Boundary conditions in groundwater modeling
- 1. CEE-432 Environmental Design Sessional Dr. Bijit Kumar Banik Professor Department of Civil and Environmental Engineering Shahjalal University of Science and Technology Contact: bijit_sustbd@yahoo.com; bijit-cee@sust.edu Lecture-8 Influence of different boundary conditions on a Groundwater model using MODFLOW
- 3. Model Design - Boundaries Boundary type Boundary Name Common Applications First kind, or Dirichlet boundary Prescribed hydraulic head or concentration Lakes, rivers, springs, constant-head wells Second kind, or Neumann boundary Prescribed flux of head or concentration Impermeable boundary, water divide, streamline, infiltration, evaporation, sinks, and sources Third kind, or Cauchy boundary Semipermeable or head dependent flux Leaky rivers, drains, seepage face
- 4. • occurs when surface water body such as rivers, lakes, canals, sea coast interact freely with the aquifer • boundary condition most constraints the model solution and is therefore the easiest to solve • at least at 1 point in the model area head must be specified First kind or Dirichlet condition
- 5. Second kind or Neumann condition
- 6. • occurs if the aquifer terminates against an impermeable material • identical to streamlines • groundwater divides are no-flux boundaries • model user must ensure that during the model simulation the chosen boundary stays unaffected by the calculation • boundary condition moderately constraints the model solution and is therefore moderately difficult to solve Second kind or Neumann condition
- 7. • represents leakage from surface water bodies where exchange of water between aquifer and surface water depends on head differences between surface water and groundwater • occurs if the river bed acts as a semipermeable membrane between the river and aquifer • Boundary condition that least constraints the model solution and is therefore the most difficult to solve. Third kind or Cauchy condition
- 8. Further typical examples 1. Type 3. Type 2. Type Aquifer Well River River Well Colmated Zone Aquifer Aquicludes Normal Flow No Flow
- 9. 1. Type (free GW) 2. Type (constrained GW) 3. Type (semipermeable riverbed) Further typical examples
- 10. 10 Example area in Hamburg-Borgfelde model Background information: Case (a) Well Well
- 11. 11 Island of Foehr (North Sea) model Background information: Case (b) Well
- 12. 12 Meander loop of the river Moselle model Background information: Case (c) Well
- 13. 1100 L/min 1 80 m3/hr 2 70 m3/hr 3 60 m3/hr 4 50 m3/hr Discharge rate Group
- 14. 14 Exercise (Main steps) 1. File → New Model (use separate folder, short name) 2. Grid → Mesh Size Grid → Layer Type Grid → Boundary Condition → IBOUND (Modflow) Grid → Top of Layers Grid → Bottom of Layers 3. Parameters → Time Parameters → Initial Hydraulic Heads Parameters → Horizontal Hydraulic Conductivity Parameters → Effective Porosity 4. Models → MODFLOW → Well Models → MODFLOW → Run
- 16. 16 Grid → Mesh Size
- 17. 17 Grid → Mesh Size
- 18. 18 Grid → Mesh Size
- 19. 19
- 20. 20 Grid → Layer Type
- 21. 21 1 2 Grid → Layer Type
- 22. 22 Grid → Boundary Condition
- 23. 23 Right click on mouse 1 2 3 2 Grid → Boundary Condition
- 24. 24 1 Create boundaries by clicking the mouse or just drag down 2 1 1 Grid → Boundary Condition
- 25. 25 1 2 1 2 Grid → Boundary Condition
- 26. 26 Grid → Top of Layers (TOP)
- 27. 27 Grid → Top of Layers (TOP)
- 28. 28 Grid → Top of Layers (TOP)
- 29. 29 Grid → Top of Layers (TOP) 1 2
- 30. 30 Grid → Bottom of Layers (BOT) 1 2
- 31. 31 Grid → Bottom of Layers (BOT)
- 32. 32 Grid → Bottom of Layers (BOT)
- 33. 33 1 2 Grid → Bottom of Layers (BOT)
- 36. 36 Parameters → Initial Hydraulic Heads
- 37. 37 Parameters → Initial Hydraulic Heads
- 38. 38 1 2 Parameters → Initial Hydraulic Heads
- 39. 39 Right click on mouse 1 2 3 2 Parameters → Initial Hydraulic Heads
- 40. 40 1 Insert boundary values by clicking the mouse or just drag down 2 1 1 Parameters → Initial Hydraulic Heads
- 41. 41 1 2 1 2 Parameters → Initial Hydraulic Heads
- 42. 42 Parameters → Horizontal Hydraulic Conductivity
- 43. 43 Parameters → Horizontal Hydraulic Conductivity
- 44. 44 1 2 Parameters → Horizontal Hydraulic Conductivity
- 45. 45 1 2 1 2 Parameters → Horizontal Hydraulic Conductivity
- 46. 46 Parameters → Effective Porosity
- 47. 47 Parameters → Effective Porosity
- 48. 48 1 2 Parameters → Effective Porosity
- 49. 49 1 2 1 2 Parameters → Effective Porosity
- 50. 50 Models → MODFLOW → Well
- 51. 51 Right click on cell (1,14,14) 1 3 2 Models → MODFLOW → Well
- 52. 52 1 2 1 2 Models → MODFLOW → Well
- 53. 53 Models → MODFLOW → Run
- 54. 54 Models → MODFLOW → Run
- 55. 55 Models → MODFLOW → Run
- 60. 60 Thank you