How do V-notch weirs work in SWMM 5?

How do V-notch weirs work in SWMM 5?

Hi Keith, As you change the Length which is actually the Top Width you change the area and hydraulic radius of the Weir. 

The height of a V-Notch weir is the Height Value in the SWMM 5 Weir Property Dialog (Figure 1) 

The Length in the Dialog for a V-Notch is the Top Width of Triangular Shaped V-Notch Weir. 

The slope of the sides of the V-Notch Weir is Square Root (1 + Top Width / Height / 2 * Top Width / Height / 2)

The full area is the Height * Height * Side Slope

The hydraulic radius is the Height / ( 2 * Height * Side Slope)

The two values Height and Length for a SWMM 5 V-Notch Weir determines the area, hydraulic radius and side slope of the weir.

Figure 1.   Parameters for a V-Notch Weir in SWMM 5

SWMM 5 Weir RTC Rules

Subject:   SWMM 5 Weir RTC Rules

This example SWMM 5 model closes a weir based on the depth at the upstream node of the Weir every 0.25 feet.  You can see the effect of the RTC rules using a Scatter plot of Weir Flow versus Weir Depth in SWMM 5 (Figure 1).   The Weir flows normally every 0.25 feet but shuts down three times using these rules which set the Weir Setting to 0.0

RULE Weir100

IF Node  WeirNode Depth > 1.75

AND Node WeirNode Depth < 2.0

THEN WEIR WEIR Setting = 0.0

Priority 2

RULE Weir101

IF Node  WeirNode Depth > 2.25

AND Node WeirNode Depth < 2.5

THEN WEIR WEIR Setting = 0.0

Priority 2

RULE Weir102

IF Node  WeirNode Depth > 2.75

AND Node WeirNode Depth < 3.0

THEN WEIR WEIR Setting = 0.0

Priority 2

RULE Weir103

IF Node  WeirNode Depth > 3.25

AND Node WeirNode Depth < 3.5

THEN WEIR WEIR Setting = 0.0

Priority 2

RULE Weir104

IF Node  WeirNode Depth > 3.75

AND Node WeirNode Depth < 4.0

THEN WEIR WEIR Setting = 0.0

Priority 2

Figure 1.  Scatter Graph of Weir flow versus Weir Node Depth.

What are the Equations for Weirs in SWMM 5, Part 2?

Subject:   What are the Equations for Weirs in SWMM 5, Part 2?

There are four types of Weirs in SWMM 5:  Transverse, Sideflow, V Notch and Trapezoidal.   The trapezoidal weir is a combination of the Sideflow and V Notch Weir and the Sideflow acts like a Transverse Weir when the flow is reversed (Figure 1).  The Weirs can have zero, one or two end contractions (Figure 2) and the Weir Length is a function of the Weir Setting and Horizontal Weir Length.  A V Notch weir works as Trapezoidal Weir when the Weir RTC Setting is less than 1.0

Figure 1.   Weir Equations in SWMM 5

Figure 2.   Valid Number of End Contractions

Figure 3.  Weir Length Calculations

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

Weirs in InfoSWMM and SWMM5

Weirs in InfoSWMM and SWMM5

Subject: Weirs in InfoSWMM

 Figure 1 shows the relationship between the weir input data and the upstream and  downstream nodes.

·         Height,

·         Crest and

·         Node Invert Elevation

 There are four types of weirs and if the weir becomes submerged downstream the Villemonte weir submergence correction is applied (Figure 2).  You can have flow reversal across the weir unless you use a Flap Gate for the weir (Figure 3). 

Figure 1:  Definition of Weir Terms

Figure 2: Villemonte Weir Submergence Correction

Figure 3:  Flow Reversal in a Weir

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.

Time Step Selection in InfoSWMM and SWMM5

1^st The time step you use in SWMM 5 is controlled from the top by the rainfall interval (Figure 1):

1.   All of your time steps should be less than the rainfall interval,

2.   The hydrology time step should be less than or equal to the smallest raingage rainfall interval in your network,

3.   The hydraulic time step should be less than or equal to the hydrology time step and should be based on the hydraulic needs of the your network.  Short length links, pump and weirs may require a smaller maximum hydraulic time step.

