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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.

a b s t r a c tKeywords: cohesive sediment settling velocity mass settling flux flocculation suspended particulate matter mud transport models New formulations are presented for the settling velocity and mass settling flux (the product of settling velocity and sediment concentration) of flocculated estuarine mud. Physics-based formulae for these are developed based on assumptions of a two-class floc population (microflocs and Macroflocs) in quasi-equilibrium with the flow. The settling velocities of microflocs and Macroflocs are related to floc size and density via the Kolmogorov microscale as a function of turbulent shear-stress and sediment concentration, including heightdependence and floc-density-dependence. Coefficients in the formulae are calibrated against an existing large data-set of in situ observations of floc size and settling velocity from Northern European estuaries. Various measures of performance show that the resulting formulae achieve an improved level of agreement with data compared with other published prediction methods. The new formulae, with the original calibration coefficients, perform well in tests against independent measurements made in two estuaries.