The current version of WEPP (Ver. 95.7) was released by the USDA Agriculture Research Service (ARS) in August, 1995, at a symposium sponsored by the Soil and Water Conservation Society of America (SWCSA). We have spent a year working with this release, and it appears to be stable and reliable. The snowmelt routines overestimate the rate of snowmelt, but the problem has been identified and is being corrected. The revised routines will be incorporated in to a new release due out shortly. Until that time, the model provides reasonable estimates for runoff and erosion for most conditions, since the erosion from snowmelt is generally much lower than from severe rainfall events.

We have developed a number of typical hillslope input files to accompany this release that describe forest road and harvest area conditions. The files and draft documentation are available from us.

The 95.7 release includes the Watershed Version. We are currently carrying out a sensitivity study with this version. We have modeled a road prism with an eroding cutslope, an eroding ditch, a culvert, and erosion or deposition in the draw below the culvert. All components appear to work relatively well except the culvert routines. The developers have been informed of these problems, and are addressing our concerns. We will shortly begin to evaluate the ability of this version to model large forested watersheds.

RECENT WORKSHOPS

We led a workshop in the R1 Engineering Training Academy with about 20 participants in April, 1996. We targeted the workshop around demonstrating a range of files we have developed to model typical conditions encountered on roads and in forested areas. The participants were keen on the potential of the model, but were concerned about the complexity of the interface and the input required to run the model.

In August, 1996, we led a workshop in Auburn, AL, sponsored by the Southern Research Station and the Alabama NRCS. In addition to road erosion, we emphasized methods for modeling tillage as practiced in the southeast as a site preparation technique. It appears that the main effect of tillage is that the surface residue remaining after tillage protects the soil from erosion in the year of tillage. In the second and third year after tillage, the remaining residue decomposes faster than it can be regenerated, and the site is at it greatest risk from erosion until the vegetation produces enough litter for soil protection. The participants realized that field work is needed to determine the exact rates of residue decomposition and accumulation following site preparation in the southeast.

SIMPLIFIED WEPP INTERFACE

One of the lessons we have learned from the workshops is that Forest Service users are finding the current WEPP interface and the large number of options it makes available confusing to casual users. To address this problem, we have begun development of a less complex interface to run forest applications on the new Forest Service IBM computer system. The applications will include insloping, outsloping, rutted, and ditched roads, skid trails, burned sites, and harvested sites. We are seeking additional funding to help speed this development.

WEPP FIELD APPLICATIONS

Participants in the Region 1 Training academy saw the benefit of WEPP for some site-specific problems. In the Manti-La Sal NF in Utah, WEPP predicted the effects of graveling a road in a watershed with an ongoing hydrologic study. WEPP showed that graveling the road led to reduced runoff and erosion from the road, and that graveling would have little impact on the hydrologic processes in the watershed.

In the Bridger-Teton National Forest, Wyoming, WEPP allowed planners to compare the advantages of graveling a road in a sensitive watershed to installing water bars and tail drains from the continuous road ditches. In this case, it was found that the most effective way to reduce sedimentation was to install waterbars and tail drains at appropriate locations, rather than gravel the entire road surface. With continuous ditches, gravel would essentially lead to the substitution of road ditch erosion for road rut erosion.

We are carrying out a WEPP computer study to determine the relationships among road topography, side-hill topography, soils and climate in sediment delivery from roads. The results show that generally the effects of topography and soils are as expected, but that the effects of climate are complex. Some climates are rainfall driven, and others are snow melt driven. This difference has a major impact on the rate of road erosion, and the likelihood of sediment delivery acoss any buffer zone downhill from a road.

FUTURE WORKSHOPS

We have no workshops planned at this time. If regions or groups wish to have a workshop on WEPP, please contact us, and we will see if we can arrange a workshop to meet their specific needs.

SOURCES OF THE WEPP MODEL AND DOCUMENTATION

Interested users can obtain the WEPP model from several sources. It is available on a CD ROM, which includes the documentation, all of the climates for the USA and a large soils data base. We have some copies of the CD for distribution to Forest Service users. Users outside of the Forest Service may be able to obtain a copy of the CD ROM from jlaflen@ecn.purdue.edu. The SWCSA sells the CD ROM along with the printed manual and two floppy disks with the WEPP program for $150 (SWCSA, 7515 Northeast Ankeny Road, Ankeny, IA 50021-9764. Tel. 515 289 2331). The program and all documentation can also be obtained from the USDA-ARS National Soil Erosion Laboratory (NSERL) WEPP Home Page

For further information on WEPP in the Woods, contact W. Elliot, Intermountain Research Station, 1221 South Main Street, Moscow, ID 83843 (Tel 208 883 2338; Fax 208 883 2318; DG: S22L04A; Internet: welliot/rmrs_moscow@fs.fed.us).