Field performance of pre-installation scour protection

Conventional sequencing of scour protection often involves installing elements of scour protection af-ter foundation installation, which can create a win-dow of time where the pile is unprotected. Pre‑installation approaches, where scour protection is placed before pile installation, can remove this window and reduce scheduling pressure, but they introduce drivability risks associated with installing large monopiles through coarse rock layers. Pene-tration through pre‑installed rock can be difficult to predict and may lead to installation hazards or pile integrity concerns (Bărbunţoiu, 2021 and Cengiz et al., 2024).
Given the limited published field (and model) ev-idence for the performance of pre-installation scour protection, this present study uses multibeam echo-sounder bathymetry from Moray West Offshore Wind Farm (Figure 1) accessed via the Marine Data Exchange to evaluate short‑term seabed response, focusing on drawdown of material and scour devel-opment at the pile wall and edge scour around the toe of the scour protection.
Moray West Offshore Wind Farm is located in approximately 36 - 48 m water depth in Moray Firth, Scotland. The development comprises 62 monopile foundations with pile diameters of 9 and 10 m.

Interpretation of post‑installation bathymetry suggests a scour protection design consisting of a 0.7 to 1.0 m thick rock layer with a top width of ap-proximately 35 - 37 m. The external side slopes are estimated to be approximately 1V:3H. Monopiles were installed using a combination of vibro‑driving and hydraulic impact driving.
The analysis across the site indicates drawdown and/or scour of material at the pile wall to a depth near equal to the thickness of the scour protection. At 50 of the 57 foundations with available pre‑installation data, post-piling seabed levels at the pile wall were at or above pre‑installation lev-els. Where levels were lower than the pre-installation seabed level, the reduction was typical-ly small, with scour protection remaining within 0.2 m of the original seabed level.
Limited scour has developed both at the pile wall and at the outer edge of the scour protection during the first several months following installation. While results of further monitoring are required to assess long term performance, the data presented here support the viability of full coverage pre installation scour protection, offering both in-stallation and performance benefits for future off-shore wind developments.