# Feeling of exposure to fluviomarine risks and adaptation strategies in the Loire estuary

Florian Drouaud, Céline Chadenas, Marine Giraud

► To cite this version:

Florian Drouaud, Céline Chadenas, Marine Giraud. Feeling of exposure to fluviomarine risks and adaptation strategies in the Loire estuary. Anthropocene Coasts, 2025, 8 (11), 10.1007/s44218-025-00082-0. http://dx.doi.org/10.1007/s44218-025-00082-0

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# Feeling of exposure to fluviomarine risks and adaptation strategies in the Loire estuary

Florian Drouaud¹*, Céline Chadenas¹ and Marine Giraud²

**Abstract**

Estuaries are low- elevation morphological areas that are highly susceptible to submersion and flooding, and par- ticularly so in view of the rising sea level. As with coastlines, where many adaptation strategies are under consid- eration (relocation, adaptation of buildings, nature-based solutions, etc.), future adaptation strategies for estuaries involve a number of different ways of converting the area, all of which must be developed on the appropriate spatial and temporal scales and in agreement with the local people. In this regard it is appropriate to examine the views of local residents in an estuarine context. Do they feel vulnerable? What are their perceptions of how planning has evolved in relation to climate change, and what are their preferences in respect of risk management? This article presents the results of an enquiry carried out downstream of the Loire estuary in an area characterized by indus- try, urban development and natural spaces. The survey involved 633 individuals whose views on the relationships between the local residents and their territory, in terms of fluviomarine risks and adaptation procedures, were collected by completing a questionnaire. The results reveal that few of the people surveyed are worried about flu- viomarine risks, although they are aware of the ongoing climate change and that areas close to where they live are under threat. On the other hand, they feel much more threatened by the industrial risk which is characteristic of the Loire estuary. In terms of adaptation strategies the results are highly consensual, although sometimes confused, and could reveal a lack of 'concern' about these topics. The results of this research highlight determining factors such as time spent in the community and at home, the elements inherent to estuarine environments, and the memory of local risks. These elements could be useful for stakeholders in large industrialized estuaries wishing to embark on an adaptation strategy or submersion risk management.

**Keywords** Feeling of exposure, Risk, Adaptation, Submersion, Estuary, Sea level rise, Flooding, Socio-spatial perception

## 1 Introduction

Estuaries are located at the land-sea interface and are par- ticularly susceptible to changes in water level, precipitation, tides, variations in salinity level, sediment and storm events (Almar et al. 2021; Le Hir 2014; Moatar & Dupont, 2016). These elements combine to form a complex entity, and as

such the future of estuaries is subject to a great many chal- lenges and uncertainties (Khojasteh et al. 2021). They are constantly changing due to both fluviomarine and anthropic influences and are characterized by the challenges of built-up areas which may be dense or less dense, port and industrial infrastructures, natural spaces and agricultural land. Just like coastlines, these areas too are vulnerable to future hazards and changes (Khojasteh et al. 2021; Tunstall 2000; Meur- Ferec et al. 2008; Wisner 2016), especially those related to the rise in sea level. Tide gauges in the Bay of Biscay register a rise of 2mm per year (Brest, 1993–2011) (Ferret 2016; Regnauld & Dubreuil 1998), to which other changes can be added (Haigh et al. 2016; Rocha et al. 2020), such as the frequency

<figure><img src="image_4.png" /></figure>

<footnote>*Correspondence:
Florian Drouaud
florian.drouaud@univ-nantes.fr
¹ Nantes Université, Littoral, Environnement, Télédétection, Géomatique,
UMR CNRS 6554, Nantes, France
² Agence d'urbanisme de la région de Saint-Nazaire, Saint-Nazaire, France</footnote>
of surges (Paskoff 1998) and storm activity (Chaumillon et al. 2017), and global projections predict a progressive increase in varying degrees within the range 30 to 70 cm and even as much as one meter, by the end of the century (Oppenheimer, et al. 2019). Overall, given the powerful effects of climate feedbacks, this rise would accelerate even more after 2100 (Oppenheimer et al. 2019).

The traditional approach to counteract the effects of flooding in estuaries is establishing polders (Weisscher et al. 2022), but also dikes in certain areas. This solution involves modification of the local ecological functions, economic concerns such as maintenance of the structure, and further risks, for example ruptures and breaches (Rambonilaza et al. 2016; Verger 2011). When introducing solutions for estuaries it is essential to consider their anthropogenic nature, as it is with the hydraulic systems that operate on floodplains. However, the anthropogenic nature may vary since development can be entirely dissimilar from one riverbank to another, so much so that it determines the geography of the area. As a result of all these natural, physical and human elements, formulating a model of the risks and sea level rise in estuaries is a complex task involving a level of uncertainty, which stakeholders must nonetheless seek to grasp in order to predict the future of the territory.

To achieve this, and given that in a neoliberal framework, the notion of resilience tends to make people responsible for adapting to climate change (Berdoulay and Soubeyran 2020), these strategies should be constructed around readiness (Glatron 2009) and awareness raising (Weichselgartner et al. 2016), and also take into account the inhabitants' connection to their territory in the context of these disruptions. As such, a study of socio-spatial perceptions is often useful for a number of reasons. Most importantly it forms part of the overall approach of portraying the vulnerability as well as analyzing the risks and management policies (Meur-Ferec et al. 2020; Wisner 2016). This work, which represents a snapshot of the territory at time T0, can then potentially be used by local decision-makers and communities for concrete action, and also reveals how prepared the local people are for the problems of risk, climate change and adaptation by highlighting any requirement for aware-raising (Yembi-Yembi et al. 2022). Studying the cognitive representations can then help bring into focus social acceptance regarding the implementation of adaptation strategies (Chadenas et al. 2023; Carlton and Jacobson 2013), an essential factor for success (Haasnoot et al. 2019), because it is precisely the way individuals perceive the possibilities that determines whether an adaptation strategy is accepted or rejected. An understanding of what determines these perceptions is therefore useful (social, cultural and geographic factors) to gain an

understanding of how opposition to or preference for certain adaptation strategies is formed (Lechowska 2018). The results of this work are aimed in general at avoiding ‘one-size-fits-all’ approaches (Guillou & Meur-Ferec 2014), as is the case with planning consultation processes, by using the appropriate communication tools and actions. The ultimate goal of the work is to reduce vulnerability to maladaptations (Magnan 2014)—bad decisions that could be taken without considering the terrain or the locality.

