Surcharged d/D in InfoSWMM and H2OMap SWMM

· November 04, 2015
The value of d/D in InfoSWMM is calculated as Link capacity or the Midpoint Capacity

Whereas the Surcharged d/D is calculated from the end node depths or
Surcharged d/D = Average depth in the middle of a link or ½ (Upstream Depth + Downstream Depth) / Maximum depth

Midpoint Capacity = the midpoint cross sectional area (based on the average depth) / the full cross sectional area

If you look at the reports d/D or Midpoint Capacity is not quite the same as the Surcharged d/D which is based on the upstream and downstream depths and not the Capacity (a function of Area).  I hope this explains why Surcharged d/D is equal to the Depth and not the same as the d/D or Midpoint Capacity.

Inverse Color Attribute Browser in InfoSWMM and H2OMap SWMM showing various output data.



How to Use the Arc Map Editor in InfoSWMM

· August 27, 2015


How to Use the Arc Map Editor in InfoSWMM


Note:  How to Use the Arc Map Editor in InfoSWMM
Step 1 is to use the Edit Feature for example the Subcatchment layer to bring up the Arc Map Editor Tool.

Step 2 is to use the Reshape Feature tool or Vertex tools to bring together mis matched Subcatchment Boundaries

Step 3 is to use save the edits and then Update the DB from the Map to recalculate the area of the Subcatchments

How to Make a Break Node in SWMM5 and InfoSWMM for Force Mains with Emojis

· February 07, 2015

🔍 The central issue being highlighted is ensuring Force Mains are kept full (or d/D equal to 1) when the pumps activate. Achieving this in SWMM 5 can be a challenge due to its single Q link solution, compared to the 4 or more flow points in the IWCS solution. 🔄 There have been past suggestions to add a break node at the end of force mains to ensure they remain full. However, this doesn't always work, especially when a gravity main exists at the end of the rising force main. The gravity main instantly takes up the flow from the long force main, keeping the downstream node depth minimal, which results in the force main not being fully filled – leading to customer dissatisfaction. 😤 A potential solution is to amplify the gravity main roughness, simulating the transition from the force main to the gravity main, which keeps the depth elevated and the force main filled most of the time.

📝 Here are the eight suggestions:

  1. ⚙️ Use a Flap Gate for the rising main with HW Force Main Coefficients.
  2. 🔧 Add a Break Node at the end of your longer Force Mains with a Surcharge Depth using the Insert Manhole Tool.
  3. ⛓️ The d/D values for the force main usually being less than 1 is due to the downstream node of the Force Main having a low depth. Adding a Break Node ensures it remains fuller.
  4. 🌊 Change the link AFTER the Break Node to a Gravity Main, and increase the roughness n value (2 to 3 times rougher) to simulate the transition losses.
  5. 📈 This action will boost the node's depth at the Force Main's downstream end, ensuring it remains full most of the time.
  6. 📊 As highlighted, the force main link has a single Q and three depths. The d in the d/D graph is derived from the midpoint depth or the average of the link's upstream and downstream depths.
  7. 🚰 In model reality, the force main is always full at the link's upstream end but is affected by the low downstream depth.
  8. 🌟 Increasing the roughness in the gravity main makes results align more closely with user expectations for the d/D value, offering a realistic representation.

🌩️ Use a Flap Gate for the rising main with HW Force Main Coefficients.
🌩️ Introduce a Break Node at the end of longer Force Mains with a Surcharge Depth using the Insert Manhole Tool.
🌩️ The typical d/D values for the force main are less than 1 due to the downstream node's low depth. Adding a Break Node ensures it remains fuller.
🌩️ Post the Break Node, change the link to a Gravity Main. Increase the roughness n value for a realistic transition.
🌩️ This ensures the node's depth at the Force Main's downstream end remains high.
🌩️ The force main link has one Q and three depths, with the d in the d/D graph derived from the midpoint depth.
🌩️ In model reality, the force main remains full at the link's upstream end.
🌩️ Increasing the gravity main's roughness offers results that align closely with user expectations and offer a touch of reality.

