# DHVSM

The DHSVM soil erosion model requires the following land use specific model parameters (dhsvm\_table):

Table 23: Dhsvm\_table

| Land use class | Leaf drip diameter (D) | Leaf drip distance (X) | Ground cover (Cg) | Canopy cover (Cc) | Manning (n) | Root cohesion (COHr) | No erosion |
| -------------- | ---------------------- | ---------------------- | ----------------- | ----------------- | ----------- | -------------------- | ---------- |
| -99            | 1                      | 2                      | 3                 | 4                 | 5           | 6                    | 7          |
| 1              | 0.005                  | 10                     | 0.65              | 0.85              | 0.2         | 15                   | 0          |
| 2              | 0.004                  | 0.5                    | 0.35              | 0.6               | 0.1         | 1.5                  | 0          |
| 3              | 0.006                  | 0.3                    | 0.3               | 0.35              | 0.05        | 10                   | 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. The root cohesion can be obtained from the EUROSEM manual (Morgan et al., 1998), see also Table 19. The “no erosion” column (0 or 1) prevents erosion from happening, for instance for water and paved land use classes.

Table 24: Guide values for root cohesion (COHr; kPa), based on Morgan et al. (1998)

| Vegetation type     | Soil cohesion (COHr) (kPa) |
| ------------------- | -------------------------- |
| Barley              | 0.2-0.6                    |
| Grass               | 1-8                        |
| Marram grass        | 1.5-15                     |
| Chaparral, matorral | 0.3-3                      |
| Alfalfa             | 10                         |
| Alder               | 2-12                       |
| Sitka spruce        | 4-12                       |
| Hemlock             | 1-8                        |
| Willow              | 6                          |
| Poplar              | 2                          |
| Maple               | 4-6                        |
| Pines               | 4-10                       |
| Coniferous forest   | 1-17.5                     |
| Candlenut           | 15-35                      |
| Acacia              | 1-5                        |

A soil class map (SoilClass) should be provided, which is subsequently used to assign soil cohesion values to the soil classes. The soil cohesion values should be provided in a table, i.e. dhsvm\_cohesion\_table:

Table 25: Dhsvm\_cohesion\_table

| Soil class | Soil cohesion (COH) |
| ---------- | ------------------- |
| -99        | 1                   |
| 1          | 10                  |
| 2          | 3                   |
| 3          | 15                  |
| …          | …                   |

The values for soil cohesion can be obtained from the EUROSEM manual (Morgan et al., 1998), which gives soil cohesion estimates per soil type based on the USDA soil texture classification.

The raindrop impact soil erodibility coefficient kr is typically between 0.1-70 J-1.

The critical stream power SPcr is typically 0.004 kg m s-3.

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 minimum water depth should be provided for stability reasons. A value of 0.001 m should give satisfying results.

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.

Table 26: Model parameters

| Model parameter                              | Model variable | Unit     | Range/default                   |
| -------------------------------------------- | -------------- | -------- | ------------------------------- |
| Leaf drip diameter                           | D              | 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                        |
| Root cohesion                                | COHr           | kPa      | 0.2-35                          |
| No erosion                                   |                | -        | 0 or 1                          |
| Soil cohesion                                | COH            | kPa      | 2-44                            |
| Raindrop impact soil erodibility coefficient | kr             | J-1      | 0.1-70                          |
| Critical stream power                        | SPcr           | kg m s-3 | 0.004                           |
| 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                             |
| Minimum water depth                          | hmin           | m        | 0.001                           |