While fairly extensive research has been done on the perception of flood risk among the inhabitants of coastal regions (Kellens et al. 2011; Rey-Valette et al. 2012; Hellequin et al. 2013; Schmidt et al. 2014; Rulleau et al. 2015; Verlynde 2018; Becu et al. 2019; Ruz et al. 2020), much less research has been done on estuaries, and although some studies do focus of the perceptions of estuary inhabitants (Cabanne 1988; Martin et al. 2020), industrial and health risks in particular (Bonnet et al. 2012; Lepesteur et al. 2008; Travers et al. 2009), there are few that address fluviomarine risks and adaptation to climate change; examples include Sylvia Tunstall (2000) on the Thames estuary and Tina Rambonilaza, Olivier Joalland and Elodie Brahic (2016) on the Gironde estuary.

The aim of the present study was therefore to investigate the views of inhabitants downstream of the Loire estuary on the risks associated with rising sea levels and the potential adaptation and management strategies that could be implemented, by means of a questionnaire. Particular attention was given to the socio-spatial aspect of their views, the relationships that local estuary residents have with the environment under threat, and how their knowledge affects the adaptation strategies that may be introduced. This study has three main objectives: 1) to characterize the relationship to the risk of marine submersion and to the SLR maintained by the inhabitants of the estuary; 2) to understand the extent to which the estuarine environment may have influenced these representations of risk and SLR; 3) to understand how the individuals surveyed conceive adaptation strategies and solutions in the estuary.

# 2 Method

## 2.1 The terrain: special features and exposure of the Loire estuary

The Loire estuary is the mouth of the Loire basin where it flows into the Bay of Biscay. It features a series of low-lying wetlands (70,000 hectares) connected by the river Loire to the Brière marsh to the north (Fig. 1), and to the Grand-Lieu lake by the river Acheneau to the south. The area can be defined by three criteria: sediment (external downstream boundary with the sedimentary plume), tide (internal upstream boundary where the salinity front meets the
<figure><img src="image_5.png" /><figcaption>**Fig. 1** Survey area: communities in low-lying areas between the external estuary and city of Nantes</figcaption></figure>

dynamic tide) and elevation (depth boundary characterized by low-lying areas). The latter of these is formed by the high points of the research area: the Britain ridge and the Guérande and Saint-Père-de-Retz hills. For this study, the northern and southern districts between the urban area of Nantes and the external estuary were considered, i.e. areas with a significant maritime influence. Towns in the Brière marsh area connected with the estuary were also taken into account due to their established susceptibility to flooding (Geffray & Ménanteau 2004; Menanteau 2009), also serving as a boundary and element for comparison.

The estuary serves as a foundation for human activities—industrial fishing, waterfowl hunting, sailing and livestock farming, and encompasses many natural habitats protected by bird and habitat directives (Chadenas et al. 2009). It has been considerably artificialized by channelization since the seventeenth century for the development of the port, and various drainage operations have changed the overall morphology (Fattal, 2002) resulting in a reduction of the surfaces exposed to tides and lowering of the water level to allow the passage of larger vessels. The rise of the salinity front (23

km upstream between 1950 and 1980), the mud flats (28 km between 1953 and 1991) and the dynamic tide (GIP LE, 2018), are significant direct consequences of artificializing the Loire estuary and attributed directly to anthropization. With the metropolitan areas of Nantes to the east and Saint-Nazaire to the west, the north of the estuary is an industrial production area with worldwide connections (the Chantiers de l'Atlantique shipyard that builds ultra-large container ships, the airport industry, the Donges oil refinery, the Cordemais power station and terminals of all kinds) thanks to the Grand Port Maritime de Nantes Saint-Nazaire, the biggest port on the Atlantic coast of France in terms of tonnage. The port facilities in the estuary are distributed across two locations: Nantes, with the Cheviré, Lavigne and Roche-Maurice sites, and Saint-Nazaire with the Montoir and Donges sites, and between them the Cordemais site. These facilities have a profound effect on the estuary landscape, especially the downstream section. According to 2019 data from INSEE (the French National Institute for Statistics and Economic Studies), a total of 191,195 people live in this part of the study area.
In the long term, the Loire estuary will indisputably be exposed to rising sea levels and the risk of marine submersion. The risks for most of the study area, however, have not yet been determined, and in fact the estuary has not experienced any really significant hazards in recent years. Although several events, such as storm Xynthia in 2010¹ and marsh floods, have already affected the shores of the estuary (Geffray and Ménanteau 2004), few built-up areas were affected compared to the southern Vendée region in February the same year. This apparent invulnerability to the hazards (and by extension SLR) and the complexity of the estuary area, all aggravated by a lack of political commitment to engage in research, has resulted in a dearth of risk prevention management covering most of the estuary and consideration of the area as a de facto low-priority area (November 2002). This intermediate zone is covered on the upstream by the Nantes Flood Risk Prevention Plan (PPRI) and on the downstream by the Saint-Brévinles-Pins and Saint-Nazaire Coastal Risk Prevention Plans (PPRL). These documents provide a framework for development based on the maximum height reached during storm Xynthia, to which is added the projected sea level rise (Xynthia + 60 cm for coastal documents and Xynthia + 1 m for the Nantes metropolitan area). The choice of these scenarios is a political decision, but a homogeneous territorialization of risk policy on the scale of the estuary appears important to a number of stakeholders, such as industrialists and elected representatives. Driven by these local concerns, a recent study was commissioned by the government to determine the flood-submersion hazard from the existing risk prevention plans. The study identified a fairly high hazard exposure in the north and south of the estuary from Xynthia 60 cm rise. In addition to this observation, pressing development problems have been identified such as Saint-Brévin-les-Pins, where the inhabitants of a 22-hectare flood-prone site are earmarked for relocation by 2028.

## 2.2 Survey protocol

The qualitative approach is generally the preferred method to understand social representations (Bertrand et al. 2006); however, a long questionnaire was chosen in this case because it has the advantage of capturing the views of a large number of people through a representative sample of estuarine residents.

