Autodesk Technologist with Information about Stormwater Management Model (SWMM) for watershed water quality, hydrology and hydraulics modelers (Note this blog is not associated with the EPA). You will find Blog Posts on the Subjects of SWMM5, ICM SWMM, ICM InfoWorks, InfoSWMM and InfoSewer.
Showing posts with label SWMM 5. Show all posts
Showing posts with label SWMM 5. Show all posts
Sunday, January 5, 2014
Saturday, August 10, 2013
SWMM 5, H2OMap SWMM and InfoSWMM Time Step Guide
Subject: SWMM 5, H2OMap SWMM and InfoSWMM Time Step Guide
If you use a variable time step in SWMM 5 or InfoSWMM/H2OMAP SWMM it is hard to gauge the proper value of the conduit lengthening. You want to use a value that does not increase the volume of the network yet does increase the length of the shortest links so you can use a longer time step. A good approximation to the time step that you want to use is shown in the image.
The Time Step Guide in seconds is Link Length / [Velocity + sqrt(g*Maximum Depth)] with the assumption that the velocity at maximum depth is about the value of the wave celerity for closed links or sqrt(g*Maximum Depth). Normally (unless pumps are involved) the average time step used during the simulation is a good gauge of the time to use for the simulation. For example, in this model run the time step used is 13 seconds which is about the conduit lengthening time step of 20 seconds * adjustment factor of 0.75
Saturday, August 3, 2013
World Wide Visitor Coverage of WWW.SWMM2000.COM
Note: For the 1^{st} time in 4 years we have had a visitor from Central Asia. This now means we have had visitors from all Google defined Geographic Regions on Earth even though we still have not had visitors from every country at www.swmm2000.com The statistics below exclude the 58 percent visitors from North America but overall we have had on September 3rd, 2011 (1st column) compared to August 3, 2013 (2nd column)
1. 40,190 Visitors to 78,840 Visitors in 2013(Cumulative)
2. 22 Continental Regions to 23 Regions
3. 157 Countries to 179 Countries
4. 5951 Cities to 6235 Cities
5. 100,180 Pageviews in 2011 to 193,142 Pageviews in 2013(Cumulative)
6. 86 Languages to 106 Languages
Statistics from 2013 
Statistics from 2011 
Variables for Controlling the Continuity Error in InfoSWMM and H2OMAP SWMM compared to SWMM 5
Subject: Variables for Controlling the Continuity Error in InfoSWMM and H2OMAP SWMM compared to SWMM 5
Time step is always a key parameter in SWMM 5 as it is the main parameter for a user to adjust in case of a significant continuity error. InfoSWMM has additional flexibility and allows the user to control the number of Picard iterations and the Node continuity stopping tolerance. SWMM 5.0.022 has the number of iterations fixed at 8 and the stopping tolerance fixed at 0.005 feet. The stopping tolerance is important because it controls the number of iterations during a time step. For example, if all of the Nodes have a current and former iteration depth difference (absolute) less than 0.005 feet then the time step is deemed converged and the node and link flow computations are stopped for that time step. In SWMM 5 since the stopping tolerance is fixed then your main option is to reduce the time step. In InfoSWMM you can also decrease the stopping tolerance, increase the number of iterations or decrease the time step. In most models it is best to alter all three parameters for the fastest model. For example, a slightly smaller maximum time step or a smaller variable time step adjustment factor, more iterations and a smaller tolerance will normally work better than just lowering the time step.
