Scour Prediction Modeling for Tidal Turbine Foundations Using SCS-2 and BRE Methodologies

Scour begins when tidal currents accelerate around a foundation, lowering local pressure and increasing bed shear stress beyond the sediment’s critical threshold. This initiates particle entrainment, followed by vortex formation downstream that excavates a horseshoe-shaped depression — deepest at the upstream shoulder and extending downstream in a tail scoured zone. The process stabilises when the enlarged foundation footprint reduces flow acceleration enough to drop shear stress below τ*ₜₕᵣₑₛₕ.

The SCS-2 methodology refines earlier empirical models by incorporating KC-dependent vortex amplification and sediment mobility classification (sand vs. silt-clay), using calibrated coefficients (Kᵥ, Kc) validated against >120 physical model tests across European MRE sites. BRE’s approach, developed from UK offshore wind experience, treats scour as a function of flow contraction ratio and relative grain size, applying reduction factors for bed cohesion and current reversibility — making it particularly suited for shallow, macrotidal estuaries with stratified sediments.

Advanced application requires coupling these models with transient hydrodynamics: tidal asymmetry (flood > ebb velocity) causes net scour migration; wave-current interaction increases Uₘₐₓ by up to 40% in spring tides; and biofouling on foundations alters effective D and surface roughness — all requiring iterative recalibration. Machine learning surrogates (e.g., Gaussian Process regression trained on CFD datasets) are now emerging to replace single-point SCS-2/BRE estimates with probabilistic scour envelopes (P₁₀–P₉₀) for reliability-based design per IEC 61400-3-2.