The role of the decision-making process on shoreline armoring: A case study in Quebec, Canada
Introduction
Coastal erosion is a natural phenomenon affecting shorelines worldwide. Ever since the establishment of human societies along shorelines, coastal defence measures have been implemented in response to coastal erosion and flooding (Charlier et al., 2005). In recent decades however, the effects of climate change added to the coastal zone development have led to an increase in artificial barriers and shoreline armoring (Dugan et al., 2011; Gittman et al., 2015; Horstman et al., 2009).
Shoreline armoring refers to the construction of coastal defence structures and of port facilities or other artificial means of supporting coastal development (Dafforn et al., 2015; Dethier et al., 2016; Gittman et al., 2015). It is estimated that 50% of the world coastlines are currently threatened by anthropic development (Dafforn et al., 2015; Manno et al., 2016) and that anthropogenic factors have been the main drivers of morphological changes in sandy coastlines in recent decades (Vousdoukas et al., 2020). Available data published in the literature show a particularly high level of shoreline armoring in the following regions: 27% in Japan in 1992 (Koike, 1996); 16% in the North Sea in 2006 (EEA, 2006); over 8% in the Mediterranean Sea in 2006 (EEA, 2006); 32% of the Northern Irish coast in 2009 (Cooper et al., 2020); 46% of England's coastline and 28% of Wales's coastline in 2010 (DEFRA, 2010); 14% in the United States in 2015 (Gittman et al., 2015); and 7,5% in Italy in 1998 (Valloni et al., 2003). Today, these levels are likely to be much higher considering the increased development of coastal zones (Horstman et al., 2009).
Shoreline armoring modifies coastal processes. Not only does it contribute to reducing the width and height of sandy beaches (Bernatchez and Fraser, 2012; Bernatchez et al., 2011a, Bernatchez et al., 2011b; Dugan et al., 2008), but it also reduces coastal ecosystems’ natural capacity to attenuate wave energy (Cooper et al., 2020; Dugan et al., 2011; Moschella et al., 2005), thereby increasing the risk of coastal erosion and flooding (Bernatchez et al., 2011a, Bernatchez et al., 2011b; Didier et al., 2015). Moreover, disturbance to coastal ecosystems caused by shoreline armoring leads to changes in species composition, abundance and diversity, and can have significant consequences on the productivity and nutrient cycles, ultimately affecting ecosystem services (Airoldi et al., 2005; Martin et al., 2005).
In the Canadian province of Quebec, on the coasts of the St. Lawrence Estuary and Gulf, municipalities have developed along the littoral, which is made up of low-lying sandy coasts, as well as sandy, clayed and rocky sedimentary cliffs sensitive to erosion (Bernatchez and Dubois, 2004). The average shoreline retreat in unconsolidated formations varies between 0.5 and 2.0 m/yr (Bernatchez and Dubois, 2004). Consequently, more than 5426 buildings will be exposed to erosion by 2065 if no adaptation measures are implemented and existing defense structures are not maintained (Bernatchez et al., 2015). Between the 1980s and the early 2000s, coastal defence structures (seawalls and rock armour) were built in emergency situations after storms events. A better approach would have been an integrated decision making process (Boyer-Villemaire et al., 2015) which should be the basis when analyzing the impacts of coastal defence measures on coastal socio-ecological systems (Baquerizo and Losada, 2008; Polasky et al., 2011). Coastal dynamics result from multi-scale non linear processes involving hydrodynamic conditions in interaction with changing topo-bathymetry and morphologic conditions (Baquerizo and Losada, 2008), which have feedback effects on ecosystems and social aspects (Polasky et al., 2011). In the context of climate change, sea level rise and extreme sea levels will increase coastal impacts (Church and White, 2011; Nicholls and Cazenave, 2010; Nicholls and Tol, 2006), but also increasing the uncertainty in decision-making (Hallegatte, 2009; Wahl et al., 2017). This site-specific complexity, together with the involvement of multiple stakeholders and agencies, must be considered in coastal zone management. In order to identify the best-adapted coastal defence measure (Jones et al., 2014), a transparent, reliable and flexible decision-making process is essential (Reed, 2008). Common approaches based on probabilistic analysis to characterise uncertainties have produced successful results in many engineering fields, but fail to manage uncertainties when the system is unpredictable, in constant evolution, and adapting to new conditions (Brugnach et al., 2008). Also, knowledge and technical progress acquired through global coastal zone research are rarely applied or they are implemented at a slow pace by coastal managers and decision-makers, who tend to analyse problems locally without considering the ecological or social impacts (Baquerizo and Losada, 2008). In that context, it is difficult to make sound decisions. However, it is important for decision-makers to integrate existing science and knowledge into their processes while being aware of the unknown or unpredictable factors (Polasky et al., 2011).
