Physical modelling of sediment transport in mountain torrents upstream of open check dams

Transcription

1 Physical modelling of sediment transport in mountain torrents upstream of open check dams Authors: Sebastian SCHWINDT Dr. Mário J. FRANCA Check dam in the region of Trent (Italy) Paper Code: EGU /04/2015 Programme Session GM7.1 Prof. Dr. Anton J. SCHLEISS

2 OVERVIEW RESEARCH BACKGROUND CASE STUDIES MODEL DESIGN MEASURING SYSTEM EVALUATION TARGET OVERVIEW 2

3 Research background Sediment and habitat dynamics (Wasserbau & Ökologie)» funding: Swiss Federal Office for the Environment (FOEN) Promotion of sediment continuity» conditioned sediment retention in upstream reaches» avoid sediment scarcity in draining channels BACKGROUND picture: Rhône, Switzerland 3

4 typical location for check dam Situation in the terrain (1) BACKGROUND picture from Hübl (2009) 4

5 Situation in the terrain (2) At channel slope change: varying sediment transport capacity Change of channel slope BACKGROUND picture from Hübl (2007) 5

6 Hydraulic aspects Floods and sediments are crucial for river ecology Large floods threaten infrastructures Challenge: Design flood protection which» provides sufficient safety for dwellers» allows dynamic river development Bank full discharge (Krimml, Austria) optimization of open check dams in terms of sediment transport continuity is required or what impact on sediment transport have flow obstacles in steep gravel bed rivers? BACKGROUND 6

7 Research approach Physical model most suitable Model design based on case studies of torrents and open check dams in the Alps No specific scale, but assures practical relevance» length ratios» similarity of sediment transport APPROACH pictures: Jenbach, Germany 7

8 MODEL DESIGN flow obstacle (open check dam) removable channel (tests with local widening) MODEL DESIGN 8

9 Design aspects Channel Roughness» channel bed composed of grains > D 84 of mobile sediment Geometry» J = 2 / 4 / 6 % Variable longitudinal slope MODEL DESIGN 9

10 Percent by weight [%] Design aspects Sediment feeding Used sediment mixture based on dimensionless curve for Alpine rivers established by Hersberger (2003) Dimensionless grain diameter D i /D m [-] Alps 60(own study) Hersberger Alps (Hersberger, (2003) 2003) Used mixture MODEL DESIGN 10

11 Design aspects Sediment feeding Supply system: Release container + conveyor belts MODEL DESIGN 11

12 Sediment output Measurement system: filter basket + scale suspended with a mobile crane wireless data transfer [1/s] MEASURING SYSTEM 12

13 Probe distance to surface [m] Ultrasonic probes Water level recording MEASURING SYSTEM 13

14 Surface flow velocity Particle image velocimetry» industrial CMOS camera (SMX-160C)» wide lens opening ( ) t t + Δt t t + Δt MEASURING SYSTEM 14

15 Particle image velocimetry» image abstraction Surface flow velocity Cropped region of interest Original image Flow direction: left to right Apply binary filter MEASURING SYSTEM 15

16 Surface flow velocity Particle image velocimetry» identification of particle movement t Flow direction: left to right t + Δt MEASURING SYSTEM 16

17 Channel width [m] Surface flow velocity Particle image velocimetry» time average of image series Stream wise velocity u [m/s] Channel length [m] MEASURING SYSTEM 17

18 Channel width [m] Surface flow velocity Particle image velocimetry» time average of image series Stream wise velocity u [m/s] Channel length [m] MEASURING SYSTEM 18

19 Channel width [m] Surface flow velocity Particle image velocimetry» time average of image series Horizontal velocity v [m/s] Channel length [m] MEASURING SYSTEM 19

20 Channel width [m] Surface flow velocity Particle image velocimetry» time average of image series Horizontal velocity v [m/s] Channel length [m] MEASURING SYSTEM 20

21 Sediment depositions Zenithal photography» same principal as for flow velocity» different time resolution (4 frames per minute) front velocity front velocity MEASURING SYSTEM 21

22 Evaluation target Derivation of flow energy balance + energy losses Derivation of transport capacity along the whole channel across obstacles (i.e. open check dam) EVALUATION TARGET 22

23 Acknowledgements to the Swiss Federal Office for the Environment (project funding) Partners: Swiss federal institute for forest, snow and landscape research Swiss federal institute of aquatic science and technology Laboratory of hydraulics, hydrology and glaciology ETH Zurich THANKS TO 23

24 Thank you for your attention. Questions? Krimmler Wasserfälle (Austria)