Iterations and Stopping Tolerances 
Sunday, July 28, 2013
Known and Unknown Variables in the Node Continuity Equation of SWMM5
Subject: Known and Unknown Variables in the Node Continuity Equation
The new node depth is calculated based on the old inflow to the node, the old outflow from the node, the old node depth, a fixed time step, node evaporation and infiltration losses, new inflow to the node, new outflow from the node and the new total surface area of the node. The inflow, outflow and surface area are updated before the new iteration based on the last iteration link flows and node depths. The node depth equation is iterated until the depth in the node is less than 0.005 feet between the current iteration or the last iteration with a maximum of 8 iterations in SWMM 5.0.020
New Iteration Node Depth = Old Node Depth + [ ½ * (New Inflow – New Outflow) + ½ * (Old Inflow – Old Outflow)  Node Losses ] / New Surface Area * Time Step
1^{st} Iteration: New Node Depth = New Iteration Node Depth
2^{nd} to 8^{th} Iteration: New Node Depth = ½ * New Iteration Node Depth + ½ * Old Iteration Node Depth
The new node depth is calculated based on the old inflow to the node, the old outflow from the node, the old node depth, a fixed time step, node evaporation and infiltration losses, new inflow to the node, new outflow from the node and the new total surface area of the node. The inflow, outflow and surface area are updated before the new iteration based on the last iteration link flows and node depths. The node depth equation is iterated until the depth in the node is less than 0.005 feet between the current iteration or the last iteration with a maximum of 8 iterations in SWMM 5.0.020
New Iteration Node Depth = Old Node Depth + [ ½ * (New Inflow – New Outflow) + ½ * (Old Inflow – Old Outflow)  Node Losses ] / New Surface Area * Time Step
1^{st} Iteration: New Node Depth = New Iteration Node Depth
2^{nd} to 8^{th} Iteration: New Node Depth = ½ * New Iteration Node Depth + ½ * Old Iteration Node Depth
Thursday, June 13, 2013
How to simulate a Quasi Steady Run in InfoSWMM, H2OMap SWMM or SWMM 5
How to simulate a Quasi Steady Run in InfoSWMM, H2OMap SWMM or SWMM 5 pic.twitter.com/4un4P19HFo
— RDickinson (@RDickinson) June 14, 2013
Friday, November 9, 2012
What are the LID Control Flow Source Options in SWMM 5?
What are the LID Control Flow Source Options in SWMM 5?
The SWMM 5 options for Low Impact Development (LID) controls on a Subcatchment are very flexible, exciting, possibly recursive and a completely integrated method to treat both the pervious and impervious flow. You can send the Subcatchment runoff to either an outlet node, impervious area of the Subcatchment, the pervious area of the Subcatchment or another Subcatchment. You can have the LID control receive a portion or all of the impervious flow OR as in the EPA SWMM 5 LID example have the LID cover the whole Subcatchment and receive both impervious and pervious flow from one or multiple upstream Subcsatchments. For example, Subcatchment Swale4 in Figure 1 is 100 pervious and has upstream runoff from the pervious and impervious areas of Subcatchments S1, S3 and S4 in Figure 1. The LID can also have either an outlet node or the pervious area of the Subcatchment on which it resides.
The SWMM 5 options for Low Impact Development (LID) controls on a Subcatchment are very flexible, exciting, possibly recursive and a completely integrated method to treat both the pervious and impervious flow. You can send the Subcatchment runoff to either an outlet node, impervious area of the Subcatchment, the pervious area of the Subcatchment or another Subcatchment. You can have the LID control receive a portion or all of the impervious flow OR as in the EPA SWMM 5 LID example have the LID cover the whole Subcatchment and receive both impervious and pervious flow from one or multiple upstream Subcsatchments. For example, Subcatchment Swale4 in Figure 1 is 100 pervious and has upstream runoff from the pervious and impervious areas of Subcatchments S1, S3 and S4 in Figure 1. The LID can also have either an outlet node or the pervious area of the Subcatchment on which it resides.
Saturday, November 3, 2012
How do Vnotch weirs work in SWMM 5?
How do Vnotch weirs work in SWMM 5?
How do Vnotch weirs work in
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 VNotch weir is the Height Value in the SWMM 5 Weir Property Dialog (Figure 1)
The Length in the Dialog for a VNotch is the Top Width of Triangular Shaped VNotch Weir.
The slope of the sides of the VNotch 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 VNotch Weir determines the area, hydraulic radius and side slope of the weir.