2^nd The report time step controls what you see in the graphics output of SWMM 5. If you see a large difference between that you see in the graphics output and the report text file it is because you have a large difference between the report time step and the average time step used during the simulation.

Solution: If there is a large discrepancy in the graphics and report text file then the best solution is to reduce the maximum time hydraulic time step so it is closer to the average time step and also to make the report time step closer to the Maximum time step (Figure 2).

Figure 1:  Relationship between the rainfall, hydrology and hydraulic time steps.

Figure 2:  Relationship between the minimum, average and maximum simulation time steps and the report time step.

Leaping Weir Example in SWMM 5 and InfoSWMM, Alternative

Leaping Weir Example in SWMM 5 and InfoSWMM, Alternative

This is an example SWMM 5 model that can be imported into InfoSWMM or H2OMap SWMM using the Exchange/Import Command.   The low flow falls over the berm of the leaping weir into a rectangular open channel but the the "falls" is governed by an OULET Depth/Discharge Type in SWMM 5.  The flow increases in the OUTLET until a depth of 1 feet is reached where the weir starts to operate.  The OUTLET increases in flow from zero to 1 feet but still flows at a reduced rate when the weir starts to operate.  The weir stops flowing when the depth goes below 1 foot on the berm.

SWMM 5 Input File Link
Background Image

Leaping Weir With Low Flow Depth/Discharge OUTLET

How do V-notch weirs work in SWMM 5?

How do V-notch weirs work in SWMM 5?

How do V-notch weirs work in SWMM 5? by dickinsonre How do V-notch weirs work in SWMM 5? Hi Keith, As you change the Length which is actually the Top Width you change the area and hydraulic radius of the Weir.  The height of a V-Notch weir is the Height Value in the SWMM 5 Weir Property Dialog (Figure 1)  The Length in the Dialog for a V-Notch is the Top Width of Triangular Shaped V-Notch Weir.  The slope of the sides of the V-Notch Weir is Square Root (1 + Top Width / Height / 2 * Top Width / Height / 2) The full area is the Height * Height * Side Slope The hydraulic radius is the Height / ( 2 * Height * Side Slope) The two values Height and Length for a SWMM 5 V-Notch Weir determines the area, hydraulic radius and side slope of the weir. Figure 1.   Parameters for a V-Notch Weir in SWMM 5 via Blogger http://www.swmm5.net/2013/08/how-do-v-notch-weirs-work-in-swmm-5.html

SWMM 5 Weir RTC Rules

Subject:   SWMM 5 Weir RTC Rules

SWMM 5 Weir RTC Rules by dickinsonre Subject:   SWMM 5 Weir RTC Rules This example SWMM 5 model closes a weir based on the depth at the upstream node of the Weir every 0.25 feet.  You can see the effect of the RTC rules using a Scatter plot of Weir Flow versus Weir Depth in SWMM 5 (Figure 1).   The Weir flows normally every 0.25 feet but shuts down three times using these rules which set the Weir Setting to 0.0 RULE Weir100 IF Node  WeirNode Depth > 1.75 AND Node WeirNode Depth < 2.0 THEN WEIR WEIR Setting = 0.0 Priority 2 RULE Weir101 IF Node  WeirNode Depth > 2.25 AND Node WeirNode Depth < 2.5 THEN WEIR WEIR Setting = 0.0 Priority 2 RULE Weir102 IF Node  WeirNode Depth > 2.75 AND Node WeirNode Depth < 3.0 THEN WEIR WEIR Setting = 0.0 Priority 2 RULE Weir103 IF Node  WeirNode Depth > 3.25 AND Node WeirNode Depth < 3.5 THEN WEIR WEIR Setting = 0.0 Priority 2 RULE Weir104 IF Node  WeirNode Depth > 3.75 AND Node WeirNode Depth < 4.0 THEN WEIR WEIR Setting = 0.0 Priority 2 Figure 1.  Scatter Graph of Weir flow versus Weir Node Depth. via Blogger http://www.swmm5.net/2013/08/swmm-5-weir-rtc-rules.html