Topographic Factor

The topographic factor, $LS_{USLE}$, is the expected ratio of soil loss per unit area from a field slope to that from a 22.1-m length of uniform 9 percent slope under otherwise identical conditions. The topographic factor is calculated:

$LS_{USLE}=(\frac{L_{hill}}{22.1})^m*(65.41*sin^2(\alpha_{hill})+4.56*sin\alpha_{hill}+0.065)$ 4:1.1.12

where $L_{hill}$ is the slope length ($m$), $m$ is the exponential term, and $\alpha_{hill}$ is the angle of the slope. The exponential term, $m$, is calculated:

$m=0.6*(1-exp[-35.835*slp])$ 4:1.1.13

where $slp$ is the slope of the HRU expressed as rise over run (m/m). The relationship between $\alpha_{hill}$ and $slp$ is:

$slp=tan\alpha_{hill}$ 4:1.1.14