CHANNEL ADJUSTMENTS IN NORTH-EASTERN ITALY AND POTENTIALS FOR CHANNEL RECOVERY

1. CHANNEL ADJUSTMENTS IN NORTH-EASTERN ITALY AND POTENTIALS FOR CHANNEL RECOVERY Nicola Surian Department of Geography, University of Padova, Italy Séminaire GESTRANS Monastére de Sainte Croix, 3 November 2010

2. CHANNEL ADJUSTMENTS AND ENVIRONMENTAL EFFECTS • Remarkable adjustments (narrowing up to 80 %; incision up to 10 m) of most Italian rivers over the last 100 years in response to a range of human activities • Effects on structures (e.g. bridges); groundwater; ecology; flood conveyance

3. Whatis the magnitudeofchannelchange ? Whendidchanges start tooccurr ? Are thesechangesstillon-going ?

4. What about bed-level adjustments ? Which are the causes of these adjustments ? TRAJECTORIES OF CHANNEL EVOLUTION

5. TRAJECTORIES OF CHANNEL EVOLUTION A B C

6. KEY QUESTIONS • How to manage/restore disturbed alluvial channels ? • What is the channel recovery that could be expected in the next few decades ?

7. INGREDIENTS FOR MANAGING/RESTORING PHYSICAL PROCESSES IN GRAVEL-BED RIVERS • Reconstruction of recent and present channel changes (trajectories of changes) • Analysis of sediment yield and fluxes (connectivity) • Models (conceptual and numerical) to assess management strategies and channel evolution

8. Outline Channel adjustments in north-eastern Italy Possible management strategies and potential for channel recovery An on-going project: “Linking geomorphological processes and vegetation dynamics in gravel-bed rivers”

9. DOLOMITES Tagliamento R. Cellina R. Piave R. VENETIAN-FRIULIAN PLAIN Brenta R. ADRIATIC SEA Venice 0 20 km

10. Caratteristiche Tratto 137 (23)

11. Changes in channel width over the last 200 years Surian et al., RRA, 2009

12. BED-LEVEL CHANGES

13. Equilibrium ? Coupling lateral and vertical adjustments Widening not always associated to aggradation What about the present condition: equilibrium or unstable condition ?

14. CAUSES OF CHANNEL ADJUSTMENTS • Channelization • Reforestation • Dams • Sediment extraction Alteration of SEDIMENT REGIME Sediment mining: extraction rates largely exceeded (10 times or more) replenishment rates

15. 1 2 3 Phases of adjustments and human interventions Phase 1: reforestation; torrent control works; channelization Phase 2: gravel mining; dams; reforestation; torrent control works; channelization

16. SEDIMENT CONNECTIVITY Cellina River Piave River (mountain reach)

17. CLASSIFICATION OF RIVER REACHES BASED ON CHANNEL ADJUSTMENTS AND SEDIMENT CONNECTIVITY

18. WHICH CHANNEL MORPHOLOGY CAN BE EXPECTED IN THE NEXT 40-50 YEARS ? • Assumptions: • No dramatic changes in land use and human activities • Effects of very large flood events (e.g. > 100 yr return period) are not teken into account

19. FUTURE SCENARIOS OF CHANNEL CHANGES ACCORDING TO DIFFERENT STRATEGIES OF SEDIMENT MANAGEMENT

20. Example 1: possible future scenarios in the Piave River (mountain reach)

21. Example 2: possible future scenarios in the Brenta River

22. Modelling long term channel evolution Use of CAESAR (Coulthard et al., 2007), a reduced complexity cellular model Tagliamento River Ziliani et al., 2010, Gravel-bed River Conference 7

23. CONCLUSIONS AND RESEARCH PERSPECTIVES • According to evolution trajectories and sediment supply/connectivity a range of conditions do exist in gravel-bed rivers of north-eastern Italy (from high potentials to high limitations for channel recovery) • The conceptual modelling can be used to set priorities, goals and to identify the type of intervention in relation to a certain goal (e.g. no action or interventions at both reach and basin scale) • Estimate of sediment transport and sediment dynamics at fluvial network scale

24. LINKING GEOMORPHOLOGICAL PROCESSES AND VEGETATION DYNAMICS IN GRAVEL-BED RIVERS Cariparo Excellence Research Project 2008-2009

25. Research group: • Department of Geography, Univ. of Padova: N. Surian, B. Golfieri, L. Ziliani • Department of Land and Agro-Forest Environment, Univ. of Padova: M.A. Lenzi, L. Picco, L. Mao, E. Rigon, G. Kaless, P. Vitti, F. Comiti (Univ. of Bolzano) • Department of Civil and Environmental Engineering, Univ. of Trento: M. Tubino, W. Bertoldi; M. Welber; G. Zolezzi • Time schedule: September 2009 – August 2012

26. DOLOMITES Tagliamento R. Cellina R. Piave R. VENETIAN-FRIULIAN PLAIN Brenta R. ADRIATIC SEA Venice 0 20 km

29. General structure of the project WP1 – Topography and remote sensing WP2 - Hydrology and hydraulics WP3 - Riparian vegetation and in-channel wood dynamics WP4 - Sediment entrainment and bedload transport WP5 - Channel morphology WP6 - Morphodynamic modelling WP7 - Project management and dissemination

30. Aims of the project • Investigation of crucial threshold conditions, e.g. sediment motion, wood jam entrainment, island establishment/erosion; • Estimation of bed-load transport flux in gravel-bed rivers; • Prediction of future channel dynamics, using different models (e.g. conceptual, physical and cellular models); • Transfer of the scientific knowledge, as well as of tools and methods, to river management and restoration

31. Techniques and their temporal and spatial scales of application

32. WP4 - Sediment dynamics and bedload transport • Thresholds for particle movement • Partial transport condition • Bed load estimate: particle path length; active channel width, depth of active layer • Methods: tracers (painted sediments and PIT); scour chains • Field work at sub-reach scale (1,5-3 km): • 3 sub-reaches in the Brenta: 6 cross sections • 2 sub-reaches in the Tagliamento: 6 cross sections

33. Tracers: painted sediments

34. Painted sediments, morphological units, effects of different flood events Mao and Surian, Geomorphology, 2010

35. Morphological effects of different flood events Surian et al., 2009; ESPL Mao & Surian, 2010, Geomorphology

36. Tracers: PIT (Passive Integrated Transponders)