Revised Universal Soil Loss Equation 2 -- Changes in 2014

Changes in RUSLE2 2014

This release of RUSLE2 contains several major enhancements including: (1) improved tools to develop and use annual and perennial vegetation descriptions, (2) tools to estimate runoff and develop a representative runoff event sequence, (3) tools to calculate and display tillage erosion on profiles with changing slope steepness, and (4) tools to make it easier to apply and remove permeable barrier systems commonly used on construction sites.

The existing documentation including Science Documentation and User's Reference Guide provide detailed descriptions of RUSLE2 as it existed in May, 2008. The changes made in the 2010 and 2014 versions are not yet embedded in these documents, but much of the new science is described in journal articles, and extensive additions have been made to the online HELP files. To access the on-line help associated with any parameter, right-click while hovering the pointer over a variable name and select "help" from the menu that is displayed.

The science behind the new vegetation tool was described by Dabney and Yoder (2012). This information supplements information in the Science Documentation and replaces information in section 9.2.4 of that document.  Dabney et al. (2014) describe the new forage removal process that was developed to interact with the new vegetation model. This information corresponds to information contained in the User's Reference Guide. A poster describing of the perennial vegetation systems enhancements is also available.

Documentation of how RUSLE2 calculates runoff was published by Dabney et al. (2011). The scheme basically predicts monthly runoff for combinations of soil, management, and climate descriptions. Also predicted are the number of runoff events per year and the gamma distribution parameters describing the population of event runoff depths. This scheme was modified by Dabney et al. (2012) who increased the gamma scale parameter equivalently to how Dabney et al. (2011) increased runoff during months with high erosivity density (rainfall intensity). In the 2014 release, except in Req areas, the default erosion calculation approach was changed from the daily disaggregated method to one based on a representative runoff event sequence. This change allows RUSLE2 to estimate annual and monthly runoff as well as erosion and to calculate a representative runoff event sequence that is suitable for linkage with an ephemeral gully model. The default return period for the largest event in the runoff event series was set to one year, but provision was made to allow the user to change the return period of any event in the series (only one at a time) in order to evaluate the effects extreme events. This feature is accessed in the "hydrology" tab of the "ARS Science" template. Advanced users using the R2_ARS_Science access level and the ARS Science template can change the erosion calculation method back to "classical RUSLE daily disaggregation" or may choose to enter site-specific measured or generated rainfall depth and erosivity data.

Documentation of the tillage translocation model were provided by Vieira and Dabney (2009) and Vieira and Dabney (2011). As implemented in the 2014 release of RUSLE2, tillage translocation (erosion or deposition) is only calculated when there are topographic breaks within contiguous management layers that include some degree of soil disturbance. The assumption is made that there is no soil transported across the upslope boundary of the first segment, nor across downslope boundary of a segment adjacent to a flow path channel or an untilled management. Thus, tillage translocation is reported to be zero for a one segment hillslope, but will be displayed if a tilled hillslope is broken up into multiple topographic segments. The tillage translocation parameters (alpha forward, alpha right, beta forward, beta right) are contained with the description of the "disturb surface" process.

Processes to add and remove permeable barriers were added to RUSLE2 in this release. In previous releases, retardance barriers were modeled as vegetation that only became effective after a "begin growth" process. The new permeable differ from vegetative barriers in that upon placement they provide immediate retardance that doesn't change over time, and their influence ends immediately upon removal. Permeable barriers are assumed to exist at the top of generally very small management segments that are normally created by cloning the management from the immediate upslope segment. A wizard to facilitate the creation of permeable barrier set has been created. The wizard acts in two steps. The upper part of the screen is a sediment barrier spacing wizard.  Using this approach a "system" of barriers can be automatically placed on the hill slope based on either a selected number or spacing of barriers.  When the upper part is complete the user applies this system with the upper "done" button and the barrier table at the bottom of the screen is filled out automatically by RUSLE2. Details of the lower table may be edited by the user. When satisfied, the user can use the second "done" button and "apply/close" to add the barrier system to the profile management list.

With this ARS release, several templates are provided.  The templates vary from basic and simple to advanced and complex. Several of the templates look like earlier releases, some display and give access to the net technology noted above. Some are focused on agricultural applications and some on highly disturbed lands such as construction sites. All the templates use US customary units except for the ARS Science.xml template, which uses SI units and provides the most detailed access to RUSLE2 parameters and results.

With this ARS release, two access levels are provided.  The R2_ARS_General access level is intended for users and consultants who wish to apply RUSLE2 with existing available databases such as the USDA-NRCS databases. This version includes control similar to that granted by the NRCS to their Field Offices.  The R2_ARS_Science.acc access level has more power to see and change parameters. It is intended for those with a thorough understanding of the RUSLE2 science as presented in the draft Science Documentation and User's Reference Guide.  Because of that presumed background, this version provides greater flexibility and control.

Please send questions or comments about this release to seth.dabney@ars.usda.gov.

References:

Dabney, S.M., D.C. Yoder, and G. Ferruzzi. 2014. Forage harvest representation in RUSLE2. Agronomy Journal 106:151-167.

Dabney, S.M. and D.C.Yoder. 2012. Improved descriptions of herbaceous perennial growth and residue creation for RUSLE2. Agronomy Journal 104(3): 771-784.

Dabney, S.M., D.C. Yoder, and D.A.N. Vieira. 2012. Application of RUSLE2 to evaluate conservation practices in alternative climate change scenarios. J. Soil and Water Conserv. 67(5):343-353.

Dabney, S.M., D.C. Yoder,  and D. 2011.  Enhancing RUSLE to include runoff-driven phenomena. Hydrologic Processes. 25: 1373-1390.

Vieira, D. A. N. and S.M. Dabney. 2011. Modeling edge effects of tillage erosion. Soil and Tillage 111: 197-207.

Vieira, D.A. and S.M. Dabney. 2009. Modeling landscape evolution due to tillage. Trans. ASAE. 52 (5): 1505-1521.