External inflows#

Note

Engine: OpenSWMM 6 — refactored. Documents openswmm.engine.Inflows.

The Inflows class registers static external inflows on nodes at configure time:

External inflows — time-series flow with optional scale/baseline.
Dry-Weather Flow (DWF) — average flow with up to 4 multiplicative patterns (monthly / weekly / daily / hourly).
Rainfall-Dependent Inflow & Infiltration (RDII) — driven by a unit hydrograph attached to a sewershed area.

For overrides applied during a running simulation (per-step lateral inflows), see Nodes.set_lateral_inflow (one-shot) or Forcing.node_lat_inflow (persistent).

Reference: openswmm_inflows.h.

Class signature#

class Inflows:
    def __init__(self, solver: Solver) -> None: ...

Key methods#

External inflows (time-series)#

Method	Action / returns
`add_external(node_idx, ts_idx, type, mfactor, sfactor, baseline, basepat_idx)()`	Attach a time-series-driven inflow to a node.
`ext_inflow_count()`	Number of registered external inflows.

type — pollutant index, or -1 for hydraulic flow.
mfactor — units conversion multiplier.
sfactor — scaling factor.
baseline — baseline flow added on top of the time series.
basepat_idx — optional pattern index multiplying the baseline.

Dry-Weather Flow#

Method	Action / returns
`add_dwf(node_idx, type, base_value, pattern_idxs)()`	Attach DWF with up to 4 patterns.
`dwf_count()`	Number of registered DWF entries.

type — pollutant index, or -1 for hydraulic flow.
base_value — average dry-weather flow.
pattern_idxs — list of up to 4 Pattern indices (monthly, daily, hourly, weekend-hourly). Use -1 to skip a slot.

RDII#

Method	Action / returns
`add_rdii(node_idx, uh_name, area)()`	Attach RDII at a node, driven by a named unit hydrograph and a sewershed area.
`rdii_count()`	Number of registered RDII entries.

End-to-end example#

from openswmm.engine import Solver, Inflows, Nodes, Tables

with Solver("site_drainage.inp", "site_drainage.rpt", "site_drainage.out") as s:
    nodes = Nodes(s)
    tables = Tables(s)
    inflows = Inflows(s)

    ts_idx = tables.get_index("WET_WEATHER_TS")
    node_idx = nodes.get_index("J1")

    # Attach a flow time series to J1 (during model edit phase, before initialize)
    s.open()
    inflows.add_external(
        node_idx=node_idx,
        ts_idx=ts_idx,
        type=-1,                  # hydraulic flow
        mfactor=1.0,              # no unit conversion
        sfactor=1.0,              # no scaling
        baseline=0.05,            # cfs baseline
        basepat_idx=-1,           # no pattern on baseline
    )
    s.initialize()
    s.start()
    while s.step():
        pass
    s.end()

    print(f"External inflows registered: {inflows.ext_inflow_count()}")

Common recipes#

Add Dry-Weather Flow with monthly + hourly patterns#

monthly_idx = tables.get_index("MONTHLY_PATTERN")
daily_idx   = tables.get_index("DAILY_PATTERN")
hourly_idx  = tables.get_index("HOURLY_PATTERN")

inflows.add_dwf(
    node_idx=nodes.get_index("J1"),
    type=-1,
    base_value=0.5,                    # average DWF
    pattern_idxs=[monthly_idx, daily_idx, hourly_idx, -1],
)

Add RDII to a node#

inflows.add_rdii(
    node_idx=nodes.get_index("J1"),
    uh_name="UH1",                     # unit hydrograph defined in [HYDROGRAPHS]
    area=12.5,                         # sewershed area
)

Combine baseline + scaling for unit conversion#

# Time series in m³/s, model in CFS:
inflows.add_external(
    node_idx=nodes.get_index("J1"),
    ts_idx=tables.get_index("INFLOW_M3S"),
    type=-1,
    mfactor=35.3147,                   # m³/s → cfs
    sfactor=1.0,
    baseline=0.0,
    basepat_idx=-1,
)

Bulk arrays#

The Inflows class is a registration surface, not a per-step data accessor. For per-step inflow values, use Nodes.get_lateral_inflow() (per-node) or OutputReader post-run (Output reader (binary .out file)).

EngineState requirements & exceptions#

Method group	Required state	Notes
registration setters (`add_*`)	`OPENED`	Must be done before `initialize()` to take effect on the run.
count accessors	`OPENED` or later	n/a

Common EngineError codes:

INVALID_INDEX — node, table, or pattern index out of range.
INVALID_TYPE — pollutant index given for a non-quality model.