Critical storm thresholds for significant morphological changes and damage along the Emilia-Romagna coastline, Italy

Abstract The definition of storm morphological thresholds along the coast of the Emilia-Romagna Region strictly depends on its configuration and variability. The region is located in northern Italy, facing the Adriatic Sea. The coastline is characterised by very different levels of economic development, ranging from natural zones with dunes to highly developed stretches protected by breakwaters and groynes. The Integrated Coastal Zone Management effort is mainly concentrated on preserving urban areas that generate significant income for the regional economy. Natural areas, while small in comparison to the urbanised zone, are important for environment preservation. Because of such a multiplicity of issues at stake, it was decided to produce two different thresholds: one for the morphological impact on natural sectors and another for inundation and damage to structures along urbanised zones. The “forcing” component of the threshold definition for natural areas was calculated by summing the effects of surge + tide + waves (run-up elevation) to find the Maximum Water Level (MWL) reached by the sea during one, ten and one-hundred year storm return periods. For urbanised zones, historical storm information was collected starting from the 1960s in order to identify the forcing conditions causing real damages. Each storm was classified in terms of wave height, period, direction and surge level. Morphological information were obtained from Lidar flights performed in 2003 and 2004 and from direct surveys undertaken in September 2008 and February 2009 as part of the monitoring programme for the MICORE Project. The computed MWL for each return period was then compared to beach elevations along natural areas in order to calculate the Dune Stability Factor (DSF), an index that accounts for the eroded sediment volume above the MWL during a storm. Based on analysis along 41 profile lines at a 500 m spacing, it was found that the 1-in-1 year return period wave height + 1-in-1 year return period surge are able to erode and/or overwash 2/3 of the dunes. The historical storm hydrodynamic information was used to estimate which wave and surge conditions are able to inundate at least 2/3 of the beach profiles. The MWL was again compared to beach elevations, this time along 63 anthropogenic profiles spaced 500 m apart (or 1/3 of the urbanised coastline). It was found that a wave heights >= 2 m and surge + tide levels >= 0.7 m are able to flood between 18% and 36% of the built-up coast. The defined thresholds are related to the present coastal characteristics and are not “static”, meaning that they are likely to change according to future evolution of the coastline. They are very important because they can be used as thresholds to issue warnings and alert the Civil Protection. Moreover they are the first thresholds defined for the Emilia-Romagna coastline and will be used as starting values to generate “dynamic” thresholds based on numerical model predictions of morphological change for a given wave and surge level.

[1]  Jr. Asbury H. Sallenger.  Storm Impact Scale for Barrier Islands , 2000 .

[2]  Paul D. Komar,et al.  Beach Processes and Sedimentation , 1976 .

[3]  Leopoldo Franco,et al.  L’Atlante delle onde nei mari italiani - Italian Wave Atlas , 2004 .

[4]  A Shoreline Risk Index for Northeasters , 1996 .

[5]  Ap van Dongeren,et al.  Modeling storm impacts on beaches, dunes and barrier islands , 2009 .

[6]  Jean Berlamont,et al.  Storm Surge Simulations in the Adriatic Sea , 1998 .

[7]  C. Armaroli.  MORPHODYNAMICS OF NEARSHORE RHYTHMIC FORMS: AN ENERGY-BASED CLASSIFICATION , 2007 .

[8]  P. Ciavola,et al.  Dynamics of a nearshore bar system in the northern Adriatic: A video-based morphological classification , 2011 .

[9]  GENERIC TREATMENT OP DUNE EROSION FOR 100-YEAR EVENT , 1988 .

[10]  J. Jiménez,et al.  FACTORS CONTROLLING VULNERABILITY TO STORM IMPACTS ALONG THE CATALONIAN COAST , 2005 .

[11]  Leopoldo Franco,et al.  The Italian Wave Measurement Buoy Network: 12 Years Management Experience , 2001 .

[12]  D. Whitman,et al.  Hurricane-induced beach change derived from airborne laser measurements near Panama City, Florida , 2007 .

[13]  Pier Vellinga,et al.  Beach and dune erosion during storm surges , 1982 .

[14]  Fausto Guzzetti,et al.  Landslide fatalities and the evaluation of landslide risk in Italy , 2000 .

[15]  Mitchell D. Harley,et al.  Evaluation of XBeach predictions for a real-time warning system in Emilia-Romagna, Northern Italy , 2011 .

[16]  Elizabeth K. Judge,et al.  Vulnerability indicators for coastal dunes , 2003 .

