The role of the decision-making process on shoreline armoring: A case study in Quebec, Canada

Highlights

• In 2017, Coastal defence measures occupied about 10% of the shoreline of Eastern Quebec, and 97.6% of them were reflective structures.

• Notable change in desired coastal defence measure by coastal actors compared to previous studies where reflective structures were preferred.

• Even if coastal actor prefers soft techniques, reflective structures continue to be the most implemented solution along Eastern Quebec's coasts.

Abstract

Shoreline armoring has repercussions on coastal processes, including reducing the width and height of sandy beaches, which affect coastal ecosystems and ecosystem services. This project, consisting of two parts, was carried out in the Canadian province of Quebec, on the coasts of the St. Lawrence Estuary and Gulf, which cover the territory of 21 coastal Regional County Municipalities (RCM). The objectives were to characterise shoreline armoring in Eastern Quebec, to determine the role played by coastal managers, coastal citizens, and coastal engineers in the coastal defence decision-making process, and to identify possible actions to be taken by each stakeholder to improve coastal engineering development. First, over 3300 km of shoreline were segmented and characterised, allowing the mapping of what proportion of the shoreline was covered by artificial structures. In 2017, coastal defence measures (CDM) occupied about 10% of the shoreline, and 97.6% of them were reflective rigid structures. The second part of the project involved three different consultations carried out in 2017 and 2018 with 300 coastal managers, 494 coastal residents and 51 professionals from environmental and engineering firms to assess their knowledge of CDM types and functions, and to discuss about the decision process leading to the CDM identification. Results of the consultations show a significant change in the type of desired solutions compared to previous studies where rigid structures were clearly preferred. But despite a greater prioritization of soft techniques by professionals from municipalities, ministries' managers and coastal citizens, the rigid structures continue to be the type of solution mostly implemented along Quebec's coasts. This difference can be explained by a number of factors: a lack of specialized knowledge; a lack of funding; a lack of collaborative process; and regulations that are too restrictive for innovative CDM. In addition to an increase of funding for preventive CDM, for long term CDM monitoring and maintenance, for case studies and pilot projects, the main solutions proposed were interdisciplinary projects based on consultation, adjustment of environmental regulations, and development of a tool that would enable decision-makers to evaluate each option in a particular context, so as to identify the most appropriate solutions and make better decisions for the long term.

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.