### 2.2.1 The questionnaire

The survey was based on a questionnaire containing 129 questions, taking around 20 min to complete. The

questionnaire was structured around questions and hypotheses presented in the introduction, and the existing literature, in particular the Triangle of Flood Risk Perception by Lechowska (2018), which considers concern, awareness-raising and preparation as primary influence variables on the perception of flood risk. A number of open questions were included in order to obtain wider views on certain topics through verbatim accounts. The formulation of other questions was largely based on the Likert scale to obtain wider variation in the answers and avoid unanswered questions. The questionnaire was divided into five sections. Section 1 covered the socio-demographic aspect, with questions designed to collect information on the individual responders (sex, age, socioeconomic class, etc.), and upon which the sampling of the surveyed individuals was based, using age and gender as the criteria. The decision was taken to include this section at the beginning and not at the end, which is often the case with surveys, because it contained a filter question that excluded individuals who were not resident in the study area in order to focus on the inhabitants of low-lying locations. At the end of this section were some questions on the characteristics and location of the respondent's home (elevation and distance from the estuary), and factors indicative of the respondent's reasons for living there (proximity to workplace, family, local amenities, etc.). Section 2 of the questionnaire concerned the relationship between the inhabitants and the estuary and their views on it, focusing in particular on the links between nature and society. Section 3 concerned natural and industrial risks, and the rise in sea level and the consequences of it, on different spatial and temporal levels. The last two sections covered adaptation measures for fluviomarine hazards—types of intervention, tools, the stakeholders responsible—and development scenarios. Finally, the respondents were asked to plot their homes on a map (in the manner of Ruz et al. 2020), to assess the relation between risk perception and locality.

### 2.2.2 Questionnaire completion strategy

The questionnaire was tested before the field phase and some of the terminology was adjusted to eliminate scientific jargon. The survey was conducted in street-intercept survey method in 24 communes downstream of the estuary, with the help of 16 geography masters' students. The study area was divided into sections to distribute the local population equally among the interviewers (Fig. 2). Three groups were formed as follows; one focused on Saint-Nazaire and the Brière marsh communities (Group 1), another focused on the north of the estuary between Donges and Saint-Etienne-de-Montluc (Group 2), and the last on the area south of the estuary (Group 3). Over the 10 days of the test period, the three

<footnote n="1">¹ This was particularly visible in Saint-Brévin-les-Pins and Saint-Nazaire downstream, and in Lavau-sur-Loire further upstream.</footnote>
<figure><img src="image_6.png" /><figcaption>**Fig. 2** Distribution of groups across the study area</figcaption></figure>

groups thus focused on a different field strategy depending on the characteristics of their particular location. For example, in view of the relatively sparse population in Group 2, there was more travelling involved for the interviewers and they had to be especially attentive to 'where and when' to appear on the streets (supermarket exits, schools, etc.).

### 2.2.3 Processing of results

All the results were entered in a database using the Sphinx software program, then exported to an Excel spreadsheet for simultaneous analysis using Sphinx and SPAD software. The main statistical processes were completed in the following order: simple table, cross-tabulation, statistical tests. The statistical tests were based on *p*-value, degree of freedom and chi-square, enabling cross-referencing of the many different categorical variables. The final section of the questionnaire—mapping of homes—was processed by QGIS, which digitized the map and georeferenced each location point provided. The scale at which respondents' homes were located was not large enough to pinpoint precise buildings, so anonymity

was maintained. A data linkage was established between the database and the points layer to facilitate processing of the map.

### 2.3 People surveyed

The survey focused on permanent residents since these are considered the ones most concerned with exposure to fluviomarine hazards, and for this reason the survey was conducted in the month of December. 684 completed questionnaires were collected, of which 633 were selected as the final sample after a verification process on the database to detect and correct any errors made during distribution and subsequent data entry.

Each group of interviewers in the field was given a quota in terms of age and gender to ensure an overall representative sample. The quotas could be adjusted by the supervising team depending on how the roll-out of the survey was progressing and in relation to the initial quota. The people surveyed consisted mainly of home owners (60%), and also primary residents (97.6%). This latter figure is significantly higher than that for the survey area overall (60% main residence compared to 85.4%
for the overall study area). On the whole, the predetermined quotas were maintained (Fig. 3), although some deviations were noted. The deviations can be linked to the constraints of the study area (problems encountering the desired categories of respondent on the day and the December weather being non-conducive to outdoor activities).

# 3 Results

## 3.1 Perception of exposure in the estuary

### 3.1.1 A feeling of exposure to industrial risk predominates over flooding and submersion risks

In response to the question 'In your opinion, is your home exposed to a risk?' (Fig. 4), respondents were asked to give their opinion on their home's exposure to coastal erosion, industrial risk, marine submersion and inland flooding. Of all the risks in general, a majority of the sample considered industrial risk to be the greatest threat to housing (50.6% positive responses). In second place and some way behind was inland flooding (27.9%), then marine submersion (18.2%). Coastal erosion was last (14.3%) and there was a relatively high percentage of 'don't knows' (7.3%).

### 3.1.2 Sea-level rise, a risk for others

In response to the question *When do you think the sea level will start to rise?* most people thought it was already happening (58.7%). A small number thought it would occur after 2100 (3.7%), while many more chose the medium/long term horizon of between 2030 and 2100 (27%). In terms of quantifying the sea level rise by 2100 (*By how much do you think the sea level will rise in metropolitan France by 2100?*), most people chose the higher estimates (Over one meter: 25.5%; Between 60 cm and one meter: 24.4%, Don't know: 23.5%). The results for the Loire estuary were around the same, with a slight tendency towards a lower estimate than for the global rise, for example 5.7% of respondents chose less than 20 cm for the global rise compared to 7.3% for the estuary. In broader terms, 58% of respondents were worried about SLR while 64% did not feel personally vulnerable (Fig. 5).

This apparent contradiction can be illustrated another way by comparing feelings of exposure linked to the individuals' homes and communities (Fig. 6, *Do you feel your community is vulnerable to the rise in sea level?* and *Do you think your home is vulnerable to the rise in sea level?* 18.2% thought their community was under

<table><caption>**Fig. 3** Survey sample</caption><thead><tr><th colspan="4">Collected sample and theoretical sample</th></tr><tr><th></th><th></th><th>Sample collected %</th><th>Theoretical quota for the study area %<br>(Sample rate = number of questionnaires per parent population (INSEE, 2018))</th></tr></thead><tbody><tr><td rowspan="2">GENDER (n = 633)</td><td>Female</td><td>54</td><td>52</td></tr><tr><td>Male</td><td>46</td><td>48</td></tr><tr><td rowspan="5">AGE (n= 631)</td><td>[15; 29]</td><td>22.8</td><td>19.1</td></tr><tr><td>[30; 44]</td><td>21.8</td><td>23.6</td></tr><tr><td>[45; 59]</td><td>24.2</td><td>24.8</td></tr><tr><td>[60; 74]</td><td>22.9</td><td>21.2</td></tr><tr><td>≥ 75</td><td>8.1</td><td>11.5</td></tr><tr><th colspan="4">Additional information about the sample</th></tr><tr><th></th><th></th><th>Sample collected %</th><th>Percentage figure for the study area (INSEE, 2018)</th></tr><tr><td rowspan="8">Socio-professional category (n = 633)</td><td>Farm worker</td><td>0.3</td><td>0.7</td></tr><tr><td>Artisan, merchant, business owner</td><td>8.9</td><td>3.1</td></tr><tr><td>Executive or professional</td><td>8.9</td><td>6.2</td></tr><tr><td>Manager or professional</td><td>11.7</td><td>15.5</td></tr><tr><td>Employee</td><td>25.1</td><td>17.2</td></tr><tr><td>Worker</td><td>7</td><td>17.4</td></tr><tr><td>Retired</td><td>25.5</td><td>26.5</td></tr><tr><td>Not working</td><td>12.5</td><td>13.4</td></tr><tr><td rowspan="3">Housing</td><td>Owner</td><td>60</td><td>74.8</td></tr><tr><td>Tenant</td><td>27.1</td><td>23.6</td></tr><tr><td>Free accommodation</td><td>13</td><td>1</td></tr><tr><td rowspan="2">Primary or secondary housing</td><td>Primary</td><td>97.6</td><td>85.4</td></tr><tr><td>Secondary</td><td>2.4</td><td>4.5</td></tr></tbody></table>
Is your home exposed to a risk?

