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

► 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.