The purpose of this article is (1) to characterise shoreline armoring in Eastern Quebec; (2) to determine the role that coastal managers, coastal citizens, and coastal engineers play in the decision-making process about coastal defences; and (3) to identify possible actions to be taken by each stakeholder to improve coastal engineering development. We conclude by explaining how a better decision-making process could lead to coastal defence measures that are better adapted to local conditions.
Section snippets
Location and geomorphological context
The study was carried out in the Canadian province of Quebec, on the coasts of the Estuary and Gulf of St. Lawrence (EGSL), covering more than 3300 km of coastlines, from Tadoussac to Natashquan on the North Shore of the St.Lawrence and from Berthier-sur-Mer on the south shore of the St.Lawrence to Pointe-à-la-Croix in Chaleur Bay, as well as in the Magdalen Islands in the gulf of St.Lawrence (Fig. 1). From the upstream end of the estuary to the Gulf of St. Lawrence, the environment changes
Methods
The study was divided in two parts: (1) coastal segmentation in which shoreline armoring was characterised; (2) consultations with coastal zone stakeholders, in which subjects related to different coastal defence measures were discussed.
Shoreline armoring in Eastern Quebec
Over 3300 km of shoreline were analysed. Artificial structures (CDMs, port facilities and other artificial objects supporting coastal development) covered about 386 km, or 11.7% of the 3300 km Eastern Quebec shoreline length. CDMs made up over 83.8% of this total, and covered 9.8% of the shoreline.
The increase in kilometers of CDM between September 2010 and 2017 is shown in Table 2. In both 2010 and 2017, over 97% of the CDMs in this region were reflective structures, especially rock armour
Discussion
Coastal zone stakeholder consultation results show that the managers, citizens and firms who were consulted during 2017 and 2018 are open to a greater CDM diversity. Coastal managers who had previously attributed their choice of reflective structures to a lack of understanding of coastal processes and hazards (Bernatchez et al., 2008; Drejza et al., 2011; Friesinger and Bernatchez, 2010), now ranked soft techniques first in four of the five coastal geomorphological types. This shift in
Conclusion
As elsewhere in the world, the coastline of Eastern Quebec has seen an increase in its artificiality in the last decades. In 2017, about 11% of the coastline was occupied by such structures, most of which (88.3%) were coastal defence measures. Until 2017, the most-used coastal defence measures were reflective structures (92,8%), while soft techniques were much less common (5.9%). The results of consultations with stakeholders in the area show that there is now a greater openness to the use of
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors would like to thank all the members of the Research Chair in Coastal Geoscience who participated in coastal characterization and in consultations organisation and execution, particularly Evelyne Arsenault, Stéphanie Friesinger, Steeve Dugas, Marie-Andrée Roy, Maude Blain, Catherine Paul-Hus, Mireille McGrath-Pompon, Christian Fraser, Ariane Jobin and Laurie Desrosiers-Leblanc. We are grateful to the Ministère de la Sécurité publique du Québec from his program for natural risks
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