USDA Forest Service · Inside FS
New tool can keep communities safe during floods and storms
How the CULVERT tool helps land managers and engineers pinpoint at-risk road-stream crossings before floods and storms strike.
Hydro-geospatial decision-support system
Pre‑field vulnerability assessment of road‑stream crossings
CULVERT (Climate and Upland Loading Vulnerability Evaluation and Risk Analysis Tool) screens road-stream crossings for flooding, soil erosion, stream-bank erosion and debris flow to prioritize field inspection, maintenance and resilient redesign.
Free account. Continental U.S. coverage. Only a project boundary is
required.
About the research project
Capabilities
- Runs from a boundary alone
- Draw or upload a project boundary; terrain, roads, crossings and rainfall are fetched or derived. More data gives more detailed results.
- Culvert asset discovery
- Identifies possible crossings where roads cross streams when no culvert inventory exists.
- Sub-meter and post-disaster DEMs
- Upload your own lidar, including post-event surveys, or fetch 10 m or 30 m USGS 3DEP elevation.
- Headwater catchments
- Nested, multi-outlet delineation resolves the small watersheds draining to each crossing.
- Road-aware hydro-enforcement
- Road-fill and breakline adjustments to the DEM route flow through road embankments at the crossings.
- Peak flood discharge
- Regional frequency analysis, Rational Method, TR-55 and TR-20 for multiple return periods, stationary or non-stationary.
- Culvert hydraulic capacity
- Peak flow compared against capacity from culvert dimensions, with FHWA HDS-5 inlet or outlet control.
- Proposed design dimensions
- Proposed width and height, nearest standard size, HW/D and outlet velocity for each return period.
- Skew, alignment and diversion
- Inlet approach angle, gradient and width continuity, and road diversion potential at each crossing.
- Erosion and sediment supply
- Process-based erosion with WEPP cloud, upland soil loss with RUSLE, and stream-bank erosion with SBEVA.
- Debris flow and plugging
- Debris-flow susceptibility, sediment and wood supply, and hydraulic plugging margin for each culvert.
- GIS-ready outputs
- Interactive map, tables and charts, shapefile and GeoPackage downloads, and a project report.
Why CULVERT
Screening a national inventory of road-stream crossings
The USGS identified roughly six million CONUS road-stream crossings by intersecting road lines with hydrography datasets, using 500,000 field observations for validation. Built for historical climates, this critical infrastructure is highly vulnerable to extreme precipitation, sediment-laden floods, and debris flows, threatening safety, economies, and aquatic passage. Since manually inspecting six million crossings is impossible, agencies need CULVERT: an automated hydro-geospatial decision-support system that flags at-risk locations, prioritizing inspections, restoration, and resilient redesign.
Assessed today
- Flooding and overtopping. Peak storm flows exceed the culvert’s hydraulic capacity.
- Upland soil erosion. WEPP and RUSLE sediment that aggrades and plugs the inlet.
- Debris flow. Sediment and woody debris surge down and choke the crossing.
- Stream-bank erosion. Channel widening undermines the culvert and road embankment.
On the roadmap
- Landslide
- Post-fire landslide
- Post-fire erosion
- Post-fire debris flow
- Future CMIP6 climate projections
- Aquatic organism passage
- Best management practices
Continental U.S. data coverage
Required datasets are integrated through open, reliable data APIs across the continental U.S.
Automated crossing identification
If you don’t have crossing locations, the tool generates candidate culvert sites from roads and streams and assesses them.
High spatial and temporal resolution
Assess risk at spatial resolutions up to 1 m or submeter scale, with temporal resolution down to 1 hour.
Pre-field prioritization
Ranks crossings ahead of field visits to direct limited maintenance budgets and inform climate-resilient sizing on all land ownerships, not only federal property.
How it works
Three-module analysis workflow
A project boundary, drawn on the map or uploaded, is the only required input. Elevation, roads, culvert locations and rainfall are fetched or derived automatically when you do not supply them; supplying your own data gives more accurate and more detailed results. Each module uses the outputs of the previous one.
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Module 1
Watershed delineation
Upload your own surveyed or lidar DEM, including sub-meter terrain collected after a flood, fire or landslide, to delineate watersheds on the landscape as it exists now. The DEM is hydro-enforced at road embankments, breached and filled, and used to delineate the watershed draining to each crossing with its stream network and longest flow path. Use your own culvert inventory, or let the tool discover possible crossings where roads meet streams. Where no DEM is available, CULVERT fetches USGS 3DEP elevation.
- User lidar or surveyed DEMs, including sub-meter and post-disaster terrain
- Hydro-enforcement with road fill and breakline burning
- Nested, multi-outlet delineation for headwater catchments
- Your culvert inventory, or crossings discovered where roads meet streams
- USGS 3DEP 10 m or 30 m elevation when no DEM is supplied
Screen recording. Click the video to pause.
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Module 2
Hydrologic vulnerability
Peak discharge is estimated for each crossing and return period from the data you have: watershed rain-gauge records, gauged streamflow series, or an event-specific storm depth or intensity, such as the storm that caused the damage. NOAA Atlas 14 is used where local records are not supplied. Regional frequency analysis, the Rational Method, TR-55 and TR-20 give peak flows with lower, expected and upper bands. These are checked against each culvert’s hydraulic capacity and used to size a replacement.
- Rain-gauge, streamflow or event-specific storm data; NOAA Atlas 14 as fallback
- Stationary or non-stationary frequency analysis with selectable homogeneity tests, outlier methods and distributions
- Peak flow with lower, expected and upper bands
- Capacity check from surveyed culvert dimensions, FHWA HDS-5 inlet or outlet control
- Proposed culvert dimensions for each return period
Screen recording. Click the video to pause.
