop3.slp outslop3.man

Inslope road leading to 

cross-drain, a fillslope, 

and a forest hillside on 

which a deposition plume 

forms

plume3.sol plume3.slp plume3.man

Rutted road with a rut 

and a road shoulder

rut2.sol rut2.slp rut2.man

Vegetation regenerating 

for 100 years after a 

complete removal of a 

forest

forest.sol tree.slp trees100.man

Forest vegetation at N

years of age

forest.sol tree.slp treeN.man

Forest with fire in the 

second year, followed by 

regeneration for 28 years

fire.sol fire.slp fire.man

Forest skid trail formed 

in year 2, followed by 28 

years of regeneration

skid.sol skid.slp skid.man

4

One of the features of the WEPP model is the ability to describe up to 10 combinations of soil 

and vegetation along a given hillslope (fig. 1). Each unique combination of soil and vegetation is 

called an overland flow element (OFE). Users must select soil and slope files with the same number 

of overland flow elements as the management file or WEPP will not run. The hillslope interface 

shows the user the number of OFE’s in the selected file in the lower left corner of the screen.

When building new files, it is generally recommended that the user first run a scenario that 

approximates the specific problem site for a single year. Only a few input values should be altered in 

one file before making another run. Certain values or combinations of values for some inputs may 

cause the model to fail to run. A step by step approach to altering input values will make it easier to 

pinpoint any problem values, as well as determine the sensitivity of the model to altered values.

Input File Descriptions

The following figures and narrative describe road and harvest area conditions provided with 
Soil 1 Soil 2

Vegetation 1 Vegetation 2

OFE1 OFE2 OFE3

Figure 1−Example of three overland flow elements describing three combinations of soil and 

vegetation along a hillslope.

w i d t h 

 R i d g e H e i g h t 

= E l e v a t i o n D i f f e r e n c e 

S g 

Forest

Stream 

or Forest

Fillslope Cutslope

Ridge Spacing

= 2 x Road Width

Figure 2−Inslope road detail

5

the WEPP Forest Files. For more details on the research behind these files, refer to Elliot and others 

(1994, 1995a, 1995b). Complementary management, soil, and slope files have been prepared for 

each forest scenario. It is recommended that the complementary file set be selected at the beginning 

of any study, and then be modified to suit site specific conditions, rather than build a file from 

scratch.

Roads

INSLOPE−The inslope.man file 

models an insloped road with one 

overland flow element. The road is 

modeled as a large ridge and the ditch 

as a furrow system with a blading 

operation on the surface (fig. 2). The 

inslope.sol file describes the rill 

erodibility of the ditch and interrill 

erodibility of the road. The inslope.slp

file describes the length and slope 

relationships of the road ditch gradient 

(Sg). If there is significant runoff or 
w i d t h 

Forest 

 

C u t s l o p e 

2 . F i l l s l o p e 

3 . F o r e s t 

O F E 

S l o p e 

R o a d 

G r a d i e n t 

1 . R o a d 

Outslope

O v e r l a n d 

F l o w 

P a t h 

O F E 

P a t h 

L e n g t h 

Slope 

Road OFE Slope = (OutSlope)2+ (RoadGradient)2

Road OFE Path Length = Road Width ×

OFE Slope

Outslope Slope

Effective width of hillslope = Road length × Road width

Road OFE Path length

Figure 3−Outslope road detail

O F E 2 , F i l l s l o p e 

O F E 1 , R o a d 

O F E 3 , F o r e s t 

 

Length of Plume

Figure 4−Details of modeling a sediment plume below a 

road

6

erosion from the cutslope, the user can increase the profile width to include the width of the cutslope, 

assuming the cutslope is behaving in a hydrologically similar manner to the road. If the cutslope is 

behaving hydrologically different from the road, then the user should model the system with the 

WEPP watershed version as a watershed with a road hillslope element and a cutslope element, both 

feeding a common channel, which is the ditch (Tysdal and others 1997).

