Understanding the Effectiveness of Scour Mitigation Techniques at Offshore Windfarms Using Experimental Modelling

Over the last three decades the offshore wind energy sector in the UK and globally has grown rapidly and the recent COP28 climate summit reinforced the North Sea Collaboration (NSEC) on the development of offshore wind which targets an installed capacity of at least 260 GW of offshore wind energy by 2050. Due to this accelerated demand for offshore wind there has been increased demand for research on scour around subsurface structures in the offshore environment. It is also beneficial to minimise the influence of subsurface foundations on the marine ecosystem and therefore scour mitigation methods that enhance marine habitats would be advantageous. This study uses experimental modelling to explore the impact of scour mitigation around monopile foundations and evaluate successful methods whilst considering the habitats living around the offshore structures.

Currently rock armour is most commonly used as an optimised scour protection layer for creating biodiversity enhancements. In this study four different scour mitigation techniques were assessed to analyse their effectiveness for scour mitigation; Textured Collars, Rock Dumping, Textured Piles and Rock Bags. All four scour mitigation techniques investigated have additional bio-enhancement capabilities and can be classed as a ‘Nature Inclusive Designs’ used to promote marine biodiversity and seaweed planting.  These scour mitigation methods include both dynamic and flow altering strategies using both the sea floor area around the monopile foundation and the foundation surface itself.  The experiments measured scour development under two different flow conditions until an equilibrium bed state developed. In some experiments, a novel Mylar Film technique was used to enable continuous measurement of scour development through structures being tested whilst simultaneously preventing water and sediment transfer. The results shown in Figure 1 suggest that under low flow conditions rock dumps and textured collars are the most effective scour mitigation technique to reduce scour depth. Textured collars prove to be the most successful for reducing scour depth under both flow conditions tested in these experiments.