<figure><img src="image_7.png" /><figcaption>**Fig. 4** Cross-analysis of the question on personal exposure applied to inland flooding, marine submersion, industrial and erosion risks</figcaption></figure>

immediate threat, while 17.8% thought their home would never be under threat, and 20.9% thought it would only be under threat after 2100. Logically, there is a significant relation between feeling of exposure to SLR and housing exposure (n = 630; p-value = < 0.01; chi² = 121.90; df = 20.00;) and of the community (n = 630; p-value = < 0.01; chi² = 72.02; df = 20.00). At the heart of this relationship are those individuals who do not feel at all exposed to SLR and believe that their commune or dwelling will never be affected by SLR (78% for the commune and 69% for the dwelling), or those who think it will happen within 100 years (52% for the commune and 54% for the dwelling). Conversely, 24% of those surveyed who felt quite exposed to SLR felt that their commune could be affected immediately, and 50% of these individuals felt that their home could suffer the same fate in the same timeframe. Also, 28% of these people think that their home could be affected within 10 years.

Individuals at the two extremes of the response modalities (“strongly agree” and “strongly disagree”) consider the exposure of their living space according to the most distant response modalities: “never” and “within 100 years” for those who do not feel exposed, and “as of now” and “within 10 years” for those who do feel exposed. The results suggest that the “within 50 years” category for the commune and for the home is more frequently selected by individuals with a more measured sense of exposure. This is especially the case for exposure to housing, where 30% of those surveyed who feel rather not exposed to SLR believe that their home could be affected within 50 years.

The respondents were therefore willing to concede the existence of SLR even in their own communities, but thought it was a threat for other people since the majority did not consider it a problem for themselves. The result can also be qualified with the significant numbers who

Worry and feeling of exposure in the face of SLR

<figure><img src="image_8.png" /><figcaption>**Fig. 5** Worry and feeling of exposure to sea level rise</figcaption></figure>
<figure><img src="image_9.png" /><figcaption>**Fig. 6** Cross-analysis of the question relating to home and municipality exposure at various horizons</figcaption></figure>

opted for the average category of within 50 years: 33.9% for municipality exposure and 31.7% for home exposure.

### 3.1.3 Attachment to the community and feeling of exposure

One of the objectives of the survey was to characterize inhabitants' sense of belonging to the place where they live, to determine whether it affected their feeling of vulnerability. Attachment to the community can be assessed by the level of agreement with various assertions (Fig. 7). The results reveal that the respondents were closely attached to their communities.

A strong relation was observed between 'feeling of exposure to SLR' and 'attachment to the community': *I like living in this neighborhood/village (n= 627; p-value = < 0.01; chi² = 36.23; df = 16.00); I am attached to this neighborhood/village (n= 626; p-value = < 0.01; chi² = 37.98; df = 16.00); I would regret having to move to*

*another neighborhood/village (n= 626; p-value = 0.03; chi² = 28.02; df = 16.00); When I leave my neighborhood/village for a while, I want to go back there (n= 625; p-value = < 0.01; chi² = 35.50; df = 16.00).*

Within this relationship, 46% of individuals who think they would miss their neighborhoods or towns if they moved do not feel at all exposed to SLR, as do 46% of individuals who say they are completely attached to their place of life, and 48% of individuals who would like to return to their place of life after having left it for a while.

## 3.2 Understanding the coastal and fluvial risks in the estuary

### 3.2.1 Natural and industrial spaces, an estuary more hypothetical than real?

To characterize the relationship that local residents have with the estuary, they were asked to give three words

<figure><img src="image_10.png" /><figcaption>**Fig. 7** Agreement with assertions characterizing attachment to the community</figcaption></figure>
that came into their minds when they heard the phrase *Loire estuary*. The words given were sorted and ranked in either first, second or third place. Those ranked in first place were most commonly related to nature, with a total of 217 references to the river, the sea, the mud, or the fauna. The second most common association was the Saint-Nazaire Bridge, a symbolic structure that links the two sides of the river mouth. Port industry was in third place, with many references to the various economic activities. More generally there were many references to the downstream area of the estuary (e.g. port, cruise liners, beach, refinery: *n* = 175) but few references to the middle section (e.g. marshes: *n* = 33) and the upstream estuary (*n* = 5). The responses were mostly positive with regard to the Loire estuary ('pleasant' 'calm' beauty'), although some were more negative, referring to pollution and climate change.

The words ranked in second place followed the same trend as for the first, but with more verbatim references to the downstream area of the estuary and negative sentiments. The words ranked third related more to the leisure pursuits practiced around the estuary (suns Bathing, fishing, sailing, rambling; n = 56). Although relationships with the estuary mainly related to the natural spaces, few specific establishments were mentioned. References to the estuary as an economic area and place of production, on the other hand, were much

more specific. Relationships with the water and risks associated with it were rare ('risk' n = 6; 'rising water' n = 5; 'danger' n = 8), except where they related to the port activities and industries which the downstream area of the estuary is reputed for.

The estuary also appears to be a space that is little-visited area and in some cases not very well known, at least according to an interpretation of the responses to the question on knowledge and use of the symbolic places on the Loire estuary (Fig. 8). With the exception of the Martinière Canal, known historically as a pleasant place for walks, and the cycle route that runs along the south bank of the river, there are few places that are both well known and well used.

