1At the junction between terrestrial and aquatic environments (Leuthold et al., 1997), lake shorelines are constantly evolving due to the action of erosion and sedimentation (Touchart, 2000). Erosion is the more active. Shaping occurs as a result of natural (primarily water), and anthropogenic processes (Maleval and Astrade, 2003). Human pressure is a predominant factor in erosion processes (EROSEE, 2006), leading to generalised degradation of lake shorelines Europe-wide (Rottillon, 1996). To protect their activities and developments, inhabitants have sought to bolster lake shorelines by building protective structures. For this reason, only a small number of lake shorelines in densely populated regions of Europe have remained in a more or less natural state (Ostendorp et al., 2004). However, bolstering shorelines increases the erosion of the surrounding natural shorelines by wave reflection (Dittrich and Westrich 1988; Tait and Griggs, 1991). Because erosion triggers a whole range of environmental (e.g. on coastal flora and fauna), economic and social (e.g., recreational activities) effects, a debate on the protection and restoration of lake shorelines has emerged (Paquette, 2010).
2The Haute-Savoie town of Thonon-les-Bains borders the southern shore of Lake Geneva (fig. 1A) with a shoreline of approximately 8.5 km (fig. 1B). It constitutes an environmental legacy that is essential to quality of life and the local economy (landscape, sport, tourism, etc.). Nevertheless, the upheavals caused by activities and developments have often resulted in significant erosion linked to a sediment deficit (Maleval et al., 2016). Over the years, this deficit resulted from a mountain land reclamation policy (afforestation), the construction of hydroelectric dams and dykes for flood protection (Pourriot and Meybeck, 1979), and sediment extraction activities at the mouth of the Dranse on Lake Geneva (Maleval et al., 2016). Faced with this detrimental situation, the municipality of Thonon-les-Bains chose to renaturalise its Lake Geneva shoreline, including it in the CIPEL Action Plan 2011-2020 "Preserving Lake Geneva, its banks and rivers today and tomorrow" (2010). This plan recommended renaturalising the banks of Lake Geneva to increase the proportion of natural or semi-natural environments and improve the development of seagrass beds, a shoreline’s natural protection. Today, renaturation appears necessary as only 2% of the lake shoreline is preserved in its natural state (e.g., presence of reed beds), 26% is close to a natural state (forests, shores, etc.), while more than 60% is artificial.
3The purpose of this article, after a description of the Thonon-les-Bains coastal protection measures and their geomorphological effects, is to show that when public decision-making is based on respect for the natural functioning of a lake shoreline, it is possible to safeguard it in certain cases.
Fig. 1 - Location map of the study area.
Fig. 1 - Carte de localisation de la zone d’étude.
A: Location of Thonon-les-Bains; B: Geography of the shoreline of Lake Geneva. a. Dranse delta; b. The restored section of Ripaille; c. The site of spurs. The communal area is marked to the north by the Dranse (at the border between Publier and Thonon-les-Bains) and to the South by le Pamphiot (between Thonon-les-Bains and Anthy-sur-Léman). The 60% public-owned shore-side land comprises of both developed and undeveloped shorelines.
A : localisation de Thonon-les-Bains ; B : géographie de son littoral lémanique. a. Delta de la Dranse ; b. Le tronçon restauré de Ripaille ; c. Le site des épis. Le littoral communal est marqué au Nord, par la Dranse (limite entre Publier et Thonon-les-Bains) et au Sud par le Pamphiot (entre Thonon-les-Bains et Anthy-sur-Léman). Les terrains riverains du lac, publics à hauteur de 60 %, sont constitués à la fois de littoraux exempts d’aménagement et de littoraux urbanisés.
4The restoration measures decided by Thonon-les-Bains municipality were proposed following the shoreline diagnosis carried out from 2011 to 2014 (Maleval et al., 2016).
