Université François Rabelais de , CNRS/INSU - UMR 6113 CETU Elmis

Influence of dam removal and past sediment mining on river morphology and biology: example of the River ()

S. Rodrigues, N. Richard, P. Juge, J. Berthomé, G. Cochet, J.R. Malavoi

DAM REMOVAL IN THE RIVER CATCHMENT AREA Context

Due to the Water Framework Directive, River incision problems dam removal is going on in France

Free migration of sediments and fish

Space and mobility for rivers

Morphological equilibrium

Masterplan « Plan Loire Grandeur Nature III » Lane's Balance (after E. W. Lane, from W. Borland) REMOVAL OF MAISONS-ROUGES’ DAM Context and study site Loire River: larger french river Removal of several dams

A tributary of the Loire: the Vienne River Catchment area of the Vienne River: 21 000 km² Stream length 370 km Dampière en Burly Belleville/Loire

Dam of Maisons Rouges

on the Vienne River < 35 m (removed in 1999) 35-60 m 60-75 m 75-115 m 115-155 m 155-200 m 200-300 m 300-500 m Dams removed 500-1000 m > 1000 m 0 100 km

After Andriamahefa, 1999, modified. Data : MNT USGS, mesh 1 km x 1 km REMOVAL OF MAISONS-ROUGES’ DAM Study site and dam features Before removal

• Confluence Vienne - • 4 m high, 200 m in width • built in 1922 • 900 000 m3 of sediments trapped Dam upstream • removed in 1999 REMOVAL OF MAISONS-ROUGES’ DAM Questions, goals and approach Questions

• Ability of the river to flush the sediment downstream and restore a morphological equilibrium • Influence on in-channel species in the dam and downstream (benthic macroinvertebrates, mussels…)

Approach

10 years sedimentological and morphological survey Analysis of habitat diversity and populations (vegetation, benthic macroinvertebrates, mussels) REMOVAL OF MAISONS-ROUGES’ DAM Approach: physical and biological survey Discharge (m3/s-1)

Removal of the dam Surveys 2000

Q5

1500 Q2

1000

500

0 28/10/1995 24/07/1998 19/04/2001 14/01/2004 10/10/2006 06/07/2009 01/04/2012 • Bed topography in 1998, 1999, 2000 a and b, 2002, 2005, 2009 (226 cross sections; less than 200 m on average) • Grain size analysis of bed sediments • Aerial photographs (constant discharge) • Analysis of vegetation, macroinvertebrates and mussels

Sedimentological and morphological survey

REMOVAL OF MAISONS-ROUGES’ DAM Results: downstream migration of sediment waves • Significant upstream scouring since dam removal

Just upstream the dam

6 km upstream REMOVAL OF MAISONS-ROUGES’ DAM Results: downstream migration of sediment waves

10 km downstream dam

Bar deposition

Sediment deposition downstream the dam •2009 and migration of large •2005 bars at a velocity of 2.5 •2002 km/year •2000b

•2000a Dam •1999 REMOVAL OF MAISONS-ROUGES’ DAM Results: sediment budgets between 2005 - 2009

Elevation (m) Cross section analysis

T0

Distance from left bank (m)

T1

T1 - T0

Fill Scour REMOVAL OF MAISONS-ROUGES’ DAM Results: cumulative sediment budgets between 2005 - 2009 Preferential sites for sediment deposition? Cumulative EVOLUTION DES FONDS ENTRE 2005 ET 2009 SUR LA VIENNE ET LA CREUSE Bilan sédimentaire Vienne et Creuse confondues volume (m3) Dam Briançon Chezelet l'Ile Trogues Nouâtre Ancien barrage Les Ormes 60000 Flow 40000

20000

) 0

2

m

( -20000

-40000

-60000

Différence de section Différence -80000 Scour Creuse -100000 By passing -120000 Fill -140000 15 20 25 30 35 40 45 50 55 60 PK (distanceDistance à la confluence from avec the la LoireLoire) (km) Repères Vienne et Creuse 05-09

REMOVAL OF MAISONS-ROUGES’ DAM Results: bed shear stress assessed from water levels t0 = rgRhsinf (sinf = f) Combined effect of dam removal LIGNE D'EAU DE LA VIENNE, PENTE ET FORCES TRACTRICES ASSOCIEES (2009, environand 100 3m.s - past1 à Nouatre) sediment mining? Alt. NGF (m) Briançon Chézelet l'Ile Bouchard Trogues Pouzay Nouâtre Les Ormes 37

36 AncienDam barrage

35

34

0.48 o/oo 33 10,8 N/m²

cote cote NGF 32 Altitude plan d'eau 2009 Repère 31 1,08o/oo Alti 2005 25,3 N/m² 0.15 o/oo 30 0.05 o/oo 3,1 N/m² 1,3 N/m² 29 1,08 o/oo 0.10 o/oo 24,6 N/m² 2,4 N/m² 28 15 20 25 30 35 40 45 50 55 60 DistancePK (distance from à la confluence the avec Loire la Loire) (km)