A rise in Pipe Inverts Across a SWMM 5 Node, What Node and Link Invert Elevations Does SWMM 5 Use?

· November 29, 2014

A rise in Pipe Inverts Across a SWMM 5 Node

Subject:  This is how SWMM 5 handles  jumps in pipe invert across a node. 
 The water surface in the node determines the flow in the link, as the depth increases due to upstream inflow eventually the downstream link will start flowing.

The Minimum Surface Area in SWMM 5 - Meaning and Usage

· March 09, 2014
The Minimum Surface Area in SWMM 5 - Meaning and Usage

 The minimum surface area in SWMM 5 is intended for manholes that have a gap between the Node Invert Elevation and the Lowest Connecting Link Invert but it also has other uses in simulation.  If there is a gap the minimum surface area is used to prevent a divide by a zero surface area in the node continuity equation.  In the case of very short links where the area of the links added to the node surface area is less than minimum surface area then the area used is the minimum surface area.  If you want the SWMM5 engine to essentially ignore the minimum surface area then set the area to a small value in the Dynamic Wave Tab of the Simulation Options Dialog (Figure 1).   This applies equally to the both Manholes and Storage nodes as shown in Figure 1.  The Surface area for the Storage Node is set equal to the Minimum Surface Area. 

1. Storage Nodes and Manholes use the same Node Continuity Equation until the Highest Link Soffit is reached and then the Manhole uses the Surcharge Equation
2. Storage Nodes and Manholes both use the Minimum Node Surface Area
Figure 1.  The Meaning of the Minimum Surface Area in SWMM 5

New Mapping Feature in InfoSewer and H2OMap Sewer for Unfilled Depth and Surcharge Depth

· December 24, 2013
New Mapping Feature in InfoSewer and H2OMap Sewer for Unfilled Depth and Surcharge Depth

This is a new features in H2OMap Sewer 10.5 SP1, Update 1 and InfoSewer SP1, Update 1.  You can now map the Maximum Unfilled Depth and Maximum Surcharge Depth during the Simulation in Map Display.

Unfilled Depth is the depth between the Rim Elevation and the Water Surface in the Manhole – the minimum is zero feet or meters

The Surcharge Depth is the Distance between the Rim Elevation and the Water Surface Elevation in the Manhole – it can be positive or negative (negative means the Node is under pressure)


What Node and Link Invert Elevations Does SWMM 5 Use?

· August 23, 2013
Note:  What Node and  Link Invert Elevations Does SWMM 5 Use?

SWMM 5 uses the following Node information from the user:
·         Node Invert Elevation,
·         The Node Rim Elevation which is the Node Invert Elevation + the Maximum node depth
·         The Ponded Area when the Ponded  Area option is used
·         The Surcharge Depth above the Node Rim Elevation

SWMM 5 uses the following link information from the user:
·         The Link Upstream Offset Depth or Offset Elevation and
·         The Link Downstream Offset Depth or Offset Elevation
·         The Link Maximum Depth or Diameter

SWMM 5 calculates the following information internally:
·         The Pipe Crown Elevation at the upstream and downstream link nodes.  The Pipe Crown is the Pipe Diameter + Link Offsets
·         The Node Highest Pipe Crown Elevation,  the new rim elevation will be used in the program
·         The Surcharge Depth above the Rim Elevation if the Node has a Surcharge Pressure Depth at the Node during the simulation,
o   If the Surcharge Depth is 0 then the program will either lose the flooded water or store the flooded water during the simulation
·         The Flooded Depth above the  Rim Elevation if the Node uses the Ponded Area Option
o   You have to enter a Ponded Area for the node AND use the Global Allow Ponding Option

SWMM 5 Rules for Pipes
·         The Pipe Invert Cannot be below either upstream or downstream node invert – the program will print a warning in the rpt file and set the offset to 0 internally,
·         The Pipe Crown Cannot be above the Rim Elevation of the Node – the program will raise the Rim Elevation when this happens and print a warning in the rpt file.

