The SWMM3 Weir Test File: A Historical Reference for Modern Hydraulic Modeling
This test file holds special historical significance in the development of stormwater modeling. Originally published in the 1981 EXTRAN 3 manual by CDM (now CDM Smith), it was specifically designed to validate orifice calculations in hydraulic networks. The file served as a critical quality assurance tool during the evolution of SWMM, supporting the transition from SWMM3 through SWMM4 and into the current SWMM5.
I documented this file's importance in a 2009 Posthaven blog post, which I have updated using various AI tools to maintain its relevance. Today, this historical test case continues to prove valuable across multiple modern modeling platforms, such as ICM SWMM—as an example. It is also on the EPA GitHub as a test model.
This Example 4 from the Extran Manual was an excellent test model for SWMM back in the early 1980s precisely because it combined several challenging hydraulic elements (multiple inflows, a weir, dynamic wave routing) into a relatively compact network that could be run on what were then very limited computer resources (we used punch cards or terminals and a mainframe computer at UF). At the time, personal computers were not invented for SWMM3, and while they existed by the time of SWMM4, they were slow, and large‐memory mainframes were not readily accessible to most modelers, so every model had to be small enough to fit into limited RAM and run in a feasible amount of CPU time. Yet this example still demonstrated SWMM’s powerful capability to capture unsteady flow conditions—like surcharging, backwater effects, and control structures—in one integrated simulation. The inclusion of a weir, various pipe shapes, and multiple inflow hydrographs showcased SWMM’s flexibility to handle both standard conveyance links and special hydraulic controls, confirming that dynamic wave routing could be effectively computed given the technology of the day. Overall, it illustrated that, despite modest hardware and software constraints, SWMM was already advanced enough to handle complex urban drainage systems, laying the groundwork for today’s much larger and more detailed models.
Yet this example still demonstrated SWMM’s powerful capability to capture unsteady flow conditions—like surcharging, backwater effects, and control structures—in one integrated simulation.
Example Real-Time Control (RTC) rule for a Weir in SWMM5
RULE Orifice1
IF SIMULATION CLOCKTIME >= 01:00:00
AND SIMULATION CLOCKTIME <= 2:00:00
THEN ORIFICE OR1@82309b-15009b SETTING = 1
ELSE ORIFICE OR1@82309b-15009b SETTING = 0
PRIORITY 1
; Opens up the orifice at hour 1 of the simulationExplanation of Components:
- RULE Orifice1:
- IF SIMULATION CLOCKTIME >= 01:00:00:
- AND SIMULATION CLOCKTIME <= 2:00:00:
- THEN ORIFICE OR1@82309b-15009b SETTING = 1:
- ELSE ORIFICE OR1@82309b-15009b SETTING = 0:
- PRIORITY 1:
- ; Opens up the orifice at hour 1 of the simulation:
Functionality:
This rule effectively opens the orifice "OR1@82309b-15009b" fully at 1:00:00 AM (one hour into the simulation) and keeps it open until 2:00:00 AM. After 2:00:00 AM, the orifice is fully closed.
Variations, Improvements, and Considerations:
- Partial Opening:
- Time-Based Gradual Opening/Closing:
- Sensor-Based Control:
- Multiple Conditions:
- Multiple Orifices:
- Rule Interaction
- Saving RTC Rules:
- RTC rules are typically written in a separate text file (e.g., "rules.txt") and then referenced in the SWMM5 input file (.inp) under the [RULES] section. You would add a line like: [RULES] FILE "rules.txt" Or you can paste the rules directly into the [RULES] section of the .inp file.
Example of a More Advanced Rule (Conceptual)
- RTC rules are typically written in a separate text file (e.g., "rules.txt") and then referenced in the SWMM5 input file (.inp) under the [RULES] section. You would add a line like: [RULES] FILE "rules.txt" Or you can paste the rules directly into the [RULES] section of the .inp file.
Let's say you want to implement a rule that mimics a PID (Proportional-Integral-Derivative) controller to maintain a target water level in a storage unit by adjusting an orifice:
;----------------------------------------------------
; 1) Depth-based control at an upstream node
; If Node 82309’s water depth exceeds 5 ft,
; fully open the weir. Otherwise, partially close it.
;----------------------------------------------------
RULE R1
IF NODE 82309 DEPTH > 5.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.5
PRIORITY 1
;----------------------------------------------------
; 2) Flow-based control on an upstream link
; If Link 8060 flow exceeds 20 cfs, fully open the weir;
; else keep it half-open.
