WEPPcloud
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WEPP

WEPP is the main runoff and erosion model used by most WEPPcloud watershed projects. In WEPPcloud, it turns your delineated watershed, soils, land cover, disturbance inputs, and climate into modeled hillslope runoff, sediment production, channel routing, and watershed-outlet summaries.

What This Is For

Use WEPP when your question is about runoff, erosion, or sediment delivery under a specific landscape condition, such as:

  • current conditions versus burned conditions,
  • treated versus untreated conditions,
  • observed recovery versus assumed recovery,
  • how much sediment comes from hillslopes versus what reaches the outlet.

In most projects, this is the central model run that all later reports and exports depend on.

What You Actually Control In The UI

On the run page, the main control is titled WEPP or WEPP-SWAT+. The top-level buttons the user actually sees are:

Visible action Where it appears What it does
Run WEPP main WEPP card Submits the whole current WEPP form, including any enabled advanced options
Prep Only WEPP Advanced Options > WEPP Exec Builds hillslope and watershed inputs without executing the WEPP binary
Run WEPP Watershed WEPP Advanced Options > WEPP Exec Runs the watershed/channel routing phase using existing hillslope outputs
Run WEPP Hillslopes and Watershed Bootstrap > Run (No Prep) Runs the bootstrapped WEPP inputs exactly as checked out, without rebuilding inputs in the browser
Run WEPP Watershed Bootstrap > Run (No Prep) Runs only the bootstrapped watershed/channel routing step

WEPP Advanced Options is where most result-changing assumptions live. These are the visible cards and controls the user actually works with:

Advanced card User-facing controls Why an end user would touch it
WEPP UI - Hourly Seepage Run hourly seepage (wepp_ui.txt) Use only for runs where hourly seepage behavior is relevant; the card itself notes this is for 7778 soils and not WEPP-PEP
Potential ET (PMET) Basal crop coefficient ratio (kcb), Readily available water fraction (rawp), Run PMET (pmetpara.txt) Switches from the default Penman ET treatment to Penman-Monteith and exposes crop-water assumptions
Frost Write frost inputs (frost.txt) plus wintRed, fineTop, fineBot, ksnowf, kresf, ksoilf, kfactor(1), kfactor(2), kfactor(3) Only for cold-region runs where frozen-soil behavior is materially important
Snow Write snow inputs (snow.txt), Rain/snow threshold temperature, Density of new snow, Snow settling density Only when snow accumulation and melt assumptions matter
Baseflow Processing Initial groundwater storage, Baseflow coefficient, Deep seepage coefficient, Watershed groundwater baseflow threshold area Important for continuous simulations when low-flow or delayed-flow behavior matters
Channel Inputs (chan.inp) Output interval override (dtchr_override, seconds), Channel hydrograph output (ichout_override), Channel TOPAZ IDs of interest (chn_topaz_ids_of_interest) Use when you need more or less channel hydrograph detail or want outputs only for selected channels
Channel Parameters Use variable channel critical shear as a function of channel slope (tcr.txt), Critical shear, Channel erodibility, Minimum channel width, Total Manning roughness coefficient allowing for vegetation (chnn), Manning roughness coefficient for bare soil in the channel (chnnbr), and optional taumin, taumax, k, n Important when channel erosion or routing behavior is a major decision driver
Bedrock Hydraulic conductivity for restrictive layer (kslast) Use when shallow restrictive layers or perched-water assumptions are important
Clip Hillslopes Clip hillslopes, Hillslope clip length Useful when very long representative hillslopes appear to overstate erosion
Soil Options Clip Soils Maximum Depth, Soils Maximum Depth, Clip Soils Minimum Depth, Soils Minimum Depth, Estimate wc and fc using Rosetta when soils have bd override, Initial soil saturation Use when the default soil-depth or starting-wetness assumptions are not defensible
Phosphorus Surface runoff concentration, Subsurface lateral flow concentration, Baseflow concentration, Sediment concentration Optional pollutant-sidecar settings for runs that need phosphorus output assumptions
Export Configuration Prep details, Geopackage export (.gpkg), Legacy ArcMap export (.shp) Choose which deliverables should be generated automatically when a run completes
Interchange Delete raw WEPP outputs after successful interchange conversion Storage-management choice; keeps interchange products while discarding raw text outputs
WEPP Exec WEPP binary version, Run WEPP Watershed checkbox, Prep Only button, Run WEPP Watershed button Execution-mode controls, including whether the main run should include channel/watershed routing
Revegetation Scenarios Cover transformation scenario, Upload cover transform file (.csv) Post-fire cover-recovery scenario control when revegetation is enabled

The most important practical distinctions are:

  • Run WEPP Watershed inside WEPP Exec controls whether the main Run WEPP submission includes watershed/channel routing, not just hillslope execution.
  • Prep Only and the Bootstrap no-prep buttons are advanced workflows for QA, export, or intentionally edited input files. They are not the normal starting point for scenario comparison.
  • Most users should leave Frost, Snow, PMET, Bedrock, and Phosphorus at defaults unless they have a specific hydrologic reason to override them.

