MODFLOW-NWT Flow#

This page groups scientific reading for flow/modflow_nwt.

Use this path when the study needs continuity with legacy structured-grid MODFLOW-NWT workflows or downstream transport/modpath and transport/mt3dms compatibility.

What Is Repeated From The Common MODFLOW Part#

flow/modflow_nwt still uses the common MODFLOW-family contract:

  • hydraulic head is the primary groundwater-flow state;

  • recharge, wells, storage, imposed heads, and drainage are normalized by the HydroModPy Flow layer before backend assembly;

  • stress periods carry the time discretization seen by the backend;

  • package semantics must be documented before interpreting a result;

  • comparison against another backend requires checking mesh, vertical representation, forcing aggregation, and boundary-condition mapping.

This repetition is intentional. The MODFLOW-NWT page should be readable without first opening the MODFLOW 6 page.

MODFLOW-NWT Specifics#

Topic

MODFLOW-NWT interpretation

Process pair

flow/modflow_nwt.

Backend family

MODFLOW-NWT.

Grid support

Structured sgrid support.

Package vocabulary

Legacy MODFLOW package route for flow, recharge, storage, boundary conditions, and outputs.

Legacy continuity

Useful for reproducing or comparing with historical studies that were calibrated around MODFLOW-NWT assumptions.

Downstream transport

Preferred path for transport/modpath and transport/mt3dms.

Focused Reading#

Typical Use Cases#

Use flow/modflow_nwt when:

  • the study is structured-grid only;

  • the target is continuity with an older MODFLOW-NWT workflow;

  • downstream particle tracking should use MODPATH;

  • downstream concentration transport should use MT3DMS;

  • a comparison needs a legacy MODFLOW-family baseline.

Be explicit when:

  • the same physical case is also run with MODFLOW 6;

  • MODFLOW 6 uses a different grid topology or XT3D setting;

  • observations or validation profiles are compared after spatial aggregation;

  • transport results depend on this upstream flow field.

Surface-Seepage Baseline Example#

For this work, the most useful MODFLOW-NWT example is the committed Nancon transient basin page:

Use it as a legacy baseline because it already places the important evidence in one reading sequence:

  1. hydrographic reference versus generated linework;

  2. simulated active-network overlay against reference;

  3. piezometric map;

  4. hydrograph;

  5. water budget.

Piezometric map from the Nancon MODFLOW-NWT run
The piezometric map is the first state figure for this legacy structured MODFLOW-NWT baseline.
Hydrograph from the Nancon MODFLOW-NWT run
The hydrograph connects the structured-grid solve to observed discharge at basin scale.
Water budget from the Nancon MODFLOW-NWT run
The budget is where recharge, ET, storage, and drainage package behaviour should be checked before drawing conclusions from one map.

That is the discipline to preserve when comparing with MODFLOW 6. Copy the scientific reading order, not every backend assumption. MODFLOW-NWT remains structured-grid and legacy-package oriented, while MODFLOW 6 must also document mesh topology, package extraction, and active-network result fields.

For the cross-backend examples and commands, see Worked Examples. For current contracts and non-contracts around simulated active networks, see Status And Limitations.

Scientific Checklist#

Decision point

What to document

Grid support

Structured sgrid support.

Legacy continuity

Whether the run is intended to reproduce or compare with older MODFLOW-NWT studies.

Package envelope

Which recharge, well, storage, and boundary-condition packages are assembled.

Comparison target

Whether the run is compared to MODFLOW 6, Boussinesq, an analytical case, or field observations.

Transport coupling

Whether the flow run must feed transport/modpath or transport/mt3dms.

Minimal Plan Shape#

[[simulation.process]]
id = "flow_main"
type = "flow"
solvers = ["modflow_nwt"]

[solver]
backend = { backend = "modflow_nwt" }

Minimal Process Interpretation#

The short TOML shape above means:

  • one flow process is requested;

  • the selected solver name is modflow_nwt;

  • HydroModPy resolves common Flow inputs to the MODFLOW-NWT route;

  • the final scientific interpretation depends on structured support, package choices, stress periods, and downstream legacy transport needs.

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