OUTSLOP3−Outslop3.man models 

an outsloped road with three OFEs: 

road with a blading operation, 

fillslope, and forest (fig. 3.). The 

outslop3.sol and outslop3.slp files 

complement this management input 

file. If there is significant overland 

flow runoff from above the 

outsloping road, then the user may 

want to add more overland flow 

elements for the cutslope and the 

forest above it. There is seldom any 

runoff or surface erosion from an 

undisturbed forest. If there has been 

a severe fire, or if the cutslope was 

recently disturbed, then they may 

contribute to the overland flow. As 

users become comfor- table with the 

management file builder, they may 

wish to alter the vegetation amount, 

spacing, and height on the cutslope 

and fillslope.

The effective width of an eroding outslope element must be determined from the equations shown in 

figure 3. Because the OFE path length is 

greater than the road width, the effective 

element width must be reduced to ensure 

that the total eroding surface area 

remains unchanged. On very steep road 

gradients (over about 15 percent), the 

road OFE path length may approach the 

distance between water bars, particularly 

if traffic has flattened the wheel tracks. 

In this situation, the PLUME3 scenario 

may be more appropriate to describe the 

flow paths.

PLUME3−The plume3.man file has 

three OFEs that model an insloped 

eroding road that drains to a buffer area 
Shoulder Rut Center Rut Shoulder

 Rut Road 

Gradient

Outslope

OFE 2: Shoulder

Shoulder

Length

Length 

OFE 1: Rut

Shoulder slope = 

 (Road Gradient2 + Outslope slope2)1/2

Shoulder length = 

 Shoulder width ∗ (shoulder slope/outslope slope)

I n s l o p e 

 

o r 

r i d g e 

 

s e c t i o n 

R i d g e 

S e c t i o n O u t s l o p e 

S e c t i o n 

r i l l 

w i d t h 

r i d g e 

s p a c i n g 

r i d g e 

h e i g h t 

width 

Ridge height, ridge spacing and rill width are entered in 

the management file builder as shown.

Initial conditions rill spacing = ridge spacing

Figure 5−Plan and section of model for an eroding 

rutted road.

7

where a plume of sediment is deposited (fig. 4). It is assumed that the width of flow is the same on 

the road as it is on the fillslope and buffer area. This file also has a blading operation on the road. 

Plume3.sol has three types of soil, one for each of the OFEs: road, fillslope, and a silt loam forest 

soil. The road soil has a very low conductivity, the fillslope moderate, and the forest a high 

conductivity (appendix A). Suggested values for other soils are given in Morfin et al. (1996). Users 

may wish to alter the conductivity of the fillslope and the forest to see the effects on the length of the 

sediment plume. Plume3.slp describes a 4 percent gradient on a 60 m road segment, a 50 percent 

gradient on a 4 m fillslope, and a 30 percent gradient on a 30 m forested hillside where the plume of 

deposited sediment forms. If there is a 

waterway near the road, then the WEPP 

model will predict the amount of 

sediment traversing the forest and 

entering the waterway.

Rut2−Wheel ruts in roads generally 

dominate the erosion processes. The 

factors that affect the rut development are 

traffic density, axle load, tire pressure, and 

aggregate quality (Whitcomb and others 

1990). Low pressure tires, regular blading, 

or high quality aggregate on the roads 

often produce rut lengths of under 10 m. 

High pressure tires produce rut lengths up 

to 50 m or more. If dips or water bars are 

included in the road design, they will limit 

the maximum rut length. The rut2.man

file describes two OFE’s − rut and 

shoulder (fig. 5). The rut OFE has a fixed 

rill spacing and rill width in the initial 

conditions scenario of the management 

file. The rill spacing value is equal to the 

distance between ruts, which is 1.5 to 1.8 

m. The rill width value is equal to the 

width of the rut, about 0.5 m. The 

management file specifies 10 traffic 

operations on the road that cause 

disturbance to a depth of 0.002 m with 

each pass. Rut2.sol models a rut with 

lower hydraulic conductivity and a 

shoulder with a higher conductivity. The 

shoulder steepness and length are 

calculated using the formula in fig. 5. Rut 

and shoulder lengths are critical in 

determining the amount of erosion and 

runoff. Rut2.slp describes the road 

gradient with the flow exiting over the 

shoulder at the end of the specified rut 

length. 
Year 1 Year 5 Year 40 Year 100

Figure 6−Model of forest regeneration

8

To determine the fate of sediments eroded from roads, users may need to consider modeling the 

road in two halves. One half, the rutted outslope half, would follow the Plume3 model, with a width 

equal to half the width shown in figure 5. The inslope half could follow the Inslope3 model if the 

inslope empties into a live- water crossing, or could be modelled in the Plume3 model if the inslope 

empties into a culvert or cross-drain, delivering water to a hillslope. The resulting sediment yields are 

added for the two road halves, or the two hillslope elements incorporated into a watershed system. It 

is unlikely that there is any significant erosion from the outslope section of the road outside of the rut.