The use of Offset Depth or Offset Elevation for the Link Offsets is based on the user choice at the bottom of the SWMM 5 GUI Map.

Or in the Tools/Preference/Operation dialog of InfoSWMM/H20MAP SWMM 




Siphon Simulation in SWMM 5 and InfoSWMM

· August 10, 2013
Subject:  Siphon Simulation in SWMM 5 and InfoSWMM

A Siphon is simulated in SWMM 5 and InfoSWMM using the basic node and link data and downstream boundary condition:

1.   Inflow can be time series, dry weather flow pattern, wet weather inflow or Subcatchment Runoff,
2.   The boundary condition can be either a free outfall, fixed or time series,
3.   The node invert, node maximum depth and node surcharge depth are defined by the user or network,
4.   The link lengths, diameters, link offset depths upstream and downstream are defined by the user of the network,
5.   The node depths, link flows, link depths and link cross sectional areas are calculated at each time based on the node continuity equation and the link momentum and continuity equation.  The link flows are a function of the friction loss, head difference across the link and the difference in the cross sectional areas of the link.
6.   In the particular model the Inflow at node MH1 fills up the MH1 depth which causes the links downstream to start flowing – the head difference across the links drives the flow up and over the siphon.

How are Flooded Time, Surcharged Time and Flooded Volume Calculated in InfoSWMM and H2OMAP SWMM?

· August 08, 2013
How are Flooded Time, Surcharged Time and Flooded Volume Calculated in InfoSWMM and H2OMAP SWMM?

The time, volume and flooded rate shown in the InfoSWMM and H2OMAP SWMM Report File Node Flooding Summary (Figure 2) are calculated as follows (Figure 1):

For All Nodes NOT Outfalls ( this includes Junctions, Storage Nodes, Dividers)

If the New Volume is greater than the Full Volume of the or there is Overflow then at each time step the Time Flooded is increased

If the New Volume is greater than the Full Volume of the or there is Overflow then at each time step the Volume Flooded is increased by the Overflow *Time Step

If the New Volume is greater than the Full Volume of the or there is Overflow AND Surface Ponding is Used then the Ponded Volume is New Volume – Full Volume

If the Node Depth Plus the Node Invert Elevation is above the Node Crown Elevation then at each time step the time surcharged is increased.   The InfoSWMM andH2OMAP SWMM Map Display variables should be FLOOD_VOLM for the No Surface Ponding option (Figure 3) and PONDED_VOL if you are using the Global Surface Ponding Option (Figure 4).
Figure 1.  Levels of Surcharged and Flooding in SWMM 5.

Figure 2.  SWMM 5 Node Flooding Summary or the InfoSWMM and H2OMAP SWMM HTML Report file.


Figure 3.  The Map Display of the Node Flooding using the No Surface Ponding Option should use the Map Display Variable FLOOD_VOLM

Figure 4.  The Map Display of the Node Flooding using the Surface Ponding Option should use the Map Display Variable PONDED_VOL which shows the Maximum Stored Pond Volume.

Maximum HGL Head Class in InfoSWMM AND H2OMAP SWMM

· August 08, 2013
Maximum HGL Head Class in InfoSWMM AND H2OMAP SWMM

You can find the node flood or surcharge maximum occurrence during a simulation in the Junction Summary Report table in InfoSWMM and H2OMAP SWMM (Figure 1)

Empty                                   if the Node Head is below or equal to the Lowest Link Connecting  Elevation
Below Link Crown            if the Node Head is below or equal to the Highest Link Connecting Crown
Below Maximum Depth   if the Node Head is below or equal to the Node Invert + Full  Depth.  The column Max Surcharge Height above Crown will also tell you how deep the Surcharge in a Node.
Surchaged                           if none of the above is true.


