Monopile Scour: Seabed Erosion at an Offshore Wind Foundation

Tidal / Storm Current

Depth-averaged current speed U 0.90 m/s

Seabed sediment grain size D₅₀ 0.30 mm

Simulation time acceleration ×20

Scour State

—

Scour depth S(t)

0.00 m

Equilibrium Sₑ

0.00 m

U / U꜀ᵣ

0.00

How it works

A vertical monopile blocks the near-bed current. Flow decelerating on the upstream face rolls up into a downward-plunging horseshoe vortex that wraps around the base, while lee-side wake vortices shed downstream — together they lift sediment out of the bed faster than the ambient flow can, cutting a scour pit at the pile toe. This is the single biggest geotechnical risk to a monopile-founded turbine: uncorrected scour reduces the pile's effective embedment and lateral stiffness.

Critical bed shear (Shields):  τ꜀ᵣ = θ꜀ᵣ(ρₛ-ρw)g·D₅₀,  θ꜀ᵣ ≈ 0.05
Critical shear velocity:       u*꜀ᵣ = √(τ꜀ᵣ/ρw)
Depth-avg. critical velocity:  U꜀ᵣ = (u*꜀ᵣ/κ)·ln(12h/k s),  ks = 2.5·D₅₀
Equilibrium scour (circular pile, Sumer & Fredsøe):
  U/U꜀ᵣ ≤ 0.5           Sₑ = 0            (no motion, no scour)
  0.5 < U/U꜀ᵣ < 1        Sₑ/D ramps 0→1.3  (clear-water scour)
  U/U꜀ᵣ ≥ 1              Sₑ/D ≈ 1.3        (live-bed plateau)
Time development:  S(t) = Sₑ·(1 − e^(−t/T))

Current speed U — faster flow raises bed shear stress and, once it exceeds U꜀ᵣ, pushes the pit toward the live-bed plateau of ≈1.3 pile diameters.
Grain size D₅₀ — coarser sand needs more shear to move, raising U꜀ᵣ and shrinking (or stalling) the scour hole for the same current.
Rock-armor protection — an armor layer of graded rock around the base raises the effective threshold so far that scour is suppressed to a shallow residual depth, the standard offshore mitigation.
Time acceleration — real scour holes develop over hours to days; this control speeds the exponential approach to Sₑ so it is watchable.

Seabed / scour pit Monopile foundation Suspended sediment

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.