An approach to assess flooding and erosion risk for open beaches in a changing climate

doi:10.1016/j.coastaleng.2013.11.009

Coastal Engineering

Volume 87, May 2014, Pages 50-76

https://doi.org/10.1016/j.coastaleng.2013.11.009 Get rights and content

Highlights

•
A methodology to assess flooding and erosion risk in coastal areas is presented.
•
Allows derivation of water levels/flood maps for extreme events
•
Allows prediction of the impacts of climate change
•
Assessment of the ‘benefits’ of different flood defence interventions
•
Results were derived for specific return periods.

Abstract

This paper examines the vulnerability to flooding and erosion of four open beach study sites in Europe. A framework for the quantitative estimation of present and future coastal flood and erosion risks is established using methods, data and tools from across a range of disciplines, including topographic and bathymetric data, climate data from observation, hindcast and model projections, statistical modelling of current and future climates and integrated risk analysis tools. Uncertainties in the estimation of future coastal system dynamics are considered, as are the consequences for the inland systems. Different implementations of the framework are applied to the study sites which have different wave, tidal and surge climate conditions. These sites are: Santander, Spain—the Atlantic Ocean; Bellocchio, Italy—the Adriatic Sea; Varna, Bulgaria—the Black Sea; and the Teign Estuary, UK—the northern Atlantic Ocean. The complexity of each system is first simplified by sub-division into coastal “impact units” defined by homogeneity in the local key forcing parameters: wave, wind, tide, river discharge, run-off, etc. This reduces the simulation to that of a number of simpler linear problems which are treated by applying the first two components of the Source–Pathway–Receptor–Consequence (S–P–R–C) approach. The case studies reveal the flexibility of this approach, which is found useful for the rapid assessment of the risks of flooding and erosion for a range of scenarios and the likely effectiveness of flood defences.

Introduction

The European coastline is one of the most densely populated and developed coasts in the world. Up to half the population of Europe's coastal states now lives within 50 km from the coastline (Eurostat, 2009), attracted to this dynamic hinterland for transportation, commercial or recreational purposes. Many of these coastal communities are vulnerable to erosion and flooding events, putting a great number of people and valuable infrastructure at risk. Similarly, coastal habitats — sandy beaches, coastal lagoons and sedimentary cliffs, etc. are also threatened, a matter made worst by coastal squeeze from these communities. This makes it vital that the imminent arrival of coastal threats should be predicted in order to enable communities and civil protection agencies to respond in a timely fashion, and for hazard-reduction measures to be in place.

However, the assessment of flooding and erosion risk on the coast is a complex problem, due to the large spatial variability of marine dynamics, geological, ecological and urban coastal environments, defence and protection measures, etc. Until the end of the twentieth century, traditional methods of estimating the sources of flood and erosion risk were dominated by the statistical analysis of historical data (Thorne et al., 2007). However, due to the short time scales covered by the majority of the available records, this often meant ignoring longer term trends, such as those resulting from climate variability and human induced sea level rise. The arrival of important advances in hydrodynamic modelling and GIS techniques, as well as a deeper understanding of the nature and impacts of climate change during the last 30 years, has allowed these complexities and limitations to be dealt with more efficiently. Climate change, with its associated rising sea level and possible increases in the frequency and/or intensity of storms and changes in wave climate, can be expected to significantly increase the risk of coastal erosion and flooding in most coastal locations (Nicholls et al., 2007). On the other hand, developments in hindcasting and climate modelling have resulted in improvements to coastal storm predictions such that the timing, intensity and other important storm variables can be forecast quite accurately up to approximately three days in advance. Finally, the improved ability to precisely model the extent of flooding or erosion over large geographical areas has been of great use in risk management.

