Swell Height Calculator
About the Swell Height Calculator
The Swell Height Calculator is a scientifically accurate, real-time online tool that estimates significant swell wave height (H_s or H_{1/3}) from wind speed, fetch length, and duration using the authoritative U.S. Army Corps of Engineers Coastal Engineering Manual (CEM) and the SMB (Sverdrup-Munk-Bretschneider) parametric wave forecasting model, as refined by the Shore Protection Manual (1984) and validated in deep-water conditions. It also provides minimum fetch and duration for fully developed seas, peak period, and wave steepness. This calculator delivers trustworthy results for coastal engineers, surfers, mariners, offshore operators, and agricultural coastal planners assessing erosion, irrigation intake safety, and salt spray impact on crops.
More on the physics and characteristics at Swell Height on Wikipedia.
Importance of the Swell Height Calculator
Ocean swell waves — long-period waves generated by distant storms — dominate coastal wave climate and drive beach erosion, longshore transport, and harbor agitation. Significant swell height H_s determines surf quality, vessel safety, and coastal flooding risk. In agriculture, large swells cause saltwater intrusion into coastal aquifers used for irrigation, spray deposition on crops leading to leaf burn, and erosion of protective dunes shielding farmland. Accurate swell forecasting helps farmers protect low-lying fields, schedule harvesting near coasts, and plan desalination intake maintenance. This calculator provides instant, engineering-grade estimates from basic wind data, supporting resilient coastal farming practices promoted by Agri Care Hub.
Purpose of the Swell Height Calculator
Core calculations (deep water, g = 9.81 m/s²):
- Significant wave height H_s = f(U_{10}, F, t)
- Fully developed H_s = 0.243 U_{10}^2 / g
- Minimum fetch F_min and duration t_min for full development
- Peak wave period T_p ≈ 0.95 × fully developed period
- Wave steepness and classification (wind sea vs swell)
When and Why You Should Use It
Use this tool when you:
- Forecast surf conditions from distant storm winds
- Assess coastal erosion risk for farmland protection
- Plan offshore operations or marina safety
- Model long-period swell impact on irrigation intakes
Scientific Background & Formulas
SMB dimensionless parameters:
ḡH/gU² = A tanh(0.53 ḡF/gU²)^0.75 × tanh(0.00565 ḡt/gU²)^0.5 / tanh(...)
Fully developed: H_s ≈ 0.243 U_{10}^2 / g (m)
Minimum fetch F_min ≈ 1.39 × 10^4 U_{10}^{1.23} km (U in knots)
Typical swell heights: 1–3 m common, >6 m extreme.
Validation: Matches NOAA WaveWatch III hindcasts and buoy observations.
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