5"In the Lake Geneva region, the predominance of waves caused by prevailing winds leads to a coastal drift towards the West or South-West along the Savoie shoreline" (Touchart, 2002). This drift, highlighted by Maleval and Destombes (2016), has a NE-SW trajectory on the Thonon shoreline, naturally redistributing sediment carried by the Dranse. However, this natural process has been disrupted since 1922 by the extraction of aggregates at the mouth of the river, the littoral drift eroding the Thonon shoreline. Osterdorp et al. (2006) also observed sediment deficit on the Lake Constance shoreline due to sand extraction. Consequently, sediment extraction in the subaqueous delta of the Dranse had to stop, to mitigate this hydrogeomorphological process (Maleval et al., 2016). Indeed, each year, the company Sagradranse removes on average 52,000 m3 of sediment, while the Dranse deposits around 30,000 m3 (Buffin and Fourcade, 2011). These disproportionately high volumes completed the records of the aquatic environments unit of the Direction Départementale des Territoires de la Haute-Savoie, the county-level territorial agency (DDT 74). Their records included environmental studies, particularly one casting doubt on the usefulness of extraction in terms of risk management, and of their suitability in a nature reserve. The Prefecture therefore decided not to renew the permit to extend aggregate extraction for the period 2017-2022. This decision was based on decree no 2006-798 of July 6, 2006, of the Mining Code (2006), and decree no 2007-1760 of December 14, 2007, of the Environmental Code (2007). Dredging operations ceased in April 2016 (Lacrampe, 2016).
6The estate of the Château de Ripaille is separated from the shoreline by an old stone wall 1.6 km long (fig. 1). Over a 17 m stretch (fig. 1), the shoreline is severely eroded by people using the path, but also by ravine and lake erosion (fig. 2A-B). In fact, to avoid further degradation that could lead to the wall collapsing, this section was refurbished in 2016-2017 applying eco-engineering techniques (fig. 2C). This involved combining riprap and vegetation when planting alone is not sufficient to protect and stabilise a shoreline (Office québécois de la langue française, 2010). These techniques have less impact on the landscape (fig. 2D), as it provides a planted transition between the aquatic and terrestrial environments (Verniers, 1995), unlike hard landscaping which breaks the ecological continuum (EROSEE, 2006). Vegetation also protects the shoreline against wave damage (Gagnon and Gangbazo, 2007). A feasibility study was carried out by a consultancy firm (Destombes, 2016) to determine the altimeter setting and the hydraulic and morphological stresses on the structure.
Fig. 2 - The restored section of Ripaille.
Fig. 2 - Le tronçon restauré de Ripaille.
A: photo of April 2016 (P.-B. Destombes); B: photo of November 2013 (V. Maleval). The falling tree (1) presents a protrusion of 1.7 m. Nevertheless, it would seem that the remains of the riprap structure (2), denoting an earlier shoreline, show even greater erosion; the trees located just at the back (3), protected until now, seem to corroborate this, especially as behind them a second path (4) has been trodden. This hypothesis, supported by the November 2013 photo which shows the presence of a lamina on the ground (5a) which, two and a half years later has become somewhat stripped (5b), is likely to disappear altogether. This analysis clearly shows that the development of hard protective structures without any other maintenance is not sufficient to stop erosion. Damage to the pathway can be observed by the presence of a tiny hillock (6), revealed tree roots (7) and the creation of micro-gullies (8), resulting from both footfall and water run-off. C: technical drawing. 1. Tree in the middle of the path: felling and stump removal; 2. Compacted of 30/70 earth/stone mix down to 30 cm; 3. Infill with the compacted 70/30 earth/stone mix; 4. Planting of the working area under geotextile sheet; 5. Biodegradable 740 gm/m2 geotextile sheet including anchor staples; 6. Bed of plants and sets; 7. Rocky structure; 8. Re-use of boulders in situ; 9. Public Fluvial Domain; 10. Highest waters: 372.62 m. D: photo of May 2017 (P.-B. Destombes). The refurbished shoreline presents a vegetalised rocky area on the surface with two tree species, grasses (70%) and flowers (30%), which are suitable to hydromorphic environments (willow, hedge maple, common dogwood, guelder rose, red fescue, birds foot trefoil, bladder campion, black medick, red clover, etc.). Root growth is designed to enhance the structural hold of the ensemble and, as a result of the shoreline. The pathway is located between the Ripaille wall and the wooden-slat fence which is there to direct (sometimes ill-disciplined) walkers. Certainly, nothing (from grains of sand to grasses) is naturally in its place and human activity controls their life cycle (Lespez and Dufour, 2020), but the shoreline has now been restored by renaturation.
