Calculator
Formula used
The key output is the wave transmission coefficient: Kt = Ht / Hi, where Hi is the incoming wave height and Ht is the transmitted wave height behind the structure.
- L = g*Tp^2 / (2*pi) (deep-water wavelength)
- xi = tan(alpha) / sqrt(Hi/L) (surf similarity parameter)
- D’Angremond: uses Rc/Hi, Gc/Hi, and xi, with practical limits.
- Briganti: alternative coefficients for wide crests.
- van Gent: tanh-form using Gc/L and Rc/Hi.
How to use this calculator
- Select units, then enter incident wave height Hi and period Tp.
- Enter structure geometry: freeboard Rc, crest width Gc, and slope V:H.
- Choose structure type to match permeability.
- Select a method. Use Manual if Kt is specified.
- Click Submit. Results appear below the header.
- Use Download CSV or Download PDF for reporting.
Example data table
| # | Method | Type | Hi (m) | Tp (s) | Rc (m) | Gc (m) | tan(alpha) | Kt | Ht (m) | Reduction (%) |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | dangremond | permeable | 1.80 | 7.00 | 0.30 | 6.00 | 0.500 | 0.288 | 0.518 | 71.2 |
| 2 | briganti | impermeable | 2.50 | 8.50 | -0.20 | 10.00 | 0.500 | 0.183 | 0.457 | 81.7 |
| 3 | vangent | permeable | 1.20 | 6.00 | 0.60 | 4.00 | 0.667 | 0.246 | 0.296 | 75.4 |
Technical guide for wave transmission assessment
1) What transmission means on site
Wave transmission quantifies how much incident wave height passes behind a low-crested or submerged barrier. The calculator reports Kt = Ht/Hi and the transmitted height Ht. For many rubble-mound and berm configurations, practical design values commonly fall between 0.10 and 0.70, depending on freeboard, crest width, and slope.
2) Key drivers: freeboard ratio Rc/Hi
Freeboard is often the strongest driver. Increasing Rc/Hi reduces overtopping and typically reduces Kt. Submerged crests (negative Rc) can yield higher transmission, especially when |Rc| is small relative to Hi. Use consistent sign convention: positive Rc means crest above still water.
3) Crest width ratio Gc/Hi and Gc/L
Wider crests provide more dissipation and lower Kt. The implemented models use either Gc/Hi (D’Angremond, Briganti) or Gc/L (van Gent). A change from Gc/Hi = 2 to Gc/Hi = 5 can noticeably lower transmission when other parameters are fixed.
4) Period and wavelength effects
The tool derives deep-water wavelength using L = g*Tp^2/(2*pi). Longer periods create larger L, which changes Hi/L and affects the surf similarity parameter. When Tp increases from 6 s to 10 s, L increases substantially, often shifting the predicted Kt.
5) Slope and surf similarity parameter xi
Slope is interpreted as tan(alpha) from inputs like 1:2. The surf similarity parameter xi = tan(alpha)/sqrt(Hi/L) represents breaking and run-up behavior at the structure. Steeper slopes raise xi and can change the exponential or tanh response in the selected method.
6) Permeable vs impermeable structures
Permeability matters because porous armor layers and cores dissipate energy. In this calculator, selecting “permeable” adjusts coefficients used by the empirical equations. As a practical check, permeable rubble-mound crests often produce lower transmitted heights than smooth, impermeable berms for the same geometry.
7) Selecting the method for your project
D’Angremond is widely used for low-crested breakwaters and provides practical bounds. Briganti is helpful when crest widths are large and transmission behavior shifts. van Gent’s tanh-form can be stable across a wide range of Gc/L. Use “Manual Kt” when you have physical model results or monitoring data.
8) Reporting and quality checks
For design reviews, report Hi, Tp, Rc, Gc, slope, method, and the computed Kt and Ht. Cross-check that inputs are realistic and that Kt trends match engineering expectation: higher crest, wider crest, and more dissipation should not increase transmission. Export CSV/PDF for traceability.
FAQs
1) What is a typical Kt range for low-crested barriers?
Many practical cases fall around 0.10–0.70, but geometry and wave climate control it. Always compare multiple methods and validate against project guidance or model data.
2) Why does negative freeboard often increase transmission?
A submerged crest allows more wave energy to pass over the top. As Rc becomes more negative relative to Hi, less energy is blocked, increasing Ht and Kt.
3) Which inputs affect Kt the most?
Rc/Hi and crest width (Gc/Hi or Gc/L) usually dominate. Tp influences wavelength and xi, and slope affects xi, which changes predicted transmission behavior.
4) When should I use the “Manual Kt” option?
Use it when a specification, physical model test, or monitoring program provides Kt. It also helps when project guidance requires adopting a conservative fixed value.
5) Why is wavelength computed with a deep-water approximation?
It offers a quick, consistent reference for L when detailed dispersion calculations are not available. For shallow or intermediate depths, verify with a wave model if sensitivity is high.
6) How should I enter the slope?
Enter V:H as 1:2 or 1/2, or enter tan(alpha) directly. The tool converts it to tan(alpha) and uses it to compute xi for the selected method.
7) Do the downloads include my last calculation?
Yes. After a successful submit, the latest result is saved for CSV and PDF export. If you change inputs, submit again to refresh the downloadable outputs.