An Innovative Wave Overtopping Measurement System to Calibrate Numerical Flood Hazard Assessment and Alert Tools

In the UK £150bn of assets and 4 million people are at risk from coastal flooding, whilst the construction of sea wall defence schemes typically cost at least £10,000/m. With reductions in public funding, rising sea level and 3200 km of coastal defences (i.e. about £3bn), cost savings are required that do not reduce flood resistance. The design of new coastal schemes and the setting of tolerable hazard thresholds requires site-specific information of wave overtopping, but this information is very rarely available from in situ measurements.

The National Oceanography Centre converted an existing wave measurement technology into a prototype overtopping measurement system “WireWall” to obtain wave-by-wave observations of overtopping velocity and volume. The system was validated against collection tanks in HR Wallingford’s flume and compared with BayonetGPE predictions. Successful trials followed at Crosby, North West England, collecting quantitative data to calibrate/validate: 1) overtopping tools; 2) flood forecasting services; and 3) site-specific safety tolerances.

Multiple WireWall systems have since been deployed at Dawlish and Penzance, South West England, for up to 12 months. Addition of new on-board processing algorithms and telemetry now enables observation-based overtopping hazard to be nowcast (within 15 minutes of detection) via the British Oceanographic Data Centre.