Help & Examples
Worked examples and how to use each tool.
Worked Example
A step-by-step walkthrough of a published FHWA case, showing the method the engine follows: inlet-control equation selection, the governing-equation diagram, and the headwater result.
FHWA HDS-5 Design Guideline 1
Watch the Calculation Explorer step through a published FHWA case (54" RCP groove-end, 200 cfs, S = 0.01), no login required. The engine reproduces the published headwater within 1% (7.925 ft vs 8.0 ft; FHWA acceptance band is ±5%). More worked examples are planned.
Open the worked example →Using the Tools
Three workflows cover most culvert work. Pick the one that matches your task.
Design & Analyze
Enter a culvert's size, flow, slope, and material to get the headwater, the governing flow regime (inlet vs outlet control), and a full performance breakdown. Start here to size a new culvert or check an existing one.
Open Design & Analyze →Multi-Scenario (Design Matrix)
Compare many diameters and materials side by side to find the smallest culvert that stays within your allowable headwater. Useful for preliminary sizing and for checking a contractor's proposed substitution.
Open Multi-Scenario →Calculation Explorer
Step through the FHWA HDS-5 method one equation at a time, with the governing-equation diagram lighting up for your inputs. The clearest way to see why a result is what it is, and a good teaching tool. Try the public worked example without an account.
See the worked example →When to reach for this vs HY-8 / HEC-RAS
| Your situation | Use | Why |
|---|---|---|
| Quick feasibility check | This platform | Answer in ~2 minutes, no setup |
| Compare multiple options | This platform | All sizes and materials in one view |
| Field verification on-site | This platform | Runs on a tablet, no install |
| Understanding the "why" | This platform | Every calculation step is visible |
| Final stamped submittal | HY-8 / HEC-RAS | Established and certified; use until our PE validation is published |
What It Is and Is Not
- An FHWA HDS-5 compliant calculation engine
- A field verification and as-built assessment tool
- A preliminary design and sizing tool
- A multi-scenario bulk comparison tool
- An educational and training resource
- Mobile and tablet friendly
- Fast: ~2 minutes vs 30+ minutes by hand
- A replacement for HY-8 or HEC-RAS
- A substitute for engineering judgment
- For complex hydraulic systems
- A finite element analysis tool
- For non-standard culvert configurations
- Certified for final stamped submittals (yet)
When to Use HY-8 or HEC-RAS Instead
- Final design for stamped construction documents
- Complex hydraulic systems or multiple culverts in series
- Regulatory submittals requiring certified software
- Projects requiring full hydraulic modeling
Who It's For
Field Inspectors & Engineers
Scenario: Assessing an existing culvert during a site inspection.
Need: An immediate answer: does this 36-inch culvert handle 50 cfs within allowable headwater?
Approach: Enter measurements on a tablet, get a pass/fail, export a field report, decide on-site.
Design Engineers: Preliminary Design
Scenario: Sizing a culvert during early project development.
Need: A quick preliminary size before investing time in a full HY-8 model.
Approach: Run the design path, get a recommended diameter across materials, document the preliminary sizing, then validate with HY-8 for the final submittal.
Reviewers & Approvers
Scenario: A contractor requests a substitution: 48-inch instead of 54-inch.
Need: Rapid verification without re-running a full design.
Approach: Compare both sizes in Multi-Scenario, see the headwater difference, decide within minutes.
Students & EITs
Scenario: Learning culvert hydraulics and the FHWA HDS-5 method.
Need: An interactive way to understand inlet vs outlet control and performance curves.
Approach: Work through the Calculation Explorer, compare to hand calculations, and build engineering intuition.
Platform Status
Core Platform Live
Circular culvert design and analysis, inlet/outlet control, the Design Matrix, 3D Section View, 2D plan view, projects dashboard, PDF calculation reports, and a Rational Method flow calculator. All live and in active use.
Physics Validation In Progress
The engine reproduces FHWA HDS-5 published examples (Design Guideline 1 within 1%) and is covered by 303 automated validation tests. A structured audit of the physics engine is ongoing, with deeper edge-case coverage in progress: flow-regime transitions, skewed inlets, and boundary-condition extremes.
Building Now In Progress
- Box culverts (RCB) per FHWA HDS-5
- Multiple barrel analysis
- Additional inlet types (mitered, beveled, tapered)
On the Horizon & Future Roadmap
- Multi-storm analysis (2, 5, 10, 25, 50, 100-yr)
- Additional culvert shapes (pipe arch, elliptical)
- Formal PE validation with a published report
- Field verification mode with GPS tagging
- Topography integration via DEM/LiDAR import
Try it yourself
Open the worked example and step through a real FHWA case in your browser. No install.
Open the worked example Feature Roadmap