Flood Hazard Assessment for a Hyper-Tidal Estuary as a Function of Tide-Surge-Morphology Interaction

Charlotte Lyddon,Jennifer M Brown,Andrew J Plater,Nicoletta Leonardi

doi:10.1007/s12237-018-0384-9

Abstract

Astronomical high tides and meteorological storm surges present a combined flood hazard to communities and infrastructure. There is a need to incorporate the impact of tide-surge interaction and the spatial and temporal variability of the combined flood hazard in flood risk assessments, especially in hyper-tidal estuaries where the consequences of tide and storm surge concurrence can be catastrophic. Delft3D-FLOW is used to assess up-estuary variability in extreme water levels for a range of historical events of different severity within the Severn Estuary, southwest England as an example. The influence of the following on flood hazard is investigated: (i) event severity, (ii) timing of the peak of a storm surge relative to tidal high water and (iii) the temporal distribution of the storm surge component (here in termed the surge skewness). Results show when modelling a local area event severity is most important control on flood hazard. Tide-surge concurrence increases flood hazard throughout the estuary. Positive surge skewness can result in a greater variability of extreme water levels and residual surge component, the effects of which are magnified up-estuary by estuarine geometry to exacerbate flood hazard. The concepts and methodology shown here can be applied to other estuaries worldwide.

Highlights

Coastal zones worldwide are subject to the impacts of shortterm, local variations in sea-level, communities and industries developed on estuaries (Pye and Blott 2014)
The results show the severity of the combined tide and storm surge event, timing of the peak of the surge relative to tidal high water and the surge skewness are important controls on flood hazard in estuarine environments
Results from four historical events are presented which show the influence of the severity of the storm surge, the influence of the timing of the surge on the total water level and characteristics of the filtered surge component on the total water level throughout the Severn estuary

Summary

Introduction

Coastal zones worldwide are subject to the impacts of shortterm, local variations in sea-level, communities and industries developed on estuaries (Pye and Blott 2014). Extreme sea levels, caused by the combination of astronomical high tides and meteorological storm surges, are a major threat to coastal communities and infrastructure (Elliott et al 2014; Quinn et al 2014; Webster et al 2014; Prime et al 2015). This is of particular significance in hyper-tidal estuaries, where tidal range exceeds 6 m (Davies 1964; Robins et al 2016). Tidal amplification and extreme surge development in hyper-tidal estuaries means concurrence of a large astronomical tide and extreme surge can be catastrophic, as seen in the Bay of Fundy, Canada (Desplanque and Mossman 1999), Meghna Estuary, Bangladesh (As-Salek and Yasuda 2001) and Severn Estuary, UK (Pye and Blott 2010)

Methods

Results

Conclusion