Integrated hydro-sedimentary river management ...

Zone Atelier Bassin du Rhône

Hydro-sedimentary monitoring of reservoir flushes in the Arc-Isère river system (French Alps)

Rhône Sediment Observatory (OSR)

Camenen, B.1, Némery, J. 2, Le Coz, J. 1, A. Paquier 1, Mano, V. 2, Belleudy, P. 2, Poirel, A. 3, Lauters F. 3, Jodeau M.4, Laperrousaz E. 5 1: Cemagref HHLY , Lyon

2: LTHE, Grenoble

3: EDF-DTG, Grenoble

4: EDF-LNHE, Chatou

5:EDF-CIH Le Bourget du Lac

Integrated hydro-sedimentary river management

Suspended Sediment Matter Fluxes

The Isère River is located in the South-East of France (French Alps) and is one of the main tributaries of the Rhône River in term of Suspended Sediment Matter (SSM). The Isère and Arc River channels were strongly constrained laterally during the two last centuries (human activity, communication routes, hydroelectric dams). Its complex and active fluvial dynamics needs a better management of sediment flux and river bed (morphology, vegetation, protection work): an integrated and concerted management at the cathment scale.

The Arc-Isère river system is characterized by important Suspended Sediment Matter (SSM) fluxes with very high concentrations during short events (30g/l during a flood event or even 100g/l if a mud flow event occurs upstream). In order to quantify SSM production, transfer, storage and input to the Rhône, a hydro-sedimentary network was deployed on critical points of the hydrographical network. Since 2005, monitoring and intense sampling campaigns were achieved to better understand SSM dynamics along the river system during major events such as annual river dam flushing or natural flood (including a 15 year return period flood in May 2008), as well as during the glacier thawing period. Numerical modelling tools are developed for the SSM advection and diffusion within the hydrographical network with a special emphasis on erosion dynamics including acceleration effects and river bed capacity.

Bank erosion on the Arc River – Mai 2008 flood

Sampling bottle

Erosion and flood risk next to the Isere River in Grésivaudan (Source SYMBHI).

Since 2008, the Arc-Isère study site was officially recognized as a collaborative study site by the ZABR (Zone Atelier Bassin du Rhône), a regional multidisciplinary observatory for the Rhône river basin, and the Rhône Sediment Observatory (OSR). It ensures the durability of the observations and studies, and the dissemination of the results. The main actors are the Cemagref (HH, Lyon), LTHE (ENSE³, Grenoble and EDF (DTG Grenoble, CIH Chambéry, and LNHE, Chatou). This study aspires to develop projects involving industrial partners (EDF, CNR), local operational partners, and multidisciplinary scientific partners (Hydrology, Hydraulics, Geomorphology, Biology, Ecology, Geochemistry, Sociology, and Risk Management). This work is supported by national French programs (ANR-Gestrans, EC2CO-Variflux) and Europeans Programs (SHARE). Protection measures including water and sediment fluxes, river bed and vegetation management need an integrated vision from upstream to downstream together with a balance between natural and artificial physical processes with land use and social representation of the river managers.

Arc River dam flushing : sediment deposits in dam reservoirs; water discharge and SSM concentration during the 2006 flushing event at Ste Marie de Cuines; simplified modelling of the SSM flux along the Arc-Isère river system. (Camenen et al., ICHE, 2008)

SSM flux measurement along the Arc-Isère

Geochemical and carbon fluxes

A significant investment was realized in the construction of a monitoring network for water discharge and Suspended Sediment matter (SSM) flux along the river system using nested boxes (Arvan River→ →Arc River→ →Isère River→ →Rhône River). Thanks to water sampling, cali bration curves were obtained to convert the SSM estimated by turbidity sensors (Hach Lange, 0-50 g/L, time step 1/2 hour). into SSM concentrations in g/L. These calibration curves were used for each station to reconstitute the continuous dynamics of SSM concentrations and for the SSM flux calculation.

The hydro-sedimentary network is used as a support for the better understanding of geochemical particulate fluxes and water quality. For instance carbon dynamics was investigated in order to determine the flux and the contribution of each form of carbon, particulate or dissolved, organic or inorganic (POC, PIC, DOC, DIC). Regarding the high SSM concentrations in the Arc-Isère system, particulate carbon is a major contributor of the total carbon flux. The close relationship between POC and SSM concentrations was used to reconstitute POC flux from turbidity-high temporal SSM measurements. The impact of geochemical fluxes will be investigated in relation with biological compartments (fishes, macroinvertebrates, benthic zone)

Fluvial forms and vegetation dynamics

Leave sampler to measure POC-coarse material Relationship between POC in SSM (TSS) and SSM concentrations (Nemery et al., in prep., 2010) - SSM flux :measurement network along the Arc-Isère river system; - Relationship between SSM estimated by the turbidity sensor (Hach Lange, 0-50g L-1) and SSM measured on water samples (Isère River) - installation of a turbidimeter and of a radar (measuring water level and surface veocity) on the Arvan River at St-Jean de Maurienne

Contribution in percentage of each form of carbon (POC, PIC, DOC and DIC) to the total carbon flux according to the class of discharge (Mano et al. , HB, 2008) 100% 80%

DIC

60%

DOC

40%

PIC POC

20% 0% 1 10 00 01 15 5 0 02 20 0 0 02 25 5 0 03 30 0 0 035 0 35 40 0,4 04 45 5 0 05 50 0 0 055 0 56 9, 2 61 2, 5

Arc-Isère collaborative study site :

GIS map indicating the erosion potential in the Arc river cathment (Master thesis M. Bertrand, 2009)

SSM flux in 2006 and 2007 at Grenoble Isère-campus station: 2,4 M of tons (PhD V. Mano, 2008).

50 -

All the information available in the Arc River catchement is now available in a geographical information system (GIS). A space segmentation and a spatial analysis were achieved by crossing topographical, geological and land use data. Thus, a flux structuring was used to categorize different sub-catchment depending on their potential contribution to the suspended sediment matter (SSM) flux. These results will be very useful for the analyses of the fine sediment contribution to the hydrographical network. In particular, the impact of glaciers on the SSM flux during the thaw will be studied.

ADCP LTHE

Hydro-acoustic (aDcp) measurements of the SSM on the Isère River.

% of the total carbon flux

Sedimentary sources of the Arc River catchment

ADCP Cemagref

3

-1

class of discharges (m s )

Local topography of gravel bars, surface grain size, bedload transport, and vegetation evolution are monitored at several locations in the Arc and Isère Rivers. 2DH and 1D models were applied to compare effects of natural floods and river dam flushings on the river bed evolution. Both metrological and numerical developments are investigated for bedload and suspended load estimation. A significant effort is made on the understanding of the interaction between fine and coarse sediments, as well as the interaction between vegetation and morphodynamics.

Description of the vicious circle between vegetation and fine sediment deposits on Isère river islands (PhD C. Allain, 2002) Morphological and surface grain size characteristic monitoring on a gravel bar in the Arc River at Ste Marie de Cuines (PhD M. Jodeau, 2007). Bedload acoustic measurement using a hydrophone and electromagnetic currentmeter (Belleudy et al., 2010) Gravel sediment transport estimation using passive integrated transponders or PIT tags (Camenen et al., River Flow, 2010).