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OpenSWMM Engine
6.0.0-alpha.4
Data-oriented, plugin-extensible SWMM Engine (6.0.0-alpha.4)
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OpenSWMM Engine
6.0.0-alpha.4
Data-oriented, plugin-extensible SWMM Engine (6.0.0-alpha.4)
|
This software is provided on an "as is" basis and the user assumes responsibility for its use. Although a reasonable effort has been made to assure that the results obtained are correct, the authors are not responsible and assume no liability whatsoever for any results or any use made of the results obtained from these programs, nor for any damages or litigation that result from the use of these programs for any purpose.
This reference manual was originally prepared by Lewis A. Rossman, Environmental Scientist Emeritus, U.S. Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory. His foundational work on the SWMM hydraulics model and its documentation is gratefully acknowledged.
See Authors & Contributors for the complete list of authors and contributors.
SWMM is a dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. The runoff component of SWMM operates on a collection of subcatchment areas that receive precipitation and generate runoff and pollutant loads. The routing portion of SWMM transports this runoff through a system of pipes, channels, storage/treatment devices, pumps, and regulators. SWMM tracks the quantity and quality of runoff generated within each subcatchment, and the flow rate, flow depth, and quality of water in each pipe and channel during a simulation period comprised of multiple time steps. The reference manual for this edition of SWMM is comprised of three volumes. Volume I describes SWMM's hydrologic models, Volume II its hydraulic models, and Volume III its water quality and low impact development models.
Figure 1-1 Elements of a typical urban drainage system
Figure 1-2 SWMM's conceptual model of a stormwater drainage system
Figure 1-3 Processes modeled by SWMM
Figure 1-4 Block diagram of SWMM's state transition process
Figure 1-5 Flow chart of SWMM's simulation procedure
Figure 1-6 Interpolation of reported values from computed values
Figure 2-1 Node-link representation of a sewer system
Figure 2-2 Comparison of dynamic wave and kinematic wave solutions
Figure 3-1 Node-link representation of a conveyance network in SWMM
Figure 3-2 Special flow conditions for dynamic wave analysis
Figure 3-3 Illustration of a surcharged node
Figure 3-4 Ponding of excess water above a junction
Figure 3-5 Profile view of example rectangular conduit (not to scale)
Figure 3-6 Outflow hydrographs for example conduit -I
Figure 3-7 Outflow hydrographs for example conduit – II
Figure 3-8 Conceptual representation of the dynamic Preissmann slot
Figure 3-9 State transitions of the dynamic Preissmann slot at a conduit end
Figure 3-10 Virtual junction representation of a conduit grade break
Figure 3-11 Workflow of one Anderson-accelerated iteration of the successive-approximation loop
Figure 4-1 Section factor versus area for a circular shape
Figure 4-2 Space-time grid for kinematic wave analysis
Figure 4-3 Outflow hydrograph for example conduit
Figure 5-1 Power law cross section shape
Figure 5-2 Geometric properties of a partly filled circular shape based on depth
Figure 5-3 Geometric properties of a partly filled circular shape based on area
Figure 5-4 Ellipsoid and arch pipe cross sectional shapes
Figure 5-5 Masonry sewer shapes
Figure 5-6 Composite cross section shapes
Figure 5-7 A Shape Curve with a depth segment shown
Figure 5-8 A natural channel transect
Figure 5-9 A transect depth increment with three compound segments
Figure 5-10 Example of a storage curve and its section view
Figure 5-11 Finding the volume at a given depth for a storage curve
Figure 6-1 Orifice orientations
Figure 6-2 Determination of effective head for an orifice
Figure 6-3 Orifice with unsubmerged inlet
Figure 6-4 Transverse weir shapes
Figure 6-5 Coefficient for triangular weirs (from Brater and King, 1976)
Figure 6-6 Definitions of submerged and surcharged weir flow
Figure 6-7 Rating curve for a vortex device compared to an orifice
Figure 7-1 Depths used for computing seepage in storage units
Figure 7-2 Concrete box culvert (from FHWA, 2012)
Figure 7-3 Example of a culvert rating curve (from FHWA, 2012)
Figure 7-4 Roadway overtopping (from FHWA, 2012)
Figure 7-5 SWMM node-link representation of a culvert with a roadway weir
Figure 7-6 Discharge coefficients for roadway weirs (from FHWA, 2012)
Figure 8-1 Substep workflow of the explicit finite-volume solver
Figure 8-2 Wet/dry and exception handling in one face flux evaluation
Figure 8-3 Hydrostatic reconstruction at a wet/dry front
Figure 8-4 Node ghost-state construction at a coupling face
