Port Sedimentation Calculator
Calculate tidal current velocities and volumetric flow through channels and inlets. Determine peak and mean velocities, Froude number, and tidal power density.
About this calculator
Despite its name, this calculator's engine models tidal current velocity through a channel or inlet rather than sediment deposition directly — sedimentation risk in ports is closely tied to how fast (or slowly) tidal currents flush a channel, which is what these outputs actually quantify. It starts from the tidal prism — the total water volume exchanged between high and low tide, found simply as basin plan area times tidal range — and applies the continuity principle that this entire volume must pass through the channel's cross-section over roughly half a tidal cycle. Modeling the tide as sinusoidal gives a clean closed-form peak velocity, V_max = pi times the tidal prism divided by (tidal period times channel area), with mean velocity over a flood or ebb phase equal to 2/pi times that peak.
From peak velocity the calculator derives a Froude number (subcritical below 1, supercritical above), a Reynolds number using seawater's kinematic viscosity to gauge turbulence, a Manning's-equation-implied channel slope, and a tidal power density (proportional to velocity cubed) relevant for tidal-stream energy assessment. Low peak velocities generally mean weaker flushing and higher sedimentation risk, while high velocities favor natural channel maintenance but can complicate navigation and increase scour around structures. The sinusoidal tidal assumption is a simplification — real tides are asymmetric (flood and ebb durations often differ) and basin geometry, freshwater inflow, and multiple tidal constituents beyond the dominant M2 all affect real-world current patterns, so use this as a first-order screening estimate rather than a substitute for site-specific hydrodynamic modeling.
Inputs
Results
Peak tidal velocity (m/s)
0.26
Peak flow rate (m³/s)
105.4
Peak power density (W/m²)
9.4
How to Use This Calculator
- Enter tidal basin area (m2), tidal range (m), and tidal period (hours) — M2 = 12.42 h.
- Enter channel width (m) and mean depth (m).
- Read tidal prism (m3) and peak tidal velocity (m/s) in the channel.
- Review the Froude number and Reynolds number to assess the channel's flow regime.
- Use the Peak Flow Rate and Peak Power Density outputs to evaluate channel capacity and tidal energy potential.
How the result changes with Tidal basin area (m²)
| Tidal basin area (m²) | Peak tidal velocity (m/s) | Peak flow rate (m³/s) | Peak power density (W/m²) |
|---|---|---|---|
| 250,000 | 0.13 | 52.7 | 1.2 |
| 375,000 | 0.2 | 79 | 4 |
| 750,000 | 0.4 | 158.1 | 31.6 |
| 1,250,000 | 0.66 | 263.5 | 146.5 |
What each input means
- Tidal basin area (m²)
- Plan area of the tidal basin or estuary landward of the inlet.
- Tidal range (m)
- Spring (or design) tidal range — difference between HW and LW.
- Tidal period (hours)
- Period of the dominant tidal constituent. M2 = 12.42 h, S2 = 12.00 h.
- Channel width (m)
- Width of the tidal inlet or navigation channel.
- Mean channel depth (m)
- Average depth of the channel below mean water level.
- Manning's n
- Manning roughness coefficient for the channel bed.
- Water density (kg/m³)
- Water density. Seawater ~1025, brackish ~1010, fresh ~1000 kg/m³.
What each result means
- Tidal prism (m³)
- Volume of water exchanged between HW and LW.
- Peak tidal velocity (m/s)
- Maximum current velocity during the tidal cycle.
- Mean velocity (m/s)
- Time-averaged velocity over a flood or ebb phase.
- Peak flow rate (m³/s)
- Volumetric flow rate at peak velocity.
- Froude number
- Fr = V / sqrt(gd). Fr > 1 indicates supercritical flow.
- Reynolds number
- Indicates turbulent (>4000) vs laminar flow regime.
- Peak power density (W/m²)
- Kinetic energy flux per unit area at peak velocity — relevant for tidal energy.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTidal basin area (m²) = 500000, Tidal range (m) = 3, Tidal period (hours) = 12.42, Channel width (m) = 50 = 7 input(s) provided
- Calculate Peak tidal velocityPeak tidal velocity = (π * tidalPrism) / (T * channelArea)0.263 = 0.263
- Calculate Peak flow ratePeak flow rate = vMax * channelArea105.4 = 105.4
- Calculate Peak power densityPeak power density = 0.5 * rhoWater * pow(vMax, 3)9.4 = 9.4
- Calculate Tidal prismTidal prism = basinArea * tidalRange1500000 = 1500000
- Calculate Mean velocityMean velocity = (2 / π) * vMax0.168 = 0.168
Engine last updated . Checked against 2 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
If this is called the Port Sedimentation Calculator, why doesn't it output a sedimentation rate?
The engine actually models tidal current velocity and flow through a channel, which is the primary physical driver of sedimentation risk in practice — weak tidal flushing lets suspended sediment settle out, while strong currents scour channels clean naturally. The outputs (peak velocity, Froude number, power density) are meant to be read as flushing-strength indicators: low peak velocity signals higher siltation risk, high peak velocity signals better natural channel maintenance but more scour risk around structures.
Why does peak velocity depend on tidal period as well as tidal range?
Peak velocity comes from V_max = π × tidal prism / (tidal period × channel area) — the tidal prism (basin area times tidal range) is the volume that must move through the channel each half-cycle, and dividing by the tidal period spreads that volume over the actual time available to move it. A shorter period (like the 12.00 h S2 constituent versus the 12.42 h M2) forces the same prism through in less time, producing a higher peak velocity for an identical basin and channel.
What does the Froude number result actually indicate here?
Froude number is peak velocity divided by the square root of gravity times channel depth; a value below 1 means subcritical (typical, calmer) flow, while above 1 indicates supercritical flow where small changes in channel geometry can produce hydraulic jumps and more turbulent, less predictable current behavior. Most tidal inlets stay subcritical, so a Froude number approaching or exceeding 1 is worth flagging as an unusually energetic channel.
How reliable is the sinusoidal tidal assumption behind these numbers?
It's a reasonable first-order approximation for a single dominant tidal constituent, but real tides are asymmetric — flood and ebb often have different durations and peak strengths — and are the sum of multiple constituents (M2, S2, K1, and others) rather than one pure sine wave. Basin geometry, freshwater inflow, and storm surge can all shift real peak velocities away from this closed-form estimate, so treat the results as a screening-level estimate rather than a substitute for site-specific numerical tidal modeling.
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