Streams And Seepage

This section is the scientific entry point for stream supports, seepage, drainage outflow, and simulation-derived active stream networks.

It sits beside Hydrology and Forcing because these concepts are not only forcing inputs. They are groundwater-surface exchange concepts. Some objects are loaded or generated as geographic supports, some become solver boundary conditions, and some are post-processed interpretations of model outputs.

The organizing idea is simple but important: do not ask “where is the river?” before asking what role the river-like object plays in the model. A line can be an observation, a computational support, a boundary condition, or a diagnostic mask. Those roles should remain separate.

Recommended Reading Path

1. Start with Conceptual Model. It introduces the physical scene first, then brings in the equations and sketches progressively: stream boundary, seepage/drainage, simulated-active network.

2. Use Worked Examples when you want examples that connect the concepts to commands, files, and figures that can actually be opened.

3. Use Status And Limitations to check what is currently supported, what is demonstrated by examples, and what is not yet a stable contract.

4. Use Stream, Ocean, And Drainage Semantics when you need solver-facing vocabulary for stream, ocean, and drainage.

5. Use Simulated Active Network when the question is how a simulated seepage or drainage field becomes an active-network view.

6. Use Nancon K-Sweep Results and Network Metrics And Extreme K-Sweep when you want concrete results, figures, and comparison metrics. The latter page is the metric map: overlap, planar bidirectional distance, and the remaining downslope distance work needed to reproduce the article-style criterion.

The pages are ordered this way because the equations are meaningful only after the modelling question is clear. A prescribed stream head, a seepage threshold, and a post-processed active mask may occupy nearby places on the map, but they do not have the same scientific status.

Object Roles

HydroModPy separates three network roles.

reference

The observed or externally loaded stream network. This is the validation target when comparing simulated activity to hydrography.

generated

A DEM/topography-derived network. It can be useful as a geomorphological diagnostic or as a modelling support, but it is not an observation.

simulated_active

The active network inferred from simulated drainage or seepage fields. It is a result interpretation, not an input network.

For scientific validation of simulated activity, the target is reference. If the run has no reference network, HydroModPy should skip the simulated-active overlap comparison rather than silently falling back to generated.

Method Roles At A Glance

Role	Question answered	What exists before solve	What exists after solve
Stream boundary	How much water is exchanged against a known surface head?	support and prescribed H_stream	computed q_stream
Seepage / drainage	Where does groundwater emerge at the surface?	support and local z_s	computed outflow_drain or q_seep
Simulated active network	Which connected network is implied by simulated emergence?	positive outflow field and routing graph	accumulation_flux, mask, metrics

Examples That Carry The Explanation

The section has one dedicated example page:

• Worked Examples

• Status And Limitations

Use these as the bridge between the concepts and the actual artifacts. They explain which example is best for:

• choosing between a stream boundary and a seepage/drainage operator;

• checking the MODFLOW 6 outflow_drain to accumulation_flux path;

• reading the Nancon MODFLOW 6 K-sweep against the observed reference network;

• using the MODFLOW-NWT Nancon basin page as a legacy baseline;

• reading comparison folders in a defensible order.

Concept Map

The map below is intentionally placed after the reading path and role table. It is a compact implementation view, not the first explanation of the concept.

The important separation is:

• stream linework can be an observed object, a generated object, or a support;

• stream-style boundaries prescribe a stage/head condition;

• seepage or drainage conditions prescribe a release law controlled by h - z_s;

• the simulated active network is computed after the groundwater solve.