Role: user

PATH Cost-Effective Quick Start

PATH Cost-Effective (PATH-CE) finds the least-cost combination of post-fire mulch treatments that meets your sediment targets, and shows you which hillslopes to treat on an interactive map.

What This Is For

After a wildfire, mulching reduces erosion — but budgets are finite and not every hillslope needs the same treatment (or any treatment). PATH-CE answers the question: which hillslopes should be mulched, and at what rate, to meet my sediment goals for the least money?

It works from Omni treatment scenarios you have already run — mulching at ½, 1, and 2 tons per acre — and compares each against the post-fire baseline. An optimization then assigns at most one treatment per hillslope so that:

every hillslope above your sediment-yield limit is treated down below it where possible, and
average-annual sediment discharge at the watershed outlet is brought down to your target,

at the lowest total treatment cost. You get a summary of the selected plan, an interactive report (treatment map, threshold sliders, and a cost surface showing how price responds to your targets), and downloadable tables.

When to Use It

You have a burned-area run (SBS map) and are weighing mulch treatment options and budgets.
You need a defensible, repeatable way to prioritize hillslopes for treatment rather than treating everything or guessing.
You want to see how treatment cost changes as sediment targets are tightened or relaxed before committing to one plan.

PATH-CE currently optimizes mulching only. If you are comparing other practices (thinning, prescribed fire), run them as Omni scenarios and compare their outputs directly.

Before You Begin

PATH-CE never creates Omni scenarios for you. It checks that the pieces below exist before solving and tells you exactly what is missing, but you must provision them first.

You need a completed WEPPcloud run with:

A fire scenario. A disturbed-land configuration with an SBS (soil burn severity) map uploaded, the watershed built, and WEPP run.
Omni scenarios. In the Omni Scenario Builder, add:
- an Undisturbed scenario, and
- a Mulching scenario for each application rate you want PATH-CE to consider, with Base scenario set to SBS Map. The ground-cover options correspond to the treatment rates: 15% ≈ ½ tons/acre, 30% ≈ 1 ton/acre, 60% ≈ 2 tons/acre.
Then click Run Omni and wait for it to finish.
Omni contrasts. In the Omni Contrasts Runner, run contrasts so each mulching scenario is compared against the SBS Map baseline. PATH-CE builds its outlet sediment numbers from these comparisons, so they are required — not optional.

If you configure a treatment in PATH-CE that has no matching Omni scenario or contrast, the run stops with a message naming what to provision.

Key Terms

Sediment yield (Sdyd) — the average-annual sediment leaving an individual hillslope, expressed per acre (metric tonnes per acre per year). A hillslope-scale number.
Sediment discharge (Sddc) — the average-annual sediment passing the watershed outlet (metric tonnes per year). A watershed-scale number.
Treatment — one mulching intensity (½, 1, or 2 tons/acre), backed by an Omni scenario. PATH-CE assigns at most one treatment per hillslope.
Untreatable — a hillslope that stays above the yield limit under every configured treatment, or whose yield increases under every treatment. These are reported separately rather than assigned a treatment.

All sediment quantities come from the WEPP/Omni model chain — they are model estimates, not measurements.

Settings

Setting	What it means	Units	Why it matters
Outlet Sediment Discharge Threshold	The most average-annual sediment you will accept at the watershed outlet after treatment	tonnes/yr (display follows your unit preference)	The main watershed-scale target. Lower values demand more treatment. A value at or above the post-fire discharge removes this requirement entirely; a value of 0 asks for the maximum achievable reduction.
Hillslope Sediment Yield Threshold	The per-hillslope yield ceiling; hillslopes above it must be treated	tonnes/acre	Controls which hillslopes are forced into the plan. Lower values pull more hillslopes in and raise cost. Default is 15.
Slope ≥ / Slope ≤	Restrict candidate hillslopes by average slope	degrees	Use when treatment is only practical (or only planned) on certain terrain. Leave blank to consider all hillslopes.
Burn Severities	Restrict candidate hillslopes by burn severity class	High / Moderate / Low	Use to target treatment at, for example, only high and moderate severity ground. Leave empty to include all.
Treatments table	Which mulch rates are available and what they cost	unit cost in $/acre; fixed cost in $	Costs drive the optimization. The label and rate are set by the chosen Omni scenario; you edit the costs.

Cost notes: per-hillslope cost is area × unit cost × rate, plus a one-time fixed cost (mobilization, staging) charged once per treatment type used anywhere in the plan. The default unit cost ($2,475/acre for all rates) and fixed costs ($500 / $1,000 / $1,500) are placeholders — replace them with local quotes before treating the dollar figures as meaningful.

