The SWMM 5 1D Components in InfoSWMM 2D

Note:  The SWMM 5 1D Components in InfoSWMM 2D

InfoSWMM 2D uses standard SWMM 5 components to connect the 1D Nodes to the 2D Mesh.  A bottom outlet orifice at the maximum depth of the node drains to a SWMM 5 Outfall at the fixed elevation equal to the Node Rim Elevation. Flow can go into or out of the Outfall from the 1D element from or to the 2D Mesh. InfoSWMM 2D automatically makes the necessary elements if 2D is used and the new elements are listed in the Hydqua.inp file, which is very similar to the Tab Delimited SWMM5 Input file. 

The HYDQUA.inp is very similar to the Excel Tab formatted file of SWMM 5 with a few additional sections and added features:

1^st Difference:   The Flood Node Data Section tell the 2D engine which Node has a 1D-2D connection and which 2D mesh element the 1D Node drains to when it is flooded.

[Flood_Node]

10309D      848

80408        131

2^nd Difference:  Outfall Nodes are created for the 2D Mesh Element connected to the 1D Node, the outfalls are Fixed Outfalls and the fixed head is the Node Rim Elevation of the 1D node listed in the Flooded Node Section

[OUTFALLS]

10208  89.900000     FREE  NO

10208A           89.900000     FIXED            94.400000     YES

10208B           89.900000     FREE  NO

10208C           89.900000     FREE  NO

10208D           89.900000     FREE  NO

10208E           89.900000     FREE  NO

10309D_OUTFALL           101.600000            FIXED           111.000000            NO

80408_OUTFALL             120.000000            FIXED           133.400000            NO

3^rd  Difference:  Bottom Outlet Orifices are created to connect the 1D node to the 2D Mesh Element Outfall with the Flood Discharge Coefficient entered by the user and a crest height equal to the maximum depth of the node

[ORIFICES]

OR1@82309B-15009B  82309B      15009B      BOTTOM    0.000000   0.850000   NO

OR1@82309D-82308D  82309D      82308D      SIDE 0.000000   0.850000   NO

10309D_ORIFICE       10309D      10309D_OUTFALL       BOTTOM    9.400000   0.030000   NO

80408_ORIFICE          80408        80408_OUTFALL         BOTTOM    13.400000 0.030000   NO  

Weir and Orifice Flow Equations for a Weir in SWMM 5

Weir and Orifice Flow Equations in SWMM 5!

1. 🌊 When we discuss the weir flow equation in SWMM 5, it's essential to understand that the weir equation is applied under specific conditions. The head (or height of water) at the weir should be between its base (invert elevation) and the top (crown). This is when the weir equation is most applicable.

2. 🕳️ Once the water level surpasses the weir crown, indicating that the weir is submerged or the head is exceptionally high, the orifice equation comes into play.

It's crucial to ensure the accurate application of these equations, as they determine the flow of water in stormwater systems and can greatly influence flood predictions and management.

Detention Basin Basics in SWMM 5

Subject:  Detention Basin Basics in SWMM 5

What are the basic elements of a detention pond in SWMM 5?  They are common in our backyards and cities and just require a few basic elements to model.  Here is a model in SWMM 5.0.022 that even has a fountain in the real pond – which we not model for now.   The components of the model are:

1.   An inlet to the pond with a simple time series – a subcatchment can be added to it in a more complicated model but for now we will just have a triangular time series,

2.   A pipe to simulate the flow into the pond from the inlet,

3.   A Storage Node to simulate the Pond that consists of a tabular area curve to estimate the depth and area relationship,

4.   A Storage Node to simulate the Outlet Box of the Pond

5.   Two Small Rectangular Orifices to simulate the low flow outflow from the pond at an elevation less than the weir

6.   A large rectangular orifice to simulate the normal inflow to the Box

7.   A rectangular weir to simulate the flow into the box when the pond water surface elevation is above the box

8.   The outlet of the Box is a circular link with a Free outfall as the downstream boundary condition

9.   The flow graph in the image shows the flow into the box starts from the two small orifices, next from the large orifice and finally from the top of the box or the weir.

SWMM 5 Clocktime RTC Rules for Pumps, Weirs and Orifices

Subject:  SWMM 5 Clocktime RTC Rules for Pumps, Weirs and Orifices

You can use the Control or RTC rules in SWMM 5 to adjust the settings of the weirs, pumps and orifices based on the clock time each day of your simulation.  Here is an example that will adjust orifice height every ½ hour for 7 orifices at one time using two sets of rules.