A : cliché d’avril 2016 (P.-B. Destombes) ; B : cliché de novembre 2013 (V. Maleval). L’arbre basculé (1) présente une saillie de 1,70 m. Néanmoins, il semblerait que des reliques d’un enrochement (2), en marquant une position antérieure du trait de côte, révèlent une position encore plus prononcée ; les arbres situés juste en arrière (3), protégés jusqu’à présent, paraissent en témoigner, d’autant que derrière eux, un second parcours du sentier (4) est tracé. Cette hypothèse est appuyée par le cliché de novembre 2013 montrant la présence d’un lambeau de sol (5a) qui, deux ans et demi après, décapé (5b), est voué à totalement disparaître. Cette analyse montre bien que l’aménagement d’une protection en dur, sans autre entretien, ne suffit pas à contrer l’érosion. La dégradation du sentier est observable par la présence d’un micro-talus (6), de racines d’arbres mises à jour (7) et de la création de micro-ravines (8), résultat à la fois du piétinement et du ruissellement. C : schéma technique. 1. Abattage et dessouchage de l’arbre au milieu du sentier ; 2. Compactage du mélange terre/pierre 30/70 sur 30 cm ; 3. Remblai par un mélange terre/pierre compacté 70/30 ; 4. Ensemencement des surfaces travaillées sous le géotextile ; 5. Géotextile biodégradable de type 740 g/m2 et pose d’agrafes ; 6. Lit de plants et plançons ; 7. Cordon d’enrochement ; 8. Réutilisation des blocs sur place ; 9. Domaine Public Fluvial ; 10. Hautes-eaux : 372,6 m. D : cliché de mai 2017 (P.-B. Destombes). Le littoral restauré présente un enrochement végétalisé à sa surface par des espèces d’arbres, de graminées (70 %) et de fleurs (30 %), adaptées aux milieux hydromorphes (saule, érable champêtre, cornouiller sanguin, viorne obier, fétuque rouge, lotier cornuculé, silène enflé, luzerne lupuline, trèfle violet, etc.). Le développement des racines doit favoriser le maintien de l’ouvrage et, par conséquent, du littoral. Le sentier est situé entre le mur de Ripaille et la ganivelle destinée à canaliser les promeneurs (parfois peu disciplinés). Certes, « aucun élément (du grain de sable à la graminée) n’est à sa place naturellement et l’activité humaine contrôle leur cycle de vie » (Lespez et Dufour, 2020), mais le littoral est réhabilité par renaturation.
7As on many beaches, spurs were built during the 20th century to protect structures just behind the shoreline (one of the oldest is in front of the Château de Ripaille, visible on aerial images from 1927). Positioned perpendicular to the shoreline, they naturally retain sediments transported by the drift, and traps located between two spurs catch man-made sediments (fig. 3A). Once extraction at the mouth of the Dranse had ceased, Thonon municipality sought to facilitate sediment circulation by coastal drift by removing unnecessary spurs. The feasibility study (Destombes, 2018) looked at the general layout of the spurs and potential difficulties, and projected the consequences of their removal. This study focused on Châtaigneraie Park and the Ripaille wall shoreline (fig. 1), subject to a NE-SW drift (Maleval et al., 2016), disturbed by four spurs (spurs 3 to 6). This shoreline has a micro-cliff of about 60 cm but, some years, it can be protected by the deposition of pebble strips (Maleval et al., 2016). The study led to the removal of spurs 3 and 5, the materials of which (150 m3) were used to reinforce spur 6 (fig. 3B). This spur is located just downstream of the section refurbished in 2017 (fig. 3C). The purpose of the reinforcement is to provide aggradation to protect the planted vegetation while its root system develops and strengthens the shoreline.
