This ppt describes my scientific activities over the last few years. It is of interest for scientists and engineers how want to know more about long-term ice jams dynamics and physical impacts. Please contact me for more info: boucher@cerege.fr

1. Étienne Boucher (LAVAL) Yves Bégin (INRS-ETE) Dominique Arseneault (UQAR) River Ice Jams Risk evaluation, driving conditions and geomorphological impacts documented from tree-rings Necopastic River, James Bay Contact: [email_address]

2. Introduction River ice breakup: a crucial moment in the annual cycle of high-latitude rivers Mechanical breakups Thermal breakups [email_address]

3. Introduction Ice jams: the most threatening hazard in northern areas

5. Introduction Planar view Profile view streamflow Year 1 Year 2 [email_address]

7. Study site: the Necopastic River (250km²) -Undisturbed -Homogeneous lithology -Constant density of forest stands -Frequent ice-scouring events / but not destructive -Climatically homogeneous Many advantages -Winter breakup = rare [email_address]

8. Amont: 15 sites Mi-bassin: 16 sites Aval: 7 sites = Ice scouring activity = No ice scouring activity Study site: the Necopastic River (250km²) [email_address]

9. = Ice scouring activity = No ice scouring activity Study site: the Necopastic River (250km²) Upper basin: 15 sites Mid-basin: 16 sites Lower-basin: 7 sites [email_address]

10. Methods At each site: 1) Quantifying geometric properties of river channel [email_address]

12. Methods At each site 3) Dendrochronological sampling [email_address]

13. Methods (dendrochronological principles) 1) Site selection Select sites that are rectilinear and of constant width, depth & slope [email_address]

14. 2) Stem selection (sensitivity) Sensitive (large) Insensitive (small) snow Ice 1) Site selection Methods (dendrochronological principles) [email_address]

15. Sensitive Insensitive RFS (Radius at the First Scar) 2) Stem selection (sensitivity) 1) Site selection Methods (dendrochronological principles) [email_address]

18. > The intensity of a an ice-jam at year « t » ( I t ) is calculated from the proportion sites recording an event that year Methods (dendrochronological principles) [email_address]

19. Hydro-climatic analysis of the tree-ring series [email_address] Nécopastic (250km²) LG-1 (1500km²)

20. Discharge (m³) Time Hydro-climatic analysis of the tree-ring series END of hydrograph recession (d) DUR_REC Duration of recession (t) DUR_RISE Duration of rise (t) PEAK Peak discharge (m³ s -1 ) DTE_PEAK Date of flood peak (d) START of hydrograph rise (d) VOL Flood volume (m³) VOL_RISE Volume during rising limb (m³)

21. Hydro-climatic analysis of the tree-ring series [email_address] Time resoltution Variable Dimensions Period Spatial scale TEMPERATURES Source: IREQ, HQ / D. Tabsoba Monthly T_min, T_max, T_mean °C 1960-2003 LG-1 PRECIPITATION Source: IREQ, HQ/ D. Tabsoba Montlhy Total precipitation (PREC) cm / day 1960-2003 LG-1 SNOW COVER Source: IREQ, HQ / D. Tabsoba Monthly Height (H) cm 1950-2003 LG-1 Monthly Water equivalent (SWE) cm 1950-2003 LG-1 Monthly Density (DENS) Kg / m³ 1950-2003 ARCTIC OSCILLATION Source: NOAA (bi) Montlhy (March-April) Index (AO) - 1950-2003 Northern Hemisphere

22. -CART modelling Hydro-climatic analysis of the tree-ring series -80% of all years (1950-2003, N=54) are well simulated with three variables [email_address]

23. Fresh snow and cold spring temperatures delay the thermal degradation of the ice Arctic Oscillation (positive phase) Hydro-climatic analysis of the tree-ring series [email_address] + -

24. Intense ice-scouring No ice-scouring Early and « flash » floods Favor intense mechanical breakups Hydro-climatic analysis of the tree-ring series [email_address]

25. Geomorphological impact Does it vary as a function of ice-jam frequency? [email_address] Frequency = 9 events / (2008-1975) = 0,27 year -1 ~ One event each three year 2008 1978 1982 1988 1991 1995 2000 2003 2007 2008 1975 Site X

26. Reconstructed ice jam frequencies Geomorphological impact [email_address]

28. Geomorphological impact Upper Mid Lower [email_address]

29. Ice scoured channels Geomorphological impact [email_address] Genetic floodplain Erosion talus Ice scouring terrace Scarred trees with recent alluviums

30. Conceptual model relating ice-jam frequencies and riverbank adjustment Geomorphological impact [email_address] F ≥ 0.2 F < 0.2

32. Funding … [email_address]