Tidal Range Calculator

Example Data Table

These examples are illustrative. Use local tide tables and your project datum for design work.

Formula Used

• Observed tidal range: Range = High − Low
• Mean water level: Mean = (High + Low) / 2
• Datum correction: High' = High + Offset, Low' = Low + Offset
• Design levels: DesignHigh = High' + HighAllowance, DesignLow = Low' − LowAllowance
• Design range: DesignRange = DesignHigh − DesignLow

Range class uses thresholds: Microtidal < 2 m, Mesotidal 2–4 m, Macrotidal > 4 m.

Project Note: Applying Tidal Range on Site

1) Why tidal range matters for construction

Tidal range controls working elevation, access, and freeboard. A 3.0 m range can expose or flood temporary platforms twice daily, affecting plant stability, haul routes, and safe approach distances. Larger ranges can also drive stronger tidal currents at channels and constrictions for safer operations overall.

2) Planning bands and quick classification

Engineers often group sites by observed range: microtidal (<2 m), mesotidal (2–4 m), and macrotidal (>4 m). In macrotidal settings, vertical movement near mid‑tide can be rapid, so lifting and pour sequencing needs tighter time control.

3) Choosing high and low water inputs

Use verified tide tables or a calibrated gauge, and record date, time zone, and location. For higher consequence work, review the residual (observed minus predicted) to reflect wind and pressure effects, then decide whether to add it as an operational adjustment.

4) Datum alignment and offsets

Tide products may reference chart datum, LAT, or a national vertical datum. If site benchmarks differ, apply a datum offset so all elevations share one reference. Even a 0.15 m datum error can consume a meaningful share of a 0.80 m low‑tide access window.

5) Allowances for conservative design

Allowances address uncertainty such as surge, wave setup, temporary works settlement, and instrument tolerance. Screening values commonly start around 0.10–0.30 m, then refine using metocean data and the project risk register. This tool adds the high allowance and subtracts the low allowance to create design levels.

6) Turning range into workable time windows

Convert elevations into “go/no‑go” gates. Example: if a barge deck must stay within ±0.50 m of a fixed platform, and the observed range is 2.80 m, only part of each tidal cycle meets tolerance. The mean water level output provides a fast midpoint check when setting shift targets.

7) Reporting and traceability

Capture inputs, offsets, allowances, and both observed and design ranges in method statements and daily reports. The CSV export supports audit trails and spreadsheet reviews, while the PDF export suits approvals and toolbox briefings. Attach the referenced tide table or gauge log for context.

8) Practical checks before field use

Confirm units and sign convention (positive up), and verify low water is below high water. Auto‑fix can swap reversed values, but you should still validate the source. Re-check range after major storms, dredging, or channel works that may change local tidal response.

FAQs

1) What should I enter for high and low tide levels?

Enter the predicted or observed high and low water elevations for the same location, date, and datum. If you only have heights above chart datum, apply the datum offset so the values match your site benchmark reference.

2) Why does the calculator ask for a datum offset?

A datum offset aligns tide data to your project reference. Tide tables may use chart datum or LAT, while your survey control may use another vertical datum. Applying one offset keeps levels comparable and reduces avoidable elevation errors.

3) How do high and low allowances affect results?

High allowance increases the design high level, and low allowance decreases the design low level. Together they expand the design tidal range to cover uncertainty such as surge, wave setup, and temporary works tolerance.

4) When should I use meters versus feet?

Use the unit that matches your source data and drawings. The tool converts internally to meters for consistency, then displays outputs in your chosen unit. Avoid mixing sources unless you verify conversions and sign conventions.

5) What does microtidal, mesotidal, and macrotidal mean here?

They are range bands used for quick screening: microtidal is under 2 m, mesotidal is 2–4 m, and macrotidal is above 4 m. Use them as planning cues, not as a substitute for site-specific studies.

6) Why is my low tide higher than my high tide?

This usually indicates reversed inputs, a sign convention mismatch, or a datum issue. You can enable auto-fix to swap values, but still confirm your tide source, the applied offset, and whether elevations increase upward.

7) Can I use the exports for reports and approvals?

Yes. The CSV is helpful for calculations logs and spreadsheet checks, and the PDF is suitable for method statements and briefings. Always include the original tide table or gauge record used to justify the inputs.