Maritime ToolNew

Wave Base, Shoaling & Depth of Closure Calculator

Calculate wave base, shoaling coefficient and the Hallermeier depth of closure for coastal design.

Last reviewed by the myCalculator Editorial Team

Input Parameters

m
s
m
m

The Hallermeier He(12h) parameter — the wave height exceeded 12 hours a year.

Calculation Results

Wave Base (L₀/2)
63.2 m
Does the Wave Feel the Bottom?
YES — 15 m is above wave base
Depth of Closure (Hallermeier)
6.4 m
Shoaling Coefficient (Ks)
0.921
Shoaled Wave Height
2.3 m (from 2.5 m)
Deep-Water Wavelength (L₀)
126.5 m
Local Wavelength (L)
95.6 m
Relative Depth (h/L)
0.157 — Intermediate water — transitional shoaling
Phase Speed (C)
10.62 m/s
Group Speed (Cg)
8.28 m/s
Orbital Diameter at Surface
2.5 m
Orbital Diameter at Seabed
2.167 m
Summary: A 9 s wave has a deep-water wavelength of 126.5 m and a wave base of 63.2 m. At 15 m the wave does feel the bottom, shoaling by a factor of 0.921 to 2.3 m. The depth of closure is 6.4 m — seaward of this, profile change is negligible.
Step-by-Step Calculation Solution
1.L₀ = gT² / (2 pi) = (9.81 x 9²) / (2 pi) = 126.5 m
2.Wave Base = L₀ / 2 = 63.2 m — orbital motion decays to ~4% of surface value here
3.Dispersion solved for k: L = 95.6 m at h = 15 m
4.n = 0.5(1 + 2kh/sinh(2kh)) = 0.78 | Cg = nC = 8.28 m/s
5.Ks = sqrt(Cg₀ / Cg) = sqrt(7.03 / 8.28) = 0.921
6.Shoaled Height = Ks x H = 0.921 x 2.5 = 2.3 m
7.Depth of Closure (Birkemeier) = 1.75 He - 57.9 (He² / gTe²) = 6.4 m
8.Seabed orbital diameter = H / sinh(kh) = 2.167 m

Formula & How Wave Base, Shoaling & Depth of Closure Calculator Works

Mathematical Formula
Wave Base = L₀/2 | Ks = √(Cg₀/Cg) | dc = 1.75 He - 57.9 (He² / gTe²)

Orbital motion under a wave decays exponentially with depth, becoming negligible at about half the deep-water wavelength — the wave base. Shoreward of that, the wave feels the seabed, slows, shortens and steepens, with the shoaling coefficient describing the height change. The Hallermeier depth of closure marks the seaward limit of significant annual profile change and is the standard boundary used to define beach nourishment and coastal structure design envelopes. Worked example: a 9 second wave has a deep-water wavelength of 1.56 × 9² = 126 m, so the wave base is about 63 m. Below that depth the water is hardly disturbed by the wave. In 15 m of water the same wave feels the bottom, slows, shortens and steepens, which is how shoaling begins. This is why seabed features inshore have a strong effect on wave height and why waves refract toward the shore.

How to Calculate Wave Base, Shoaling & Depth of Closure Calculator (Step-by-Step)
  1. Enter Deep-Water Wave Height (m) (m): Input your target parameter value.
  2. Enter Wave Period (s) (s): Input your target parameter value.
  3. Enter Local Water Depth (m) (m): Input your target parameter value.
  4. Enter Hs Exceeded 12 Hours per Year (m) (m): Input your target parameter value.
  5. Apply Formula: Calculate using Wave Base = L₀/2 | Ks = √(Cg₀/Cg) | dc = 1.75 He - 57.9 (He² / gTe²).
  6. Review Results: View exact computed answers, metrics, and worked mathematical proofs.
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Frequently Asked Questions (FAQs)

What is wave base?

The depth at which orbital motion becomes negligible, conventionally half the deep-water wavelength. Below it the seabed is undisturbed by that wave, which is why storm swell reworks sediment far deeper than local wind chop.

What is the depth of closure used for?

It defines the seaward limit of the active profile for beach nourishment design, coastal structure siting and sediment budget calculations. Beyond it, annual bed level change is negligible.

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