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Module 3
Hydrogeomorphic vulnerability
Five methods rate how much sediment, debris and wood each watershed can deliver to its crossing, and how likely the culvert is to plug or divert flow. They run on the delineated watersheds and the DEM you supply, so a post-event survey carries changed channel geometry and slopes into every score. WEPP cloud simulates runoff, erosion and sediment delivery with a process-based model; CPDV scores plugging and diversion from channel width and gradient, inlet approach angle, road profile, and sediment and wood supply; RUSLE estimates upland soil loss; SBEVA rates stream-bank erosion; and WDFM flags debris-flow potential. The selected scores are combined into one EHVI score per crossing.
- Process-based erosion and sediment delivery (WEPP cloud)
- Plugging and diversion risk (CPDV)
- Upland soil loss (RUSLE)
- Stream-bank erosion (SBEVA) and debris-flow potential (WDFM)
- Field-measured bankfull width and culvert slope used when supplied
- Adjustable method weights and parameters
- One EHVI ranking per culvert
Screen recording. Click the video to pause.
Methods
Hydrologic and hydrogeomorphic methods
Each crossing’s contributing watershed is delineated from a digital elevation model, then scored with the hydrologic and geomorphic models below. Results appear on an interactive map where you can toggle the DEM, watersheds, streams, roads and crossings, and click any culvert for its method-by-method breakdown.
| Method | What it does | Best used when |
|---|---|---|
| Hydrologic vulnerability | ||
| Non-stationary regional frequency analysis Design storms under a changing climate | Estimates design-storm magnitudes (for example the 25- or 100-year event) by pooling records across a hydrologically similar region and letting the distribution shift over time. | Historical stationarity no longer holds: trending precipitation under climate change, or short or sparse rain-gauge records at the site. |
| SCS TR-55, TR-20 and Rational Method Peak discharge with confidence bands | Turns design rainfall into a peak discharge for the contributing watershed using curve-number runoff (TR-55 and TR-20) or Q = C·i·A (Rational), reported as lower, expected and upper bands. | Sizing for peak flow: TR-55 and TR-20 for small-to-mid rural and forested basins, the Rational Method for very small, fairly uniform drainage areas. |
| Culvert hydraulic capacity Can the crossing pass the design flow? | Checks the estimated design discharge against the crossing’s hydraulic capacity: headwater-to-diameter ratio (HW/D), tailwater and outlet velocity. | You need to know whether a culvert is hydraulically undersized or scour-prone, not only whether its watershed is hazardous. |
| Proposed design dimensions What size should the crossing be? | Solves for the culvert size that passes the design discharge for each return period: proposed width and height, the nearest standard size, HW/D, outlet velocity, and headwater and tailwater depths. | Planning a replacement or new installation, or checking an existing culvert against a resilient design. Works without existing culvert dimensions. |
| Hydrogeomorphic vulnerability | ||
| WEPP Watershed Erosion Prediction Project (cloud) | Physically based, event-scale modeling of runoff, hillslope erosion and sediment delivery, run on WEPP cloud. | You need process-based erosion and sediment yield, including post-fire conditions, rather than an empirical estimate. |
| CPDV Culvert Plugging and Diversion Vulnerability | Scores seven crossing-scale factors: width continuity, gradient continuity, inlet approach angle (skew), road diversion potential, debris-flow susceptibility, sediment and wood supply-connectivity, and hydraulic plugging margin. They are blended into one score with adjustable weights. | The concern is a culvert plugging with sediment or wood, or flow leaving the channel and running down the road, rather than only exceeding its hydraulic capacity. Uses the hydrologic headwater ratio when Module 2 has run. |
| RUSLE Revised Universal Soil Loss Equation | Predicts long-term average hillslope soil loss from rainfall, soil, slope-length, cover and practice factors. | Gauging the upland sediment supply that can aggrade and plug a culvert on agricultural, range and disturbed forest slopes. |
| SBEVA Stream-Bank-Erosion Vulnerability Assessment | Rates how prone the channel banks near a crossing are to widening, scour and lateral failure. | Bank instability or channel migration could undermine the culvert or its road embankment. |
| WDFM Watershed Debris-Flow Model | Flags watersheds capable of generating sediment and debris surges that can choke a crossing. | The basin is steep and confined, or recently burned or disturbed and prone to debris flows. |
| EHVI Ensemble Hydrogeomorphologic Vulnerability Index | Averages the scores of the selected methods (WEPP, CPDV, RUSLE, SBEVA and WDFM) into a single 0 to 5 vulnerability score and category for each crossing. | You want one overall ranking to prioritize crossings, especially where the individual models disagree. |
Validated at the Santee Experimental Forest (South Carolina lowlands) and the Hubbard Brook Experimental Forest (New Hampshire uplands).
Intended users
Applications by user group
GIS analysts and field engineers
Delineate watersheds, pull design rainfall, and export ready-to-use shapefiles and reports to focus field visits on high-priority crossings.
Land managers and policy makers
A ranked picture of at-risk crossings across all lands, to prioritize inspections, justify funding and plan climate-resilient redesigns.
Researchers and scientists
Peer-reviewed methods (regional frequency analysis, TR-55/TR-20, WEPP, CPDV, RUSLE, SBEVA, WDFM) with downloadable inputs and outputs for reproducible research.
Research
Peer-reviewed publications
- 2025
- 2025
- 2024
- 2023
- 2022
- 2021
News
Media coverage
Collaborators and funding
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U.S. Department of Transportation Major funding
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USDA Forest Service
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University of North Georgia
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University of Idaho
Start a CULVERT assessment
Create a free account to delineate watersheds and assess the road-stream crossings in your project area. A sample dataset from the Santee Experimental Forest is available for evaluation.