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United States Department of Agriculture

Agricultural Research Service

WEPP Release Notes
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Changes in WEPP 2012.8

WEPP model version 2012.8 was released on October 3, 2012. The following is a list of changes since the 2010.1 release:

WEPP Model Updates:

  1. Incorporated Li Wang’s (Washington State University) new channel routing code in the model. These are options used for larger watersheds in addition to the standard CREAMS and EPIC methods. The new channel routing options are read from the chan.inp input file.
  2. Fixed tile drainage to output water removed from soil layers.
  3. Added tile drainage runoff to pass file as an input to channel.
  4. Added irrigation and tile drainage to water balance output files.
  5. Fixed the watershed pass files to have correct formatting when more than 75 hillslopes are present.
  6. Added alternate hourly percolation from Erin Brooks (University of Idaho) as an alternative to the daily updating. This code is executed only if a special input file, wepp_ui.txt is present. Requires special format (version 7778) soil file.
  7. Added more frozen soil hydraulic conductivity factors for different land use types. These are read from an expanded frost.txt input file.
  8. Fixed a bug where the watershed event-by-event output listed no sediment yield if an impoundment was the watershed outlet.
  9. Increased number of breakpoint climate inputs for a single day to 200.
  10. Kinetic energy of rainfall was not being reset every day. The net effect was that the kinetic energy, and consequently the crust reduction factor, are greatly overestimated when there is a high energy storm followed by many non rain dry days.
  11. Fixed bug in snow drifting routine.

WEPP Windows Interface Updates:

  1. Added new channel routing options to user interface as part of the watershed run options and also the text file output.
  2. Updated user interface to be able to run external Python programs to process WEPP files. Included water balance Python program as an example.
  3. Added window to set more frozen soil hydraulic conductivity factors for different land use types.
  4. Updated the install and WEPP interface program to work with Windows 7 with the default installer settings.
  5. Fixed bug in user interface on Windows 7 where import directories would load the wrong location.
  6. Fixed Plant width in user interface conversion English to Metric bug.
  7. Fixed bug where fixed date irrigation exceeded 100 events.
  8. Updated WEPP Windows help files to newer HTML Help format.

Comments on changes between WEPP model 2008.907 and 2010.1

WEPP model version 2010.1 was released on January 28, 2010. The following is a list of changes since the 2008.907 release:

1.      Fixed problem where watershed runoff may be larger than precipitation – This change was to correct a bug in the water balance when upland lateral subsurface flow was added to channels.

2.      Fixed problem where soil water content could exceed soil porosity – This change was to correct a bug under very mild freezing conditions where the top 10cm of the soil could exceed the maximum soil water content.

3.      Fixed problem where negative soil moisture outputs reported – This change was to correct a problem in surface temperature when freezing soil under certain half thaw conditions.

4.      Added soil thermal conductivity adjustment input – Additional input was added to frost.txt customization file to adjust thermal conductivity of unfrozen soil.

5.      Adjusted output formatting – Main model text output file has added decimal places to display very small soil loss values.

6.      Plant output formatting – The OFE column in the plant output was missing. The rill and interrill cover values were reversed.

7.      Added frozen water soil content to graphics output – This contains frozen soil water amount by layer and also total.

8.      Fixed evapotranspiration in graphics output – The total evapotranspiration amount was not always the sum of the soil and plant transpiration amounts.

9.      Fixed water balance issues – The updated computed runoff values were not being used in all cases. The runoff values may be adjusted by reduction of runoff volume caused by infiltration during the recession for partial equilibrium hydrographs.

10. Updated Single Storm Hydrograph – Used updated runoff values to compute. Allowed more lines to be output to show a more complete hydrograph.

11. Fixed deep percolation problem caused by thin bottom soil layer -  If the bottom soil layer is very thin the deep percolation will be restricted causing the soil profile to hold more water. The code has been adjusted to round the bottom soil layer to a 20cm boundary to get full percolation.

12. Added subsurface runon and snow columns to water balance output.

13. Fixed contouring bug where out-of-date contouring scenarios were applied.

14. Fix for freeze/thaw energy getting out of bounds causing large erosion results.

15. Rainfall intercepted by residue – is separated from soil evaporation output, previous WEPP versions included this in Es.

16. Rainfall on snowpack – the rainfall interception amount is now set to zero if there is any snow depth on the day of rainfall.

17. Contouring Fix – Chezy depth-discharge coefficient was being calculated incorrectly.

18. Sediment Yield in Multiple OFE hillslopes – Fix to calculate sediment based on rill width and not topmost rill width which may cause sediment yield to exceed soil loss.

