Physical Processbased Model

Empirical models have constraints of applicability limited to ecological conditions similar to those from which data were used in their development.

Further, USLE cannot deal with deposition; its applicability limits large areas and watersheds. Based on these considerations, several process-based models have been developed (e.g. WEPP, EUROSEM, LISEM (Lal, 2001) ).

Table 4. Operative functions and input parameters of Morgan, Morgan & Finney Soil erosion model

- kinetic energy of rainfall (J/m2)

- volume of overland flow (mm)

- rate ofdetachment by raindrop impact (kg/m?)

- transport capacity of overland flow (kg/m?)

- Annual rainfall (mm)

- Number ofrainy days in the year

- Intensity of erosive rain (mm/h).

- Percentage ofrainfall contributing to permanent interception and stream now(%) .

E/E0 - Ratio ofactual (E) to potential (E) evaporation.

MS - Soil moisture content at field capacity or 1/3 bar tension (% w/w).

BD - Bulk density ofthe top layerMg/m3)

RD - Top soil rooting depth (m) defined as the depth of soil from the surface to an impermeable or stony layer, to the base of A horizon; to the dominant root base.

K - Soil detachability index(g/() defined as the weight of soil detached from soil mass per unit ofrainfall energy.

S - Steepness of the ground slope expressed as slope angle.

C - Crop cover management factor. Combines C and P factors of the USLE

Water Erosion Prediction Project (WEPP) Model

WEPP is an example of widely used physically process-based erosion model (Renard et al., 1996). It was developed as a system modeling approach for

Water phase:

Where,

Sediment phase:

predicting and estimating soil loss and selecting catchment management practices for soil conservation. Basic erosion and deposition equations in WEPP are based on the mass balance formulation that uses rill and inter-rill concept of soil erosion, which is a steady-state sediment continuity equation. The WEPP model computes erosion by rill and inter-rill processes. The sediment delivery to rill from inter-rill is computed by following equation -

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