In this paper, the most recent advances in hydrodynamic and morphological modelling are applied in order to identify the sources of risk of coastal flooding and erosion (hazards) and their interaction with existing coastal defences (pathways) at four study sites across the Europe. Despite the different models and techniques used at each study site, a consistent analysis framework, provided by the SPRC approach, has been followed. This system evaluates how the Sources (waves, tide, storm surge, mean sea level, river discharge, run-off), through the Pathways (coastal defence units), affect the Receptor (inland system) generating Consequences or damages (economical, social, environmental, affected population, land losses) (see Zanuttigh, 2011, Narayan et al., in this issue). The first step is the identification of the main features to be analysed (beaches, coastal defences, inland areas) at each site and the most relevant marine and river dynamics (waves, sea level, tide, storm surge, river discharge, run-off) that define the Sources. Within the region of interest a number of sources, N_s, are identified. These are chosen to sufficiently characterise the major sources of hydrodynamic forcing within the system. A source may comprise a wave climate (wave height, wave period, wave direction) or other sets of variables describing tides, surges, river discharges or mean sea levels. Then, the coastline is divided into N_p homogeneous “pathway” units. This segments and classifies the entire shoreline into a limited number of coherent typologies, encompassing man-made and geomorphological features. Finally, the hinterland is divided into N_i “receptors” or impact units, which are regions with similar properties and susceptible to similar threats, perhaps dictated by elevation, land use or ecology or geomorphology. After establishing the impact units, we need to define the different hazards that affect them through the pathways and characterise their statistical distribution.

The approach is exemplified in a practical fashion through the application of key parts of the proposed analysis framework to four different study sites, located in Italy, Bulgaria, Spain and the UK. The Italian case study at Bellocchio is focused mainly on the application of a high resolution flooding model and the advantages of using LiDAR as input for such models. It also analyses the role of existing flood and erosion management in the degree of exposure and presents a comparison of the results of flooding considering a) different time slices (current and future epochs) and b) failure scenarios. The second study site, Varna in Bulgaria, provides detailed coverage of storm surge modelling and the selection of scenarios which are represented as Intensity–Duration–Frequency (IDF) plots. It presents a comparison of the application of 3 morphodynamic models and qualitative flooding and erosion maps for a variety of scenarios. The Spanish contribution places more attention on the definition of sources and hazards and their statistical characterisation, applied to a specific local scale area, i.e. Santander in northern Spain. They focus on the first steps of the methodology, downscaling the sources into the area around Santander while defining and characterising flooding and erosion hazard pdfs (f(z)). Finally, the study site from South Devon in the UK applies statistical analysis to existing hydrodynamic data in order to generate erosion and flood maps, for present and future scenarios, through GIS technologies.

Section snippets

Site description

The Po River delta and the adjoining coast, which developed out of the Adriatic Sea, are surrounded by the Venice lagoon in the north and the sandy coastal zone of the Romagna (Ravenna) with the Po plain to the rear, at the South up to the promontory of Gabicce, where the Apennines Mountains meet the Adriatic Sea. It covers an area of 73,000 ha, of which 60,000 is reclaimed land and the remainder are brackish lagoons, with dams or open foreshores and emerging sandy banks.

The impact of this site

Site description

The Varna study site is located in the Western Black Sea, between capes Ekrene and Galata (Fig. 8). It covers four beaches in the Western Black Sea region — Golden sands, Kabakum, Varna Central and Karantinata, all of which are subject to frequent flooding and chronic erosion.

The Bulgarian Black Sea coast has eastern exposure and storms which typically approach from the NE, E and SE can cause serious damage to coastal regions (Valchev et al., 2007). Historical records of extreme hydro-climatic

Site description

The study of this site focuses on the definition of sources and hazards and their statistical characterisation in specific locations along the coast of Santander Bay, Northern Spain. This area is one of the largest inlets on the Cantabrian Coast (2270 ha) and is characterised by several morphodynamic elements (Fig. 14): Sardinero, Loredo and Somo beaches, outside the bay, Magdalena-Peligros and Puntal beaches, in the spit, and the bay. Since the 18th century, and due to the development of the

