Tuesday 1st of july – 16:30
16:30
Multi-site comparison of gravel travel distance using RFID tracking in the Rhône River: feedback and operational recommendations for river restoration
AUTHORS
PEETERS Alexandre, VÁZQUEZ-TARRÍO Daniel, CASSEL Mathieu, MORA Christophe, PIÉGAY Hervé
France
Short Abstract: Human activities have altered the hydro-sedimentary processes in the Rhône River, resulting in a loss of river habitats and biodiversity. To mitigate these physical effects, gravel augmentation operations were conducted in three bypassed channels of the Rhône River. One of these operations was combined with the removal of a groyne field to promote sediment supply through bank erosion. The effectiveness of these interventions was evaluated by tracking the mobility of the introduced gravels. Approximately 4700 tagged pebbles (RFID) were deployed at five sites, and their location surveyed 2-5 times over periods of 3-6 yrs, depending on the site. The multi-site comparison enabled the identification of key factors influencing bedload transport, including the occurrence and intensity of floods, particle size, channel morphology, bed texture and local hydraulic conditions. It showed that bedload transport was more effective in dynamic reaches than in reaches with a paved bed. Operational recommendations for gravel augmentation projects were developed, focusing on site selection, appropriate grain sizes and sediment volumes for injection. Replenishment sites should be selected based on local shear stresses and the specific objectives of the project, whether aimed at improving benthic habitats (i.e., by replenishing existing riffles or creating new ones) or riparian habitats (i.e., by restoring gravel bar dynamics to promote pioneer vegetation). Gravel augmentation and groyne field removal were complementary.
16:50
Effectiveness of restoration in the Old Rhine river (France): a retrospective analysis of a decade of fish community monitoring records.
AUTHORS
STAENTZEL Cybill, BEISEL Jean-Nicolas, REYJOL Yorick, BARILLIER Agnès
France
Short Abstract: Restoration of highly anthropized river environments represents a major challenge due to the profound alterations in these ecosystems and their associated processes. Restoration actions on the Old Rhine (Upper Rhine, France) have been implemented since 2013 to improve aquatic habitat quality and support associated biodiversity. This study evaluates the effectiveness of three types of intervention over a period of up to 12 years post-implementation, using a BACI protocol and monitoring more than 20,000 data points on fish communities and aquatic habitats. The interventions studied include gravel augmentation and controlled bank erosion, with or without the installation of artificial transverse groynes. Our results showed a diversification of aquatic habitats within the restored areas; however, this diversification remains localized to the intervention zones, with no significant downstream propagation. Certain types of intervention created unprecedented conditions in the river, fostering the emergence of hydraulic and thermal aquatic refuge zones that are favorable to juvenile fish. The impact of invasive alien species on the structure of fish communities was also discussed. Ultimately, the results provided insights into a crucial question regarding the effectiveness and durability of restoration actions in these heavily anthropized environments, with strong potential for application to other river systems.
17:10
Impact of large-river restoration measures on the taxonomic and functional composition of the macroinvertebrate community (Danube, Austria)
AUTHORS
FUNK Andrea, BONDAR-KUNZE Elisabeth, RECINOS BRIZUELA Sonia, HEIN Thomas
Austria
Short Abstract: Restoration of large floodplain rivers is an important but challenging task, as they have an exceptional high biodiversity but are also constraint by multiple human uses. We present the results of an innovative restoration pilot project “Pilot Project Bad Deutsch-Altenburg” conducted at one of the last free-flowing sections of the River Danube close to Vienna in Austria, where restoration efforts are evaluated based on the taxonomical and functional composition of the macroinvertebrate community. Different restoration measures, i.e., reconnection of a former isolated side-channel, creation of a secondary channel, groyne-field adaptation and bank re-naturalization, i.e., removal of riprap along the banks, were implemented and outcome evaluated in a short and long-term monitoring program. First results show that the open reconnection of the floodplain channel has led to a clear shift in the macroinvertebrate community towards a typical rheotopic grazer-based community whereas bank re-naturalization and other instream measures had an indirect impact on the availability of habitat area of this typical targeted community.
17:30
Restoration of the Hem river and minimal scientific monitoring: objectives achieved?
AUTHORS
ROLAN-MEYNARD Marlène, TUAUX Sophie, JOURDAN Stéphane, ARCHAIMBAULT Virginie, RIVIÈRE Rémy, ALTCHENKO Yvan, MAURICE Elodie, ROBILLIARD Julie, RIGAULT Benoît, GELEZ William, VIVIER Anne
France
Short Abstract: The restoration of rivers is a major issue, supported by public policies (WFD, Habitats Directive and soon NRL), and considered one of the main levers for mitigating the effects of global change. Although more and more restoration actions are being implemented on French and European watercourses, the effect of these actions on the rivers and associated communities remains poorly understood. The objective of the Demonstration sites network (DSN) and Minimal scientific monitoring (MSM) is to acquire knowledge on the response of freshwater ecosystems to restoration actions.Hem river at Tournehem-sur-la-Hem (north of France) is a DSN site. Thanks to strong mobilization of local structures from the start, the project was fully monitored, according precisely to the MSM and beyond for certain compartments. Even before the end of restoration works, the arrival of migratory fish species and lowering water level in key areas are the first convincing results. In 2025, the site will benefit of an 8-year monitoring (restoration work was implemented in 2017-2018), making it possible to collect numerous physico-chemical, hydrobiological and hydromorphological data. I.S.Rivers 2025 will be an opportunity to take stock of the restoration project on the Hem River and the knowledge acquired through MSM monitoring: Have the objectives for restoring the natural functioning of the river been achieved? Is there a gain in flood prevention? What feedback has been provided for the implemented scientific monitoring?
17:50
A synopsis of the RhônEco programme: a long-term observatory of the Rhône River ecological restoration.
AUTHORS
LAMOUROUX Nicolas, OLIVIER Jean Michel, CASTELLA Emmanuel, CATTANÉO Franck, COLAS Fanny, EME David, FORCELLINI Maxence, LEBRUN Camille, LOGEZ Maxime, PANSU Johan, RIQUIER Jérémie
France
Short Abstracts : RhônEco is a transdisciplinary research program whose main objective is to evaluate and predict the effects of ecological restoration measures on the Rhône River. Restoration combined (1) the increase in minimum flows downstream of dams, (2) the physical rehabilitation of floodplain channels, (3) channel widening and (4) sediment recharges. Monitoring covered up to 30 years and began before the restoration operations. A synthesis carried out in 2024 confirms significant changes in fish and macroinvertebrate community structure, in both the Lower and Upper Rhône, in the main and floodplain channels. However, these changes are not fully explained by the restoration alone. As expected, the relative abundance of species adapted to fast-flowing rivers increased in several sites, as well as the diversity of floodplain channels. Nevertheless, responses were often due to a few taxa. In a context of rapid global change (e.g., flow rates, temperature and water uses), the ongoing RhônEco programme will attempt to better understand and predict the success or failure of restoration measures. For this purpose, we will enlarge the scope of habitat and biological monitoring.