Forests

TREES100−Trees100.man is a 100 

year forest regeneration file with one 

OFE and 21 different plant and yearly 

scenarios. Each scenario represents 5 

years of continuous growth, with the 

rate of growth and the generation of 

surface residue dependent on both the 

biomass conversion ratio for the given 

forest age and the precipitation 

amount and distribution (Arnold and 

others 1995). The predicted amounts 

of above ground biomass and surface 

residue generated are similar to 

observed and reported values. This file can not be altered by the WEPP management file builder, so 

with a text editor, users can alter vegetation spacing, canopy diameter, and growth rate (altered with 

the biomass conversion ratio) to suit specific conditions. The predicted distribution of biomass and 

surface residue during a growing season can be observed with the Graphics viewer by specifying 

"yes" in the Hillslope interface for Graphics. The output file generated for the graphics option is 

0.32 Mb per year simulated, so be sure that there is adequate disk space to store this file before 

specifying "yes" or the run will crash with little explanation. Tree.slp and tree.sol input files are 

provided to run this management file. If you want to run this program for the full 100 years, be sure 

that you have plenty of disk space to store the climate input file and the output files. 

Also included with the WEPP Forest Files are files for each age of trees, with the generic file 

name tree**.man. The most sensitive forest vegetation parameter values are presented in appendix A. 

Sensitivity studies have shown that neither the biomass production nor the subsequent erosion rates are 

particularly sensitive to any of these values except the biomass conversion ratio. Users are encouraged 

to compare the vegetation growth predicted by WEPP with forest conditions in their own areas to see 

how the conditions compare and to see whether adjusting the input values has any effect on the 

predicted erosion rates for their sites.

FIRE−Fire.man is a 30 year forest file with one OFE. This file models an undisturbed forest in year 

one, with a fire in year 2, and vegetation regenerating for the remainder of the years (fig. 7). Fire.sol

and fire.slp describe typical forest conditions for use with this file. The hydraulic conductivity in the 

soil file has been reduced from 15 to 10 mm/h reflect hydrophobicity which has been observed on 

some soils (Robichaud 1996). Users may wish to study the sensitivity of erosion rates to the fraction 
year 1 year 2 year 3-6

Figure 7−Model of forest fire

Figure 8−Highly disturbed skid trail in forest

9

of standing and flat residue burned as entered in the management file builder in the "Yearly Cropland 

Management Annual Burning" window.

Skid−Skid.man is a 30 year file with 

one OFE. This file describes an 

undisturbed forest in the first year with a 

skid operation of one pass of 0.2 m 

depth in year 2, and regeneration on the 

skid trail for the remainder of the years.

Skid.sol and skid.slp should be used with 

this management file. Users may wish 

to incorporate the skid yearly scenarios 

in the management file builder into 

multiple OFE files combining skid trails, 

harvest areas, and undisturbed riparian 

zones, to better describe a harvested hillslope. The tillage intensity (User Summary page 35 and 

Technical Documentation pages 9.8 and 9.9) describes the percent of surface residue buried on the 

skid trail.

The model is sensitive to the buried residue value, just as skid trails can become highly erodible 

if the majority of surface residue is removed or incorporated into the soil. Users may wish to alter 

this value in the surface effects operation window to see the impact of degree of surface disturbance 

on soil erosion. Skidding also reduces the hydraulic conductivity, from 15 mm/h in undisturbed 

forest, to 10 mm/h or less, the amount of reduction depending on the soil (Elliot and others 1995b).

The Skid model tillage effects 

can be modified to model the effects 

of other tillage activities, like tillage as 

a site preparation treatment in forest 

management. The timing of tillage, 

depth and amount of incorporated 

residue can be altered with the 

management file builder.
10

References

Arnold, J.G., M.A. Weltz, E.E. Alberts, and D.C. Flanagan. 1995. Chapter 8. Plant growth 

component IN: Flanagan, D.C., and M.A. Nearing (eds.). USDA-Water Erosion Prediction 

Project Hillslope Profile and Watershed Model Documentation. NSERL Report No. 10. W. 

