Rhone river bypass section - Pierre-Bénite
Rhone river bypass section - Pierre-Bénite
Key features of the case study
Rhone river restoration is multi-sites, concerning four bypass sections on Upper Rhone (Chautagne, Belley, Brégnier-Cordon) and Rhone upstream Lyon (Pierre-Bénite). Same measures have been implemented on the different sites: increase and ensure minimum flows and naturalize flows regime. These measures have been implemented in august 2000 to Pierre-Bénite, july 2004 to Chautagne, july 2005 to Belley and winter 2005 to Brégnier-Cordon. Next, same restoration measures will be applied in three other downstream Rhone bypass sections (Montélimar, Donzère-Mondragon and Péage-de-Roussillon). Flows manipulations go with twenty-five former channels restorations (see Rhone river former channels case studies).
Site description
Rhone river has been deeply impacted by human activities for centuries. First most important interventions were during nineteenth century with systematic river dyking for protection against floods. River control works continue during twentieth century with arrangements for fluvial shipping and dam constructions for hydropower. Rhone river has been channelled and historical stream is today a succession of bypass-sections, from Geneva to the Camargue. Sites concerning by restoration are located in this Bypassed Rhone (Rhone Court-Circuité in French - RCC), also named Historical Rhone or Old Rhone. However, pressures are not the same according to the bypass section considered. From upstream to downstream, first bypass section is Chautagne, 10 km long. It is upstream bounded by Motz dam and minimum flow instream was set 10-20 m3 s-1. Belley bypass section downstream from Chanaz dam is the longest with 18 km. Minimum flow in this section was set 25 m3 s-1 from december to march, 28 m3 s-1 from april and october-november and 60 m3 s-1 from july to september. Brégnier Cordon section, last of Upper Rhone, is bypassed by Brégnier-Cordon dam. Pierre-Bénite bypass is in Middle Rhone, just downstream of Lyon. It is 10 km long and minimum flow set 10 or 20 m3 s-1. Geographical context is different from others bypass sections because it is located right inside one of the more important French industrial area. However in every bypass section pressures and stakes are important. Preservation of natural environments and their ecological richness is undoubtedly recognized as the first issue. Aim is also to preserve the groundwater resources and to ensure flood protection. Economical and social needs must be considered (hydroelectric production, water resource, recreational activities, etc.). At last watershed size of Rhone river is an additional constraint. Pressures must be considered also on many tributaries (industrial waste, domestic waste, etc…).
Pressures have lot of consequences on Rhone river hydrosystem structure and process. First, dams and canals modify hydrological regime (quantity and variability), stream and groundwater flow, and lower groundwater level. Upstream dams are also problem for sediment transport. Bank erosions are observed and former channels are disconnected from main stream. Deterioration of water quality is other consequence. These physical dysfunctions have deep impacts on ecological structures and processes. Fish habitat is damaged and natural environment as a whole is disturbed. At all, in a social way, alteration of landscape quality is also underlined problem.
Measures selection
Rhone river restoration program had four complementary aims. First was to preserve natural environment and its ecological richness. Second was to maintain groundwater level and water resource. Third was to manage flood by restoration of natural flood expansion areas. Forth was to maintain tourist and recreational activities around Rhone river. Increase minimum flow is one of different measures implemented in order to achieve these aims.
Minimum flows in different bypass sections have been worked out from statistical hydraulic models predicting the local hydraulic conditions in a stream reach (Lamouroux et al., 1999). Minimum flow increase and flow seasonal variations are different in each bypass section. Chautagne bypass section flow has been increase from 10-20 m3 s-1 to 50 m3 s-1 (september to april) or 70 m3 s-1 (may to august). In Belley bypass section, flow has been established to 60 m3 s-1 (september to february), 90 m3 s-1 (march and may), to 100 m3 s-1 (april) and to 80 m3 s-1 (june to auguste). Brégnier-Cordon bypass section regime flow has been modulated to 80 m3 s-1 (november to march), 100 m3 s-1 (april to may and September to October) and 150 m3 s-1 (june to august). At last, in Pierre-Bénite bypass, flow has been increase from 10-20 m3 s-1 to 100 m3 s-1.
Financial partners
Financial partners are : SMIRIL, Syndicat du Haut-Rhône, CNR, Agence de l'Eau Rhône-Méditerranée-Corse, Etat (Ministère de l'Aménagement du territoire et de l'Environnement, DIREN, DRIRE), Région Rhône-Alpes, Service de la Navigation, ONF, VNF, Département Rhône, Ain, Savoie, Isère, FRAPNA, CORA, FDPPMA, Fédération Chasse, EID, EU.
