Plan crest levels using reliable overtopping estimates fast. Adjust reduction factors for material and angle. Check safety limits, then export the calculation summary easily.
This calculator uses simplified, dimensionless overtopping discharge relationships. The base scaling is: q = q* · √(g · Hm0³), where q is discharge per meter width.
For sloping structures, the tool uses an Iribarren-based split: ξ = tan(α) / √s0, with s0 = Hm0 / L0 and L0 = g·T²/(2π). A combined reduction factor is applied as γ = γf·γβ·γb.
Non-breaking branch (surging guidance): q* = 0.2 · exp(−2.6 · Rc/(γ·Hm0)). Breaking branch (plunging guidance): q* = 0.067 · exp(−4.75 · Rc/(γ·Hm0·ξ)). The tool selects a branch using ξ = 2.0 as a practical divider.
For vertical walls, a compact fit is used for a first estimate: q* = 0.047 · exp(−2.35 · Rc/Hm0). Always validate against project guidance for final design.
| Structure | Hm0 (m) | Tm-1,0 (s) | Rc (m) | Slope (V:H) | γf | γβ | γb | q (L/s per m) | Risk band |
|---|---|---|---|---|---|---|---|---|---|
| Sloping | 2.0 | 6.0 | 2.0 | 1:2 | 0.55 | 1.00 | 1.00 | ~0.2 to 0.6 | Low |
| Sloping | 3.0 | 7.0 | 1.5 | 1:3 | 0.70 | 0.90 | 0.90 | ~1 to 6 | Moderate |
| Vertical | 2.5 | 6.5 | 1.0 | — | — | — | — | ~5 to 20 | Moderate–High |
Overtopping is assessed as a mean discharge per metre of crest, q. Projects define target limits for pedestrians, vehicles, crest roads, or protected assets behind the structure. Lower limits reduce spray, while higher limits may still be acceptable where access is controlled and drainage is planned.
Wave height Hm0 dominates because discharge scales with √(g·Hm0³). Wave period influences deep-water wavelength and steepness, changing the Iribarren number and the selected regime. Crest freeboard Rc is the main geometric control; small increases can reduce q exponentially. Slope, surface roughness, and wave approach angle modify the response through reduction factors. Crown width and crest detailing may further reduce flow, but the effect is project specific and should be treated cautiously.
The Iribarren number ξ = tan(α)/√s0 separates breaking from non‑breaking behaviour for many revetments. Lower ξ typically indicates plunging waves and more energetic run‑up losses. Higher ξ suggests surging waves with longer uprush and different overtopping statistics. Treat the regime as guidance; local depth, berms, and armour layout can shift behaviour. When ξ is near the boundary, compare both branches to understand the uncertainty range.
Roughness factor γf accounts for dissipation on armour layers, steps, or blocks; smoother faces approach 1.0. Wave angle factor γβ reduces overtopping for oblique attack, but only when direction and structure alignment are stable. Berm or geometry factor γb captures additional energy loss from berms and transitions. The combined γ multiplies these effects, so small changes can materially shift q. Keep factors within published ranges and document the chosen basis.
Use the calculator to screen alternatives: vary Rc, slope, and roughness while holding offshore conditions consistent. Record each scenario in the example table format, then export CSV or PDF for design notes. For final design, confirm with site‑specific guidance, physical modelling, or validated numerical studies, and include safety margins for sea level, settlement, and wave climate change.
q is the mean overtopping discharge per metre of structure crest. It represents the average flow passing the crest during the sea state, not individual wave volumes or instantaneous peak splashes.
Use the spectral mean period Tm-1,0 when available. If only a peak period is known, use a conservative equivalent and document the assumption for traceability.
Select γf based on surface type and published guidance. Smooth concrete is near 1.0, while rock armour or stepped faces are lower. Keep values within recommended ranges.
The tool uses the Iribarren number to distinguish breaking and non-breaking response on sloping structures. This affects the dimensionless discharge relationship used to estimate q.
It is a simplified screening indicator only. Always compare the computed discharge to your project’s allowable limits for people, vehicles, equipment, and protected areas.
Not always. The calculator applies a mild reduction to represent dissipation on wider crests, but real behaviour depends on geometry, parapets, roughness, and drainage details.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.