Figure 1.  Junction Summary Report in InfoSWMM

Figure 2.  Maximum Surcharge Height above Crown Definition

InfoSWMM (d/D v. Surcharge d/D)

· August 07, 2013
Subject:   InfoSWMM (d/D v. Surcharge d/D)

What is the difference between the output variables d/D and Surcharge d/D in InfoSWMM and H2OMap SWMM

The d/D is calculated as link capacity based on the midpoint depth of water in the link or Link depth/ Link Maximum Depth
            Since the depth in the link is restricted to the Maximum Depth the d/D value is always between 0 and 1

The Surcharged d/D is calculated from the end node depths at each end of the link

            The two node depths are averaged and the value of Surcharge d/D is the Average Node Depth / Link Maximum Depth,
The value of Surcharge d/D varies from 0 to a large number depending on the maximum depths of the nodes and the possible surcharge depth of the nodes

The value of d/D is based on the middle of the link and the value of Surcharge d/D is based on the average of the node depths at the end of the link.  They may be and often are different.   However, if you have a Surcharge d/D greater than 1 it will indicate at least one end of the link is surcharged.  A Surcharge d/D may be greater than 1 with a d/Dless than 1 due to the ends of the node being surcharged and not surcharged.

·         A Surcharged d/D indicates that at least one end of the link is Full, but
·         A d/D value less than 1 does not preclude that one end may be Surcharged.

Figure 1.  Plot of d/D and Surcharged d/D in InfoSWMM.

Example FM SWMM 5 model with and without Surcharge Depth

· August 06, 2013
Subject:   Example FM SWMM 5 model with and without Surcharge Depth

You need to use the surcharge depth for a Force Main in SWMM 5 to allow the engine to find the right point on the pump curve and pump up the rising main.  If you do not use a surcharge depth then the flow MAY be very small in the rising main due to a small head difference.  Of course the flow in the force main depends on the pump curve you have entered but having the right downstream head of depth for the link matter as well.  The attached model was created in SWMM 5.0.022 



Force Main Friction Loss in InfoSWMM and the Transition from Partial to Full Flow

· August 05, 2013
Subject:  Force Main Friction Loss in InfoSWMM and the Transition from Partial to Full Flow
You can model Force Main friction loss in InfoSWMM using either Darcy Weisbach or Hazen Williams as the full pipe friction loss method (see Figure 1 for the internal definition of full flow).   A function called ForceMain in InfoSWMM whose purpose is to compute the Darcy-Weisbach friction factor for a force main using the Swamee and Jain approximation to the Colebrook-White equation .  No matter which method you use for full flow the  program will use Manning's equation to calculate the loss in the link when the link is not full (see Figure 2 for the equations used for calculating the friction loss – variable dq1 in the St Venant equation for InfoSWMM).   The regions for the different friction loss equations are shown in Figure 3.    

There is no slot in InfoSWMM for the full pipe flow as a surcharged node in InfoSWMM uses this point iteration equation (Figure 4): 
dY/dt = dQ / The sum of the Connecting Link values of  dQ/dH 
where Y is the depth in the node, dt is the time step, H is the head across the link (downstream – upstream), dQ is the net inflow into the node and dQ/dH is the derivative with respect to H of the link  St Venant equation.  If you are trying to calibrate the surcharged node depth, the main calibration variables are the time step and the link  roughness:
 1.   Mannings's N
2.   Hazen-Williams or
3.   Darcy-Weisbach 

The link roughness is part of the term dq1 in the St Venant solution and the other loss terms are included in the term dq5.  You can adjust the roughness of the surcharged link  to affect the node surcharge depth.   The point iteration continues until the sum of the flow in the node is zero – basically the new depth in the node either increases or decreases the friction loss in the force main so that net flow at the node is zero.  This is why it is important to use the right time step to ensure that the net flow is zero when the pumps turn on and off. 

Figure 1.  How the full pipe condition is defined in InfoSWMM - both ends have to be full





Figure 2:  Friction equations used in SWMM 5 for a Force Main.


Figure 3:  Regions of Friction loss equations in SWMM 5.


Figure 4.  The Node Surcharge Equation is a function of the net inflow and the sum of the term dQ/dH in all connecting links. Generally, as you increase the roughness the value of dQ/dH increases and the denominator of the term dY/dt = dQ/dQdH increases.