### 3.2.2 Exposure of the estuary; coast and marshland

Verbatim references in response to the open question *Do you think some places on the Loire estuary will be less affected by the sea level rise than others?* may help to understand how the spatial risk is distributed in people's minds (Fig. 9). Three types of space overall were referred to directly as being especially vulnerable to SLR. First of all the 'seashore' or coastline, mentioned by 16% of the sample, followed by Brière marsh (9.2%) and finally the banks of the Loire estuary (8%). The association with the coast was also found in the most frequently cited cities, with Saint-Nazaire (9.7%, followed by

<figure><img src="image_11.png" /><figcaption>**Fig. 8** Knowledge and visit of symbolic places on the estuary</figcaption></figure>
<figure><img src="image_12.png" /><figcaption>**Fig. 9** Word cloud of the places on the estuary most affected by SLR for survey respondents</figcaption></figure>

Saint-Brévin-les-Pins, 6.5%) and Donges (3.1%). Activities and environments were also mentioned, primarily the port activity (3.5%) and marshes (7.4%). This latter observation may be linked to the very specific perception of the Brière region as a marshland which is frequently inundated and closely associated with the Regional Natural Park. This being the case, not only does the'maritime dimension' of the space, in the sense of 'the relationship that local people have with the sea, as reflected in their preferences, images and collective perception in particular' seem to be the most powerful risk factor, but the marshes are more a source of concern than the estuary itself because they are low-lying areas.

### 3.2.3 Effects of elevation and distance on the feeling of exposure to fluviomarine risks

To find out whether the relationship with the estuary and its environment affect the perception of fluviomarine risks, it is worth exploring how local residents imagine their own situation in the estuary through questions on elevation and distance, such as *At what elevation do you think your home is situated? How far from the Loire estuary do you think your home is?*

There was a strong relation between the elevation variable and the feeling of vulnerability to SLR (n = 630; *p*-value = < 0.01; *chi*² = 39.94; df = 16.00) the risk of marine submersion (n = 631; *p*-value = < 0.01; *chi*² = 57.90; df = 8.00). Several significant contributions to the chi-square statistic were observed when response categories were cross-referenced, including 55% of people who think they live more than 10 m above sea level, and 34% of people who say they live at sea level, do not feel exposed to SLR. In this respect the link between the feeling of exposure to marine submersion and estimation of elevation is even more marked: 86% of people who don't feel exposed to the risk of flooding say they live between

5 and 10 m above sea level, and 91% live above 10 m. Conversely, 41.5% of people who feel exposed to this risk think they live at sea level, and 25% between 1 and 5 m. The results suggest a link between perception of altitude and feelings of exposure to water-related coastal hazards; those above 5 m feel they are in danger.

The accuracy of elevation estimates was further assessed by cross-referencing the perceived elevation and the actual elevation determined for the respondents' locations. The estimates were then used to identify a potential relationship between the perceived space and risk perception. Several significant relationships were noted with elevation estimate (good estimation, overestimation and underestimation), in particular with the feeling of exposure of the home (n = 632; *chi*²: 44.521; *p*-value: 0.002; df: 21) and the community (n = 632; *chi*²: 41.676; *p*-value: 0.005; df: 21) to sea level rise, and also to the risks of submersion (n = 631; *chi*²: 29.974; *p*-value: 0.00003; df: 6) and flooding (n = 630; *chi*²: 26.532; *p*-value: 0.00001; df: 6).

Individuals who estimated their home to be over 10 m in elevation were therefore mostly accurate (n = 96); these were mainly people who lived in Britain ridge and the Guérande hills, the places of marked relief in the estuary. A large proportion (n = 123) who estimated they lived at a low elevation of 1 to 5 m were actually higher than they thought. These respondents were distributed evenly across the estuary although in greater concentrations downstream. Finally, some individuals who thought their homes were higher than 10 m overestimated the elevation (n = 33). These respondents were concentrated in the low-lying areas of Saint-Nazaire; areas reclaimed from the sea (Fig. 10). These observations could testify to the influence that perception of the estuary has on the feeling of exposure within a space that is known and used.
<figure><img src="image_13.png" /><figcaption>**Fig. 10** Perception of home elevation in the Loire estuary</figcaption></figure>

Finally, an example of distance estimation between
home and estuary to complete the section on relation-
ship between feeling of exposure and spatial percep-
tion. Although distance is closely correlated with the
feeling of exposure to SLR (n = 629; p-value = 0.04;
chi² = 31.94; df = 20.00), it is even more related to the
feeling of exposure to marine submersion (n = 630;
p-value = < 0.01; chi² = 93.90; df = 10.00). The relation-
ship between the sense of proximity to the estuary and
exposure to marine submersion is evident when you
look at the contributions to the chi square statistic,
both for respondents who thought they were close and
exposed (less than 500 m) and those who thought they
were distant and safe (between 5 and 10 km: n = 89;
94.7%; over 10 km). Thus, 37.5% of people who think
they are less than 500 m from the shore feel exposed to
marine submersion, while 95% of those between 5 and
10 km and 97% of those more than 10 km away feel safe.
However, these perceptions can sometimes be mislead-
ing for two reasons: 1) it is not always easy to evaluate

distance (significant margin of error in estimates above
5 km); 2) the morphology of the estuary means that the
risk can extend a long way inland, so those who think
they are far from the shore and therefore safe may actu-
ally be susceptible to risk.

3.3 Adaptation strategies and solutions for estuary inhabitants

3.3.1 Poor knowledge of coastal risk management
   and prevention tools

The people surveyed had relatively limited knowl-
edge of risk management and prevention tools; only
32% of individuals were aware of the existence of the
Coastal Risk Prevention Plan (PPRL)—the regulatory
document governing coastal risks in France, and 30%
didn't know if their homes were covered by the plan.
Others had misunderstood, erroneously believing the
PPRL didn't concern them (32% answered'my home is
involved'and 38% answered'my home is not involved').
For those who claimed to be familiar with the PPRL,
it was generally seen as a predominantly restrictive tool for development (73.8%), with no public consultation (47.5%), but nonetheless useful (71.3%). In addition, only 10% of respondents were aware of the PCS (Municipal Safeguard Plans), which are local prevention tools at municipal level. The purpose and objectives of the document were largely unknown, with 26.4% of individuals answering 'Don't know'.

### 3.3.2 Everything except doing nothing?

To address the issue of solutions for adapting to sea level rise (*Are these adaptation measures effective*?), none of the proposed measures stands out clearly from the rest, except for nature restoration which is clearly considered more effective than the others (76.8%). Other solutions such as dykes, adapting architectural elements of buildings and relocating housing and infrastructure were also considered effective in a quasi-similar way, with 63.4%, 61.2% and 61.8 respectively. Nature based solutions were sometimes more challenging (42% 'not effective' for dunes and 16.7%'don't know' for salt marshes and wetlands). 94.1% of the sample considered it the government's responsibility to implement solutions, followed by local authority responsibility: 92% regional, 89.8% department and 88.5% municipality.