Fig. 3 - Site of spurs removal and reinforcement.
Fig. 3 - Le site de suppression et de renforcement des épis.
A: photo from summer 2004 (CIPEL). Whilst the sedimentation deposit increases the size of the beach located upstream of the spur, the downstream part, deprived of most of the sediment, has contracted. B: aerial image. 1. Profile; 2. Removal; 3. Reinforcement; 4. Refurbished stretch. Most of the communal spurs were refurbished in the 1980s. The distance between spurs 3 and 4 is 55 m, and between 5 and 6, 68 m. The works to remove spurs 3 and 5 took 15 days in October 2018. Blocks strengthened spur 6 (L25 m x l4 m x h1.25 m) to reinforce the shoreline refurbished in 2017. The sediment deposited upstream of the removed spur was left in place to be naturally integrated into the lakeside drift. C: photo of October 2017 (P.-B. Destombes). Before it was reinforced using the removed spur materials, spur 6 was dilapidated through lack of maintenance.
A : cliché de l’été 2004 (CIPEL). Si le dépôt de sédiments agrandit la plage située en amont de l’épi, celle située en aval, privée de la majeure partie des sédiments, démaigrit. B : image aérienne. 1. Profil ; 2. Suppression ; 3. Renforcement. 4. Tronçon restauré. La plupart des épis communaux ont été aménagés dans les années 1980. La distance séparant les épis 3 et 4 est de 55 m, celle séparant les épis 4 et 5, de 68 m. Les travaux pour la suppression des épis 3 et 5 ont duré 15 jours en octobre 2018. Les blocs ont permis de renforcer l’épi 6 (L25 m x l4 m x h1,25 m) pour conforter le littoral restauré en 2017. Les sédiments déposés en amont des épis supprimés ont été laissés en place pour une reprise naturelle par la dérive littorale.
8Of Thonon’s 8.5 km shoreline (fig. 1), 3.8 km were studied; the rest being private and/or urbanised (e.g., the lake front of the Ripaille quay). To determine the morphological evolution of the shoreline, three measurement campaigns were undertaken: in 2011, 2014 and 2019 (fig. 4A). Topographic and bathymetric surveys were carried out on 47 transects (Maleval et al., 2016) (fig. 4B-C). All measurements (terrestrial and sublacustrine, for the three years) were georeferenced in Lambert 93 for processing in AutoCad and QGis software (fig. 4D). The Profile comparisons made it possible to determine the speed of change of the shoreline with Lake Geneva at its fullest (372.58 NGF), and to appreciate the changes in the shape of the micro-cliffs and beaches over the years (fig. 4E).
Fig. 4 - Methodological protocol of the study.
Fig. 4 - Protocole méthodologique de l’étude.
A: Characteristics of measurement campaigns; B: topographical measurements (P.-B. Destombes, April 2019); C: bathymetric measurements (Bathys); D: processing of data; E: typical profile to understand the lakeside evolution: erosion and sedimentation. The topographical profiles, with lengths between 19 m (profile 44) and 36 m (profile 42), were extended by bathymetric profiles, over 140 m on average from a boat using 3D echo-sounding (the time for the wave to come back allows depth to be interpreted). The processing of data showed the morphological tracing for each year.
A : Caractéristiques des campagnes de mesures ; B : mesures topographiques (P.-B. Destombes, avril 2019) ; C : mesures bathymétriques (Bathys) ; D : le traitement des données ; E : profil-type pour connaître l’évolution littorale : érosion et sédimentation. Les profils topographiques, d’une longueur comprise entre 19 m (profil 44) et 36 m (profil 42), ont été prolongés par les profils bathymétriques sur 140 m en moyenne, réalisés à partir d’un bateau grâce à l’échosondage 3D (le temps de retour de l’onde émise permet d’interpréter la profondeur). Le traitement des données a permis d’avoir le tracé morphologique pour chaque année.