RULE R1a 

; Half hour setting

IF SIMULATION CLOCKTIME = 0:30:00 

OR SIMULATION CLOCKTIME = 1:30:00  

OR SIMULATION CLOCKTIME = 2:30:00 

OR SIMULATION CLOCKTIME = 3:30:00 

OR SIMULATION CLOCKTIME = 4:30:00 

OR SIMULATION CLOCKTIME = 5:30:00 

OR SIMULATION CLOCKTIME = 6:30:00 

OR SIMULATION CLOCKTIME = 7:30:00 

OR SIMULATION CLOCKTIME = 8:30:00 

OR SIMULATION CLOCKTIME = 9:30:00 

OR SIMULATION CLOCKTIME = 10:30:00

OR SIMULATION CLOCKTIME = 11:30:00

OR SIMULATION CLOCKTIME = 12:30:00 

OR SIMULATION CLOCKTIME = 13:30:00  

OR SIMULATION CLOCKTIME = 14:30:00 

OR SIMULATION CLOCKTIME = 15:30:00 

OR SIMULATION CLOCKTIME = 16:30:00  

OR SIMULATION CLOCKTIME = 17:30:00 

OR SIMULATION CLOCKTIME = 18:30:00 

OR SIMULATION CLOCKTIME = 19:30:00 

OR SIMULATION CLOCKTIME = 20:30:00 

OR SIMULATION CLOCKTIME = 21:30:00 

OR SIMULATION CLOCKTIME = 22:30:00

OR SIMULATION CLOCKTIME = 23:30:00

THEN ORIFICE R1 SETTING = 0.90

AND  ORIFICE R2 SETTING = 0.90

AND  ORIFICE R3 SETTING = 0.90

AND  ORIFICE R4 SETTING = 0.90

AND  ORIFICE R5 SETTING = 0.90

AND  ORIFICE R6 SETTING = 0.90

AND  ORIFICE R7 SETTING = 0.90

RULE R1b

; hour setting

IF SIMULATION CLOCKTIME = 0:00:00

OR SIMULATION CLOCKTIME = 1:00:00

OR SIMULATION CLOCKTIME = 2:00:00

OR SIMULATION CLOCKTIME = 3:00:00

OR SIMULATION CLOCKTIME = 4:00:00

OR SIMULATION CLOCKTIME = 5:00:00

OR SIMULATION CLOCKTIME = 6:00:00

OR SIMULATION CLOCKTIME = 7:00:00

OR SIMULATION CLOCKTIME = 8:00:00

OR SIMULATION CLOCKTIME = 9:00:00

OR SIMULATION CLOCKTIME = 10:00:00

OR SIMULATION CLOCKTIME = 11:00:00

OR SIMULATION CLOCKTIME = 12:00:00 

OR SIMULATION CLOCKTIME = 13:00:00

OR SIMULATION CLOCKTIME = 14:00:00 

OR SIMULATION CLOCKTIME = 15:00:00

OR SIMULATION CLOCKTIME = 16:00:00

OR SIMULATION CLOCKTIME = 17:00:00

OR SIMULATION CLOCKTIME = 18:00:00 

OR SIMULATION CLOCKTIME = 19:00:00 

OR SIMULATION CLOCKTIME = 20:00:00 

OR SIMULATION CLOCKTIME = 21:00:00 

OR SIMULATION CLOCKTIME = 22:00:00 

OR SIMULATION CLOCKTIME = 23:00:00

THEN ORIFICE R1 SETTING = 0.5

AND  ORIFICE R2 SETTING = 0.5

AND  ORIFICE R3 SETTING = 0.5

AND  ORIFICE R4 SETTING = 0.5

AND  ORIFICE R5 SETTING = 0.5

AND  ORIFICE R6 SETTING = 0.5

AND  ORIFICE R7 SETTING = 0.5

Drainage Wells or a Vertical Exfiltration Trench in InfoSWMM

Subject:  Drainage Wells or a Vertical Exfiltration Trench in InfoSWMM

Note, this is just one way to model an Exfiltration Trench.  The source for the image below is Rice Creek Watershed. 

You can make a storage node to simulate the trench with the following characteristics:

·         Functional or Shape Curve to describe the shape of the trench,

·         Infiltration parameters to simulate the infiltration flow out of the bottom or sides of the trench,

Step 1:  Define the shape and geometrical characteristics of the Infiltration Trench

Step 2: Define the soil infiltration characteristics of the trench

Step 3:  Run the simulation.  The Storage Volume Summary tells you the volume infiltrated and the average outflow.

Step 4:  Output Manager will also show the infiltration  outflow, the depth and the volume of the infiltration/storage node.

Step 4:    Infiltration losses out the side and bottom of the orifice.