On the broader scale of adaptation strategies (Fig. 11: Which scenarios do you consider most effective for the Loire estuary?), there is a clear necessity to act (53.8% considering 'Do nothing' not to be an effective strategy), the 'maintain' and 'relocate' solutions were seen as equally effective (51.7% and 49.2%, respectively).

Despite the uniformity, an open-ended question (Fig. 12) provided more insight into the choices of certain individuals. In the case of 'maintain', the answers referred to the speed, practicality, reliability and popularity of the strategy; for 'relocate', there was a sense of powerlessness in the face of nature, the need for a solution on a grand scale or a long-term obligation; for 'do nothing' it was the absolute need to protect assets and interests.

### 3.3.3 Old residents and new arrivals: between relocation, non-intervention and maintenance, each to his own strategy

37% of the respondents in the sample had been living in the area in which their community was located for less than 10 years, and 37.8% moved into their present home within the same period. Length of residence and length of time in the commune ("How long have you lived in your dwelling?"; "How long have you lived in your commune?") are two variables that have a highly significant

## The evaluation of the effectivity of adaptation scenarios in the estuary

<figure><img src="image_14.png" /><figcaption>**Fig. 11** Cross-analysis of perceived relevance of adaptation scenarios: Supporting assets with solid infrastructure; Allowing nature to take its course and unhindered evolution of the coastline; Moving assets and relocating properties, infrastructure and people</figcaption></figure>
<table><caption>Fig. 12 Issues referred to in response to the question 'Can you tell me why you prefer this scenario?'</caption><thead><tr><th rowspan="2">Respondent's Positioning<br>Exemplary Arguments Representing a Corrosion<br>Proposed strategies</th><th colspan="3">Preferred Strategy</th><th colspan="3">Rejected Strategy</th></tr><tr><th>Practical and Philosophical arguments</th><th>Economic arguments</th><th>Temporal arguments</th><th>Practical and Philosophical arguments</th><th>Economic arguments</th><th>Temporal arguments</th></tr></thead><tbody><tr><td>Maintaining<br>solid structures with dikes, groins, etc.</td><td>"Efficient and swift, unlike other solutions."<br>"Avoiding relocation and preserving/protecting residences."<br>"Already proven, has been in existence for a long time."<br>"A solution widely accepted by the population."</td><td>"The least costly scenario, cheaper than paying compensation."</td><td>"Effective, especially in the short term."</td><td>"Inability to maintain, it's shifting."<br>"The solution has its limitations, as observed during Xynthia."</td><td>"Costly solution."</td><td>"A solution that is only temporary."</td></tr><tr><td>Do nothing<br>Allowing natural progression, non-intervention</td><td>"The nature does things well."<br>"Nature is stronger than us, and it always reasserts itself."<br>"Simple to implement."</td><td>"It's the least expensive option."</td><td>"The only remaining solution because it's too late to take action."<br>"It's necessary to let things happen now to anticipate rising sea levels."</td><td>"It is essential to protect both properties (residences) and interests (employment, tourism), so it is impossible and inconceivable to let nature take its course."</td><td>-</td><td>-</td></tr><tr><td>Relocate<br>Move goods, infrastructure, and people to a new location.</td><td>"There is no use in fighting, nature is stronger."<br>"The best way to avoid endangering human lives."<br>"The only large-scale solution to rising sea levels."<br>"Human beings have always migrated."</td><td>"Less costly than maintaining and upkeeping protective structures."</td><td>"Obligation in the long run."<br>"The only course of action because it's too late."<br>"The need to anticipate."</td><td>"Scenario too uncertain."<br>"Complicated to implement."<br>"Impossible to relocate everyone."</td><td>"Relocating is too expensive."</td><td>"A solution that is only temporary and does not address the underlying causes, does not resolve the issue."</td></tr></tbody></table>

relationship with the approval of certain adaptation strategies ("In the Loire estuary, which scenario seems most effective to you?").

There is a strong relation between length in residence and relevance of the 'relocate' strategy (chi²: 44.449; df: 24; p-value: 0.007). Based on cross-tab analysis, 42.5% of people living in their homes for over 50 years consider the "move" strategy to be "not at all" effective. 38% of people who have lived in their homes for less than a year consider the "move" strategy to be very effective. Up to 20 years in their dwelling, people find the "move" strategy fairly effective (33% of people living from 11 to 20 years) (Fig. 13).

The relation with relevance of the 'do nothing' strategy is also significant (chi²: 48.817; df: 24; p-value: 0.002). Indeed, above 20 years in residence, the results suggest that individuals tend to consider the laissez-faire strategy as effective or very effective. 1) 24% of people who have lived in their home for less than a year consider the "laissez-faire" strategy to be very effective; 2) 24% of people who have lived in their home for 1 to 10 years, and 21% of those who have lived there for 11 to 20 years, consider the "laissez-faire" strategy to be fairly effective.

Finally, in terms of length in residence and the 'maintain' strategy (chi²: 36.603; df: 24; p-value: 0.048), 59% of people who have lived in their homes for between 41 and 50 years consider the maintenance strategy to be very effective.

On a broader scale, these results show a similar tendency the same results for length of time in the

commune. For example, length of time in the commune and the relevance of the maintain strategy (chi-square: 20.649; ddl: 8; p-value: 0.008), where 44% of the oldest residents (who have lived in the commune for over 20 years, n = 147) find the maintain strategy very effective. Overall, the results suggest that newcomers to the community (ranging from a few months to 10 years, n = 236/633) and to their homes (from a few months to 10 years, n = 327/628) are more inclined toward strategies of 'adapting to the situation' or relocating assets.

