---
name: swmm-water-quality
description: >
  Validate water-quality config JSON and extract pollutant load
  summaries from SWMM report files.  Completes SWMM engine coverage:
  pollutant buildup/washoff simulation support and load reporting.
  Agent-invisible until PR3 wiring — do not register in intent_map or
  tool_registry until the wiring PR lands.
---

# SWMM Water Quality Skill

> **Status:** PR1 — builder emission + config validation only.
> Agent wiring (intent_map, tool_registry, MCP) deferred to PR3.

## Purpose

Complete SWMM engine coverage for pollutant buildup/washoff simulation
and load reporting.  This skill provides:

1. `validate_wq_config.py` — validate a WQ config JSON before passing
   it to the builder.
2. `extract_wq_loads.py` — extract WQ load summaries from a SWMM RPT
   (added in PR2).

The water-quality sections (`[POLLUTANTS]`, `[LANDUSES]`, `[COVERAGES]`,
`[BUILDUP]`, `[WASHOFF]`, `[LOADINGS]`) are emitted by
`skills/swmm-builder/scripts/build_swmm_inp.py` via the
`--water-quality-json` flag.

## WQ config JSON schema

Top-level keys (all required when the key is present; empty arrays are valid):

```json
{
  "pollutants": [...],
  "landuses": [...],
  "coverages": [...],
  "buildup": [...],
  "washoff": [...],
  "loadings": [...]
}
```

### `pollutants` entries

| Field | Type | Default | Notes |
|---|---|---|---|
| `name` | string | required | No spaces |
| `units` | string | required | `MG/L`, `UG/L`, or `#/L` |
| `c_rain` | float | `0` | Concentration in precipitation |
| `c_gw` | float | `0` | Concentration in groundwater |
| `c_ii` | float | `0` | Concentration in RDII |
| `k_decay_per_day` | float | `0` | First-order decay (1/days) |
| `snow_only` | bool | `false` | Buildup during snow only |
| `co_pollutant` | string | `"*"` | Co-pollutant name or `"*"` |
| `co_fraction` | float | `0` | Co-pollutant fraction (0–1) |
| `init_conc` | float | `0` | Initial dry-weather concentration |

### `landuses` entries

| Field | Type | Default | Notes |
|---|---|---|---|
| `name` | string | required | |
| `sweep_interval` | float | `0` | Days between sweeping (0 = no sweeping) |
| `availability` | float | `0` | Fraction of buildup removed by sweeping (0–1) |
| `last_sweep` | float | `0` | Days since last sweep at start |

### `coverages` entries

| Field | Type | Notes |
|---|---|---|
| `subcatchment` | string | Must reference an existing subcatchment |
| `landuse` | string | Must reference a defined land use |
| `percent` | float (0–100) | Percent coverage; per-subcatchment sum must be ≤ 100 |

### `buildup` entries

| Field | Type | Notes |
|---|---|---|
| `landuse` | string | Must reference a defined land use |
| `pollutant` | string | Must reference a defined pollutant |
| `func_type` | string | `POW`, `EXP`, or `SAT` (`EXT` not supported in v1) |
| `c1` | float | Max buildup (kg/ha or count/ha when normalizer=AREA) |
| `c2` | float | Rate constant |
| `c3` | float | Third coefficient (unused for EXP/SAT) |
| `normalizer` | string | `AREA` or `CURBLENGTH` |

### `washoff` entries

| Field | Type | Notes |
|---|---|---|
| `landuse` | string | Must reference a defined land use |
| `pollutant` | string | Must reference a defined pollutant |
| `func_type` | string | `EXP`, `RC`, or `EMC` |
| `c1` | float | Coefficient 1 |
| `c2` | float | Coefficient 2 (0 for EMC) |
| `sweep_removal` | float (0–1) | Fraction removed by sweeping |
| `bmp_removal` | float (0–1) | Fraction removed |

### `loadings` entries (optional)

| Field | Type | Notes |
|---|---|---|
| `subcatchment` | string | Must reference an existing subcatchment |
| `pollutant` | string | Must reference a defined pollutant |
| `init_buildup` | float | Initial buildup mass |

## Scripts

- `scripts/validate_wq_config.py` — standalone CLI validator
- `scripts/extract_wq_loads.py` — RPT load extractor (added in PR2)

## Validation constraints

Enforced by both `validate_wq_config.py` and `build_swmm_inp.py`:

- Referential: every `[BUILDUP]`/`[WASHOFF]` landuse/pollutant must exist
- Referential: every `[COVERAGES]`/`[LOADINGS]` subcatchment must exist
- Enum: `units` ∈ {`MG/L`, `UG/L`, `#/L`}
- Enum: buildup `func_type` ∈ {`POW`, `EXP`, `SAT`} (EXT rejected with message)
- Enum: washoff `func_type` ∈ {`EXP`, `RC`, `EMC`}
- Range: coverage `percent` ∈ [0, 100]; per-subcatchment sum ≤ 100
- Range: `sweep_removal`, `bmp_removal`, `co_fraction` ∈ [0, 1]