Unsworth, C. and Austin, M. and Van Landeghem, K. and Couldrey, A. and Whitehouse, R.J.S. and Fairley, I. (2026) Estimating and validating bedform migration rates from large scale operational models. In: MARID 2026 (8th International Conference on Marine and River Dune Dynamics), 13-15 April 2026, Enschede, the Netherlands.
Full text not available from this repository.Abstract
The growing demand for offshore renewable energy highlights the essential role that subsea power cables play. The successful deployment of these cables depends on understanding natural processes on the sea floor and the interaction between cables and the seabed which is often poorly understood (Figure 1a). This interaction can lead to cable exposure and damage, but it can also lead to “self-burial” of the cable (Sumer et al. 2001). The often unexpected and high costs of cable repair, and the disruption to the service they provide, often render submarine cables uninsurable. This jeopardises the resilience of our energy and communications supplies, and the ambitious energy transition. Around our coasts, cables from existing and planned offshore windfarms may traverse sand banks or fields of mobile sand waves (Figure 1b). Sand banks are often considered key habitats, and many of which are designated as parts of marine protected areas. Mobile sandwave fields are also important bedload transport routes and changes to them may impact the wider sediment budget. Therefore, recovery needs to be quantified if/when these features are disturbed for cable laying and/or trenching. The natural variability of marine sediments, and particularly sand banks and sand waves, is needed to inform regulators on the appropriate methods of estimating and measuring these processes, yet many of the sand banks are un-monitored for these processes – which makes designing surveys and environmental regulators setting guidance difficult. As a first order test, a method of estimating sand bank mobility has been created using publicly available data to estimate sand bank mobility and define the spatial resolution and temporal frequency of bathymetry surveys needed to adequately measure the mobility (or lack of) of sand banks around the Welsh Coastline. To quantify the processes driving sediment transport on these sand banks, hourly data from the Scottish Self Sea Model (SSW v3, Barton et al. 2024) was used to drive a sediment transport model over 12 months . Grain size samples from the British Geological Survey and CEFAS were used to set the D50. This procedure produced a unit sediment transport rate (m2 s-1) at hourly intervals and model nodes. A tidal residual was calculated for the calendar year 2010, for two sites on the Welsh coast which are likely to the trenched for offshore wind electricity cables (Constable bank, and Turbot bank). In order to know if the yearly sediment transport residual was realistic, these estimates were compared against measurements of yearly sediment transport via available repeated multibeam echosounder data. Using the method of (Nittrouer et al. 2008), annual unit sediment transport rates were calculated, and are within an order of magnitude of the model’s estimates. We found this result satisfactory given the limitations of the modelling and the often orders-of magnitude error found when trying to estimate sediment transport rates (Amoudry and Souza 2011). Bedform derived sediment transport rates on Constable bank, where there are an array of bedform scales and low angle bedforms, were consistently under predicting the model’s estimates. We believe this is due to a loss of measured sediment transport via the bedform tracking method due to the migration of smaller bedforms. (Zomer et al. 2021) recently found that migration of secondary bedforms over their (low angle) hosts can account for the same or double amount of sediment transport as the hosts’ migration. We estimate the migration of these smaller bedforms and consequently, an estimate of the loss due to aliasing of the bedform tracking method. Using the bedform dimensions and modelled sediment transport rates, we can thus estimate the spatial resolution and temporal frequency that these sand banks need to be surveyed; in order to get a direct measurement of their mobility and the regional sediment transport regime. This method will be expanded and tested in the broader NW European shelf.
| Item Type: | Conference or Workshop Item (Poster) |
|---|---|
| Subjects: | Maritime > General |
| Divisions: | Maritime |
| Depositing User: | Helen Stevenson |
| Date Deposited: | 08 Apr 2026 08:16 |
| Last Modified: | 08 Apr 2026 08:16 |
| URI: | http://eprints.hrwallingford.com/id/eprint/1729 |
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