> For the complete documentation index, see [llms.txt](https://futurewater.gitbook.io/sphy-manual/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://futurewater.gitbook.io/sphy-manual/manual/sphy-manual-3.1/appendix-3-soil-erosion-model-input/hsfp.md).

# HSFP

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

**Table 41: Hspf\_table**

| Land Use Class | Ground Cover (CR) | Soil Scour Detachment (KGER) | No Erosion |
| -------------- | ----------------- | ---------------------------- | ---------- |
| **-99**        | 1                 | 2                            | 3          |
| **1**          | 0.65              | 0.03                         | 0          |
| **2**          | 0.5               | 0.2                          | 0          |
| **3**          | 0.35              | 0.5                          | 0          |
| **…**          | …                 | …                            | …          |

Ground cover is similar to all other soil erosion models, specified per land use class. The soil scour detachment coefficient (KGER) is a model parameter that is a soil erodibility parameter for detachment by runoff. The “no erosion” column (0 or 1) prevents erosion from happening, for instance for water and paved land use classes.

The P-factor map indicates the support practice factor, which indicates how conservation measures reduce soil erosion, which factor is often considered to be 1.

The rainfall detachment coefficient KRER is similar to the USLE K-factor. The Wischmeier et al. (1971) formulations are used (see section 2.8) when this is left empty. In that case, a sand, clay and organic matter map should be provided in the PEDOTRANSFER section of the config file (even when the pedotransferfunctions are not used (i.e. if PedotransferFLAG = 0). The rainfall detachment exponent JRER is an exponent in the detachment by raindrop impact formulation.

Similar model parameters exist for the washoff detachment, i.e. KSER and JSER, and for scour detachment, i.e. KGER and JRER. The soil scour detachment KGER should be left empty when the land use specific values are provided in hspf\_table.

The fraction by which detached sediment storage decreases per time step is defined by AFFIX.

**Table 42: Model parameters**

| Model Parameter                           | Model Variable | Unit | Range/Default |
| ----------------------------------------- | -------------- | ---- | ------------- |
| **Ground cover**                          | CR             | -    | 0-1           |
| **Soil scour detachment**                 | KGER           | -    | 0.01-0.5      |
| **No erosion**                            |                |      | 0 or 1        |
| **Support practice factor**               | SMPF           | -    | 0-1           |
| **Rainfall detachment coefficient**       | KRER           | -    | 0.14-0.45     |
| **Rainfall detachment exponent**          | JRER           | -    | 1.5-3         |
| **Washoff detachment coefficient**        | KSER           | -    | 0.1-5         |
| **Washoff detachment exponent**           | JSER           | -    | 1.5-2.5       |
| **Soil scour detachment coefficient**     | KGER           | -    | 0.01-0.5      |
| **Soil scour detachment exponent**        | JGER           | -    | 1-2           |
| **Fraction of sediment storage decrease** | AFFIX          | -    | 0.05          |