David J McGovern, Suzana Ilic, Andrew M Folkard, Stuart J McLelland, Brendan J Murphy


This paper presents the results of an experiment designed to assess the time-development of scour around an offshore wind turbine collared monopile over a number of tidal cycles. One collar shape and location was investigated. The scour developed more slowly and the scour depth was shallower than for the case of a smooth monopile throughout the majority of the first half-cycle. This difference reduced quite rapidly during the second half-cycle and the scour depth at the end of two tidal cycles was essentially the same as for the smooth monopile. The time development of the scour was compared with results from existing empirical models for the time-development of scour under unidirectional flow. As expected, these models give a much smoother evolution of scour and different scour rates than those measured. Time variation in scour depth was better reproduced with a simplified approach for prediction of the time-varying development of scour. This also highlighted a problem with estimation of the time scale for the development of the equilibrium scour depth. Further investigations are needed before this alternative scour protection is completely rejected.


scour; scour reduction; offshore wind farms; collared monopile; scour in tidal flow

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Breusers, H.N.C., Nicollet, G., and H.W. Shen. 1977. Local scour around cylindrical piers, Journal of Hydraulic Research, IAHR, 15(3), 211–252.http://dx.doi.org/10.1080/00221687709499645

Dey, S., Sumer, B. M., and J. Fredsoe. 2006. Control of Scour at Vertical Circular Piles under Waves and Current, Journal of Hydraulic Engineering, 132, 270-279.http://dx.doi.org/10.1061/(ASCE)0733-9429(2006)132:3(270)

Escarameia, M. 1998. Laboratory Investigation of Scour around Large Structures in Tidal Waters. Proceedings of 3rd International Conference on Hydro-Science and Engineering, Berlin, ICHE.

Harris, J. M., Whitehouse, R. J. S., and T. Benson. 2010. The Time Evolution of Scour around Offshore Wind Turbines, Proceedings of the Institution of Civil Engineers - Maritime Engineering, 163, 3-17.http://dx.doi.org/10.1680/maen.2010.163.1.3

Kumar, V., Ranga Raju, K. G., and N. Vittal. 1999. Reduction of Local Scour around Bridge Piers using Slots and Collars, Journal of Hydraulic Engineering, 125, 1302 - 1305.http://dx.doi.org/10.1061/(ASCE)0733-9429(1999)125:12(1302)

Margheritini, L., Martinelli, L., Lamberti, A., and P. Frigaard. 2007. Scour Around Monopile Foundation for Off-shore Wind Turbine in Presence of Steady and Tidal Currents, Proceedings of the 30th International Conference on Coastal Engineering, World Scientific, 2330-2342.

Melville, B. W. 1975. Local Scour at Bridge Sites, Auckland University, Auckland.

Melville, B. W., and Y.M. Chiew. 1999. Time Scale for local Scour at Bridge Piers, Journal of Hydraulic Engineering, 125, 59-65.http://dx.doi.org/10.1061/(ASCE)0733-9429(1999)125:1(59)

McGovern,D. 2011. The interaction of tidal currents with offshore wind turbine monopiles: An experimental study of flow, turbulence, scour and reduction of scour around monopile. PhD Thesis, Lancaster University.

Nielsen, A.W. and E.A. Hansen. 2007. Time-varying wave and current-induced scour around offshore wind turbines, Proceedings of the 26th International Conference on Offshore Mechanics and Arctic Engineering, American Society of Mechanical Engineers, 5, 399–408.

Odgaard, A. J. and Y. Wang. 1987. Scour prevention at bridge piers, Proceeding of Hydraulic Engineering National Conference, ASCE, 523-527.

Richardson, E.V., Harrison, L.J., Richardson, J.R., and S.R. Davis. 1993. Evaluating Scour at Bridges (2nd ed.): Federal Highway Administration Hydraulic Engineering Circular, April 1993 revision, FHWA-IP-90-017, Washington, DC, 237 p.

Soulsby, R. L. 1997. Dynamics of Marine Sands. A Manual for Practical Applications, Thomas Telford, London.


Sumer, B. M., Whitehouse, R. R. S., and A. Torum. 2001. Scour Around Coastal Structures: a Summary of Recent Research, Coastal Engineering, 44, 153-190.http://dx.doi.org/10.1016/S0378-3839(01)00024-2

Sumer, B. M., Christiansen, N., and J. Fredsoe. (1992) Time Scale of Scour around a Vertical Pile, Proceedings of the 2nd International Offshore and Polar Engineering Conference, International Society for Offshore and Polar Engineering, 3, 308–315.

Whitehouse, R. J. S. 1998. Scour at Marine Structures: A Manual for Practical Applications, Thomas Telford, London.http://dx.doi.org/10.1680/sams.26551

DOI: http://dx.doi.org/10.9753/icce.v33.sediment.113