Erodability (or erodibility) is the inherent yielding or nonresistance of soils and rocks to erosion. A high erodability implies that the same amount of work exerted by the erosion processes leads to a larger removal of material. Because the mechanics behind erosion depend upon the competence and coherence of the material, erodability is treated in different ways depending on the type of surface that eroded.
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Soils
The most commonly used model for predicting soil loss from water erosion is the Universal Soil Loss Equation (USLE) (also known as the K-factor technique), which estimates the average annual soil loss
where R is the rainfall erosivity factor, K is the soil erodibility , L and S are topographic factors representing length and slope, and C and P are cropping management factors.
Other factors such as the stone content (referred as stoniness), which acts as protection against soil erosion, are very significant in Mediterranean countries.
Shear stress model
Geological and experimental studies have shown that the erosion of bedrock by rivers follows in first approach the following expression known as the shear stress model of stream power erosion:
where z is the riverbed elevation, t is time, K_\tau is the erodability,
Note that
Unit stream power model
An alternative model for bedrock erosion is the unit stream power, which assumes that erosion rates are proportional to the potential energy loss of the water per unit area:
where
where Q is the water discharge of the river [m3/s], and W is the width of the river channel [m].
Relative differences in long-term erodability can be estimated by quantifying the erosion response under similar climatic and topographic conditions with different rock lithology.