;----------------------------------------------------
RULE R2
IF LINK 8060 FLOW > 20.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.5
PRIORITY 2
;----------------------------------------------------
; 3) Time-of-day control
; From 06:00 to 10:00, close the weir;
; otherwise open it fully.
;----------------------------------------------------
RULE R3
IF SIMULATION CLOCKTIME >= 06:00
AND SIMULATION CLOCKTIME < 10:00
THEN WEIR 90010 SETTING = 0.0
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 3
;----------------------------------------------------
; 4) Date-based control
; During the month of June, open the weir fully;
; otherwise keep it partially closed.
;----------------------------------------------------
RULE R4
IF SIMULATION MONTH = 6
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.3
PRIORITY 4
;----------------------------------------------------
; 5) Day-of-week control
; On weekends (Saturday=7 or Sunday=1 in SWMM’s system),
; reduce weir setting by 50%, else keep it fully open.
;----------------------------------------------------
RULE R5
IF SIMULATION DAY = 7
OR SIMULATION DAY = 1
THEN WEIR 90010 SETTING = 0.5
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 5
;----------------------------------------------------
; 6) Multiple conditions combined
; Example: If Node 82309 depth > 6.0 ft AND Link 8060 flow > 25 cfs,
; THEN open the weir fully. Otherwise, keep it at 0.75.
;----------------------------------------------------
RULE R6
IF NODE 82309 DEPTH > 6.0
AND LINK 8060 FLOW > 25.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.75
PRIORITY 6
;----------------------------------------------------
; 7) System-wide flow control
; If the total system outflow (SYSTEM FLOW) exceeds 200 cfs,
; close the weir. Otherwise, open it.
;----------------------------------------------------
RULE R7
VARIABLE Q8040 = LINK 8040 FLOW
VARIABLE Q8100 = LINK 8100 FLOW
EXPRESSION Net_Inflow = Q8100 + Q8040
IF Net_Inflow > 90
THEN WEIR 90010 SETTING = 0.0
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 7
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RTC SWMM5 version of the original SWMM3 Model
Summary of of the Input FIle
Project Configuration Analysis:
- Hydraulic Routing Parameters
- Flow Units: CFS (cubic feet per second)
- Routing Method: Dynamic Wave with the following specifications: Inertial Damping: None Normal Flow Limited: Both upstream and downstream Force Main Equation: Hazen-Williams Head Tolerance: Default configuration System Flow Tolerance: 5 Lateral Flow Tolerance: 5
- Temporal Configuration
- Simulation Period: 01/01/2002 00:00:00 to 01/01/2002 08:00:00
- Critical Time Steps: Reporting Interval: 15 minutes Wet Weather Step: 15 minutes Routing Step: 20 seconds Rule Step: 0 seconds (continuous evaluation)
Network Infrastructure Components:
- Node Configuration
- 9 Junctions with elevations ranging from 101.6 to 128.2 ft
- 1 Free outfall at elevation 89.9 ft
- Maximum junction depth range: 8.8 to 42.7 ft
- Conveyance System
- 9 Conduits with varying characteristics: Diameters: 4.0 to 6.0 ft (circular sections) Manning's n: 0.015 to 0.034 Lengths: 300 to 5100 ft
- 1 Transverse weir (ID: 90010) Crest Height: 3.0 ft Discharge Coefficient: 3.33
Control Logic Implementation:
The system implements 7 hierarchical control rules (R1-R7) managing weir 90010:
- Depth-based control (Priority 1)
- Flow-based control (Priority 2)
- Time-of-day operation (Priority 3)
- Seasonal control (Priority 4)
- Weekly scheduling (Priority 5)
- Multi-condition control (Priority 6)
- System-wide flow management (Priority 7)
Inflow Configuration:
- Three defined inflow nodes (80408, 81009, 82309)
- Time series data structured with: Peak flows: 40-50 CFS Duration: 3 hours Uniform distribution pattern
The PID RTC SWMM5 version of the original SWMM3 Model
