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Disturbed Land Soil Lookup Table (PowerUser Panel → Modify Disturbed Parameters)

The disturbed land soil table in WEPPcloud contains parameters that define soil properties for various land use categories and soil textures. These parameters are essential for modeling erosion and hydrology in disturbed lands using the WEPP (Water Erosion Prediction Project) model. The table includes data for combinations of land use (e.g., agriculture crops, forest, bare) and soil texture (clay loam, loam, sand loam, silt loam).

Each project has its own disturbed land-soil-lookup table that can be modified through the PowerUser Panel.

This page is the parameter reference. For the recommended calibration order, what to calibrate first, and how to think about undisturbed versus post-fire tuning, see WEPPcloud Calibration Guidance.

Table of Parameters

Additional Notes and Other Parameters of Interest

Effective Hydraulic Conductivity (avke)

Determined from field data. Do not change unless you have a good reason.

• Units: mm/h
• Guidelines:
  • Treat this as a field-based parameter, not a general-purpose calibration knob.
  • In some west-of-Cascades settings, the disturbed-versus-undisturbed difference in this parameter may matter less than it does in drier inland settings.

Interrill Erodibility (ki)

Interrill areas are the sheet flow zones between small channels (rills) on a hillslope. Interrill erodibility measures the soil's susceptibility to detachment by raindrop impact and shallow sheet flow. It is influenced by:

• Soil texture
• Surface cover (e.g., vegetation, mulch)
• Soil structure and cohesion

Units: kg·s/m⁴
Note: Do not change.

Rill Erodibility (kr)

Rills are small channels formed by concentrated flow on hillslopes. Rill erodibility is the soil’s susceptibility to detachment by concentrated flow (not raindrop impact). Rill erosion is generally more intense on steeper and/or longer slopes and can cause greater sediment transport than interrill erosion.

Units: s/m
Note: Do not change in most projects.

Regional caution:

• Emerging West Cascades guidance suggests that lower kr values may fit some settings better.
• Treat that as expert-guided regional adjustment, not as a general default.

Critical Shear Stress (τc)

This is the minimum hydraulic shear stress required to initiate detachment of soil particles in rills. Below this threshold, the flow is not energetic enough to detach soil. It acts as a resistance parameter in rill erosion models.

Units: N/m² or Pa
Note: Do not change.

Basal Crop Coefficient (pmet_kcb)

The Kcb parameter for the FAO Penman-Monteith equation approximates net evapotranspiration from meteorological data as a replacement for direct measurement of evapotranspiration.

Units: None
Guidelines:

• For forests, use default: 0.95 (well-watered conditions).
• For undisturbed calibration, values near 1.2 can increase ET and reduce annual water yield, while values near 0.65 can reduce ET and increase annual water yield.
• No need to modify for disturbed conditions, as the reduction in ET is accounted for by a reduction in LAI within the model.

For more information, see: Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56, Chapter 7 - ETc - Dual crop coefficient (Kc = Kcb + Ke)

Rain-Snow Temperature Threshold

Found under WEPP Advanced Options - Snow.

Units: °C
Range: -3 to 1
Guidelines:

• Use 0 for CLIGEN.
• Use 0 for Daymet.
• Use -2 for GridMET.

Underlying Bedrock Conductivity (ksat for restrictive layer - kslast)

Found under WEPP Advanced Options - Bedrock

Units: mm/h
Default: Based on SSURGO values (ksat of the last horizon / 100, or other rules).
Range: 0.001–0.1
Guidelines:

• 0.001 strongly restricts deep seepage and tends to keep more water in lateral flow and runoff pathways.
• 0.1 allows more drainage to the baseflow reservoir and can reduce quick runoff response.
• Use this as a structural watershed-hydrology parameter, not as a first-response substitute for poor climate or watershed setup.

Baseflow Coefficient

Found under WEPP Advanced Options - Baseflow Processing.

Units: per day
Range: 0.01–0.10
Guidelines:

• 0.01 gives a longer recession, on the order of about 100 days.
• 0.04 gives a shorter recession, on the order of about 25 days.
• The historical WEPPcloud limit of 0.04 came from earlier disturbed-land guidance, not a hard WEPP model limit.
• Some small watersheds, especially in the 40-100 ha range, may require higher coefficients such as 0.05-0.07 per day to match observed recession behavior.
• When observed streamflow data are available, estimate this from the slope of the recession limb rather than tuning by trial and error alone.
• Start with the project default and only increase the coefficient when the simulated baseflow recession is too slow relative to observations or other defensible calibration targets.

Channel Critical Shear Stress (τc)

Found under WEPP Advanced Options - Channel Parameters

Units: N/m² or Pa Range: 0.05 (fine silt) and 170 coarse cobble Guidelines:

• This is the minimum shear stress required to initiate the movement of sediment particles on the bed of a channel (such as a river, stream, or canal).
• In simple terms, it's the threshold force per unit area that water flow must exert on the channel bed to start erosion or sediment transport.
• For practical calibration, channel critical shear is often started from the channel bed D50 particle size in mm.
• Higher values generally mean less channel erosion; lower values generally mean more channel erosion.
• Example regional guidance:
  • 70-170 for coarse-bed West Cascades style channels.
  • about 20-50 for more erosion-prone Inland Pacific Northwest settings.
  • about 35-40 for North Idaho examples such as Mika Creek.
  • about 70 near Eugene, Oregon.
  • about 83 for some Oregon/Washington municipal watershed settings.

ksatadj

Specifies hydrophobicity adjustment

Units: None Guidelines:

• Currently, we set the hydrophobicity for high severity burn only. But it could be changed as desired. Note that in the model the hydrophobicity is by burn severity applied to all four soil textures of high severity.
• The ksatadj value of "1" specifies hydrophobic soils. Users can then change the lower limit of hydraulic conductivity (lkeff parameter value), which would restrict infiltration and allow more surface runoff.

Related Docs

• WEPPcloud Calibration Guidance
• WEPP Advanced Options
• Observed Model Fitting