Figure 1. Parameters for a VNotch Weir in SWMM 5

Thursday, November 1, 2012
Weekend DWF Patterns in H2OMAP SWMM and InfoSWMM
Dry Weather Flow in InfoSWMM and H2OMap SWMM
Dry Weather Flow in InfoSWMM
Dry weather flow can be added to any node in H2OMAP SWMM. The dry weather flow is computed as the average flow * the monthly pattern * the daily pattern * hourly pattern * the weekend daily pattern to give the Dry Weather Flow at any time step (Figure 1). Since the four types of patterns (Figure 2) are all multiplied together then for Saturday and Sunday the hourly pattern and the weekend hourly pattern will both be used. This will have the effect of overestimating the flow if the multipliers are greater than 1 and underestimating theflow if the multipliers are less than one. You should enter the Pattern X for the Weekend Hourly Pattern in H2OMAP SWMM where
X = Weekend Hourly Pattern / Hourly Pattern
So that when the pattern X is multiplied by the Hourly Pattern the program will use the intended Weekend Pattern.
Figure 1. How Dry Weather Flow is Computed in H2OMAP SWMM
Figure 2. The Four Types of Time Patterns in H2OMAP SWMM, InfoSWMM and S

Tuesday, October 30, 2012
Format of the SWMM 5 Interface File
Note: Format of the SWMM 5 Interface File
Here is an example and Figure 1 shows the format (from Iface.c in SWMM 5)
SWMM5 Interface File
This is from the 1st line of the SWMM 5 Model in the Title/Notes Section of the Data
900  reporting time step in sec
1  number of constituents as listed below:
FLOW CFS
1  number of nodes as listed below:
10208
Node Year Mon Day Hr Min Sec FLOW
10208 2011 02 22 00 00 00 0.000000
10208 2011 02 22 00 15 00 0.000000
10208 2011 02 22 00 30 00 0.000000
10208 2011 02 22 00 45 00 0.000000
10208 2011 02 22 01 00 00 0.000000
Here is an example and Figure 1 shows the format (from Iface.c in SWMM 5)
SWMM5 Interface File
This is from the 1st line of the SWMM 5 Model in the Title/Notes Section of the Data
900  reporting time step in sec
1  number of constituents as listed below:
FLOW CFS
1  number of nodes as listed below:
10208
Node Year Mon Day Hr Min Sec FLOW
10208 2011 02 22 00 00 00 0.000000
10208 2011 02 22 00 15 00 0.000000
10208 2011 02 22 00 30 00 0.000000
10208 2011 02 22 00 45 00 0.000000
10208 2011 02 22 01 00 00 0.000000
Figure 1. Graph of the lines in the SWMM 5 Interface File 
Wednesday, October 24, 2012
InfoSewer to InfoSWMM Import Tips
Subject: InfoSewer to InfoSWMM Import Tips
Subject: InfoSewer to InfoSW
The direct import of InfoSewer to
1. Make sure that the Flow Units in InfoSWMM Run Manager match the default flow units in InfoSewer so that the DWF values are comparable,
2. Make sure that the Output Flow Units in InfoSWMM match the Output Flow Units in InfoSewer so direct comparisons are easier, 3. Add a Pump On and Pump Off depth to the Pumps in InfoSWMM so that the pumps work better in a fully dynamic solution, 4. The Fixed Pump Curves of InfoSewer should be checked in the Pump Curve section of InfoSWMM to make sure they are comparable, 5. The InfoSWMM conduit step lengthening option should be used to speed up the model if you have short links in InfoSewer, 6. You can check the overall balance in the two modeling platforms by comparing the System Load Graph in InfoSewer to the Total Inflow Graph inInfoSWMM.
Figure 1 Dialog for Importing InfoSewer to InfoSWM

How to Use the SWMM 5 Excel Tool with InfoSewer CSV Files
How to Use the SWMM 5 Excel Tool with InfoSewer CSV Files
How to Use the SWMM 5 Excel Tool
1. Export Link and Manholes in InfoSewer for your current Scenario to CSV files,
2. Set up the Excel Add on for SWMM 5 by using the command Tools, and Configure Tools (see below)
3. Run SWMM 5 and edit the data in Excel, you should be able to copy and paste the information from the CSV files into the correct SWMM 5 sections.