Steps

On your run page, enable the Path CE mod. The PATH Cost-Effective panel appears on the run page.
Read the Omni Preconditions section of the panel and confirm you have provisioned the Omni scenarios and contrasts described above.
Set the Outlet Sediment Discharge Threshold. To pick a realistic value, open the Omni Scenarios report and note the post-fire (SBS Map) outlet discharge — your target should normally sit below it. Leaving it at 0 asks for the maximum achievable reduction (see Interpreting Results).
Set the Hillslope Sediment Yield Threshold, or keep the default of 15 tonnes/acre.
Optional: restrict candidates with the slope and burn-severity filters.
In the Treatments table, keep the rates you provisioned in Omni and remove any you did not. Enter your unit and fixed costs. Use Add Treatment to bring back a removed rate.
Click Run PATH Cost-Effective. Your settings are saved as part of the run — there is no separate save step.
Watch the status panel. A run validates preconditions, prepares data, solves, sweeps nearby thresholds (for the report's sliders), and renders the report. The first run takes the longest; repeat runs reuse the sweep when only sub-integer threshold changes were made.
When the run completes, review the summary and open the resources in the Run Results panel.

Interpreting Results

Solution is the first thing to check:

Optimal — your thresholds are achievable, and the plan shown is the least-cost way to meet them.
Second-best (thresholds infeasible) — no combination of the configured treatments can meet your targets. PATH-CE instead reports the plan that maximizes outlet-discharge reduction under the same per-hillslope rules. This is expected when the outlet threshold is 0 or set very low. If you wanted a least-cost plan, raise one or both thresholds and rerun.

Other summary fields:

Output	What it represents	How to read it
Selected Hillslopes	Number of hillslopes assigned a treatment	The size of the plan. The map in the report shows where they are.
Total Cost / Total Fixed Cost	Variable (area-based) and one-time costs in $	Only as reliable as the costs you entered.
Total Sddc Reduction	Combined outlet-discharge reduction from the selected treatments (tonnes/yr)	How much the plan improves the outlet.
Final Sddc	Modeled outlet discharge after treatment (tonnes/yr)	Compare against your threshold and the post-fire value.
Untreatable	Hillslopes no configured treatment can fix	These stay above the yield limit regardless of budget. Consider whether other practices apply there.

The Run Results panel links the interactive report and CSV downloads (selection, per-hillslope final yields, untreatable hillslopes, and the full threshold sweep). In the report, the sliders and cost surface re-solve at whole-number threshold combinations so you can explore cost sensitivity; your exact configured run is marked distinctly, and its numbers match the summary.

Assumptions and Limits

All sediment values are model estimates from the WEPP/Omni chain. They are most useful for comparing options and prioritizing; absolute values carry the uncertainty of the underlying model chain. Field review is still needed before implementation.
Only mulch treatments are optimized, and only the rates you provisioned in Omni.
Sediment quantities are metric tonnes throughout, including where treatment rates are labeled "tons/acre" (the label reflects mulch application convention). The hillslope yield unit is metric tonnes per acre.
Untreatable hillslopes are excluded from the plan by design, even where treating them would help the outlet. They are surfaced in the report instead.
On runs whose Omni contrasts were built in grouped mode, burn severity is assigned per group from its dominant land cover, and a group dominated by unburned ground may have no severity at all — the burn-severity filter is most meaningful on per-hillslope contrast runs.
The report's sliders explore whole-number thresholds only; your configured run uses your exact values.

Troubleshooting

"Omni scenario summaries are missing treatment scenario(s) …" — a treatment in your table has no matching Omni scenario. Add the Mulching scenario (base scenario: SBS Map) and click Run Omni, or remove that treatment row.
"… no completed 'sbs_map'-control contrasts …" — the Omni contrasts for that treatment have not been run. Open the Omni Contrasts Runner and run contrasts against the SBS Map control.
Messages about missing watershed files — the watershed has not been built (or was rebuilt without its outputs). Rerun the watershed steps, then rerun Omni.
"A PATH Cost-Effective run is already in progress" — wait for the current job to finish; each run replaces the previous results.
"Report not rendered: subcatchments.WGS.geojson not found" — the run's map export files are missing, so the report was skipped. The optimization results and CSVs are still valid.
Every run says Second-best — your thresholds are stricter than any treatment combination can satisfy. Raise the outlet threshold toward the post-fire discharge, raise the yield threshold, or add higher mulch rates in Omni.