Novel use of social media to assess and improve coastal flood forecasts and hazard alerts

Abstract

Coastal communities and infrastructure need protection from flooding and wave overtopping events. Assessment of hazard prediction methods, used in sea defence design, defence performance inspections and forecasting services, requires observations at the land-sea interface but these are rarely collected. Here we show how a database of hindcast overtopping events, and the conditions that cause them, can be built using qualitative overtopping information obtained from social media. We develop a database for a case study site at Crosby in the Northwest of England, use it to test the standard methods applied in operational flood forecasting services and new defence design, and suggest improvements to these methods. This novel approach will become increasingly important to deliver long-term, cost-effective coastal management solutions as sea-levels rise and coastal populations grow. At sites with limited, or no, monitoring or forecasting services, this approach, especially if combined with citizen science initiatives, could underpin the development of simplified early warning systems.

Comparison of deep-water-parameter-based wave overtopping with wirewall field measurements and social media reports at Crosby (UK)

“…However, the distribution of this critical foreshore width suggests that the 200 m in front of the structure mostly influences wave overtopping at Crosby, with the first 30 m being the most critical-with tan(m) = 1:10 (or cot(m) = 10). This finding supports the conclusion of Brown et al (2021) who found that the height of the beach within about 10 m of the structure toe had a strong influence on wave overtopping for any given wave and water level conditions. As the first 200 m in front of the structure is also the most dynamic (Fig.…”

“…In December 2013, an open-access community Facebook page was established for Crosby with the title, "I'm at Crosby beach and the weather is …" (Facebook Page) and community members were able to report when wave overtopping of any magnitude occurred (Brown et al, 2021). Using the photographs from the page (Fig.…”

“…6. Example photo obtained from the Facebook page, posted by a community member on February 8th , 2016, showing significant wave overtopping at Crosby, UK (Brown et al, 2021).…”

“…More recently, two novel methods have been applied at Crosby (Northwest England), where the 900-m long coastal defence experiences overtopping every spring tide with an onshore wind. The first makes use of crowd-sourcing (or citizen science) methods, where residents of Crosby indicate-with photos via social media-when and where wave overtopping occurs (Brown et al, 2021). This approach is similar to the use of "YouTube" videos by Sandoval and Bruce (2018) to identify and analyse wave overtopping events.…”

A novel system for in-situ, wave-by-wave measurements of the speed and volume of coastal overtopping.

“…Traditional ume studies are also often focussed on extreme conditions 20 , making the predictions from current numerical tools even more uncertain for the more frequently occurring, less energetic ("nuisance") type of overtopping that can nevertheless pose a hazard to pedestrians 21 , as well as contributing to ood events. Currently the uncertainties in the overtopping predictions for extreme conditions are estimated as a factor of 3, but for more frequently occurring conditions, and/or less common sea wall structures, these uncertainties rise to orders of magnitude.…”