Combination Hazard of Extreme rainfall, storm Surge & high Tide on estuarine infrastructure

Project Description

UK estuaries are at risk from combination flooding. Sea-level rise and predicted changes to UK storm patterns (affecting both surge and river flows) will alter the joint probability of multiple hazard events, making previous understanding of risk, and mitigation measures, potentially obsolete. Existing probabilistic methods for assessing combination hazard (e.g. FD2308) provide only water level hazards, with limited detail on where and when issues may occur, and vitally cannot readily accommodate revised estimates of event distributions due to sea-level rise and climate change.

Combination hazards, therefore, present a clear risk to project partner's infrastructure in estuaries (e.g. Flood defences, railways, roads, water treatment works, nuclear power stations), both under present conditions - and more with greater uncertainty in the future. The ability to better forecast the specific locations and timings of such combination hazards will enable effective planning and timely warnings to industry operators, partners and the public.

All of our project partners (Network Rail, Atkins, Ove Arop Foundation, Welsh Water, Environment Agency, EDF Energy & Bangor University) have considerable investments in areas prone to estuarine flooding including flood defences (EA), rail networks (Network Rail), water supplies (Welsh Water) and nuclear power stations (EDF Energy). The scale of national exposure to combination hazard is phenomenal. Taking the Humber alone, the projected economic costs of the 2015 surge tide occurring with 0.3m of sea level rise would be £12.5bn in direct flood damage and £10.8bn in consequential losses. Quite simply, our project partners cannot ignore how combination hazard may increase with climate change.

CHEST will assess if the management of combined river-surge-wave-tide flooding in UK estuaries (and surrounding low-lying areas) needs to be amended, especially in the light of sea-level rise and changing climates.

This leads to three objectives: 1. Establish if the interaction between the combination hazards of rivers, surge, waves and tides is important to resolve for estuarine flood risk; 2. Determine which of these factors and in what combination pose the greatest risk. i.e. What is the sensitivity to the different hazards and does it differ in different locations (a) within an estuary (b) between different estuaries?; 3. With sea-level rise and climate change - ascertain whether the relative importance of the combination hazards change or shift. i.e. with SLR do surges become more dominant?

To achieve these objectives, CHEST will use novel, fast numerical models (developed in previous NERC and EA funded projects) to simulate the combination hazard for two contrasting pilot studies (Humber and Dyfi estuaries) where the primary project partners have particular concerns. In a second phase the CHEST modelling framework will be documented, packaged and where necessary tailored to a wider group of additional project partners allowing the application to estuaries around the UK.