# 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                          |