[TITLE]
;;Project Title/Notes
Example 4 of Extran Manual -
Weir
[OPTIONS]
;;Option Value
FLOW_UNITS CFS
INFILTRATION HORTON
FLOW_ROUTING DYNWAVE
LINK_OFFSETS DEPTH
MIN_SLOPE 0
ALLOW_PONDING NO
SKIP_STEADY_STATE NO
START_DATE 01/01/2002
START_TIME 00:00:00
REPORT_START_DATE 01/01/2002
REPORT_START_TIME 00:00:00
END_DATE 01/01/2002
END_TIME 08:00:00
SWEEP_START 01/01
SWEEP_END 12/31
DRY_DAYS 0
REPORT_STEP 00:15:00
WET_STEP 00:15:00
DRY_STEP 01:00:00
ROUTING_STEP 0:00:20
RULE_STEP 00:00:00
INERTIAL_DAMPING NONE
NORMAL_FLOW_LIMITED BOTH
FORCE_MAIN_EQUATION H-W
VARIABLE_STEP 0.00
LENGTHENING_STEP 0
MIN_SURFAREA 0
MAX_TRIALS 0
HEAD_TOLERANCE 0
SYS_FLOW_TOL 5
LAT_FLOW_TOL 5
MINIMUM_STEP 0.5
THREADS 1
[EVAPORATION]
;;Data Source Parameters
;;-------------- ----------------
CONSTANT 0.0
DRY_ONLY NO
[JUNCTIONS]
;;Name Elevation MaxDepth InitDepth SurDepth Aponded
;;-------------- ---------- ---------- ---------- ---------- ----------
80408 124.6 13.4 0 0 0
80608 118.3 16.7 0 0 0
81009 128.2 8.8 0 0 0
81309 117.5 12.5 0 0 0
82309 112.3 42.7 0 0 0
10309 101.6 9.4 0 0 0
15009 111.5 13.5 0 0 0
16009 102 18 0 0 0
16109 102.8 22.2 0 0 0
[OUTFALLS]
;;Name Elevation Type Stage Data Gated Route To
;;-------------- ---------- ---------- ---------------- -------- ----------------
10208 89.9 FREE NO
[CONDUITS]
;;Name From Node To Node Length Roughness InOffset OutOffset InitFlow MaxFlow
;;-------------- ---------------- ---------------- ---------- ---------- ---------- ---------- ---------- ----------
8040 80408 80608 1800 0.015 0 0 0 0
8060 80608 82309 2075 0.015 0 2.2 0 0
8100 81009 81309 5100 0.015 0 0 0 0
8130 81309 15009 3500 0.015 0 0 0 0
1030 10309 10208 4500 0.016 0 0 0 0
1570 15009 16009 5000 0.0154 0 0 0 0
1600 16109 16009 500 0.015 0 0 0 0
1630 16009 10309 300 0.015 0 0 0 0
1602 82309 16109 5000 0.034 0 0 0 0
[WEIRS]
;;Name From Node To Node Type CrestHt Qcoeff Gated EndCon EndCoeff Surcharge RoadWidth RoadSurf Coeff. Curve
;;-------------- ---------------- ---------------- ------------ ---------- ---------- -------- -------- ---------- ---------- ---------- ---------- ----------------
90010 82309 15009 TRANSVERSE 3.0 3.33 NO 0 0 YES
[XSECTIONS]
;;Link Shape Geom1 Geom2 Geom3 Geom4 Barrels Culvert
;;-------------- ------------ ---------------- ---------- ---------- ---------- ---------- ----------
8040 CIRCULAR 4 0 0 0 1
8060 CIRCULAR 4 0 0 0 1
8100 CIRCULAR 4.5 0 0 0 1
8130 CIRCULAR 4.5 0 0 0 1
1030 TRAPEZOIDAL 9 0 3 3 1
1570 CIRCULAR 5.5 0 0 0 1
1600 CIRCULAR 6 0 0 0 1
1630 TRAPEZOIDAL 9 0 3 3 1
1602 CIRCULAR 5 0 0 0 1
90010 RECT_OPEN 3.0 3.0 0 0
[CONTROLS]
;----------------------------------------------------
; 1) Depth-based control at an upstream node
; If Node 82309’s water depth exceeds 5 ft,
; fully open the weir. Otherwise, partially close it.
;----------------------------------------------------
RULE R1
IF NODE 82309 DEPTH > 5.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.5
PRIORITY 1
;----------------------------------------------------
; 2) Flow-based control on an upstream link
; If Link 8060 flow exceeds 20 cfs, fully open the weir;
; else keep it half-open.
;----------------------------------------------------
RULE R2
IF LINK 8060 FLOW > 20.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.5
PRIORITY 2
;----------------------------------------------------
; 3) Time-of-day control
; From 06:00 to 10:00, close the weir;
; otherwise open it fully.
;----------------------------------------------------
RULE R3
IF SIMULATION CLOCKTIME >= 06:00
AND SIMULATION CLOCKTIME < 10:00
THEN WEIR 90010 SETTING = 0.0
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 3
;----------------------------------------------------
; 4) Date-based control
; During the month of June, open the weir fully;
; otherwise keep it partially closed.
