swmm-builder git:20260609.399e1d7A

Immutable. This exact content is served forever at /api/v1/blob/f0ec493b09300dd1.

---
name: swmm-builder
description: Assemble a runnable SWMM INP deterministically from subcatchment geometry/attributes, merged parameter JSON, network JSON, and climate references. Use when creating auditable INP + manifest artifacts for downstream swmm-runner/calibration.
---

# SWMM Builder (INP assembly layer)

## Contract
Build a runnable SWMM `.inp` using explicit file inputs:
- `subcatchments.csv` (shape/area/outlet/routing basics)
- merged params JSON from `swmm-params`
- network JSON from `swmm-network`
- rainfall/time-series references from `swmm-climate`
- optional options config JSON

The builder writes:
- final SWMM INP text (`--out-inp`)
- manifest JSON (`--out-manifest`) with source paths + SHA256 + key metadata
- strict validation diagnostics for critical sections (`[OPTIONS]`, `[RAINGAGES]`, `[TIMESERIES]`, `[SUBCATCHMENTS]`, `[SUBAREAS]`, `[INFILTRATION]`, and current network sections)

## Inputs
### Subcatchments CSV schema (required)
Required columns:
- `subcatchment_id`
- `outlet`
- `area_ha`
- `width_m`
- `slope_pct`

Optional columns:
- `rain_gage` (falls back to default gage from climate/config)
- `curb_length_m` (default `0`)
- `snow_pack` (default blank)

### Params JSON (required)
Expected to match `skills/swmm-params/scripts/merge_swmm_params.py` output:
- `sections.subcatchments` (`id`, `pct_imperv`)
- `sections.subareas` (`id`, runoff/subarea fields)
- `sections.infiltration` (`id`, Green-Ampt fields)
- Required fields are now validated strictly with type/range checks (for example `%Imperv` and routing percentages must be `0..100`).

### Network JSON (required)
Expected to match `skills/swmm-network` schema (`junctions`, `outfalls`, `conduits`, etc.).
Builder now validates required network fields used to emit `[JUNCTIONS]`, `[OUTFALLS]`, `[CONDUITS]`, `[XSECTIONS]`, `[COORDINATES]`, and `[VERTICES]`.

### Climate references (required in MVP)
Provide either:
- `--timeseries-text` directly, or
- `--rainfall-json` produced by `swmm-climate/format_rainfall.py` (must include `outputs.timeseries_text`)

For `[RAINGAGES]`, provide either:
- `--raingage-json` from `swmm-climate/build_raingage_section.py`, or
- rely on default deterministic gage generation from rainfall `series_name`.

`--raingage-json` supports both the original single-gage form and a multi-gage form:

```json
{
  "gages": [
    {
      "id": "RG1",
      "rain_format": "VOLUME",
      "interval_min": 5,
      "scf": 1.0,
      "source": {"kind": "TIMESERIES", "series_name": "TS_RG1"}
    },
    {
      "id": "RG2",
      "rain_format": "VOLUME",
      "interval_min": 5,
      "scf": 1.0,
      "source": {"kind": "TIMESERIES", "series_name": "TS_RG2"}
    }
  ]
}
```

The timeseries text must include rows for every referenced `series_name`, and each subcatchment `rain_gage` must reference one of the emitted gage IDs.

Validation behavior:
- Missing critical fields fail fast with explicit section-scoped errors.
- `[TIMESERIES]` rows are validated for series-name consistency and basic token/time/value correctness.
- Manifest includes `validation` plus `validation_diagnostics` metadata.

## Scripts
- `scripts/build_swmm_inp.py`
  - single entrypoint that reads all inputs and writes INP + manifest.

## MCP
MCP wrapper location:
- `mcp/swmm-builder/server.js` (was previously `skills/swmm-builder/scripts/mcp/`; moved during the mcp/ root restructure)

Exposed tools:
- `build_inp` — assemble a runnable SWMM INP + manifest from
  subcatchments CSV, area-weighted params JSON, network JSON, rainfall
  JSON + timeseries text, and an options-config JSON. Required args:
  `subcatchmentsCsvPath`, `paramsJsonPath`, `networkJsonPath`,
  `outInpPath`, `outManifestPath`. Optional: `rainfallJsonPath`,
  `raingageJsonPath`, `timeseriesTextPath`, `configJsonPath`,
  `defaultGageId`. The subcatchments CSV must carry `outlet` values
  that point to real upstream junctions (use
  `swmm-network-mcp.assign_subcatchment_outlets` first if it currently
  points to the literal outfall).

## Smoke example

The builder requires upstream outputs from `swmm-params` and `swmm-climate`.
Generate them first, then call `build_swmm_inp.py`:

```bash
# 1. Generate merged params from the bundled examples
mkdir -p /tmp/builder-smoke
python3 skills/swmm-params/scripts/landuse_to_swmm_params.py \
  --input skills/swmm-params/examples/landuse_input.csv \
  --output /tmp/builder-smoke/landuse.json
python3 skills/swmm-params/scripts/soil_to_greenampt.py \
  --input skills/swmm-params/examples/soil_input.csv \
  --output /tmp/builder-smoke/soil.json
python3 skills/swmm-params/scripts/merge_swmm_params.py \
  --landuse-json /tmp/builder-smoke/landuse.json \
  --soil-json /tmp/builder-smoke/soil.json \
  --output /tmp/builder-smoke/merged_params.json

# 2. Format rainfall from the bundled climate example
python3 skills/swmm-climate/scripts/format_rainfall.py \
  --input skills/swmm-climate/examples/rainfall_event.csv \
  --out-json /tmp/builder-smoke/rainfall.json \
  --out-timeseries /tmp/builder-smoke/rainfall_timeseries.txt

# 3. Build the INP
python3 skills/swmm-builder/scripts/build_swmm_inp.py \
  --subcatchments-csv skills/swmm-builder/examples/subcatchments_input.csv \
  --params-json /tmp/builder-smoke/merged_params.json \
  --network-json skills/swmm-network/examples/basic-network.json \
  --rainfall-json /tmp/builder-smoke/rainfall.json \
  --config-json skills/swmm-builder/examples/options_config.json \
  --out-inp /tmp/builder-smoke/example_model.inp \
  --out-manifest /tmp/builder-smoke/example_manifest.json
```

## MVP limitations
- Generates core hydrology/hydraulics sections only.
- No automatic polygon export, LID controls, snowpack, RTC rules, or pollutant quality in this pass.
- Assumes one raingage source for all subcatchments unless `rain_gage` is explicitly set per row.