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

Transcription

1 Université François Rabelais de Tours, CNRS/INSU - UMR 6113 CETU Elmis Influence of dam removal and past sediment mining on river morphology and biology: example of the Vienne River (France) S. Rodrigues, N. Richard, P. Juge, J. Berthomé, G. Cochet, J.R. Malavoi

2 DAM REMOVAL IN THE LOIRE RIVER CATCHMENT AREA Context Due to the Water Framework Directive, dam removal is going on in France River incision problems Free migration of sediments and fish Space and mobility for rivers Morphological equilibrium Lane's Balance (after E. W. Lane, from W. Borland) Masterplan «Plan Loire Grandeur Nature III»

3 After Andriamahefa, 1999, modified. Data : MNT USGS, mesh 1 km x 1 km 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: km² Stream length 370 km Dampière en Burly Belleville/Loire Dam of Maisons Rouges on the Vienne River (removed in 1999) Dams removed < 35 m m m m m m m m m > 1000 m km

4 Study site and dam features Before removal Confluence Vienne - Creuse 4 m high, 200 m in width built in m 3 of sediments trapped upstream Dam removed in 1999

5 Questions REMOVAL OF MAISONS-ROUGES DAM Questions, goals and approach 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)

6 Discharge (m 3 /s -1 ) REMOVAL OF MAISONS-ROUGES DAM Approach: physical and biological survey 2000 Removal of the dam Surveys Q Q /10/ /07/ /04/ /01/ /10/ /07/ /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

7 Sedimentological and morphological survey

8 Results: downstream migration of sediment waves Significant upstream scouring since dam removal Just upstream the dam 6 km upstream

9 Results: downstream migration of sediment waves 10 km downstream dam Bar deposition Sediment deposition downstream the dam and migration of large bars at a velocity of 2.5 km/year b 2000a 1999 Dam

10 Results: sediment budgets between Elevation (m) Cross section analysis T 0 Distance from left bank (m) T 1 T 1 - T 0 Fill Scour

11 Results: cumulative sediment budgets between Cumulative volume (m 3 ) Preferential sites for sediment deposition? EVOLUTION DES FONDS ENTRE 2005 ET 2009 SUR LA VIENNE ET LA CREUSE Briançon Chezelet Bilan sédimentaire Vienne et Creuse confondues Dam l'ile Trogues Pouzay Nouâtre Ancien barrage Les Ormes Flow Différence de section (m2) Scour By passing Creuse Fill PK (distance à la confluence avec la Loire) Distance from the Loire (km) Repères Vienne et Creuse 05-09

12 cote NGF REMOVAL OF MAISONS-ROUGES DAM Results: bed shear stress assessed from water levels t 0 = rgr h sinf (sinf = f) Alt. NGF (m) Combined effect of dam removal and past sediment mining? LIGNE D'EAU DE LA VIENNE, PENTE ET FORCES TRACTRICES ASSOCIEES 3 (2009, environ 100 m.s -1 à Nouatre ) Briançon Chézelet l'ile Bouchard Trogues Pouzay Nouâtre Les Ormes Dam Ancien barrage o/oo 10,8 N/m² o/oo 1,3 N/m² 0.15 o/oo 3,1 N/m² PK (distance à la confluence avec la Loire) Distance from the (km) 1,08o/oo 25,3 N/m² Altitude plan d'eau ,08 o/oo 0.10 o/oo 24,6 N/m² 2,4 N/m² Repère Alti 2005 Scour By-passing Fill

13 Results: sediments mobility Shear stress (N.m -2 ) Force tractrice critique (N.m -2 ) Critical bed shear stress (assessed from D 90 ) t c pour D 90 (points) t générale pour 100 m 3.s -1 à Nouatre (droite) Pk (distance confluence à la Loire, km) Bed shear stress (for Q = 100 m 3 /s -1 at Nouatre*) c r r t c = = fct ( s w) g. D Shear force = Gravity force u* D Force tractrice critique (N.m -2 ) Critical bed shear stress (assessed from D 50 ) t c pour D 50 (points) t générale pour 100 m 3.s -1 à Nouatre (droite) Bed shear stress (for Q = 100 m 3 /s -1 at Nouatre*) Distance from the Loire (km) Pk (distance confluence à la Loire, km) Threshold of motion for a given grain size *Q = 100 m 3 /s -1 at Nouatre is reached 60% of time

14 Biological survey

15 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?

16 Influence of dam removal on Margaritifera auricularia 4 4 stations were surveyed Bed topography (cross sections spaced 10 m on average) geolocation GPS and tagging 2000b 2000a Dam 1

17 Number of mussels REMOVAL OF MAISONS-ROUGES DAM Results: influence of dam removal on Margaritifera auricularia Dam Flow : 283 mussels 2009: more than 90 mussels disapeared (1/3 of the population) 0 Sation 1 Sation 2 Sation 3 Sation 4 Number of mussels Dam Flow Difference Small increase upstream (habitat) Significant decrease downstream Sation 1 Sation 2 Sation 3 Sation 4

18 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?

19 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,

20 Thank you for your attention

21 Results: bed shear stress assessed from water levels PROFIL LONGITUDINAL DE LA VIENNE ET LA CREUSE Points durs Will the river incise its bed? altitude NGF du talweg Distance from the Loire (km) PK (distance à la confluence avec la Loire) Possible vertical scouring Creuse Vienne Points durs Bedrock outcrops Scour By-passing Fill