Enter project cases
Formula used
This tool uses the common breaker-index relationship between breaking wave height (Hb) and breaker depth (db):
- db = Hb / γb
- Hb = γb × db
- db,design = (db × SF) + allowance
γb depends on breaker type, beach slope, and wave conditions. Use project guidance to select an appropriate value.
How to use this calculator
- Select units and a breaker index preset that fits your site.
- Choose the number of cases for quick scenario testing.
- For each case, pick whether Hb or db is known.
- Enter the known value and optionally override γb.
- Add a safety factor and allowance for design conservatism.
- Press Calculate to view results above the form.
- Download CSV or PDF to share with your team.
Example data table
| Scenario | Known | Value | γb | SF | Allowance | Result (db,design) |
|---|---|---|---|---|---|---|
| Armor layer check | Hb | 2.50 m | 0.78 | 1.10 | 0.20 m | 3.73 m |
| Seawall toe | Hb | 1.80 m | 0.78 | 1.05 | 0.10 m | 2.52 m |
| Temporary works | db | 2.00 m | 0.78 | 1.00 | 0.00 m | 2.00 m |
Example values are illustrative. Always verify with project standards and site data.
Project context and decision impact
Breaker depth helps engineers locate where waves reach the limiting depth and break, guiding toe levels, armor sizing, and temporary work limits. A depth error can shift the break point and raise runup, overtopping, and scour demand at the structure.
Inputs you can verify on site
The calculator accepts either breaking wave height Hb or breaker depth db. Hb can come from buoy records, hindcasts, or nearshore transformation. db can come from bathymetry sections, dredge surveys, or design profiles. Use consistent units for each case.
Breaker index selection and typical ranges
The breaker index γb links height and depth using Hb = γb × db. Common starting values are about 0.78 for spilling, 0.90 for plunging, and 1.10 for surging conditions. Typical engineering ranges often fall between 0.55 and 1.20. For example, if Hb is 2.5 m and γb is 0.78, db is about 3.21 m before applying design margins.
Safety factor and allowance logic
Design breaker depth is calculated as db,design = (db × SF) + allowance. SF reflects model uncertainty and sensitivity; many teams apply 1.05–1.20 depending on consequence and data quality. Allowance adds fixed clearance for tolerances, sediment mobility, or survey error. With SF 1.10 and allowance 0.20 m, the example becomes db,design ≈ 3.73 m.
Multiple cases for scenario testing
Use 2–5 cases to compare alternatives quickly: baseline, storm condition, construction window, or revised bathymetry. Separate cases also help you document sensitivity to γb or Hb without overwriting your main inputs.
Interpreting warnings and notes
If γb is outside the typical range, the output notes flag it for review. A safety factor below 1.0 reduces conservatism and should be justified. If db,design falls below computed db, the note indicates the design depth is not conservative.
Exporting and reporting for teams
Download CSV to review assumptions in spreadsheets or attach to method statements. Download the PDF report to share a report with supervisors, clients, or QA reviewers. The report lists each case, inputs, and computed depths clearly.
Good practice checks before use
Confirm that Hb represents breaking conditions at the section, not deepwater height, unless you have transformed it. Use project standards for γb and SF. Re-run after updated surveys, because profile changes can affect db materially. Record the date, data source, and preset used. Keep calculation notes with drawings.
FAQs
What is breaker depth (db)?
Breaker depth is the water depth where a wave reaches its limiting steepness and breaks. It helps set toe levels, armor placement elevations, and nearshore design checks for stability, runup, and scour.
How do I choose the breaker index (γb)?
Select γb from your project guidance or calibration. As a starting point, use about 0.78 for spilling, 0.90 for plunging, and 1.10 for surging. Refine using site slope, wave spectrum, and local observations.
Can I calculate with known depth instead of known height?
Yes. Choose “Breaker Depth (db)” as the known value, enter db, and the calculator will compute the corresponding breaking wave height Hb using Hb = γb × db.
What safety factor is appropriate?
Safety factor depends on consequence, data quality, and uncertainty in nearshore transformation. Many designs use 1.05–1.20. Use higher values for limited surveys, sensitive assets, or temporary works exposed to storms.
What does the allowance represent?
Allowance is an added clearance applied after the safety factor. Use it for construction tolerances, settlement, expected sediment movement, survey uncertainty, or required freeboard between the calculated and adopted design depth.
How do metric and imperial units affect results?
The equations are dimensionless, so results remain consistent. Use meters for metric and feet for imperial, and keep all inputs within the same system for each case.
Why am I seeing warnings in the notes column?
Warnings flag inputs outside typical ranges or choices that reduce conservatism, such as γb beyond common limits or safety factor below 1.0. They are prompts to review assumptions, not automatic errors.