Figure 9-1 One 1D–2D co-advance batch and the explicit marcher's substep loop within it
Figure 9-2 Wetting cases of a planar-bed triangular cell and the wetted-edge face gate
Table 1-1 Development history of SWMM
Table 1-2 SWMM's modeling objects
Table 1-3 State variables used by SWMM
Table 1-4 Units of expression used by SWMM
Table 2-1 Features and limitations of dynamic wave and kinematic wave solutions
Table 3-1 Surface area adjustments for various dynamic wave flow conditions
Table 3-2 Conditions under which Anderson acceleration reverts to standard iteration
Table 5-1 Geometric properties for open channel shapes as functions of water depth
Table 5-2 Geometric properties for open channel shapes as functions of flow area
Table 5-3 Geometric properties for the power law shape
Table 5-4 Geometric properties of a full circular cross section
Table 5-5 Full area and hydraulic radius of custom ellipsoid and arch pipe sections
Table 5-6 Number of entries in geometric property tables for masonry sewer shapes
Table 5-7 Geometric parameters of masonry sewer sections
Table 5-8 Geometric properties for a sediment filled circular cross section
Table 5-9 Properties of the rectangular section of a rectangular-triangular shape
Table 5-10 Geometric parameters for rectangular-round shapes
Table 5-11 Geometric properties for rectangular–round shapes
Table 5-12 Properties in the rounded top section of a modified basket handle shape
Table 5-13 Area at maximum flow to full area for standard closed conduits shapes
Table 5-14 Critical depth formulas for simple section shapes
Table 6-1 Pump curves recognized by SWMM
Table 6-2 Kindsvater-Carter constants for rectangular weir coefficient
Table 6-3 Rectangular broad-crested weir coefficients (ft1/2/sec)
Table 6-4 Formulas for flow derivatives of various types of weirs
Table 7-1 Relative depth at maximum width for select cross section shapes
Table 7-2 Types of minor losses in drainage systems (from Frost, 2006)
Table 7-3 Hazen-Williams C-factors for different pipe materials
Table 7-4 Darcy-Weisbach roughness heights for different pipe materials
Table 8-1 Dry-state constants of the explicit finite-volume solver
Table 9-1 Wetting and drying thresholds and guards of the 2D solver
Table C-1 Circular section properties as function of area
Table C-2 Circular section properties as function of depth
Table D-1 Standard elliptical pipe sizes
Table D-2 Elliptical section properties as function of depth
Table E-1 Standard arch pipe sizes
Table E-2 Arch pipe section properties as function of depth
Table F-1 Area of masonry sewers as function of depth
Table F-2 Width of masonry sewers as function of depth - I
Table F-3 Width of masonry sewers as function of depth - II
Table F-4 Hydraulic radius of masonry sewers as function of depth
Table F-5 Depth of masonry sewers as function of area - I
Table F-6 Depth of masonry sewers as function of area - II
Table F-7 Section factor for masonry sewers as function of area - I
Table F-8 Section factor for masonry sewers as function of area - II
Table G-1 Manning's roughness coefficient n for open channels
Table G-2 Manning's roughness coefficient n for closed conduits
Table G-3 Manning's roughness coefficient n for corrugated steel pipe
Table H-1 Culvert codes
Table H-2 Culvert coefficients
| Symbol | Description |
|---|---|
| A | cross section flow area within a conduit (ft²) |
| Ā | average cross section flow area along a conduit (ft²) |
| Ā̄ | average cross section flow area along a conduit over a time period (ft²) |
| Afull | full cross section area of a conduit (ft²) |
| Amax | cross section area at depth where a conduit's section factor is a maximum (ft²) |
| AO | area of an orifice opening (ft²) |
| ASP | surface area of water ponded above a node (ft²) |
| AS | surface area of a node and its connected links (ft²) |
| ASL | surface area of flow within a link (ft²) |
| ASlast | surface area of a node the last time it was not surcharged (ft²) |
| ASmin | minimum surface area associated with a node (ft²) |
| ASN | surface area associated with a storage node (ft²) |
| AW | area of a weir opening (ft²) |
| b | bottom or top width (depending on shape) of a conduit's cross section (ft) |
| c | wave celerity (ft/sec) |
| cI | inlet control constant for submerged culverts |
| cW | coefficient for a weir-type flow divider (ft1/2/sec) |
| Cd | orifice discharge coefficient (dimensionless) |
| CHW | Hazen-Williams C-factor coefficient (dimensionless) |
| CO | equivalent orifice constant for a surcharged weir (ft5/2/sec) |
| Cr | Courant number (dimensionless) |
| Cw | weir coefficient (ft1/2/sec) |
| D | circular pipe diameter (ft) |
| et | potential evaporation rate at time t (ft/sec) |
| E | elevation of a node's invert (ft) |
| EC | specific head at critical depth (ft) |
| f | Darcy-Weisbach friction factor (dimensionless) |
