Erosion prediction models are commonly used to estimate soil loss under different site and management conditions. Common models include the Universal Soil Loss Equation (USLE), Revised Universal Soil Loss Equation (RUSLE), and Water Erosion Prediction Project (WEPP). Among these models, USLE has been widely used for estimating erosion in forestry. The U.S. Department of Agriculture Forest Service guide by Dissemeyer and Foster (1984) provides step-by-step guidance for predicting erosion on forest land by considering key factors that contribute to soil loss. Access the guide using the embedded link or QR code. Below are the specifics on using the USLE method for estimating soil erosion potential on harvest sites. For estimating soil erosion on harvest sites, the six operational areas within a timber harvest site (forest roads, skid trails, stream management zones (SMZs), stream crossings, harvest area, and landings) can be categorized into tilled (topsoil removed) and untilled groups (no topsoil removed). SMZs and harvest areas fall into the untilled group, while the rest fall into the tilled group. Soil erosion needs to be estimated from each operational category in order to get the overall average erosion from the harvest site. All references to Figures and pages refer back to the USLE manual (not in this info sheet). The equation for estimating erosion in USLE-Forest is:
Department of Agriculture Forest Service1 guide by Dissemeyer and Foster (1984) provides step-by-step guidance for predicting erosion on forest land by considering key factors that contribute to soil loss. Access the guide using the embedded link or QR code.
Below are the specifics on using the USLE method for estimating soil erosion potential on harvest sites. For estimating soil erosion on harvest sites, the six operational areas within a timber harvest site (forest roads, skid trails, stream management zones (SMZs), stream crossings, harvest area, and landings) can be categorized into tilled (topsoil removed) and untilled groups (no topsoil removed). SMZs and harvest areas fall into the untilled group, while the rest fall into the tilled group. Soil erosion needs to be estimated from each operational category in order to get the overall average erosion from the harvest site. All references to Figures and pages refer back to the USLE manual (not in this info sheet). The equation for estimating erosion in USLE-Forest is:
Erosion rate (tons/acre/year) = R×K×LS×CP
Where,
The amount of rainfall contributing to erosion is measured as the number of rainfall erosion index units. In Kentucky, this value varies from ~ 150 in eastern region to ~ 250 in the western region. The USLE method uses a rainfall index provided in Figure 1, page 3 in the manual.
Soil erodibility is a measure of a soil's susceptibility to erosion. Usually, the soil erodibility value varies with the soil type. To check the K factor for a particular harvest site, see page 36 in the USLE manual or visit the UC Davis SoilWeb 2. You can also scan the QR code to access the Web, enter the harvest site location, and locate the corresponding K-factor.
The combined influence of slope length and gradient on erosion is considered in this step. Field measurements of slope gradient can be done using a clinometer (percent slope), while slope length can be measured with a tape or by pacing. The values for LS factors can be found in Table 1, page 5, or Figure 3, page 6 in the USLE manual. For instance, with a slope of 5 percent and a length of 50 feet, the LS value is 0.379.
Operational areas need to be categorized as tilled or untilled, and to obtain this value, you must evaluate the subfactors and multiply them together to get the CP value. If a subfactor is not applicable, assign it to a value of 1. The subfactors are given below.
1https://www.ars.usda.gov/ARSUserFiles/60600505/RUSLE/A%20guide%20for%20predicting%20sheet%20and%20rill%20erosion%20on%20forest%20land.pdf2https://casoilresource.lawr.ucdavis.edu/gmap/