19. Interface fix for CLIGEN PAR file generation – skew parameter was not being calculated correctly when a new PAR file was created from observed data.

20. Interface Change Cover Calibration Tool – In the initial conditions record the rill and interrill cover parameters are filled in with the target cover %.

21. Interface Fix Irrigation – More days can be handled in the fixed date irrigation schedules.

Comments on changes between WEPP model 2006.5 and 2008.907

WEPP model version 2008.907 was released on October 3, 2008. The following is a list of changes since the 2006.5 release:

Modifications of Winter Hydrology Subroutines in WEPP
(Shuhui Dun and Joan Wu, Washington State University July 1, 2008)

A detailed description of the winter hydrology changes is available here - winter hydrology changes as a PDF file. A short description follows and is also available as a PDF file here - winter hydrology changes (short).

  1. Solar radiation on sloped surface - Diffusive radiation is now also considered.

  2. Cloud cover- We now use solar radiation under clear sky, instead of extraterrestrial solar radiation, as the maximum solar radiation that can reach a horizontal surface, in estimating cloud cover.

  3. Start time of storm events- When using break-point climate input data, we use the input value, instead of a randomly generatedtime, for the start time of a rainfall event.

  4. Snow accumulation - We have corrected a problem in snow consolidation. The previous version WEPP 2006.5 tends to underestimate snow density and overestimate snow depth when a precipitation event last several days because snow-pack settling was not estimated during a precipitation event and when there is no snowmelt. We have also corrected the problem with rain on a snow pack so that rain will not infiltrate or run off before the liquid-water-retaining capacity of the snow is reached.

  5. Snowmelt- The following problems have been corrected: 
    (i) dew-point temperature was originally estimated following a sine function during a day and is now taken directly from the weather input;
    (ii) the coding of the equation for adjusting wind velocity was incorrect, and we now apply a simpler equation from the ACE; and 
    (iii) we have incorporated the ACE’s convection-condensation equation for heavily forested areas into the snowmelt routines of WEPP.

  6.  Frost simulation - 
    i. More, finer soil layers (10 layers in each original soil layer), instead of only two layers (tilled and untilled), are used in frost simulation.
    ii. The problem of mixed use of energy flux and energy amount is corrected.
    iii. In the present version, soil temperature one meter below the frozen zone is estimated following an annual air-temperature curve, instead of the assumption that this temperature is always 7 °C. 
    iv. Unsaturated hydraulic conductivity and soil water potential in the winter routines are now estimated following Saxton and Rawls (2006) instead of the method of P. Kalita. 
    v. Saturated hydraulic conductivity of frozen soil is taken as the unsaturated hydraulic conductivity at a soil water content of porosity minus ice content. 
    vi. A subroutine has been added to compute soil water redistribution when frost is present.

Other changes include the following:

  1. Fix for multiple strip erosion errors.

  2. The graphics file supports both English and metric units. The units in the graphics file are determined by what units were used in the simulation.

  3. In the winter output file a column for residue depth was added to see the residue effect on frost formation.

  4. More support in the Windows interface for international climates by making it easier to search for similar US stations.

  5. A senescence date can be used for perennial plants.

  6. Fixed plant output file formatting for larger canopy heights.

  7. Several input files for forest conditions have been corrected.

  8. An impervious pavement management was added to the installed management files.

  9. The Windows interface slope editor now supports upto 50 segments per hillslope.

  10. Climate interpolation close to state boundaries was fixed.

  11. WEPP Version 2008.907 has significant changes in the winter processing. Under winter conditions the model will produce more winter runoff events. These changes to better simulate freeze/thaw conditions can also increase the model runtime, up to 8 times that of the 2006.5 version of WEPP. Different management scenarios and residue can also have large differences in runtime depending on the amount of freeze/thaw cycles that result.

    To allow some flexiblity in the level of winter processing detail a new file was added to control winter frost processing. If the file 'frost.txt' is present in the directory with the other WEPP input files it controls whether water redistribution is done for frost and how many fine layers are used in frost simulation. In addition the thermal conductivity of snow and residue can be specified along with the lower limit for hydraulic conductivty in frozen soil. The file contains 2 lines the first line with 3 integers:

    1 or 0 = whether to run the water redistribution as part of the frost simulation, default 1 (run redistribution)
    1..10 = number of fine layers in each of the 2 top wepp layers, default 10
    1..10 = number of fine layers in each of the remaining wepp layers, default 10

    The second line contains thermal conductivity factors for snow and residue and a kfactor to control the lower limit of hydraulic conductivity in frozen soil. There are three floating point values on the line:

    Ksnowf - The first is the factor by which to adjust the default snow thermal conductivity, range 0.1 to 10.0, default 1.