## 4 Discussion

The results of this survey indicate that the risks of inland flooding and marine submersion cause very little personal concern in the estuary, although many individuals appear to be informed about climate change. Down-playing the risks of submersion in this way, or projecting them into the remote future, is a common phenomenon (Lorenzoni et al. 2007), and in a broader sense, individuals tend to under-estimate the risks that affect them (Weinstein 1989). These results, however, can also be linked to the length of time since the last occurrence of these major events. In contrast to other studies chronicling recent, significant risk events (Chadenas et al. 2023), the Loire estuary has experienced no major events recently; significant floods on the Loire, such as the one in 1910, are a distant memory, and Storm Xynthia in 2010 caused a certain amount of damage in Saint-Nazaire and Lavaus-Loire but there were no casualties. The relatively small-scale nature of submersion-flooding events could
<table><thead><tr><th rowspan="2">% in rows<br>The remaining percentages in rows are IDK</th><th colspan="4">Relevance of the relocation strategy</th><th colspan="4">Relevance of the do nothing strategy</th><th colspan="4">Relevance of the maintain strategy</th></tr><tr><th>--</th><th>-</th><th>+</th><th>++</th><th>Tot - IDK</th><th>--</th><th>-</th><th>+</th><th>++</th><th>Tot - IDK</th><th>--</th><th>-</th><th>+</th><th>++</th><th>Tot - IDK</th></tr></thead><tbody><tr><th rowspan="7">Length of time in residence</th><th>&lt;1 year</th><td>18%</td><td>14,5%</td><td>20%</td><td>38%</td><td>90,5%</td><td>34%</td><td>18%</td><td>12%</td><td>24%</td><td>88%</td><td>19%</td><td>17%</td><td>27%</td><td>25%</td><td>88%</td></tr><tr><th>1-10 years</th><td>11%</td><td>22%</td><td>31%</td><td>25%</td><td>89%</td><td>23%</td><td>24%</td><td>24%</td><td>23%</td><td>94%</td><td>17%</td><td>21%</td><td>29%</td><td>27%</td><td>94%</td></tr><tr><th>11-20 years</th><td>16%</td><td>18,5%</td><td>33%</td><td>20%</td><td>87,5%</td><td>39%</td><td>17%</td><td>21%</td><td>11%</td><td>88%</td><td>12%</td><td>18%</td><td>23%</td><td>35%</td><td>88%</td></tr><tr><th>21-30 years</th><td>16%</td><td>20%</td><td>22%</td><td>27%</td><td>85%</td><td>38%</td><td>27%</td><td>9%</td><td>11%</td><td>87%</td><td>16%</td><td>19%</td><td>26%</td><td>27%</td><td>88%</td></tr><tr><th>31-40 years</th><td>18%</td><td>24,5%</td><td>12%</td><td>37%</td><td>91,5%</td><td>39%</td><td>24%</td><td>8%</td><td>21%</td><td>92%</td><td>15%</td><td>22%</td><td>14%</td><td>42,5%</td><td>93,5%</td></tr><tr><th>41-50 years</th><td>9%</td><td>18%</td><td>31%</td><td>28%</td><td>86%</td><td>46%</td><td>28%</td><td>3%</td><td>5%</td><td>82%</td><td>16%</td><td>0%</td><td>10%</td><td>59%</td><td>85%</td></tr><tr><th>&gt;50 years</th><td>42%</td><td>38%</td><td>10%</td><td>3%</td><td>93%</td><td>56%</td><td>12%</td><td>7%</td><td>22%</td><td>97%</td><td>6%</td><td>22%</td><td>14%</td><td>55%</td><td>97%</td></tr></tbody></table>

<table><thead><tr><th rowspan="2">Length of time in commune</th><th>New arrivals (&lt; 10 years)</th><th>15%</th><th>17%</th><th>23%</th><th>36%</th><th>91%</th><th>26%</th><th>20%</th><th>17%</th><th>28%</th><th>91%</th><th>18%</th><th>20%</th><th>27%</th><th>25%</th><th>90%</th></tr><tr><th>Residents for 10-20 years</th><td>15%</td><td>18%</td><td>29%</td><td>25%</td><td>87%</td><td>38%</td><td>20%</td><td>17%</td><td>11%</td><td>86%</td><td>13%</td><td>18%</td><td>26%</td><td>29,5%</td><td>86,5%</td></tr><tr><th>Older residents (&gt; 20 years)</th><td>20%</td><td>21%</td><td>20%</td><td>28%</td><td>89%</td><td>44,5%</td><td>21%</td><td>8%</td><td>14%</td><td>87,5%</td><td>16%</td><td>14%</td><td>17%</td><td>44%</td><td>91%</td></tr></thead></table>

Non-significant relationship Relationship that contributes most to Chi2

<caption>**Fig. 13** Table of bivariate relationships between length of time in housing and commune with coping strategies. Reading: 24% of people who have lived in their home for less than a year consider the "do nothing" strategy to be effective</caption>

explain this down-playing of the risk, just as their occurrence sometimes explains overestimation (Wachinger et al. 2013). Experiencing such an event alters the perception (Lujala et al. 2015) and can therefore vary between places and communities (Brilly & Polic 2005; Zinda et al. 2021); when a place is not often affected by events such as these, they are perceived as unimportant. But while the memory of risk events, including both absence and presence of them, and both memory and reality, is often a key element (Bickerstaff & Simmons 2009), [...]"the problem is often not simply a lack of awareness of local risk [...], but rather an assessment of such risk that underestimates the impact of rare, extreme events"(Burningham

et al. 2008, p. 20). The submersion risk is perceived as particularly unimportant, and in Saint-Nazaire the perception is also influenced by episodes of urban flooding linked to a rainwater drainage system which is too small for the purpose, and this has become part of the collective memory in recent years. It is possible that the people of Saint-Nazaire are conflating the two phenomena based on this recent memory.

These mental strategies for processing information that is 'under one's nose' (Hermand & Chauvin 2008) are often the result of cognitive bias, which leads people to project the risk onto others. Individuals may thus tend to either shift the risk to another nearby place, nominating
some district or village close to their own, or to a place further away, nominating some distant or foreign location as opposed to the place where they live (Flanquart 2016). The bias is toward optimism; individuals shift the risk onto other communities, who in turn do the same. In this survey, the risk is transferred to another nearby place—from the individual's home to the municipality. For the sample, however, SLR is just as much a local concern as a national one. This effect should be considered in the context of the spatial nature of the feeling of exposure: this feeling when linked with a sense of powerlessness (Uzzel 2000) tend to diminish as the territorial scale broadens (Navarro & Michel-Guillou 2014).

Another element to take into consideration is the uncertainty surrounding climate changes such as sea level rise. Uncertainty about the source of a risk can lead to a general underestimation of the risk; uncertainty where there are multiple risks in particular may even provoke a sense of powerlessness that may inhibit people's impulse to act (Wachinger et al. 2013; Lammel, 2015). The feeling of powerlessness is partly linked to knowledge but also to the complexity of the phenomenon and the geographical area concerned. Where the uncertainty is great, individuals are sometimes inclined to do nothing (Flanquart 2016), but uncertainty can also lead to the precautionary principle (Chevassus-au-Louis 2007) which leads 'risk-averse' individuals (Peretti-Watel 2000, p. 73) to implement all the possible solutions and strategies simultaneously, which is more the case with this sample.