;----------------------------------------------------
RULE R4
IF SIMULATION MONTH = 6
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.3
PRIORITY 4
;----------------------------------------------------
; 5) Day-of-week control
; On weekends (Saturday=7 or Sunday=1 in SWMM’s system),
; reduce weir setting by 50%, else keep it fully open.
;----------------------------------------------------
RULE R5
IF SIMULATION DAY = 7
OR SIMULATION DAY = 1
THEN WEIR 90010 SETTING = 0.5
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 5
;----------------------------------------------------
; 6) Multiple conditions combined
; Example: If Node 82309 depth > 6.0 ft AND Link 8060 flow > 25 cfs,
; THEN open the weir fully. Otherwise, keep it at 0.75.
;----------------------------------------------------
RULE R6
IF NODE 82309 DEPTH > 6.0
AND LINK 8060 FLOW > 25.0
THEN WEIR 90010 SETTING = 1.0
ELSE WEIR 90010 SETTING = 0.75
PRIORITY 6
;----------------------------------------------------
; 7) System-wide flow control
; If the total system outflow (SYSTEM FLOW) exceeds 200 cfs,
; close the weir. Otherwise, open it.
;----------------------------------------------------
RULE R7
VARIABLE Q8040 = LINK 8040 FLOW
VARIABLE Q8100 = LINK 8100 FLOW
EXPRESSION Net_Inflow = Q8100 + Q8040
IF Net_Inflow > 90
THEN WEIR 90010 SETTING = 0.0
ELSE WEIR 90010 SETTING = 1.0
PRIORITY 7
[INFLOWS]
;;Node Constituent Time Series Type Mfactor Sfactor Baseline Pattern
;;-------------- ---------------- ---------------- -------- -------- -------- -------- --------
80408 FLOW 80408 FLOW 1.0 1.0
81009 FLOW 81009 FLOW 1.0 1.0
82309 FLOW 82309 FLOW 1.0 1.0
[TIMESERIES]
;;Name Date Time Value
;;-------------- ---------- ---------- ----------
82309 0 0
82309 0.25 40
82309 3.0 40
82309 3.25 0
82309 12.0 0
;
80408 0 0
80408 0.25 45
80408 3.0 45
80408 3.25 0
80408 12 0
;
81009 0 0
81009 0.25 50
81009 3.0 50
81009 3.25 0
81009 12 0
[REPORT]
;;Reporting Options
CONTROLS YES
SUBCATCHMENTS ALL
NODES ALL
LINKS ALL
[TAGS]
[MAP]
DIMENSIONS -1113.687 2165.261 10650.527 7792.630
Units None
[COORDINATES]
;;Node X-Coord Y-Coord
;;-------------- ------------------ ------------------
80408 10115.790 7536.840
80608 7463.160 7536.840
81009 9989.470 2421.050
81309 7568.420 2421.050
82309 4957.890 7536.840
10309 389.470 2421.050
15009 4978.950 2421.050
16009 2494.740 2421.050
16109 2494.740 7536.840
10208 -578.950 4947.370
[VERTICES]
;;Link X-Coord Y-Coord
;;-------------- ------------------ ------------------
[Polygons]
[LABELS]
;;X-Coord Y-Coord Label
2431.580 1052.630 "EXAMPLE 4 OF EXTRAN MANUAL" "" "Arial" 12 1 1
9780.790 8204.590 "Inflow" "" "Arial" 10 0 0
4655.530 8141.960 "Inflow" "" "Arial" 10 0 0
9694.740 2084.210 "Inflow" "" "Arial" 10 0 0
How does this look in ICM InfoWorks and ICM SWMM?
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InfoSWMM Engine == OneSWMM for InfoDrainage and ICM SWMM
Full Reference for the 1981 version of Extran for SWMM3
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EPA-600/2-84-109b
Final Draft, November 1981
Sixth Printing, July 1983
STORMWATER MANAGEMENT MODEL USER'S MANUAL VERSION III Addendum I EXTRAN
by
Larry A. Roesner
Robert P. Shubinski
John A. Aldrich
Camp Dresser & McKee Inc.
Annandale, Virginia 22003
EPA COOPERATIVE AGREEMENT NO. CR8O5664
Project Officer
Douglas C. Ammon
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268Closing Note
Thank you for reading these articles. I appreciate your engagement and support. Thank you again, and I hope you'll join me on this ongoing journey of learning and discovery. Until next time you read one of these posts.
The articles in this newsletter highlight temporal asymmetries. They discuss topics that, while only universally relevant at some times, become crucial for those in need. These pieces are resources, and they are ready to let you know and help when specific circumstances arise.