Solver features
This is where the equations get a vote. Solver features are alternatives to released EPA SWMM behavior that you explicitly select, and they can change your results. Changes to ownership and integration have their own software architecture page.
You have to turn these on
These features are disabled unless selected. The default solver already includes unpublished EPA 5.3 improvements and corrections to that development version, as described in the default solver baseline. Feature selections are identified in reports and compatibility documentation.
Available features
| Domain | Feature | Default | Opt-in effect |
|---|---|---|---|
| Hydraulics | True-ellipse hydraulics | EPA_LEGACY |
Uses one mathematical ellipse for custom horizontal and vertical sections |
| Hydrology | Antecedent Moisture Model RDII | EPA behavior | Generates temperature-sensitive RDII from standard and baseflow AMM components and combines it with native RTK at assigned nodes |
Hydraulics
Hydraulic features can change conduit geometry, conveyance, storage, flow, or
depth. TRUE_ELLIPSE changes custom horizontal and vertical ellipse sections.
See the hydraulic feature index for selection and scope, or the true-ellipse detail page for its equations, modeling implications, and verification.
Hydrology
The Antecedent Moisture Model RDII extension generates rainfall-dependent infiltration/inflow from reusable standard and baseflow AMM components. It uses existing rain gages and project temperature data, and its flow can be combined with native RTK RDII at the same node.
Models enable AMM with [AMM_MODELS], [AMM_COMPONENTS], and [AMM_RDII].
Released EPA SWMM rejects these sections.
Requirements for non-EPA solver features
An alternative formulation needs more than an interesting idea and an options flag. It must be:
- explicitly enabled;
- documented as non-EPA behavior;
- covered by focused behavior and compatibility tests;
- visible in reports or public configuration; and
- excluded from the default EPA-compatible path.
Treat a feature selection as a model change. Read its detailed page before enabling it, and compare critical projects against a trusted EPA SWMM release.