| fC | monthly climate adjustment factor (dimensionless) |
| fE | storage node evaporation factor (dimensionless) |
| fS | weir submergence adjustment factor (dimensionless) |
| F | cumulative depth of infiltrated water (ft) |
| Fr | Froude number (dimensionless) |
| g | acceleration of gravity (ft/sec²) |
| hL | minor head loss per unit length of a conduit (ft/ft) |
| hW | height of the opening for a weir-type flow divider node (ft) |
| H | hydraulic head (ft) |
| Hcrown | elevation of the crown of the highest conduit at a node (ft) |
| He | effective head seen by an orifice or weir (ft) |
| HIS | minimum head at a culvert's inlet for it to be submerged (ft) |
| HIU | maximum head at a culvert's inlet for it to be unsubmerged (ft) |
| Hmax | maximum head at a node before flooding occurs (ft) |
| HOutfall | head assigned to an outfall node (ft) |
| K | cross section flow conductance (cfs) (equal to \(nAR^{2/3}\)) |
| KI | inlet control constant for unsubmerged culverts |
| Km | minor loss coefficient (dimensionless) |
| KS | soil saturated hydraulic conductivity (ft/sec) |
| L | conduit length or weir crest length (ft) |
| Le | effective weir crest length (ft) |
| MI | inlet control exponent for unsubmerged culverts |
| n | Manning roughness coefficient (sec/m1/3) |
| P | wetted perimeter of a conduit's cross section (ft) |
| qE | uniformly distributed evaporation rate along a channel (cfs/ft) |
| qL | total uniformly distributed outflow rate along a conduit (cfs/ft) |
| qMIN | minimum flow needed to activate a flow divider node (cfs) |
| qS | uniformly distributed seepage rate along a conduit (cfs/ft) |
| qSN | seepage rate per unit area for a storage node (cfs/ft²) |
| Q | flow rate within a conduit, pump, or regulator link (cfs) |
| Qdiv | flow rate diverted to a second outflow conduit from a flow divider node (cfs) |
| QEN | evaporation loss rate from a storage unit node (cfs) |
| Qfull | normal uniform flow rate for a full conduit (cfs) |
| QIC | culvert flow rate under inlet control (cfs) |
| Qin | total inflow rate to a node (cfs) |
| QLN | total loss rate from a storage unit node (cfs) |
| Qnorm | normal uniform flow rate (cfs) |
| Qout | total outflow rate leaving a node (cfs) |
| Qovfl | excess flow that overflows a node (cfs) |
| Q̄net | average net inflow minus outflow over a time step (cfs) |
| QSN | seepage loss rate from a storage node (cfs) |
| R | hydraulic radius of flow cross section in a conduit (ft) |
| R̄ | average hydraulic radius of flow cross sections along a conduit (ft) |
| Re | Reynolds number (dimensionless) |
| Rfull | hydraulic radius of a conduit cross section when full (ft) |
| s | seepage rate per unit area for a conduit (ft/sec) |
| Scf | culvert slope correction factor |
| Sf | friction slope (ft/ft) |
| S0 | conduit slope (ft/ft) |
| t | time (sec) |
| U | flow velocity at a point along a conduit (ft/sec) |
| Ū | average flow velocity along a conduit (ft/sec) |
| V | node assembly volume (ft³) |
| VP | ponded volume (ft³) |
| VN | storage node volume (ft³) |
| VNfull | volume of a storage node when full (ft³) |
| W | top width of the water surface at a point along a conduit (ft) |
| W̄ | average top width of the water surface along a conduit (ft) |
| Wmax | maximum width of a conduit cross section (ft) |
| x | horizontal distance (ft) |
| y | vertical distance (ft) |
| yI | inlet control constant for submerged culverts |
| Y | depth of flow within a conduit or of water in a storage unit (ft) |
| Ȳ | average depth of flow along a conduit (ft) |
| Yc | critical depth within a conduit at a given flow rate (ft) |
| Yfull | full depth of a conduit, orifice opening or weir height (ft) |
| YN | normal flow depth (ft) |
| Y* | smaller of the critical and normal flow depth in a conduit (ft) |
| Z | elevation of a conduit's invert (ft) |
| ZO | elevation of the bottom of an orifice's opening (ft) |
| ZW | elevation of a weir's crest in its lowest position (ft) |
| α | generic coefficient |
| β | the square root of a conduit's slope divided by its roughness |
| ∆t | time step (sec) |
| ε | convergence tolerance |
| ε | Darcy-Weisbach roughness length (ft) |
| γ | exponent in power law cross section shape |
| η | Manning's roughness coefficient (sec/ft1/3) \(\left( equal\ to\ \frac{n}{1.486} \right)\) |
| σ | inertial damping factor |
| θ | time weighting factor, relaxation factor, or subtended angle |
| φ | distance weighting factor |
| θd | soil moisture deficit (dimensionless) |
| μ | kinematic viscosity (ft²/sec) |
| ω | pump speed setting or degree to which a regulator is opened |
| ψS | soil capillary suction head (ft) |
| Ψ | conduit section factor (equal to \(AR^{2/3}\)) (ft8/3) |
| Ψfull | section factor of a conduit at full depth (ft8/3) |
| Ψmax | maximum section factor for a conduit (ft8/3) |
1.13.2