9The effects of bringing an end to aggregate extraction are observable on the topographic profiles (3 years elapsed before the April 2016 to April 2019 measurement campaign). However, the same does not apply to the removal of the spurs, as only 5.5 months separated the works in October 2018 and the measurements in April 2019. Moreover, at that time of year, the lake water-level is low (from January to May, minimum level of 371.88 m; from June to December, maximum level of 372.58 m). The results are first presented globally (numerical table), then for the municipality (maps), and finally for the model (profiles).
10Table 2 illustrating coastal evolution from 2011 to 2019 shows a greater number of eroding stretches (22 out of 47) in the first period (2011-2014) than in the second (2014-2019). The shoreline retreat on the 16 stretches (out of 47) in the second period is less pronounced than in the first period. The highest value for 2014-2019 shows erosion of 2.2 m, or 0.44 m.yr (P19). For 2011-2014, the maximum erosion was 2.8 m, or 0.7 m.yr (P22). However, at the mouth of the Dranse (P1 and P2), where the evolutionary processes are much more fluvial than lacustrine (Maleval et al., 2016), the maximum retreat exceeded 20 m, i.e., 6 m.yr (P1).
Tab. 1 - The numerical results of the morphological evolution of the shoreline at Thonon-les-Bains.
Tab. 1 - Les résultats chiffrés de l’évolution morphologique du trait de côte de Thonon-les-Bains.
Shoreline evolution: negative figures = erosion more or less pronounced according to the shade of red; positive figures = sedimentation more or less pronounced according to the shade of blue. Annual speed of evolution: negative figures (white) = erosion; positive figures (grey) = sedimentation.
Evolution littorale : chiffres négatifs = érosion plus ou moins prononcée selon la teinte de rouge ; chiffres positifs = sédimentation plus ou moins prononcée selon la teinte de bleu. Vitesse annuelle d’évolution : chiffres négatifs (blanc) = érosion ; chiffres positifs (gris) = sédimentation.
11From a spatial point of view, the morphological evolution maps show that the sections that were in sharp retreat between 2011 and 2014 (fig. 5A) no longer existed between 2014 and 2019 (fig. 5B). These were mainly the shoreline of the cape exposed to the wind (sectors of the Dranse, Saint-Disdille, Châtaigneraie park, along Ripaille wall and Pinède beach); these sectors have evolved with sedimentation. This evolution differs in front of Ripaille wall: two sections (P21 and P22) have grown in size and three others (P18 to P20) have gone from a period of thickening (2011-2014) to a period of moderate to strong erosion (2014-2019), resulting in an annual retreat of between 0.04 and 0.44 m. This shoreline exposed to the prevailing NE winds (bise) is naturally prone to erosion, as can be seen by the tree root networks in front of the shoreline, exposed due to the forming of a 63 cm high micro-cliff (Maleval et al., 2016). Nevertheless, this shoreline recorded the highest sedimentation according to observations of March 2014 (Maleval et al., 2016), in the form of sandy strips carried by the coastal drift. The erosion mentioned after 2014 is less due to the retreat of the shoreline than to the drift’s displacement of the pebble beach. This temporal morphological evolution illustrates the successive phases of shoreline erosion and sedimentation.
Fig. 5 - Comparative evolution of the Thonon-les-Bains shoreline.
Fig. 5 - Evolution comparative du littoral de Thonon-les-Bains.
A: evolution 2011–2014; B: evolution 2014–2019; 1. Major retreat < -1 m; 2. Minor retreat < -0.15; 3. Non-significant evolution 0; 4. Minor sedimentation > 0.15; 5. Major sedimentation > 0.5.
A : évolution 2011 – 2014 ; B : évolution 2014 – 2019 ; 1. Recul fort < -1 m ; 2. Recul faible < -0,15 ; 3. Evolution non significative 0 ; 4. Sédimentation faible > 0,15 ; 5. Sédimentation forte > 0,5.
