I

Social

■ market forces

■ wealth distribution

■ demography

■ social stability

Rate of soil erosion

EROSION CAUSED SOIL DEGRADATION

Political

- polices

- legislation

- political stability

Figure 4: Factors of soil erosion; causes of soil erosion and interactions between them (Lai, 2001)

CD 3

Soil erosion prediction and assessment has been a challenge to researchers since the 1930s' and several models have been developed (Lal, 2001). These models are categorized as empirical, semi-empirical and physical process-based models. Empirical models are primarily based on observation and are usually statistical in nature. Semi-empirical model lies somewhere between physically process-based models and empirical models and are based on spatially lumped forms of water and sediment continuity equations. Physical process-based models are intended to represent the essential mechanism controlling erosion. They represent the synthesis of the individual components which affect erosion, including the complex interactions between various factors and their spatial and temporal variabilities.

Some of the widely used erosion models are discussed below: Empirical Models Universal Soil Loss Equation (USLE)

USLE is the most widely used empirical overland flow or sheet-rill erosion equation. The equation was developed to predict soil erosion from cropland on a hillslope. The equation is given by -

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