Riprap Design — HEC-23 & HEC-14 stone sizing

What is Riprap Design?

Size protective stone for channel banks, bridge piers and abutments, spurs, culvert outlet aprons, open-bottom culverts and wave-exposed slopes — FHWA HEC-23 and HEC-14, matched to standard FHWA gradation classes.

When would you use this?

Specifying bank protection where a channel velocity is already known.
Sizing a scour countermeasure at a bridge pier or abutment.
Designing the apron below a culvert outlet.
Checking stone someone else specified against the published relationships.

How Delta Hydro Studio handles it

Seven applications over one engine, each using its own governing HEC-23 or HEC-14 relationship rather than one formula stretched to fit.
Every result is matched to a standard FHWA gradation class, so the answer is something a supplier can deliver — not a number you then have to translate.
Refuses what it cannot defend: a bank steeper than the rock angle of repose, a size past Class X, an application whose coefficient tables are not published in the source material.
Surfaces the HEC-23 abutment discontinuity at Fr = 0.80, where the guideline changes equation form and the answer steps by about half again.

How to use it

1
Pick the application — what you are protecting decides the equation.
2
Enter the flow conditions: velocity, depth, and the geometry that applies.
3
Review the required D50, the matched gradation class and the layer thickness.
4
Export the design with its full derivation, or send a velocity in from Channel Analysis or the Culvert Designer.

Methodology & references

Full equations, assumptions, and literature references appear inside the in-app methodology panels for this tool, aligned with South African guidance (SANRAL TRH, SANCOLD, DWS technical manuals) and international references (USDA NRCS, FHWA HDS) where applicable.

Outputs & exports

Export professional Word and Excel report packs, tabulated results, and GIS-friendly layers depending on the tool. Screenshots in marketing materials are refreshed as the UI evolves — the studio always reflects the latest layout.

Ready to run Riprap Design?

Free tier available — no credit card required to explore.

Launch in Studio Book a demo

FAQ

Why does the tool sometimes refuse to give an answer? +

Because some inputs describe a design that cannot work. A bank at or past the rock angle of repose is unstable before any water reaches it, and no stone size fixes that. A required D50 past Class X needs a project-specific gradation rather than an extrapolated class. In both cases the tool says what is wrong instead of returning a plausible number.

Which gradation class do I get? +

The smallest standard FHWA class whose lower D50 bound supplies your requirement. Matching the lower bound is the conservative reading — a class is a band, and a supplier delivering anywhere inside it still meets the design.

Are all ten HEC-23 applications available? +

Seven are. Embankment overtopping, design wave and filter design need coefficient tables that are not published in the source material we work from, and we would rather show them as unavailable than ship a guessed coefficient that looks exactly like a real one on a drawing.

Do I need a desktop GIS install to use Riprap Design? +

No. Delta Hydro Studio runs in the browser — upload inputs, run calculations, and export professional outputs without local GIS installs for most workflows.

Is there a free tier? +

You can start free on the Stream plan with credits to explore tools. Several hydraulic and delineation tools remain accessible without a paid subscription.

Where are my data and calculations stored? +

Projects live in your Delta Hydro Studio workspace. Export Word, Excel, and GIS formats when you need offline archives or submittals.