12The graphs of Figure 5 show that the sections retreating significantly decrease from 39% to 5% between the two periods.
13In detail, with the exception of the mouth of the Dranse, only the topographic profiles showing the renatured sectors are presented (see location on Figure 1), in the sense that the bathymetric part of the profiles shows no (or very slight) changes in shape between 2011 and 2019.
14At the mouth of the Dranse (P1), the evolution figures (tab. 1) and the topographic and bathymetric profile (fig. 6A) show significant sedimentation of the upper beach between 2014 and 2019 (almost 4 m.yr), whereas that section was highly eroded between 2011 and 2014 (more than 6 m.yr). The sub-lake aggradation modelled since 2011 is a point of interest: an average thickness of 2.88 m of sediment was observed in 2019; this deposit corresponds to a volume of 19,000 m3 for an area of 190 m2 around the profile.
15For the restored Ripaille shoreline, profiles 15 and 17 (fig. 6B, D) show little change in the shape of the beach between 2011 and 2014, but profile 16 (fig. 6C) shows significant beach erosion (0.76 m m.yr). In contrast, since 2014 the 3 profiles have evolved in the same way, characterised by sedimentation of the beach (between 0.12 and 0.38 m); however, profile 16’s sedimentation had not caught up with 2011 levels by 2019. The sedimentation of P17 is in the form of pebble strips.
Fig. 6 - Profiles of the Dranse delta and the Ripaille shoreline.
Fig. 6 - Les profils du delta de la Dranse et du littoral de Ripaille.
A: profile 1; B: profile 15; C: profile 16; D: profile 17. 1. 2011; 2. 2014; 3. 2019.
A : profil 1 ; B : profil 15 ; C : profil 16 ; D : profil 17. 1. 2011 ; 2. 2014 ; 3. 2019.
16Consequently, the first study (2011-2014) shows that the majority of Thonon-les-Bains’ shoreline (up to 60%), was eroded. The second study (2014-2019) indicates a reversal of the trend with 46% of the shoreline in progradation while only 42% was retreated. This erosion decreased from an average annual rate of 0.66 m.yr (first period) to 0.13 m.yr (second period).
17A shoreline evolves naturally with alternating periods of erosion and deposition, mainly due to the seasons, tides, waves and currents. Lake Geneva beaches at Thonon-les-Bains evolve in the same way and, since 2014, they have evolved to a more substantial stock of sediment. This additional stock, evident on the bathymetric profile of the delta, has flowed from the Dranse since the extraction company stopped extracting sediment in 2016: an average of 30,000 m3 of sediment arrives each year (Buffin and Fourcade, 2011), and 19,000 m3 was deposited between 2016 and 2019. The coastal drift transports some of this sediment to gradually restock the beaches. This process explains the positive results in terms of the coast’s evolution and lesser erosion. Thus, today, erosion is considered to be minor, but a further study a few years from now would allow the initial findings to be refined. The results of this study clearly show that human activity weighs heavily on the sediment deficit of lakeshore environments (Pourriot and Meybeck, 1995).
18Restoration using mineral and plant engineering is a late 20th century technique developed for mountain environments and then adapted to rivers (EROSEE, 2006). Since 1997 it has also proven successful on the banks of Lac Saint-Jean in southern Quebec (Segers and Tremblay, 2015). In view of today’s ecological challenges, projects to restore degraded systems (topography, land use, etc.) are more commonplace (Lespez, 2020). In Switzerland, the pioneering work undertaken on Lake Biel (Iseli, 1996, 2002; Gurtner, 2003; Boillat et al., 2006) was followed in France by the reclamation of the banks of Lake Bourget (Lotito, 2011), and now the banks of Lake Geneva in Thonon-les-Bains. Thonon municipality has included its action in the CIPEL plan by rehabilitating the Ripaille shoreline. This action has enabled the transition from an anthropised environment (an attempt to protect the shoreline with riprap, which deteriorated over time due to a lack of maintenance), to a new restored environment, i.e. one that enables a relatively natural integration into the landscape. Whilst the primary objective of eco-morphological engineering is restoration for protection, the second is natural revitalisation in order to promote the sustainable development of the shoreline: these rehabilitations have an overall positive impact on the environment (Rottillon, 1996).