Lafayette IN: USDA-ARS National Soil Erosion Research Laboratory.

Burroughs, Jr., E. R., and J. G. King. 1985. Surface erosion control on roads in granitic soils. 

Proceedings of the Symposium sponsored by the committee on Watershed 

Management/Irrigation and Drainage, ASCE. April 30 - May 1, Denver, CO.

Elliot, W.J., R.B. Foltz, and C.H. Luce. 1995a. Validation of the Water Erosion Prediction Project 

(WEPP) Model for Low-Volume forest roads. Sixth International Conference on Low-Volume 

Roads, Washington, DC: Transport and Road Research Board and Natural Research Council. 

pp 178-186.

Elliot, W.J., R.B. Foltz, and M.D. Remboldt. 1994. Predicting sedimentation from roads at stream 

crossings with the WEPP model. Presented at the 1994 International Winter Meeting of the 

ASAE, Paper No. 947511, St. Joseph MI: ASAE. 10 pp.

Elliot, W.J., P.R. Robichaud, and C.H. Luce. 1995b. Applying the WEPP erosion model to timber 

harvest areas. Proceedings of the ASCE Watershed Management Symposium. New York: 

ASCE: 83-93.

Flanagan, D.C., and S.J. Livingston (eds.). 1995. WEPP User Summary. NSERL Report No. 11, W. 

Lafayette IN: National Soil Erosion Research Laboratory. 131 pp.

Flanagan, D.C., and M. A. Nearing (eds.). 1995. WEPP Hillslope Profile and Watershed Model 

Documentation. NSERL Report No. 10, W. Lafayette IN: National Soil Erosion Research 

Laboratory. 

Morfin, S., B. Elliot, R. Foltz, and S. Miller. 1996. Predicting effects of climate, soil, and 

topography on road erosion with WEPP. Presented at the 1996 ASAE Annual International 

Meeting, Paper no. 965016, ASAE, 2950 Niles Road, St. Joseph, MI 49085-9659. 

Page-Dumroese, D. S., M. F. Jurgensen, R. E. Brown, and G. D. Mroz. 1997. Evaluation of 

sampling techniques to measure bulk density of soils with abundant rock fragments. Under 

Review for Soil Sci Soc Am J.

Robichaud, P. R. 1996. Spatially-varied erosion potential from harvested hillslopes after prescribed 

fire in the interior northwest. Moscow ID: University of Idaho Library, PhD dissertation.

Tysdal, L. M., W. J. Elliot, C. H. Luce, and T. Black. 1997. Modeling insloped road erosion 

processes with the WEPP Watershed Model. Accepted for presentation at the ASAE 1997 

International Meeting. Manuscript available from second author.

Whitcomb, W.G., M.T. Yapp, and M. Myers. 1990. Aggregate surfacing design guide. Final 

Report, Contract 53-04H1-8-6230. Portland, OR: USDA Forest Service.
11

Appendix A−Forest Parameter Values

Values for Soil File Parameters

General Relationships for all forest soil files:

Soil Albedo 20%

Saturation on Jan 1. 75%

CEC (meq/100g) ≅ 0.8 ∗ clay content (%) 

(Users should consult local soil scientists for better estimates)

Sand, silt, and clay contents are the percentage of the soil fraction below 2 mm diameter.

Kr and TAUc can be predicted with Rangeland erodibility equations in the User Summary pp 18, 27.

Ki for an unbladed road can be predicted with Rangeland erodibility equations in the User Summary p 

27, and Ki for a bladed road can be predicted with Cropland equations in the User Summary p 26.