[17]  P. Garès.  Predicting flooding probability for beach/dune systems , 1990 .

[18]  J. Benavente,et al.  Coastal flooding hazard related to storms and coastal evolution in Valdelagrana spit (Cadiz Bay Natural Park, SW Spain) , 2006 .

[19]  S. Leatherman,et al.  Beach Erosion Potential for Severe Nor'easters , 2001 .

[20]  L. Wright,et al.  Morphodynamic variability of surf zones and beaches: A synthesis , 1984 .

[21]  N. Plant,et al.  Forecasting Hurricane Impact on Coastal Topography , 2010 .

[22]  Pascal Bernatchez,et al.  Integrating anthropogenic factors, geomorphological indicators and local knowledge in the analysis of coastal flooding and erosion hazards , 2011 .

[23]  C. Meur-Férec,et al.  Influence of high water levels on aeolian sand transport: upper beach/dune evolution on a macrotidal coast, Wissant Bay, northern France , 2004 .

[24]  Jochen Horstmann,et al.  High-resolution mapping of Bora winds in the northern Adriatic Sea using synthetic aperture radar , 2010 .

[25]  L. Cavaleri,et al.  Long term wave hindcast in the Adriatic Sea , 1996 .

[26]  B. Collins,et al.  The Framework of a Coastal Hazards Model - A Tool for Predicting the Impact of Severe Storms , 2009 .

[27]  R. Davis,et al.  An Intensity Scale for Atlantic Coast Northeast Storms , 1992 .

[28]  P. Lionello,et al.  © Author(s) 2006. This work is licensed under a Creative Commons License. Natural Hazards and Earth System Sciences , 1966 .

[29]  Gerhard Masselink,et al.  The Effect of Tide Range on Beach Morphodynamics and Morphology: A Conceptual Beach Model , 1993 .

[30]  Tiago Garcia,et al.  An integrated method for the determination of set-back lines for coastal erosion hazards on sandy shores , 2006 .

[31]  Clara Armaroli,et al.  Geomorphic coastal vulnerability to storms in microtidal fetch-limited environments: application to NW Mediterranean & N Adriatic Seas , 2009 .

[32]  C. Houser,et al.  Sensitivity of post‐hurricane beach and dune recovery to event frequency , 2009 .

[33]  Robert A. Holman,et al.  Extreme value statistics for wave run-up on a natural beach , 1986 .

[34]  Andrew D. Short,et al.  Wave, beach and dune interactions in southeastern Australia , 1982 .

[35]  Ping Wang,et al.  Morphological and Sedimentological Impacts of Hurricane Ivan and Immediate Poststorm Beach Recovery along the Northwestern Florida Barrier-Island Coasts , 2006 .

[36]  Kenneth Pye,et al.  Decadal-scale variation in dune erosion and accretion rates: An investigation of the significance of changing storm tide frequency and magnitude on the Sefton coast, UK , 2008 .

[37]  Ap van Dongeren,et al.  82. MICORE: DUNE EROSION AND OVERWASH MODEL VALIDATION WITH DATA FROM NINE EUROPEAN FIELD SITES , 2009 .

[38]  G. Gambolati,et al.  A century of land subsidence in Ravenna, Italy , 2005 .

[39]  John J. Marra,et al.  Wave runup, extreme water levels and the erosion of properties backing beaches , 2001 .

[40]  R. Holman,et al.  A simple model for the spatially-variable coastal response to hurricanes , 2007 .

[41]  Philip L. Chaney.  Storm Overwash and the Knickpoint Effect: Northwest Florida Coast, USA , 2007 .

[42]  J. Pompe,et al.  Mitigating damage costs from hurricane strikes along the southeastern U.S. Coast: A role for insurance markets , 2008 .

[43]  D. Roelvink,et al.  Modelling storm impacts on beaches, dunes and barrier islands , 2009 .

[44]  M. Deserti,et al.  Impact of storms along the coastline of Emilia-Romagna: the morphological signature on the Ravenna coastline (Italy) , 2007 .

[45]  Randall A. Wise,et al.  Sbeach: Numerical Model for Simulating Storm-Induced Beach Change, Report 3 : User's manual , 1989 .

[46]  Carl R. Froede.  The Impact that Hurricane Ivan (September 16, 2004) Made across Dauphin Island, Alabama , 2006 .

[47]  David P. Callaghan,et al.  Quantifying the storm erosion hazard for coastal planning , 2009 .

[48]  Hilary F. Stockdon,et al.  Empirical parameterization of setup, swash, and runup , 2006 .