EPA SWMM Stormwater & Urban Hydrology (.inp)

@modelscript/swmm (languages/swmm) provides zero-regex parsing, 1D Saint-Venant dynamic wave hydraulic routing, DAE lowering, and Modelica 3.x projection for US EPA Stormwater Management Model (SWMM 5.x) urban drainage, sewer collection, and flood mitigation networks.

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Supported Extensions & Standards

Extension	Format	Description
.inp	EPA SWMM Input File	Industry-standard stormwater network deck (junctions, conduits, outfalls, subcatchments, pumps, weirs, orifices)

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Key Capabilities

1. 1D Saint-Venant Dynamic Wave Routing

• Models open-channel and pressurized sewer hydraulics via the one-dimensional Saint-Venant equations of unsteady flow:
  • Conservation of Mass (Continuity):$$\frac{\partial A}{\partial t}+\frac{\partial Q}{\partial x}=q_{\text{lateral}}$$
  • Conservation of Momentum:$$\frac{\partial Q}{\partial t}+\frac{\partial }{\partial x}\left(\frac{Q^2}{A}\right)+gA\frac{\partial H}{\partial x}+gA{S}_f=0$$where $H=z+d$ is hydraulic head, $S_f$ is friction slope, and $S_0$ is conduit bed slope.
• Uses Manning's open-channel equation for friction slope:$$Q=\frac{k_m}{n}A{R}_h^{2/3}{S}_f^{1/2}⟹S_f=\frac{n^{2}Q|Q|}{k_m^2{A}^2{R}_h^{4/3}}$$where $n$ is Manning roughness, $A$ is flow cross-sectional area, and $R_h=A/P_{\text{wetted}}$ is hydraulic radius.

2. Node & Link Hydraulic Structures

• Junctions & Storage Units: Continuous water stage mass conservation:$$A_{\text{node}}\frac{d{H}_i}{dt}=\sum Q_{\text{in}}-\sum Q_{\text{out}}+Q_{\text{inflow}}-Q_{\text{flood}}$$
• Conduits: Circular, rectangular, trapezoidal, and irregular natural river cross-sections with entrance/exit minor head loss coefficients.
• Outfalls: Free, normal, tidal, and fixed water elevation boundary conditions.
• Regulators: Orifices, transverse/side-flow weirs, and variable-speed lift pumps.

3. Direct DAE Lowering

• Compiles the entire stormwater collection network into @modelscript/runtime's DAEBuilder struct-of-arrays linear memory arena.
• Enables co-simulation of municipal drinking water networks (@modelscript/epanet) and drainage networks within the same computational arena.

4. Bidirectional Modelica 3.x Projection

• Projects SWMM nodes and channels into Modelica.Fluid open-channel tanks, flow conduits, and boundary reservoirs.

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Pre-Flight Diagnostics

The SWMM linter verifies network graph integrity and hydraulic feasibility before simulation:

13 rules10 error3 warning Run with msx swmm lint

All severitieserrorwarning

Code	Rule	Severity	Message
M8201	dangling-node-reference	error	Link '<linkId>' references undefined <role> node '<nodeId>'.
M8202	adverse-conduit-slope	warning	Conduit '<conduitId>' has adverse slope: inlet elevation (<value>) is lower than outlet elevation (<value>).
M8203	missing-cross-section	error	Conduit '<conduitId>' has no hydraulic cross-section definition in '[XSECTIONS]'.
M8204	unsupported-outfall-type	error	Outfall '<outfallId>' specifies unsupported boundary condition type '<type>'.
M8205	surcharge-overflow-risk	warning	Junction '<junctionId>' rim elevation (<value>) is lower than connected conduit crown (<value>), creating surcharge overflow risk.
M8206	duplicate-node-id	error	Duplicate node identifier '<nodeId>' declared in network.
M8207	duplicate-link-id	error	Duplicate link identifier '<linkId>' declared in network.
M8208	negative-roughness	error	Conduit '<conduitId>' specifies non-positive Manning's roughness coefficient (n = <n>).
M8209	zero-length-conduit	error	Conduit '<conduitId>' specifies non-positive length (<len>).
M8210	isolated-network-node	warning	Junction '<nodeId>' has no connected conduits or hydraulic links (isolated node).
M8211	subcatchment-outlet-not-found	error	Subcatchment '<subId>' references non-existent discharge outlet '<outletId>'.
M8212	weir-offset-negative	error	Weir '<weirId>' specifies negative crest height offset (<offset>).
M8213	invalid-discharge-coefficient	error	Link '<linkId>' specifies non-positive discharge coefficient (Cd = <cd>).

Generated from languages/swmm/src/errors.ts. All languages →

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CLI Usage

# Inspect junctions, conduits, outfalls, and subcatchments
msx swmm inspect UrbanDrainage.inp

# Run pre-flight semantic diagnostics
msx swmm lint UrbanDrainage.inp

# Route steady-state hydraulic flow using Manning formulation
msx swmm route-flow UrbanDrainage.inp

# Lower network topology into ModelScript linear DAE arena
msx swmm to-dae UrbanDrainage.inp

# Project into Modelica 3.x fluid network components
msx swmm to-modelica UrbanDrainage.inp -o StormwaterNetwork.mo