Limitations of Universal Soil Loss Equation

 The equation involves the procedure for assigning the values of different associated factors on the basis of practical concepts. Therefore, there is the possibility to introduce some errors in the selection of the appropriate values, particularly those based on crop concepts. Normally R and K factors are constants for most of the sites/regions in the catchment, whereas, C and LS vary substantially with the erosion-controlled measures, used. The following are some of the limitations of the USLE:

 Empirical

The USLE is a totally empirical equation. Mathematically, it does not illustrate the actual soil erosion process. The possibility to introduce predictive errors in the calculation is overcome by using empirical coefficients.

 Prediction of Average Annual Soil Loss

This equation was developed mainly on the basis of average annual soil loss data; hence its applicability is limited for estimation of only the average annual soil loss of the given area. This equation computes less value than the measured, especially when the rainfall occurs at high intensity. The storage basin whose sediment area is designed on the basis of sediment yield using USLE should be inspected after the occurrence of each heavy storm to ensure that the sedimentation volume in the storage basin is within the limit.

 Non-computation of Gully Erosion

This equation is employed for assessing the sheet and rill erosions only but can not be used for the prediction of gully erosion. The gully erosion caused by concentrated water flow is not accounted for by the equation and yet it can cause a greater amount of soil erosion.

 Non-computation of Sediment Deposition

The equation estimates only soil loss, but not soil deposition. The deposition of sediment at the bottom of the channel is less than the total soil loss taking place from the entire watershed. Nevertheless, the USLE can be used for computing the sediment storage volume required for sediment retention structures., Also, the USLE equation can be used as a conservative measure of potential sediment storage needs, particularly where sediment basins ranges typically from 2-40 ha and runoff has not traveled farther distance, and basin is intended to serve as the settling area. Again, if the drainage on any site is improperly controlled and gully erosion is in extensive form, then this equation underestimates the sediment storage requirement of the retention structure.

During the estimation of the contribution of hillslope erosion for basin sediment yield, care should be taken as it does not incorporate sediment delivery ratio. This equation cannot be applied for predicting the soil loss from an individual storm, because the equation was derived to estimate the long-term mean annual soil loss. The use of this equation should be avoided for the locations, where the values of different factors associated with the equation, are not yet determined.