Scour By-passing Fill

REMOVAL OF MAISONS-ROUGES’ DAM Results: sediments mobility

Shear stress (N.m-2) 100

)

-2 c u*D 90 t pour D (points) t c 90  = = fct  80 3 -1 c (rsrw)g.D Critical bed shear t généraleBed pour shear 100 m stress.s à Nouatre (for Q (droite) = 100 70 m3/s-1 at Nouatre*) 60 stress (assessed

50 from D90) 40

30

20 Shear force

10

Force tractrice critique (N.m critique tractrice Force  = 0 Gravity force 10 15 20 25 30 35 40 45 50 55 60 Pk (distance confluence à la Loire, km)

30 Bedtc pour shear D50 (points) stress (for Q = 100

) -2 mt3 générale/s-1 at Nouatre*) pour 100 m 3.s-1 à Nouatre (droite) 25

20 Critical bed shear 15 Threshold of motion stress (assessed for a given grain size 10 from D50) 5

Force tractrice critique (N.m critique tractrice Force 0 10 15 20 25 30 35 40 45 50 55 60 DistancePk (distance from confluence the Loire à la Loire, (km) km)

*Q = 100 m3/s-1 at Nouatre is reached 60% of time

Biological survey

REMOVAL OF MAISONS-ROUGES’ DAM Results: influence of dam removal on Margaritifera auricularia Margaritifera auricularia

Length : 20 cm Endangered specie Life duration : 150 years Habitat : stabilized gravels - Small and old populations (recruitment?), - needs fish for reproduction (which ones?) Status : protected by IUCN, protected in France,…- sensitive to river degradation (fine sediments…)

Rediscovered in the Vienne in 1998 Were the populations of Margaritifera auricularia affected by the migration of bedload sediment waves coming from the dam?

REMOVAL OF MAISONS-ROUGES’ DAM Influence of dam removal on Margaritifera auricularia

4

4 stations were surveyed 2009 3 - Bed topography (cross sections 2005 spaced 10 m on average) 2002

- geolocation GPS and tagging 2000b 2 2000a Dam 1999 1 REMOVAL OF MAISONS-ROUGES’ DAM

Results: influence of dam removal on Margaritifera auricularia Barres sédimentaires en Number of mussels 1999 120 Dam Flow -Pertes les plus importantes au niveau des zones courantes (station 100 2002 2009 2002: 283 mussels de l’A10 et de Mougon) 80 2009: more than 90 60 mussels disapeared -Trouvées quand sur les stations de et A10? 40 (1/3 of the population)

20

0 Sation 1 Sation 2 Sation 3 Sation 4 Number of Flow mussels Dam 15 Difference 2002-2009 10 5

0 Small increase upstream Sation 1 Sation 2 Sation 3 Sation 4 -5

(habitat) -10 Significant decrease -15 downstream -20 -25

-30 REMOVAL OF MAISONS-ROUGES’ DAM Results: influence of dam removal on Margaritifera auricularia

Ex. of station 2 Is the decrease of mussels due to sediment transport? Mussels (30 in 2002, 4 in 2009)

V029 Left bank

Mussels populations were mainly located near the banks (30 m) - Not due to burying because mussels were present in 2002 and bedload waves migrated in 1999 in this part of the river… Hypothesis: - Erosional context induced by dam removal ? - Spawning areas of Petromyzon marinus? REMOVAL OF MAISONS-ROUGES’ DAM Conclusion and Perspectives

In 10 years, large bedload waves migrated 27 km downstream of the dam (celerity of 2.5 km/year) Sediment trapping occured in the abandonned sediment mining sites Detailled topographical surveys at past sediment mining sites

Regressive erosion is due to dam removal but also probably past sediment mining (stopped in 1998) Study of bedrock outcrops and lateral migration of the river

Margaritifera auricularia was found in the Vienne in 1998 but the populations are decreasing (excepted upstream of the dam). Topographical survey and tagging, influence of Petromyzon,…

Thank you for your attention

REMOVAL OF MAISONS-ROUGES’ DAM Results: bed shear stress assessed from water levels Will the river incise its bed ?

PROFIL LONGITUDINAL DE LA VIENNE ET LA CREUSE Points durs

36

35

34

33

32

31

30 Creuse 29 Possible Vienne Points durs altitude NGF du NGF altitude talweg 28 vertical

27 scouring

26

25 Bedrock

24 outcrops 15 20 25 30 35 40 45 50 55 60 Distance from the Loire (km) PK (distance à la confluence avec la Loire)

Scour By-passing Fill