Regional Coastal Monitoring Programmes
Many countries with a sea border need man-made defences to protect them from coastal hazards such as flooding. In the UK 3,200 kilometres of coastline are defended, particularly in seaside towns and cities. Sea walls are designed to protect people, property and infrastructure from the harm caused by large waves that can occur when a severe storm happens at the same time as a high tide (Figure 1).
When planning sea defences a lot of data are needed to understand the potential hazards that might occur in decades to come. Numerical tools (e.g. EurOtop) use this data to test suitable sea wall designs. The tools do this by estimating the "overtopping hazard" for each design i.e. what volume of water might come over the wall during storm conditions. Accuracy of the tools is assessed by checking outputs against measurements of overtopping volumes during storms. Field experiments have previously used large tanks placed behind the sea wall to catch the water that comes over. Such experiments are very costly and can be difficult to do, so only a few have been made. They also only provide a limited amount of data and none at all on the speed of the water that overtops: an important factor for public safety. This lack of measurements means there is large uncertainty in the numerical estimates of the hazards, so sea defences are overdesigned to have large safety margins and may therefore cost much more than they need to.
This project aims to take a low-cost instrument that has previously been used to measure waves in the open ocean, and convert it into a system ("WireWall") that will measure coastal overtopping hazard. The system will employ a 3-dimensional grid of capacitance wires that sense contact with saltwater. This signal will be used to measure the volume and speed of overtopping at vulnerable locations on the 900-metre-long sea wall at Crosby in the North West of England. This sea wall is reaching the end of its design life and intense monitoring of the local conditions has begun to aid the design of a new wall (Figure 2).
The WireWall interest group met at the NOC in Liverpool on 26th June 2018. The meeting saw colleagues from the NOC and HR Wallingford join forces with our partners, coastal authorities, consultants and researchers to discuss the progress so far and what's next for the innovative project. Lots of lively discussion was had with new challenges identified. Over lunch there was also the opportunity to get some hands on experience with a demonstration rig that showcased the technology that will be used.