What Happens When You Click Run

The visible buttons trigger different API-backed actions:

  1. Run WEPP This submits the serialized form to /rq-engine/api/runs/<runid>/<config>/run-wepp. The payload includes any enabled advanced-option values, such as soil clipping, baseflow settings, export flags, and reveg_scenario. WEPPcloud stores those run settings, queues the WEPP hillslope workflow, and then loads the run-summary and results panels when the job finishes.

  2. Prep Only This submits to /rq-engine/api/runs/<runid>/<config>/prep-wepp-watershed. It builds hillslope and watershed inputs only. It does not execute the full model.

  3. Run WEPP Watershed This submits to /rq-engine/api/runs/<runid>/<config>/run-wepp-watershed. Use it when hillslope outputs already exist and you want only the watershed/channel routing pass. The UI itself warns that this requires a prior full WEPP run.

  4. Bootstrap Run WEPP Hillslopes and Watershed or Run WEPP Watershed These use the no-prep bootstrap routes /rq-engine/api/runs/<runid>/<config>/run-wepp-npprep and /rq-engine/api/runs/<runid>/<config>/run-wepp-watershed-no-prep. They assume you have already cloned, edited, committed, and checked out the desired input files through Bootstrap. They skip normal preparation and rerun with the current bootstrapped inputs.

After a successful run, the controller fetches:

  • /runs/<runid>/<config>/report/wepp/results/
  • /runs/<runid>/<config>/report/wepp/run_summary/

That is why the Run Results area updates only after the queued job completes.

Run, Prep, And Report Surfaces

Run surface

The run surface is where you configure and queue model execution. This is where scenario choices, advanced options, and export-on-completion choices are submitted.

Prep surface

Prep Only is the user-facing way to build WEPP inputs without executing the model. This is most useful when:

  • you are checking whether inputs were built correctly,
  • you want prep artifacts for QA or export,
  • you are using bootstrap and plan to edit inputs outside the browser.

Report surface

After a successful run, Run Results exposes the outputs users typically need first:

  • Watershed Loss Summary
  • Return Periods Report
  • Summary by Landuse Report
  • Sediment Characteristics Report
  • TotalWatSed3 CSV
  • TotalWatSed2 CSV
  • The Deval in the Details Report
  • GL Dashboard
  • Storm Event Analyzer when available
  • Prep Details
  • Post WEPP Geopackage Features Export
  • Post WEPP Geodatabase (ESRI) Features Export
  • Average Annual Report
  • Yearly Report
  • Daily Runoff / Lateral Flow / Baseflow Graph

Read these as different views of the same run:

  • use Watershed Loss Summary for outlet-scale planning numbers,
  • use Summary by Landuse Report and mapped outputs to find source areas,
  • use Return Periods Report for frequency-style interpretation,
  • use the water-balance reports to understand whether a result is being driven by runoff generation, lateral flow, or baseflow.

Single-storm output is explicitly flagged in the UI as deprecated and unsupported. For event-scale work, the page points users to Storm Event Analyzer instead.

How To Interpret WEPP Results

The most important distinction is scale:

  • hillslope outputs tell you where runoff and sediment are generated,
  • channel and watershed outputs tell you what is routed downstream,
  • outlet values do not tell you which hillslopes caused the problem by themselves.

The second distinction is time scale:

  • event-style outputs help explain storm behavior,
  • annual and return-period outputs are better for planning and comparison,
  • a single dramatic event can coexist with moderate long-term averages.

The strongest end-user use of WEPP is usually comparative:

  • baseline versus burned,
  • untreated versus treated,
  • observed recovery versus assumed recovery,
  • one advanced-option choice versus another.

Core Model Assumptions And Limits

  • WEPP is a physically based model, but it still simplifies the watershed into representative hillslopes and channels rather than modeling every field feature directly.
  • Runoff is generated through infiltration-excess and saturation-excess mechanisms, so soil properties and starting wetness matter.
  • Channel routing is only included when watershed/channel routing is enabled.
  • Many advanced cards only write optional WEPP text inputs such as frost.txt, snow.txt, tcr.txt, or pmetpara.txt. If you enable them, you are replacing the default internal behavior with your chosen override values.
  • Baseflow Processing is not implemented for single-storm climates.
  • Very local features such as short road ditches, small berms, culverts, or engineered controls may not be represented unless another workflow models them explicitly.
  • Results are only as defensible as the watershed delineation, soil inputs, climate record, land cover, burn severity, and treatment scenario behind them.
  • A good outlet number does not prove the source-area pattern is correct. Review hillslope and channel outputs too.