SHETRAN

The SHETRAN soil erosion model requires the following land use specific model parameters (shetran_table):

Table 21: Shetran_table

Land use class	Leaf drip diameter (dl)	Leaf drip distance (X)	Ground cover (Cg)	Canopy cover (Cc)	Manning (n)	No erosion
-99	1	2	3	4	5	6
1	0.005	10	0.65	0.85	0.2	0
2	0.004	0.5	0.35	0.6	0.1	0
3	0.006	0.3	0.3	0.35	0.05	0
…	…	…	…	…	…	…

The leaf drip diameter should be specified per land use class, with a typical value of around 0.005 m. See Table 4.2 of (Wicks, 1988) for values per land use class. The leaf drip distance is similar to the plant height used in the other models. The same holds for ground and canopy cover, for which the latter is ignored in case the vegetation module is used. Table 4.2 of Wicks (1988) gives also suggestions for these model parameters. The Manning’s roughness should be specified for all land use classes. The “no erosion” (0 or 1) column prevents erosion from happening, for instance for water and paved land use classes.

The raindrop impact soil erodibility coefficient kr is typically between 0.1-70 J-1, while the overland flow soil erodibility coefficient kf is typically between 0.5-20 ∙ 10-6 kg m-2 s-1.

The flow and sediment density can be assumed to be 1100 and 2650 kg m-3, respectively.

The particle diameter of the three textural classes should be provided, which can be assumed similar to the values provided by Morgan & Duzant (2008) for the MMF model.

The median grain size D50 can be provided, but when left empty, the median grain size will be estimated from the particle diameter and texture maps.

The width-to-depth ratio is used to determine the size of the rills, for the calculation of the flow velocity. Typical values range from 1-3.

The immediate deposition is determined using a transport capacity equation, for which two options are available, i.e. (1) Yalin (1963) and (2) Engelund & Hansen (1967).

Table 22: Model parameters

Model parameter	Model variable	Unit	Range/default
Leaf drip diameter	dl	m	0.003-0.007
Leaf drip distance	X	m	0-50
Ground cover	Cg	-	0-1
Canopy cover	Cc	-	0-1
Manning	n	s m-1/3	0.01-0.5
No erosion		-	0 or 1
Raindrop impact soil erodibility coefficient	kr	J-1	0.1-70
Overland flow soil erodibility coefficient	kf	kg m-2 s-1	0.5-20 ∙ 10-6
Flow density	ρ	kg m-3	1100
Sediment density	ρs	kg m-3	2650
Particle diameter	δc, δz, δs,	m	2 ∙ 10-6, 60 ∙ 10-6, 200 ∙ 10-6
Median grain size	D50	µm	1-2000
Width-to-depth ratio	WD	-	1-3
Capacity equation			1 or 2