The reason for the strong perception of industrial risk in relation to other types of risk could be in the way the respondents view the Loire estuary, since they mainly associate it with industrial activity (84.3% agree or partially agree that the estuary is characterized by industrial activity and 71.8% by natural spaces). The perception of the estuary as an industrial area seems to influence the perception of risk. The influence of industrial port landscapes is well-known in estuaries (Bonnet et al. 2012), possibly due to the imposing presence of certain facilities such as the Donges refinery and the Saint-Nazaire shipyards. On port property alone, 1,460 hectares are given over to industry, with a total of 756 installations and buildings, 55 km of roads, 35 km of railway lines and 12 km of quays. This also prompts reflection on the weight of spatial representations in the assessment of the risks and their prioritization, and also perceptions, material presence and the influence of visuals:"[...] the material presence itself — form, shape, texture, including relative normality or invisibility — may affect people and their sense of place, whether in positive or negative ways. (Bickerstaff and Simmons 2009, p.7). This perception of industrial risk, however, could also be based on the local economic and social context; the port of Saint-Nazaire

employs around 28,500 people. In terms of fluviomarine risks, we know that the local significance attached to bodies of water, whether rivers, lakes or the ocean, can be linked to how the risks related to water are perceived (Quinn et al. 2019). In other words, the local perception of water can influence the acceptance or rejection of certain risk management strategies or solutions. Given the absence of images linked to water-related risks, the negligible sense of exposure to the risk and limited assimilation of adaptation solutions is not surprising.

In relation to spatial influence variables, individual perceptions of the home elevation are equally important in determining a feeling of exposure. Little study has been done on elevation (Navarro et al. 2021) but it seems to attest to the way the estuary is perceived in the minds of certain individuals, especially in low-lying areas. For those who overestimated their elevation, a sense of immunity was observed that could stem from a spatial relationship influenced by the presence of structures on the landscape, such as dykes and embankments (Ludy & Kondolf 2012; Bradford et al. 2012). This is the case in Saint-Nazaire, for example, where the old hydraulic connections between the marsh and the estuary have now been backfilled. In terms of distance estimation, the survey results tend to agree with the literature (O'Neill et al. 2016; Coquet et al. 2018): the further from the coastline, the more the feeling of exposure diminishes, and the relationship between marine submersion risk and the 'maritime dimension' is unclear in the estuary—are maritime influences sufficiently ingrained in the collective imagination that estuary inhabitants can identify the issues and risks? The implication in the results is that the estuary is not strongly associated with the maritime perspective, so it would appear essential to disseminate basic geographical knowledge about the estuary—its low-lying morphology and maritime nature—so that local residents don't just discover the truth about their situation on the day a catastrophe occurs (Paulet 2002). These results demonstrate the importance of creating a “flood landscape” in areas where the source of the hazard may seem remote. Large estuaries are generally low-lying retro-littoral areas where submersion can travel several kilometers inland.

In the scientific literature, a number of authors mention time spent at home and in the community, and also age, as having a major influence on decisions (Altman & Low 1992; Scannell & Gifford, 2010; Bonaiuto et al., 2016; Gotham, et al. 2017; Navarro 2022). This phenomenon is noted particularly in individuals who have recently moved into the area; they are more concerned because they are not yet familiar with their environment (Philippenko et al. 2021): “The ability to recognize and read such clues takes time and is a skill that new residents in particular are likely to lack” (Burningham et al. 2008, p.
20). In line with this, it can be asserted that attachment to place (Hidalgo & Hernández, 2001) has genuinely influenced the perceptions observed in this sample, in terms of asset relocation in particular. Long residence in the area correlates with a stronger attachment to the community and is often associated with reluctance to relocate. This form of attachment to place is known as 'rootedness' (Lewicka 2011). It seems then that attachment may be a key variable in understanding 'resistance to change' [...] and [...] the 'role played by territorial objects' [...] (Sebastien 2016) in the context of territorial reorganization prompted by climate change and the corresponding projects (Devine-Wright, 2009).

## 5 Conclusion

The results of this survey show that a large proportion of estuary inhabitants are aware of the environmental issues. The individuals in the sample were not experts, but they were able to visualize the possible adaptation strategies. In order to shed more light on the social acceptance of adaptation strategies and solutions in an estuarine context, it would be useful to deepen this research by studying new explanatory factors and by applying it to others estuaries. Many of these individuals, however, did not feel that fluviomarine risks concerned them; the challenge is therefore about engendering concern rather than informing.

While some influencing factors concerning the approach to perception of risk on the coast and inland are documented in the literature, certain estuary-specific factors nonetheless stand out. These specific factors can be defined by a number of elements characteristic of the area, such as the dominating industry, the landscape being at low elevations which is sometimes unperceived by residents, and the scant history of flooding and submersion. But it is also essential to highlight the absence of a risk management policy for the intermediate section of the estuary, between the metropolitan area of Nantes and the river mouth. Will the recent work on hazards in the estuary, which began in 2021, provide an opportunity to initiate discussions on fluviomarine risks between stakeholders and estuary residents? In some places the dialogue has already begun, with various reflections on the subject of adaptation of the estuary's assets, such as the decommissioning of the dyke at Corsept and a competition to design a submersible area in Saint-Nazaire. Will this help to establish the Loire estuary as a recognized territory (Menard 2009)? Since there is no specific adaptation strategy for estuaries and scant consideration of them in scientific research projects, this survey of the perception of coastal and fluvial risks in the downstream area of an estuary meets a significant need: to raise the profile of estuarine issues, which are at the interface between sea and land, and also between the inhabitants and the territorial stakeholders.

## Authors' contributions

Design, supervision, processing and writing by Florian Drouaud. Design, proof-reading by Céline Chadenas. Processing assistance by Marine Giraud.

## Funding

Agence d'urbanisme de la région de Saint-Nazaire; Pôle Métropolitain de Nantes-Saint-Nazaire; UMR LETG CNRS 6554.

## Data availability

Not applicable.

## Declarations

### Ethics approval and consent to participate

The survey presented in this study is anonymous. Respondents to the questionnaire answer questions only if they volunteer to do so ("By continuing, do you agree to answer this questionnaire?"). The information collected is reserved for use by the Nantes University. In accordance with the amended "informatique et libertés" law of 1978 and the General Regulation on Data Protection (RGPD) which came into force in 2018, any person may obtain communication and, where appropriate, rectification or deletion of information concerning them, by contacting the person in charge of the survey. The Data Protection Officer (DPO) of the Nantes University will be kept informed of this request. Any person may also, for legitimate reasons, object to the processing of data concerning him or her.

## Competing interests

Not applicable.

Received: 15 November 2023 Revised: 30 April 2025 Accepted: 2 May 2025

Published online: 19 May 2025

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