- 1. Recent MODFLOW Developments By Christian Langevin (USGS), Joseph Hughes (USGS), and Martijn Russcher (Deltares) Presented at the Deltares Hydrology International User Days Deltares Campus, Delft, The Netherlands November 30, 2023
- 2. Outline • Background • MODFLOW 6 Framework • Flow Model • Transport Model • Advanced Capabilities • Concluding Remarks
- 3. MODFLOW Development Team • Wes Bonelli, UCAR • Scott Boyce, USGS • Joseph Hughes, USGS • Christian Langevin, USGS • Joshua Larsen, USGS • James McCreight, UCAR • Eric Morway, USGS • Sorab Panday, GSI • Scott Paulinski, USGS • Alden Provost, USGS • Michael Reno, UCAR • Martijn Russcher, Deltares
- 5. Groundwater Modeling (before computers) Arlen Harbaugh (retired USGS) works on the Long Island, New York, electric analog model. Each panel represents a different model layer.
- 7. MODFLOW 1984 Modular concept was inspired by stereo system components
- 8. Many Different MODFLOW Packages… Packages have become more complex over time, and in many cases, they model a physical process
- 9. History • MODFLOW introduced almost 40 years ago • Referred to as a ”community model” • Designed to be modular, teachable, portable, and extensible • Thorough documentation • Stable funding
- 10. MODFLOW Versions and Variants Core Version 1984 1988 1996 2000 2005 Variants NWT LGR USG GWM SEAWAT GSFLOW CFP OWHM Development Paths 2017
- 12. MODFLOW 6 Overview • First released in 2017 • Consolidation of existing functionality • Multiple model types in a single simulation • Multiple model instances in a single simulation • Flexible construction and solution of matrix equations
- 13. Development Philosophy • Preserve and protect • Modularity • Capabilities • Portability • Readability • Documentation • Open and Free • Continuous Integration
- 14. Model Types Groundwater Flow (GWF) Groundwater Transport (GWT) Published and available now Groundwater Energy Transport (GWE) Coming soon Particle Tracking (PRT) Surface Water Flow (SWF) Watershed Linear Network Flow (LNF) In development
- 15. Typical Groundwater Flow Simulation This figure shows a typical simulation with one groundwater flow model that is solved by a numerical solution.
- 16. Multi-Model Groundwater Flow Simulation This figure shows two separate groundwater flow models that are tightly coupled (at the matrix level) and solved simultaneously by a numerical solution. Coupling between the two models is facilitated by an “exchange”.
- 17. MODFLOW 6 Groundwater Flow (GWF) Model
- 18. Discretization Types in MODFLOW 6 DIS (Regular Grid) DISV (Layered Unstructured Grid) DISU (Fully Unstructured Grid) ”Layered” = same grid applies for each layer No formal layer concept
- 19. Supported Groundwater Flow Formulations • Traditional “conductance-based” formulation • Newton-Raphson formulation (provides stability for water table problems)
- 20. What happens with the Newton Formulation? Qrecharge 1 2 3 h1 h2 h3 ”dry” Heads are calculated by MODFLOW and may be below the cell bottom ”dry” partially saturated
- 21. Flux Approximations • MODFLOW 6 has two different ways to calculate the flow between two cells: • Two-point flux approximation • Multi-point flux approximation (XT3D)
- 22. Two-Point Flux Approximation • Flow between two cells is calculated using the head difference between the two cells • Common approach that works well for most problems
- 23. Multi-Point Flux Approximation (XT3D) • Gradient reconstruction method (Provost et al. 2017) • Originally developed to represent anisotropic groundwater flow • Improves accuracy for grids with irregular geometric connections • Computationally more expensive than two- point standard approximation
- 24. Water Mover • Generalized package for transferring water from one MODFLOW package to another package • Water can be transferred from a “provider” to a “receiver” subject to simplified rules • All transfers are tracked in a water budget
- 25. GWF Model Coupling • GWF models can be coupled using a GWF-GWF “exchange” • Exchange input file contains geometrical data for connection between neighboring nodes Ln n m Lm Δw Model 1 Model 2
- 26. MODFLOW 6 Groundwater Transport (GWT) Model
- 27. Highlights of the GWT Model Grid Types Flow Formulations Transport Processes Advanced Transport Packages Multiple Chemical Species Multi-Domain • Standard conductance-based • Newton • Advection • Dispersion • Sorption • Decay/Growth • Sources/Sinks • Streams • Lakes • Wells • Unsaturated Zone
- 28. ”Keating” Flow and Transport Problem
- 29. Multi-Model Flow and Transport Configurations
- 30. Coupled Variable-Density Flow and Transport • SEAWAT capabilities now available in MODFLOW 6 • Buoyancy Package • Viscosity Package • Capabilities • Structured or unstructured grids • Traditional or Newton flow formulation • Advanced packages • Multi-model simulations
- 31. Variable-Density Example • Based on classic Henry saltwater intrusion problem • Use Newton formulation for stable wetting and drying • Include tidally varying sea-level boundary condition
- 33. Advanced Capabilities MODFLOW API Parallel Simulations
- 34. MODFLOW-API • Full control of MODFLOW while it’s running • Well-defined interfaces based on Basic Model Interface (BMI) standard • Access to MODFLOW internal variables (as a copy or pointer) during runtime • Uses a shared library (DLL) version of MODFLOW 6 based on the same code as the executable version • API use cases • Couple MODFLOW with another model • Prototype or develop new MODFLOW packages • “Observe” MODFLOW behavior during a simulation Hughes et al. (2022)
- 35. How does it work? finalize update initialize Create (CR) Define (DF) Read and Prepare (RP) start end Last Time Step TIME STEP LOOP YES NO Allocate and Read (AR) Calculate (CA) Output (OT) Final Processing (FP) Time Update (TU) Deallocate (DA) Main Program mf6 = ModflowApi(‘libmf6.dll’) mf6.initialize() current_time = 0. end_time = mf6.get_end_time() while current_time < end_time: mf6.update() current_time = mf6.get_current_time() mf6.finalize() Python Driver Program
- 37. Parallel MODFLOW 6 • Officially released June 2023 in MODFLOW Version 6.4.2 • Long-standing collaborative effort between Deltares and USGS • Designed to be easily extended for new models • Technical Details • Domain decomposition approach • Based on the Message Passing Interface (MPI) • Based on PETSc (Portable, Extensible Toolkit for Scientific Computation) • Supports GWF, GWT and variable-density flow and transport
- 38. Concept
- 43. In Summary • MODFLOW 6 is the current version of the USGS Modular Hydrologic Simulator • In MODFLOW 6, the “package” concept has been extended to include models, resulting in a multi-model hydrologic simulator • We are continuing to extend simulation capabilities by adding new models to the framework and by using the MODFLOW-API to couple with other existing models