Success criteria
Ecological response
In Pierre-Bénite bypasse section, structure of fish communities has been heavily modified in accordance with scientific predictions. Proportion of typical fish in running waters rose from 15% to 43%. This change is dynamic. It is primary involved in early fish development stages, through improvement of conditions of reproduction. There is also significant changes in macroinvertebrate community structure with a wider distribution of potamies or reophile taxa (eg P. pusilla, B. fuscatus, A. fluviatilis) previously present but localized. Some invertebrates typical of large rivers have emerged. There are also some invasive species which traduce larger scale phenomenon in Rhone river. Only continuation of monitoring could indicate sustainability of these biological changes. In Chautagne bypass section main channel, average discharge velocity was doubled after minimum flow increase. Results for fish are variables since 2004. Nevertheless, it appears that trend of species running waters increase (from 11-21% especially ) is confirmed on different stations. It partially reverse trend of evolution since dam construction. Salmonid populations (trout and grayling), interesting on Chautagne bypass section, remain in small numbers. In Belley bypass section stream, results of fish sampling conducted in September 2006 and 2007 confirm the knowledge acquired in 2004 and 2005. Fish populations are generally healthy. High proportion of fish sampled have integrated reproductive fraction of population. Nevertheless, the results obtained in 2006 are less demonstrative than those acquired previously. It is due to sharp abundance decline of some species in samples (grayling, dace, minnow, nase, loach). This observation reflects not only significant decrease in species abundance but also is probably due to sampling conditions (historical flows prior ro fishing, weather…). Aquatic habitat change models related to hydraulic carcteristics expected to increase "species of running water” proportion (grayling, barbel, bleak, nase, dace). Proportion of "running water species is relatively stable over the period (2004-2007). This is due to diminution of nase, dace and grayling population sampled in 2006 and 2007. Future observations will determine actual response of fish communities following minimum flow increase. Concerning macro-invertebrates of main channel, results show rate reophile population increase. It’s based on diminution of gammarids population and on very strong increase in Potamanthus luteus (densities tripled) and Orthocladiinae population (density more than doubled). In Brégnier-Cordon bypass section, fish sampling didn’t give different results from those from initial state. Calculation of metrics proposed in scientific monitoring dashboard shows increase in running water species proportion. This is mainly due to bleak and barbel river population increase. These two species are mainly represented in juveniles of the year. Accordingly, this result should be interpreted in this context and in perspective of mid-term evolution of fish community.
Hydromorphological response
Monitoring before and after implementation of the project
Monitoring objectives
There are double objectives of restoration evaluation and two monitoring levels are distinguished. First level is based on a descriptive approach of restoration effects. Potential restoration effects are measured in main channel and former channels in a single way and comparative way on a larger scale. Second monitoring level targets the analysis on hydrosystem functional responses. This monitoring depending on types of restoration measures, environment (channel or lône) and considered compartments (hydrological, geomorphological and ecological). Objective of this monitoring is to inform futures hydroecological models. It can also be used as predictive feedback for other restoration actions.
Monitoring actors
ZABR. Cemagref. University of Lyon. CNRS (UMR 5023 & UMR 5600). Geneva University - LEBA.
Monitoring structures
Structure of monitoring is not easy to describe because restoration measures hadn’t been implemented simultaneous on the four bypass sections. In Pierre-bénite monitoring measures before minimum flow increase have focused on physical and biological compartments. There is flow steadily chronic since 1995 and physical chemistry measurements made every year since 1995 to 1999. Biology is approached by two compartments. Electric fishing sampling (number of species, frequency of different species, size class distribution of target species, number of species) realized annually since 1995 to 1999. Other biological monitoring is on invertebrates (total taxon richness, number of species occurring, number of species frequenting the deep zones) since 1995 to 1999. Chautagne bypass section has been monitoring on fish and invertebrates compartments in 2003, Belley in 2004 and Brégnier-Cordon in 2005-2005 under same protocols as Pierre-Bénite. After restoration monitoring has also focused on same compartment and has been made using same methods on the different sites. Fish sampling are realized every year and macroinvertebrate sampling every two year. Monitoring must continue for all sites, all compartments, using same methods and same time steps.
Socio-economic aspects
Contact person within the organization
Extra background information
References
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Related Measures
- No measures have been assigned to this project.
