No abstract

No abstract

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.

The hydrodynamics around the mouth of the Teign estuary (UK) have been simulated using two coastal area numerical modelling systems. Model performance statistics were calculated to assess the accuracy of the predictions of the measured currents at a number of locations around the estuary mouth. The relative mean absolute error was used as it is applicable to vectors as well as scalars and measures all types of errors. An adjusted relative mean absolute error was also used to reduce the effect of measurement error. A classification table was adopted that categorises the results according to the size of the error. In additions, time series and scatter plots were used to judge the performance of the modelling systems. Most numerical models are run and compared to data in a subjective manner. This paper demonstrates how model performance statistics can be used to calibrate and/or validate hydrodynamic models in a more objective way. Statistics were used to compare model runs that used different amounts of data. This case study will inform the debate about the optimum mix of modelling and measurement. Calm conditions during a spring tide were simulated, as was a relatively large storm. The two modelling systems gave more or less equal performance when run in engineering mode (where default values were used for most of the system settings). In each case, one modelling system performed better than the other at some locations and worse than it at other locations. One model was also run using a scientific approach, where different amounts of information were used to alter the model settings and sensitivity tests were performed. The modelling showed that using more data does not necessarily lead to better model predictions. New methods for incorporating data into the operation of a model need to be evaluated thoroughly before they can be used without site-specific calibration.

The drive for marine offshore renewables developments has led to focussed requirements for scour hazard assessment relating to foundations and the cabling necessary for in-field transmission and power export. Foundations can represent a significant proportion of the installed capital costs of a renewable energy device so the offshore renewable energy community can benefit from the sharing of information and the development of common approaches to scour and geotechnical issues. Foundation options including monopiles, multi-piled tripods and jackets, gravity bases, or suction piles are being considered for a variety of offshore renewable installations. This paper concentrates on scour assessment challenges in currents and waves, including scour experience at built foundations, time-series predictions of scour and considerations with respect to the evaluation of heterogeneous soils.Scour at offshore structures RJS Whitehouse, JM Harris, TR Mundon and J Sutherland HRPP466 3