1. Mikaël Attal School of GeoSciences Alaknanda River, India Linkage between sediment transport and supply in mountain rivers I – Mountain rivers II – Spatial and temporal variations in sediment availability + link with sediment supply III – Sediment export as a result of interplay between flood magnitude and sediment availability IV – Large grains and large floods

2. I. Mountain Rivers Glen Etive, Loch Etive (Scotland)

3. I. Mountain Rivers  Calibre and amount of sediment transported out of a reach during an event = f (flow competence, transport capacity AND sediment availability)

4. II – Spatial and temporal variations in sediment availability + link with sediment supply Sediment supply is episodic and spatially variable  influences availability Spatial Temporal

5. II – Spatial and temporal variations in sediment availability + link with sediment supply Spatial variations due to changes in sources Glacially-derived (Marsyandi River, Himalayas) Steep landscape (Feather River, California) Low-relief, soil mantled (Apennines, Italy)

6. Glacially- derived Steep landscape Low-relief, soil mantled Downstream distance (km) Marsyandi River, Himalayas Attal and Lavé, 2006 Spatial variations due to changes in sources II – Spatial and temporal variations in sediment availability + link with sediment supply

7. Glacially- derived Steep landscape Low-relief, soil mantled Downstream distance (km) Celano Gorge, Apennines, Italy Whittaker et al., 2010 Spatial variations due to changes in sources II – Spatial and temporal variations in sediment availability + link with sediment supply

8. Glacially- derived Steep landscape Low-relief, soil mantled Downstream distance (km) Adams Creek, Sierra Nevada, California Sediment supply is spatially variable  influences availability Attal et al., 2015 Spatial variations due to changes in sources II – Spatial and temporal variations in sediment availability + link with sediment supply

9. Temporal variations due to episodic sediment supply II – Spatial and temporal variations in sediment availability + link with sediment supply

10. Episodic sediment supply: point sources Benda and Dunne, WRR, 1997 Google Maps Mosaic Canyon, Death Valley

11. 10 cm

12. Benda and Dunne, WRR, 1997 Signal seems to diffuse with increasing basin size? Episodic sediment supply: point sources

13. Lane et al., 2008: powerful storms in UK Episodic sediment supply: basin-scale events External drivers of sediment supply: storms / typhoons, earthquakes. Dadson et al., 2003, 2004; Yanites et al., 2010: Chi-Chi earthquake (1999) + typhoon Toraji (2001) in Taiwan Pratt-Sitaula et al., 2004: monsoon intensification in Marsyandi valley, Himalayas, 50- 35 and ~8 ka ago? ~100 m Sediment supply is temporally variable  influences availability Temporal variations due to episodic sediment supply

14. III – Sediment export as a result of interplay between flood magnitude and sediment availability Largest floods will not necessarily export the largest amount of sediment River under-capacity Amount vs transport capacity Grain size vs competence

15. Amount of sediment available Turowski, 2012; Turowski et al., 2013 Q s = cQ λ λ > 1: “flood-depositing” http://www.slideshare.net/Nisqually/aggradation-and-sediment-in-the-nisqually-river Nisqually River, WA III – Sediment export as a result of interplay between flood magnitude and sediment availability

16. Turowski, 2012; Turowski et al., 2013 Q s = cQ λ λ > 1: “flood-depositing” λ < 1: “flood-cleaning” Paradise Creek, E Australia, 2011 (Baggs Sargood et al., 2014) Amount of sediment available III – Sediment export as a result of interplay between flood magnitude and sediment availability

17. Q s = cQ λ λ > 1: “flood-depositing” λ < 1: “flood-cleaning”  Alternating behaviour in space and time  Inferred strong link with sediment supply from hillslopes (supply synchronous with aggrading phases)  “Extreme” aggradation can make the river transport- limited for centuries to millennia  grain size becomes the limiting factor for entrainment / transport Paradise Creek, E Australia, 2011 (Baggs Sargood et al., 2014) Turowski, 2012; Turowski et al., 2013 Amount of sediment available III – Sediment export as a result of interplay between flood magnitude and sediment availability

18. Grain size of sediment available Strong source control:  Grain size of sediment transported can be limited by coarseness of sediment available Low relief soil-mantled landscapes Attal et al., 2015 Reworking of fine grained sediment (e.g., conglomerate bedrock) Mather and Hartley, 2005 Quebrada Tambores, Chile III – Sediment export as a result of interplay between flood magnitude and sediment availability

19. Strong source control:  Grain size of sediment transported can be limited by flow competence Marsyandi River, Himalayas Wide range of sizes available:  River picks what it can (threshold for entrainment)  Influence of boulders? Grain size of sediment available III – Sediment export as a result of interplay between flood magnitude and sediment availability

20. IV – Large grains and large floods Influence of boulders on sediment export during floods  Development of stable step-pool morphology Only high magnitude events can break the steps and free the sediment “trapped” (and expose bedrock) Daluis Gorge, SE France Influence of extreme flood events