Erosion of the Sava riverbed in Croatia and its foreseeable consequences

1. Erosion of the Sava riverbed in Croatia and its foreseeable consequences Gordon Gilja, Faculty of Civil Engineering, University of Zagreb, Croatia – ggilja@grad.hr Dijana Oskoruš, Meteorological and Hydrological Service, Croatia – oskorus@cirus.dhz.hr Neven Kuspilić, Faculty of Civil Engineering, University of Zagreb, Croatia – kuspa@grad.hr

2. Erosion of the Sava riverbed in Croatia andits foreseeable consequences • Introduction • Deepening of the Sava riverbed • Hydrological indicators of morphological changes • Consequences of riverbed degradation • Conclusions Contents: 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 2

3. Natural stable in their mean height position natural balance of sediment transport Regulated Shortened length Increased longitudinal slope >I Increased flow velocity >v and >v* Increased shear stress >τ Inception of sediment motion Morphological changes in riverbed Problem orientation? 1. Introduction Alluvial channels Alluvial channels: 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 3

4. 1. Introduction • gravel exploitation at 12 locations in the Zagreb area • flood protection • planned water accumulations for future HEPP Sava river basin Sava river basin 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 4

5. 2. Deepening of the Sava riverbed Identifiers • 1. Problem: • thermal power plant (TE-TO Zagreb) shut down due to the low Sava River and discontinued supply of cooling water • 1. Solution: • construction of submerged wier for water level stabilization • 2. Problem: • Jankomir overflow activation disrupted (1900 m3/s  2350 m3/s) • 2. Solution: • none 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 5

6. 3. Hydrological indicators of morphological changes 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 6

7. 3. Hydrological indicators of morphological changes 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 7

8. 4. Consequences of riverbed degradation • Structures are designed to withstand conditions relevant at the time of construction • If the conditions change, the balance of forces affecting the structure is disrupted • Hydraulic structure in the river reduces the local discharge profile, causing backwater effects and disruption of the flow pattern, resulting in increased velocity and unit discharge, as well as increase in local shear stress. • Loss of bridge stability due to flow impact partakes with 55% in overall bridge stability losses 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 8

9. 4. Consequences of riverbed degradation Example – Mičevec railway bridge on Sava river 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 9

10. 4. Consequences of riverbed degradation 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 10

11. 4. Conclusions • Although stages are a good indicator of the changes in the riverbed morphology, they are not an independent physical value – they need to be supplemented with discharge • Discharge curve changes with the riverbed degradation, which means it needs to be regularly audited and updated • Lack of monitoring causes lower awareness about the problems relating to structures in riverbeds 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 11

12. Thank you for your attention Questions ? Gordon Gilja, Faculty of Civil Engineering, University of Zagreb, Croatia – ggilja@grad.hr Dijana Oskoruš, Meteorological and Hydrological Service, Croatia – oskorus@cirus.dhz.hr Neven Kuspilić, Faculty of Civil Engineering, University of Zagreb, Croatia – kuspa@grad.hr 504 - Erosion of the Sava riverbed in Croatia and its foreseeable consequences BALWOIS 2010 Page 12