Site description

The UK study site is from Plymouth Sound to Exe Estuary, which is located in southwest England, as shown in Fig. 21. The area encompasses a 100 km stretch of coastline bordered by the English Channel. It is one of the most diverse coastal settings in Europe, incorporating a range of habitats from exposed rocky and shingle coast to sheltered mud of flooded valleys or “Rias” together with densely populated urbanised and industrial zones of Plymouth Sound and Torbay. Therefore, it is a unique and

Discussion

The range of study of sites — Bellocchio, Varna, Santander and Plymouth, although characterised by low open beaches, offer a variety of characteristics in terms of the level of development and coastal protection existing in each area, as well as to the hydro/meteorological forcings acting on them. This, combined with the varying availability of data (bathymetry, topography, wave, tides, storm surge), allowed for the implementation of a series of models and analysis techniques that exemplify the

Conclusions

The application of a methodology to assess flooding and erosion risk in coastal areas is presented. The approach is focused on the first two steps of the Source–Pathway–Receptor–Consequences (SPRC) model and, among other things, allows:

•
derivation of water levels/flood maps for events more extreme than have been recorded so far
•
derivation of results for specific return periods
•
prediction of the impacts of climate change
•
assessment of the ‘benefits’ of different flood defence interventions
•
prediction

Acknowledgments

The authors are very grateful to all researchers involved in the development of this paper and the results presented in it, in particular to Jose M. Horrillo-Carballo and Raul González, from University of Plymouth and Gerardo Durán, from UNAM for their technical support. Additional credit goes to Nikolay Valchev from IO-BAS; Panayotis Prinos, Yannis Krestenitis, Yannis Androulidakis and Katerina Kombiadou from AUTH; Ralf Weisse from HZG; and Alexander Polonsky from MHI for their contribution to

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¹: Currently, School of Engineering, Cardiff University, Cardiff CF24 3AA, UK.

²: Currently, College of Engineering, Swansea University, Swansea SA2 8PP, UK.

View full text

An approach to assess flooding and erosion risk for open beaches in a changing climate

Highlights

Abstract

Introduction

Section snippets

Site description

Site description

Site description

Site description

Discussion

Conclusions

Acknowledgments

Coast. Eng

Coast. Eng.

Ocean Eng.

Coast. Eng.

Coast. Eng.

Coast. Eng.

Coast. Eng.

Coast. Eng.

Coast. Eng.

GOS, un reanálisis de marea meteorológica de 60 años de alta resolución para el sur de Europa

I Encuentro Oceanografía Física Española

Literary review of historical storm events in the western Black Sea

Analysis of the catastrophic storm in February 1979 near the Bulgarian Black sea coast

Oceanology

A third-generation wave model for coastal regions, Part 1: model description and validation

J. Geophys. Res.

Wave modelling—where to go in the future

Bull. Am. Meteorol. Soc.

Ensemble modelling of tides, surge and waves

An Introduction to Statistical Modeling of Extreme Values

Planning Policy Statement 25: Development and Flood Risk

MIKE 21 & MIKE 3 Flow Model FM—Sand Transport Module. Rep. Horsholm, Denmark

DIGIMAP Collection

Statistics in focus

Analysis of extreme marine events causing flooding in Varna region

Turk. J. Fish. Aquat. Sci.

Variability and trends in the directional wave climate of the Southern Hemisphere

Int. J. Climatol.

The TELEMAC modelling system

Hydrol. Process. SI

An s-coordinate density evolving model of the northwest European continental shelf: 1, Model description and density structure

J. Geophys. Res.

Modelling extreme wave events (present and future scenarios) in Southwest England

Climate change 2007: synthesis report

The Habitats Directive: Selection of Special Areas of Conservation in the UK. Report NO. 270

The NCEP/NCAR 40-year reanalysis project

Bull. Am. Meteorol. Soc.

Self-Organizing Maps

Dynamics and Modelling of Ocean Waves