kein Wässerchen trüben

Transcription

1 Bundesamt für Wasserwirtschaft Institut für Wasserbau und hydrometrische Prüfung Federal Agency for Watermanagement Institute for Hydraulic Engineering and Calibration of Hydrometrical Current-Meters kein Wässerchen trüben 1

2 Bundesamt für Wasserwirtschaft Institut für Wasserbau und hydrometrische Prüfung Different Interests in Sediments (Salzach River Case) Wien, 16 December 2011 Michael Hengl 2

3 Overview The catchment Interests (examples and local solutions) How to deal with different interest? Statements to questions 3 / 24

4 Catchment km², MQ = 250 m³/s, HQ 100 = m³/s 4 / 24 H y d r a u l i c s M o d e l T e s t s C a l i b r a t i o n W i e n - S e v e r i n g a s s e

5 Loehnersbach Interest: retain bedload to protect human life Photo: Wildbach- und Lawinenverbauung, Gebietsbauleitung Ober- und Mittelpinzgau This is just 1 example of many Photo: IWB 5 / 24

6 Hallein Interest (1 st of 3): stable riverbed (flood protection water level and bank stability) Photo: IWB Photo: IWB 6 / 24 This is just 1 example of many

7 Hallein Interest (2 nd of 3): as less as possible sediments (operation of hydro power station) Photo: Bernhard Sackl This is just 1 example of many 7 / 24 Photo: TU Graz

8 Hallein Interest (3 rd of 3): sediment transport only on the left side (operation of hydro power station) 8 / 24

9 Hallein Interest (3 rd of 3): sediment transport only on the left side (operation of hydro power station) Photo: IWB 9 / 24 Photo: IWB

10 City of Salzburg Interest: stable riverbed (flood protection) Photo: IWB Photo: IWB It s the same as in Hallein and many other places 10 / 24

11 Erosion (m) Downstream City of Salzburg Interest (1 st of 3): more bedload from upstream (reduce expense for flood protection and ecological measures) Year Mean bed level, river km Photo: IWB This reach is the Austrian German border and about 60 km long 11 / 24

12 Downstream City of Salzburg Interest (2 nd of 3): raise the riverbed to a new stable situation (flood protection, ecological improvement of river and wetlands) Photo: Christian Wiesenegger 12 / 24 Photo: Land Oberösterreich

13 Downstream City of Salzburg Interest (2 nd of 3): raise the riverbed to a new stable situation (flood protection, ecological improvement of river and wetlands) Depth [m] 13 / 24

14 Downstream City of Salzburg Interest (3 rd of 3): do not increase sedimentation in wetlands (conserve ecological status) Photo: IWB 14 / 24

15 Different Interests: only conflicts or a chance to reconcile? Reduce sediment transport Increase sediment transport Sediment transport only in designated areas Retain sediments, e.g. to raise the riverbed Mobilize sediments, e.g. to improve ecology We have to work much more together with a view on the whole catchment 15 / 24

16 Working together means Any local measure concerning sediment transport has to be checked: How will the measure effect the river upstream? What are the effects downstream (river and floodplains)? This has to be done in space and time! Points or reaches of interest 16 / 24

17 That was the first part of my talk AND NOW finally as a countdown Short Statements to 5 questions 17 / 24 H y d r a u l i c s M o d e l T e s t s C a l i b r a t i o n W i e n - S e v e r i n g a s s e

18 Climate change and sediment transport: what s the strongest challenge? My opinion: We have to know how the land cover is changing! Example: dying glaciers means more loose material on one hand, warmer climate means more vegetation on the other hand. But how fast does the vegetation cover grow and what are the risks of temporarily increased erosion in our alpine catchments? 5 Photos: IWB 18 / 24

19 Sediment monitoring: is the current sediment monitoring sufficient? gaps? It is still a challenge to get good quality information concerning: Bedload transport (quantity) Gradation of bedload and erosion areas (quality) We need a database for sediment data and related data like changes in geometry (catchment based) / 24

20 Major knowledge gaps in sediment management that would need more research? Main gap is: response due to changes in the catchment over long distances and with time! We need to know how sediments are mobilized and deposited (depending on different hydrological events, morphological systems and man made structures) We need to know how fast bedload is transported (different grain sizes have different velocities) We still need more knowledge about processes. Only after that we are really able to manage catchments! / 24

21 Wien - Severingasse Hydraulics Model Tests Calibration Do we know enough about the status of the sediment regime? Any river has a dynamic sediment regime! An answer is only possible if we have: Data from the past and at least an estimation of the future development which include developments in the catchment (not only in the future but also in the past and in the present). What we need is the same as mentioned in the questions just before! 21 /

22 Artificial floods downstream of big reservoirs: suitable to improve ecological status and reactivate the sediment regime downstream? If only water is used to create artificial floods, this measure is only temporary effective. In the long run we need water + sediment (with appropriate grain size distribution)! Photo: IWB A gravel bed river is only sustainable if it is regularly fed by gravel from the catchment! Consider: how large and important is the clogged part of the catchment for the river reach in focus? / 24

23 Summary We need solutions concerning the catchment and different interests in the catchment It s necessary to think in space and time Data are essential (including method of collecting) Knowledge of processes (mobilisation, transport, sedimentation) / 24

24 Bundesamt für Wasserwirtschaft Institut für Wasserbau und hydrometrische Prüfung Thank you for your attention! 24

25 Bundesamt für Wasserwirtschaft Institut für Wasserbau und hydrometrische Prüfung 25

26 Downstream City of Salzburg Interest (2 nd of 3): raise the riverbed to a new stable situation (flood protection, ecological improvement of river and wetlands) 26 / 24