Table A1. Suggested values for forest soil files if no other soils information

File 

Name

OFE Location Ki 

(kg s/m4)

Kr

s/m

TAUc 

(N/m2)

Conductivity

(mm/h)

Inslope 1 Bladed Road 3e+006 0.0003 1 0.4 *

Outslop3 1 Bladed Road 3e+006 0.0003 1 0.4 *

2 Fillslope 4e+006 0.0003 1 6

3 Forest 2e+006 0.003 2 15

Plume3 1 Bladed Road 3e+006 0.0003 1 0.4

2 Fillslope 4e+006 0.0003 1 6

3 Forest 2e+006 0.003 2 15

Rut2 1 Rut 3e+006 0.0003 1 0.4 *

2 Shoulder 3e+006 0.0003 1 3

Tree 1 Forest 2e+006 0.003 2 15

Fire 1 Forest 2e+006 0.003 2 10

Skid 1 Forest 2e+006 0.003 2 10

Mitigation Effects

Gravelling Road Surface Change Road Surface Rock content to 90%

Change road surface conductivity to 3 mm/hr *

Rocking Ditches on Inslope Change TAUc to 10

* On coarse-textured granitic roads, conductivity ≈ 3 mm/hr (6 mm/hr if gravelled)
12

Management File Parameter Values

Table A2. Suggested initial conditions for forest situations

Parameters Road Fillslope Forest

Bulk Density (g/cc) 1.8 1.4 1.2

Canopy Cover (%) 0 0 90

Days since last tillage 100 300 500

Days since last harvest 400 300 500

Interrill Cover (%) 0 10 100

Residue Type Road Cutfill Tree

Residue Cropping System Fallow Perennial Perennial

Total rainfall since last tillage (mm) 250 1000 1000

Ridge height after last tillage (m) 0.006 0.1 0.1

Rill cover (%) 0 10 100

Random Roughness after tillage (m) 0.006 0.05 0.1

Rill spacing (use 0 for autocalc.) (m) 2.0 0 0

Rill width (use 0 for autocalc.) (m) 0.5 0 0

Total dead root mass (kg/m2) 0 0.001 0.5

Total submerged residue mass (kg/m2) 0 0.003 0.5

Table A3. Cropland plant scenario parameter values for road conditions

Parameters Inslope Outslop3 Plume3 Rut2

OFE 1 2 3 1 2 3 1 2

Biomass energy ratio 2 2 15 150 2 15 150 2 4

Canopy cover (%) 0.1 0.1 50 80 0.1 50 80 0.1 0.1

Plant stem dia (mm) 1 1 6 80 1 6 80 1 1

Biomass after 

 senescence (%) 1 1 90 70 1 90 70 1 1

Max canopy height (m) 0.15 0.15 0.6 3 0.15 0.6 3 0.15 0.15

In-row plant spacing 

(m)

5 5 0.06 0.73 5 0.06 0.73 5 1

Max. perenial root 

mass (kg/m2) 0.001 0.001 0.15 0.5 0.001 0.15 0.5 0.001 0.001

Max leaf area index 1 1 2 4.6 1 2 4.6 1 1

Table A4. Cropland Plant Scenario parameter values for Fire.man:

Parameter Year1 Year2* Year3 Year4 Year5 Year6

Biomass energy ratio 90 90 10 20 30 40

Canopy cover (%) 45 45 80 100 100 100

Plant stem diameter (m) 0.25 0.25 0.006 0.006 0.012 0.02

Biomass after senescence (%) 20 20 20 20 20 20

Max. canopy height (m) 20 20 0.8 1.5 2 2.5

In-row plant spacing (m) 3 3 0.08 0.04 0.08 0.1

Max. peren. root mass (kg/m2) 0.5 0.5 0.05 0.05 0.1 0.7

Max leaf area index 10 10 1 1.2 1.4 1.6

* Fire burned on Aug. 10 with 40% standing residue burned and 40% flat residue burned.
13

Table A5. Cropland Plant Scenario parameter values for Skid.man file:

Parameter Year1 Year2 Year3 Year4 Year5

Biomass energy ratio 90 10 20 30 40

Canopy cover (%) 45 50 100 100 100

Plant stem diameter (m) 0.25 0.006 0.008 0.01 0.012

Biomass after senescence (%) 20 90 80 70 60

Max. canopy height (m) 20 0.4 0.8 1.5 2

In-row plant spacing (m) 3 0.1 0.08 0.04 0.08

Max. perennial plant

root mass (kg/m2) 0.5 0.2 0.05 0.1 0.5

Max leaf area index 10 1 1.2 1.4 1.6

General parameters for plant scenarios in the Trees100.man file:

