The nature of scour development and scour protection at offshore windfarm foundations

• Published in: Marine pollution bulletin 2011-01, Vol.62 (1), p.73-88
• Main Authors: Whitehouse, Richard J.S., Harris, John M., Sutherland, James, Rees, Jon
• Format: Article
• Language: English
• Subjects: Aluminum Silicates - chemistry; Applied sciences; Buildings. Public works; clay; Clay (material); data collection; Earthwork. Foundations. Retaining walls; Electric power generation; Energy; Environmental Monitoring; Exact sciences and technology; Foundations; Geologic Sediments - chemistry; Geological Phenomena; Geotechnics; Hydraulic constructions; Marine; marine environment; monitoring; Monopile; Natural energy; Oceans and Seas; Offshore; Offshore engineering; Offshore structure (platforms, tanks, etc.); Offshore structures; Power Plants; Sand; Scour; Scour protection; Sediments; Water Movements; water pollution; Wind; Wind energy; wind farms; Windfarm
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2010.09.007

► The paper presents a unique dataset on scour at offshore windfarm foundations with associated analysis and interpretation. ► Results are presented for the first time contrasting sand and clay influenced environments. ► Data indicates that the scour depth can change over both short time-scales, on a tidal and storm event level, as well as progressively over longer time-scales. ► Scour data for foundations with placed rock armour protection material is compared to those without protection. ► The scour without scour protection is within expected limits and secondary scour around placed protection can be deeper. Analysis and interpretation of monitoring data for the seabed bathymetry local to offshore windfarm foundations has shown how the scour develops in time and highlighted variations between sites with different seabed sediment characteristics, i.e. sands and clays. Results from European offshore windfarms have generated a unique dataset for comparison with previously published data. Where surficial sediment is underlain by a marine clay the scour (to date) has been limited, whilst those with unconstrained depths of sandy sediments show scour as deep as 1.38 times the monopile diameter. Scour protection has been installed at some sites for structural stability of the foundation or for cable protection. The flow interaction with the protection causes edge scour or secondary scour in the seabed around the protection. In some cases this scour is deeper than the unprotected case. The analysis has resulted in an improved evidence base for scour in the marine environment.