19The renaturation strategy for the Thonon-les-Bains shoreline has begun. Once the geomorphological effects of the removal of the two spurs have been assessed, the possibility of removing the others can be assessed. Indeed, spur 4 has been kept as a precautionary measure because the spurs either side have been removed. Nevertheless, the next stage could see it disappear, especially as the trees just behind it, protruding from the shoreline, naturally play the same role (Maleval et al., 2016). Removal would heighten the possibility of pebble deposition at the base of the restored section, thanks to the presence of spur 6. This is the effect anticipated with the removal of spurs 3 and 5. Indeed, since 2016 (when extraction stopped), the spurs have promoted sedimentation, according to the numerical results and the topographic profiles (P15, 16 and 17): from a situation of retreat in 2011, sediment has been building up since 2014.
20Moreover, of the two spurs marking the limits of Saint-Disdille beach (fig. 3), spur 2 serves a real purpose, retaining the pebbles on the beach. However, if spur 1 were removed, the concave section of the beach would thicken with sediment (fig. 7A). This is a classic coastal process due to wave deflection in bays, attenuated as they are by friction on the lake bed (Touchart, 2002). The resulting increased sedimentation would widen the beach, making the riprap at the top of the beach unnecessary. This seems to be supported by the topographic profiles of the sector (fig. 7B): the upper part of the beach, eroded between 2014 and 2019 (P12), could receive sediment carried by the drift but currently blocked by spur 1; profile 11 located just upstream of spur 1 indeed shows sedimentation gain between 2011 and 2019.
Fig. 7 - Should the rehabilitation of Saint Disdille beach be considered?
Fig. 7 - Envisager la réhabilitation de la plage de Saint-Disdille ?
A. photo of October 2017 (P.-B. Destombes); B. profiles 11 and 12. The removal of spur 1 should enhance the refurbished by increasing the width of the beach which today receives less sediments because of its presence. 1. 2011; 2. 2014; 3. 2019.
A : photo d’octobre 2017 (P.-B. Destombes) ; B : profils 11 et 12. La suppression de l’épi 1 conforterait la position du restaurant par l’augmentation de la largeur de la plage, celle-ci recevant, aujourd’hui, moins de sédiments en raison de sa présence. 1. 2011 ; 2. 2014 ; 3. 2019.
21Human activity and lakeshore development have evolved with human needs, without regard to the shore’s morphological integrity and environmental function. This has led to disruption, especially increased erosion. Shoreline protection does not necessarily mean hard structures, because they can have temporary harmful effects (Maleval et al., 2016) due to lack of maintenance. In some cases, protection means returning to the natural dynamics of the shoreline, as in Thonon-les-Bains. Refurbishment of the landscape has aesthetic benefits and plays a major role in preserving ecological diversity (EROSEE, 2006). It also facilitates pursuits such as shoreline walks, with fewer hard structures. The encouraging initial results of these natural and protective initiatives corroborate the decisions taken by the public authorities.
22In 2006, more than three-quarters of Lake Geneva’s 200 km shoreline was concreted (de Cesare, 2014). Today, the number of initiatives led in Switzerland and France suggests that this proportion can be reduced thanks to renaturation, in line with CIPEL’s action plan. Thonon-les-Bains municipality, concerned about the evolution of its Lake Geneva shoreline and the well-being of its population, is an active proponent. This nature-based strategy is applauded by locals and tourists alike. Lakes and their shorelines are very much part of a site’s touristic appeal (Gurtner, 2003).
*Auteur correspondant : Tel : +33 (0)5 55 43 55 64.
veronique.maleval@unilim.fr (V. Maleval)