Canopy Cover after senescence 50. %

Biomass after senescence 70. %

Max. perennial plant root mass 2.7 kg/m2

Decomposition Constants 0.0074

Table A6. Vegetation growth parameter values in Trees100.man plant scenarios

Year Biomass Energy 

Ratio

Stem Dia

(m)

Canopy 

Height (m)

Plant Spacing 

(m)

Length of 

Senescence

(Days)

Leaf Area 

Index

0 5 0.01 0 0.03 30 0.1

1 10 0.01 0.1 0.03 35 1.4

5 50 0.02 1 0.2 40 2.2

10 80 0.04 1.5 0.4 45 3

15 120 0.06 2 0.6 50 3.8

20 150 0.08 4 0.8 60 4.6

30 470 0.12 11 1.0 90 6.2

40 600 0.16 15 1.4 130 7.8

50 710 0.20 18 1.8 170 8.5

60 800 0.24 21 2.2 210 8.7

70 850 0.28 23 2.6 250 8.9

80 890 0.32 25 2.9 270 9.1

90 910 0.36 27 3 290 9.3

100 930 0.4 29 3 300 9.5
14

Appendix B−Deleting Unwanted Files

Generally users will only be interested in a small subset of the files available to run WEPP, and 

will quickly generate new files to meet their specific needs. In order to reduce the hard disk space 

storage necessary, increase speed of interface response, and to simplify file selection, we recommend 

that unneeded files be deleted. There are many agricultural management and soil files that the user 

will not need. Generally, all the files referring to corn and soybeans including rotations beginning 

with C*.man or B*.man should be deleted. Wheat files are also generally not needed unless the user 

is modeling wheat as a mitigation measure. Files of grasses, alfalfa, and fallow may be useful for 

initially describing some forest regeneration conditions where forbs or grasses dominate, so users 

may wish to keep these files. If the user wishes to recover deleted files, the WEPP program can be 

installed again, and all files previously installed and deleted will be reinstalled, while leaving any new 

files undisturbed.

There are three common ways you may delete unwanted agriculture, rangeland, or forest files: in 

DOS (del filename.xxx), a file manager utility in Windows, or with the WEPP interface.

To delete files with the WEPP interface, select the File Action Bar. Under the File list, select 

File Utilities (Print/Delete) and a "Do what?" screen will appear. Under that screen, select the 

Print/Delete Selected Input files. A list of all the hill, climate, soil, slope, management, channel, 

impoundment, and scenario input files will be shown in a pop up screen. Press the del key when you 

have highlighted the file you want to delete. For information about Action Bars refer to page 96, and 

for a description of some agriculture files provided with the WEPP program see pages 118−129 of 

the WEPP User Summary.

Output files can be deleted with the same methods. Output files are named by the run name 

entered in the first box of the WEPP hillslope interface. To conserve disk space, it is a good practice 

to delete unwanted output files when they are no longer needed. The graphics files (*.wgr) are 

particularly large, and can soon fill up many hard disks.

Appendix C-Source of WEPP Hard Copy 

WEPP program disks, a hard copy of the WEPP user summary and user guide, and the CD-ROM 

disk containing both the soils and the climate databases were released at the WEPP/WEPS 

Symposium in August 1995. These materials can be obtained from the Soil and Water Conservation 

Society of America at 7515 NE Ankeny Road, Ankeny, IA 50021. The cost is $150 ($125 for 

SWCSA members). The society can be reached at 1-800-THE-SOIL or 515-289-2331. 
Multiply WEPP/SI Units by to get customary U.S. Units

mm (millimeters) 0.0394 in. (inches)

m (meters) 39.4 in. (inches)

m (meters) 3.28 ft (feet)

m2 (square meters) 10.8 ft2 (square feet)

m3 (cubic meters) 35.29 ft3 (cubic feet)

ha (hectares) 10,000 m2 (square meters)

ha (hectares) 2.47 acres

kg (kilograms) 2.2 lbs (pounds)

t (metric tonnes) 1,000 kg

t (metric tonnes) 1.1 short tons

kg/m2 (kilograms per sq m) 10 t/ha (metric tonnes per ha)

kg/m2 (kilograms per sq m) 27 tons/a (short tons per acre)

kg/m2 (kilograms per sq m) 0.04 lbs/ft2 (pounds per ft square)

15

Appendix D-Useful Conversions