     Kresf - The second is the factor by which to adjust the default residue thermal conductivity,  range from 0.1 to 10.0, default 1. The factor is multiplied by the baseline thermal conductivity value, which is 0.05 (W/m C) for residue.

    KFactor – The third value is to control the lower limit of hydraulic conductivity in frozen soils, range >0 to 1.0, default 0.00001.

     If the file is not present the default values are used. In the winter output file these settings are written out just as a cross reference.

Comments on changes between WEPP model versions 2004.7 and 2006.5

WEPP model version 2006.5 was released on May 18, 2006. The following is a list of changes since the 2004.7 release:

Subsurface lateral flow processing was added by Shuhui Dun and Joan Wu at Washington State University. More details about the processing can be found here. The water output file has a new column that indicates the amount of subsurface lateral flow for each day of the simulation. The pass files generated for watershed simulations have a new element name SUBEVENT to indicate any subsurface flow. The main output file for watershed simulations contains a field for the subsurface flow. In watershed simulations all upstream subsurface flow from hillslopes is added into the channel.

The soil file input can now include an optional restricting layer that defines the hydraulic conductivity of a restricting layer and the anisotropy (horizontal vs vertical) of the entire soil profile. A description of the new soil file can be found here. The new soil file has a different version number to indicate if the restricting layer is present. Existing soil files will work with the 2006.5 WEPP model.

WEPP rock correction factor change from Susan Skirvin, ARS Tucson Arizona. A detailed description of the change can be found here.

When 2006 version soil files are used the minimum saturated hydraulic conductivity is set at 0.000000108 mm/hr during the simulation. For other soil versions the minimum saturated hydraulic conductivity is set at 0.07 mm/hr.

Radiation inclinations are computed separately for each OFE in a watershed simulation to more accurately account for snow melt.

Formatting changes in several output files to account for more hillslope or channel identifiers and to fix column alignments.

Comments on changes between WEPP model versions 2002.7 , 2004.6 and 2004.700

 WEPP model version 2002.7 was publicly released in July 2002.   WEPP model version 2004.6 was released on July 6, 2004 with the following changes:

  1. The 2004.6 version includes several bug fixes and improvements, particularly to the model water balance and handling of plant and residue interception water. 

  2. Fixes to watershed version where program would stop execution in the TABLE function.

An error was identified in WEPP model version 2004.6 in predicting peak runoff rates for some situations, leading to unrealistic runoff and erosion rates. The 2004.700 updated model executable released September 14, 2004 corrects the problem. 

Comments on changes between CLIGEN versions 4.2 and 5.2

 CLIGEN version 4.2 was modified to version 4.3 to allow simulation using single climate station parameter input files, instead of the old "stations" and state procedure.   No changes were made in v4.3 to computations within CLIGEN.   Version 4.3 is used with the new sets of individual station parameter files provided by the USDA-Forest Service, Moscow, ID.   Corrected and extended input parameter sets for individual U.S. stations have been provided by the U. S. Forest Service, Moscow, Idaho. (Many derived from Arlin Nicks' original data.)

CLIGEN version 4.2 was subsequently recoded to conform to the "Water Erosion Prediction Project (WEPP) Fortran-77 Coding Convention".   The code structure was radically simplified and the code extensively commented.   Corrections to peak intensity calculations proposed by Dr. Bofu Yu, were added to the code, to make peak intensity responsive to differences in latitude as originally intended.   The new code has been verified to give results identical to Dr. Yu's.   Logic has also been added to CLIGEN version 5.2 to ensure that the random numbers upon which Cligen's outputs are based on are of satisfactory quality.

Because CLIGEN uses single parameters to derive daily values for the entire month, three schemes of interpolation/disaggregation were coded to provide more continuous daily values between the monthly ones. These are:

1. simple linear interpolation.

2. Fourier series.

3. a modified linear interpolation which preserves the mean value of the parameter for the month.

The impact of these interpolation schemes on predictions of runoff and soil loss by WEPP is still under evaluation.

To facilitate use of CLIGEN by user interfaces, the following command line options were added: -S state number, -s station number, -i input filename, -o output filename, -b beginning year, -y years duration, -r random seed, -I0 no interpolation (default), -I1 linear interpolation, -I2 Fourier interpolation, -I3 interpolation to preserve the monthly means, -?, -h help.

The CLIGEN code is continuing to be evaluated and modified as necessary.

More information about CLIGEN 5.2 is available at:

Last Modified: 10/3/2012
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