Manhole Elevations in InfoSWMM and SWMM 5

Subject: Manhole Elevations in InfoSWMM and SWMM 5

Starting from the bottom of the manhole you have these regions of computational interest:

1.   Manhole Invert to the lowest link invert – the node continuity equation is used with the area of the manhole being the default surface area of a manhole,

2.   Lowest Link Invert to the Highest Link Crown Elevation – the node continuity equation is used with surface of the node being normally half of the surface area of the incoming and outgoing links,

3.   Highest Manhole Pipe Crown Elevation to Manhole Rim Elevation – the node surcharge algorithm in which the surface area of the manhole is not used and the surcharge depth is iterated until the inflow and the outflows of the node are in balance,

4.   The region above the Manhole Rim Elevation which can use one of four options to calculate the depth and/or flow out of or into the manhole:

1.   No Surcharge Depth is entered and No Ponding area is used – the excess water into the manhole is lost to the network and shows up as internal outflow in the continuity tables,

2.   A Ponding Area is used and the excess flow will  pond on the surface of the manhole and later go back down into the conveyance pipes.

3.   A Surcharge Depth is used and the depth will continue to be calculated using the node surcharge algorithm in which the surface area of the manhole is not used and the surcharge depth is iterated until the inflow and the outflows of the node are in balance,

4.   A Dual Drainage system is simulated and the excess flow of the manhole is simulated in the street gutters or the actual street,

5.   You use a 1D/2D linkage between the 1D manhole and 1D links to a 2D Mesh and simulate the flow out and the flow into the manhole using a bottom outlet orifice that switches automatically between weir and orifice flow based on the depth on top of the manhole. 

Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices in SWMM 5

Note:  Orifice Critical Depth for Separating Weir Flow from Orifice Flow for Bottom Outlet Orifices

The Critical height is the opening where weir flow turns into orifice flow. It equals (Co/Cw)*(Area/Length) where Co is the orifice coeff., Cw is the weir coeff/sqrt(2g), Area is the area of the opening, and Length = circumference of the opening. For a basic sharp crested weir, Cw = 0.414.  All of the units are based on the internal SWMM 5 units of American Standard.

For a circular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * Orifice Opening / 4

For a rectangular orifice the Critical Height is:

Critical Height = Orifice Discharge Coefficient / 0.414 * (Orifice Opening*Width) / (2.0*(Orifice Opening+Width))

The Orifice Critical Depth changes dynamically as the orifice is opening and closing for a bottom outlet orifice.  The critical depth separating the orifice weir flow from orifice flow for a side outlet orifice is the height of the orifice.

Simulating a Blocked Pipe in SWMM 5 and InfoSWMM

Note:  For example, you can use the Simulation Elapsed time as the Premise and a complete closure of the orifice as the action to simulate a blockage in a portion of the network.  A circular orifice can be used to simulate a circular pipe and of course a rectangular orifice can simulate a rectangular pipe.

Example RTC rule for the opening and closing of the orifice in SWMM5

Here is an example Real Time Control (RTC) rule for the opening and closing of  an orifice 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 simulation

Orifice Open and Close Speed and the Target Setting

Orifice Open and Close Speed and the Target Setting

In SWMM 5 there is an orifice parameter called setting which opens or closes the orifice opening by modifying the depth of the orifice.  The setting is  based either on a RTC rule of the orifice or the Flap Gate condition of the orifice and can be between 0 and 1.  Closed is 0; Open is 1.  The difference is that the target setting is what the setting should be based on the condition of the Flap Gate or the RTC Rules and the setting is the value actually used in the model. 

The open and close speed of the orifice modifies the orifice setting by changing the orifice setting based on the open and closing speed using the equation:

New Orifice Setting = Old Orifice Setting + (Target Setting – Orifice Setting) * Time Step / Orifice Open and Close Speed

If your target setting and the current orifice setting are both 1 or 0 then the orifice Open and Close option does not change the orifice setting.  New Settingequals Old Setting in that case.  If the target and  setting are out of phase then the Open and Close Option will function correctly.  For example, if the Openand Close Speed is 1 hour then the orifice setting will open and close in a one hour period.  The table shown below shows how the orifice setting changes as a function of the speed and the difference between the target and orifice settings.   The setting starts out open but the target says closed – the orificethen closes over a 1 hour period.  At one hour the target setting is 1 and the orifice will then open over a one hour period.

Table - Link OR1@82309b-15009b

                                Setting               Target         

Days         Hours                                                

0              00:00:00    1.00                  0.00           

0              00:15:00    0.74                  0.00           

0              00:30:00    0.50                  0.00           

0              00:45:00    0.25                  0.00           

0              01:00:00    0.00                  0.00           

0              01:15:00    0.25                  1.00           

0              01:30:00    0.50                  1.00           

0              01:45:00    0.75                  1.00           

0              02:00:00    1.00                  1.00           

0              02:15:00    0.75                  0.00           

0              02:30:00    0.50                  0.00           

0              02:45:00    0.25                  0.00           

0              03:00:00    0.00                  0.00           

0              03:15:00    0.00                  0.00           

0              03:30:00    0.00                  0.00            

0              03:45:00    0.00                  0.00           

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