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DSD-INT 2018 Experiences from modelling a branched lowland river in NE Germany with Delft3D FM Suite - Ley

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Presentation by Rita Ley, Federal Institute of Hydrology, Germany, at the Delft3D - User Days (Day 1: Hydrology and hydrodynamics), during Delft Software Days - Edition 2018. Monday, 12 November 2018, Delft.

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DSD-INT 2018 Experiences from modelling a branched lowland river in NE Germany with Delft3D FM Suite - Ley

  1. 1. Experiences from modelling a branched lowland river in NE Germany with Delft3D FM Suite Rita Ley, Markus Promny German Federal Institute of Hydrology (BfG)
  2. 2. Structure 1. Project 2. Study area: the river Havel 3. 3 grid variations 4. Model results 5. Summary 6. Conclusion 12.11.2018 2Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  3. 3. 1. Project 12.11.2018 Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley 3 Geesthacht Gnevsdorf Tangermünde Rathenow Berlin © GeoBasis-DE/ BKG 2017 Untere Mittelelbe Havelpolder Havelstauregime
  4. 4. 1. Project: River Havel 12.11.2018 4 gauge water model area pilot study area Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  5. 5. 2. Study area: the river Havel • 23 km river Havel: 12.11.2018 5Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  6. 6. 2. Study area: the river Havel Digital elevation model: – land and water – resolution: 1m 12.11.2018 Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley 6
  7. 7. 2. Study area: the river Havel • about 23 km mainflow (navigation channel), lowland river • impoundment, weir Brandenburg • width (navigation channel): ≥ 75 m, river widenings • lakes, secondary channels, trenches, navigation channel • flow velocity: 0.1 – 0.7 m/s (flood), • mean flow rate: 72 m³/s, pluvial regime • very low slopes • water surface slope: 5 – 20 cm / 20 km • mean bed slope < 0.01% 12.11.2018 Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley 7
  8. 8. 3. grid variations Grid generation ➢ Search for an optimal grid for this river section Combination of curvilinear and triangular parts? Test of 3 Grids: A: wide curvilinear grid over all flow paths B: small curvilinear grid restricted to the main channel C: detailed grid with curvilinear parts for all channels setting: • same borders, structural lines and bed level • similar orthogonality, smoothness and edge lengths 12.11.2018 8Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  9. 9. 3. grid variations 12.11.2018 9 A: wide curvilinear grid: over all mid-water flow paths element sizes: • curvilinear part: from 20x20 m • triangles: up to 400 m grid A channel water area Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  10. 10. 3. grid variations 12.11.2018 10 A: wide curvilinear grid Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  11. 11. 3. grid variations 12.11.2018 11 B: small curvilinear grid restricted to the main channel element sizes: • curvilinear part: side length from 20 m • triangles: up to 400 m grid A channel water area Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  12. 12. 3. grid variations 12.11.2018 12 B: small curvilinear grid restricted to the main channel Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  13. 13. 3. grid variations 12.11.2018 13 Version C: detailed curvilinear grid element sizes: • curvilinear part: from 20 m • triangles: up to 400 m grid A channel water area Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  14. 14. 3. grid variations 12.11.2018 14 Version C: detailed curvilinear grid Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  15. 15. 0 20 000 40 000 60 000 80 000 100 000 120 000 140 000 160 000 180 000 200 000 < 25 25 - 50 50 - 100 100 - 200 200 - 300 > 300 Quantitygridelements Longest element edge [m] Cumulative Curve of edge lengths - longest element edge Grid A, wide curvilinear grid 3. grid variations 12.11.2018 15 Quantity and size of grid elements < 25 m 25-50 m 50-100 m 100-200 m 200-300 m > 300 m Longest element edge Cumulative Curve of edge lengths - longest element edge Grid A, wide curvilinear grid Grid B, small curvilinear grid Grid C, detailed curvilinear grid Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  16. 16. 4. model results water level, MQ, no calibration 12.11.2018 16Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley A B C
  17. 17. 4. model results example: secondary channels 12.11.2018 17 elevation [m] Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  18. 18. C 4. model results 12.11.2018 18 B A example: secondary channels: flow velocity at mean flow Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  19. 19. 4. model results 12.11.2018 19 A B C example: secondary channels: water depth at mean flow Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  20. 20. 4. model results example: lake 12.11.2018 20 elevation [m] Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  21. 21. B 4. model results example: lake flow velocity at mean flow 12.11.2018 21 C A Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  22. 22. 4. model results example: lake water depth at mean flow 12.11.2018 22 C B A Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  23. 23. 4. model results 12.11.2018 23 A broad curvilinear B small curvilinear C detailed curvilinear Expense to build grid: least medium high computing time [h] DFM_OUTPUT _FlowFM [GB] computing time [h] DFM_OUTPUT _FlowFM [GB] computing time [h] DFM_OUTPUT _FlowFM [GB] Testcase 1 19 days 5 2.3 1 0.95 3 1.3 Testcase 2 29 days 6.5 3.7 4.4 1.5 3.5 2.15 Testcase 3 24 days 3 1.2 1.9 Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  24. 24. 5. Summary water level flow velocity computing time size output file expense grid building: A: least B: medium C: high 12.11.2018 24 similar for all grids large differences: Grid A: slow and largest output files Grid B: fast and smallest output files Grid C: between A and C Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  25. 25. 6. Conclusion Arrangement of grids ➢ less influence on model results ➢ strong influence on: ▪ computational time ▪ size of output files ▪ expense to bild grid ➢ especially for large models: Grid layout determines the practicability of a model! 12.11.2018 25Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley
  26. 26. 12.11.2018 Delft3D User Days 2018, Hydrodynamics in rivers Rita Ley 26 Thank you for your attention Dr. Rita Ley Bundesanstalt für Gewässerkunde Referat M2 D-56068 Koblenz Tel +49 261 1306 5927 Mail: Ley@bafg.de

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