Tuesday, October 23, 2012
How to Use the Variable Flow Percentage Flow Splitter in InfoSewer
Subject: How to Use the Variable Flow Percentage Flow Splitter in InfoSewer
Subject: How to use the Flow Splitter in In
InfoSewer, which is an extension in Arc Map, does need to have slit split defined where gravity mains merge together to determine the amount of flow in each of the downstream conduits (Figure 1). The options for the flow splitterin each of the downstream links are:
1. Automatic Allocation
2. Fixed Flow Percentage
3. Variable Flow Percent
4. InflowOutflow Curve
At an outfall where the invert of the outfall pipe is raised compared to the inverts of the incoming and outgoing pipes a flow split of Variable Flow Percentage or Inflow/Outflow curve may work better (Figure 2).
Figure 1. Options for Performing a Flow Split in InfoSewer
Figure 2. The Effect of the flow split can be used to model complex situations in a dendritic model with outfalls.

Tuesday, October 9, 2012
SWMM 5 Control Rules for Pumps
Subject: SWMM 5 Control Rules for Pumps
If you want to define the setting for a pump between the Pump On and Pump Off depths then an IF statement based on the Pump flow will work better as in this example, which changes the setting for the pump between a depth of 18 and 20 meters. The IF statement based on flow will ensure the rule only applies when the Pump Control depth is moving from the Pump On depth to the Pump Off depth and NOT between the Pump Off and Pump On depth. Figure 1 shows how the Pump Flow is related to the Pump Setting.
If you want to define the setting for a pump between the Pump On and Pump Off depths then an IF statement based on the Pump flow will work better as in this example, which changes the setting for the pump between a depth of 18 and 20 meters. The IF statement based on flow will ensure the rule only applies when the Pump Control depth is moving from the Pump On depth to the Pump Off depth and NOT between the Pump Off and Pump On depth. Figure 1 shows how the Pump Flow is related to the Pump Setting.
RULE CONTROL_Rule2
IF PUMP PUMP1 FLOW > 0.000000
AND NODE WELL HEAD > 18.000000
AND NODE WELL HEAD < 20.000000
THEN PUMP PUMP1 SETTING = 0.700000
PRIORITY 2.000000
Figure 1 Pump Flow is related to the Pump Setting 
Saturday, October 6, 2012
Hydrology and Floodplain Analysis (5th Edition)
Hydrology and Floodplain Analysis (5th Edition) [Hardcover]
Philip B. Bedient (Author), Wayne C. Huber (Author), Baxter E. Vieux (Author)Lambda Calculus and Link Variables in the InfoSWMM, H2OMAP SWMM and SWMM 5 Dynamic Wave Solution
Subject: Successive underrelaxation for the SWMM 5 Dynamic Wave Solution
SWMM 5 uses the method of Successive underrelaxation to solve the Node Continuity Equation and the Link Momentum/Continuity Equation for a time step. The dynamic wave solution in dynwave.c will use up to 8 iterations to reach convergence before moving onto the next time step. The differences between the link flows and node depths are typically small (in a non pumping system) and normally converge within a few iterations unless you are using too large a time step. The number of iterations is a minimum of two with the 1^{st} iteration NOT using the underrelaxation parameter omega. The solution method can be term successive approximation, fixed iteration or Picard Iteration, fixedpoint combinatory, iterated function and Lambda Calculus. In computer science, iterated functions occur as a special case of recursive functions, which in turn anchor the study of such broad topics as lambda calculus, or narrower ones, such as the denotational semantics
of computer programs (http://en.wikipedia.org/wiki/
In the SWMM 5 application of this various named iteration process there are three main concepts for starting, iterating and stopping the iteration process during one time step:
· The 1^{st} guess of the new node depth or link flow is the current link flow (Figure 3) and the new estimated node depths and link flows are used at each iteration to estimate the new time step depth or flow. For example, in the node depth (H) equation dH/dt = dQ/A the value of dQ or the change in flow and the value of A or Area is updated at each iteration based on the last iteration's value of all node depths and link flows.
· A bound or a bracket on each node depth or link flow iteration value is used by averaging the last iteration value with the new iteration value. This places a boundary on how fast a node depth or link flow can change per iteration – it is always ½ of the change during the iteration (Figure 1).
· The Stopping Tolerance (Figure 2) determines how many iterations it takes to reach convergence and move out of the iteration process for this time step to the next time step.
Figure 1. Under relaxation with an omega value of ½ is done on iterations 2 through a possible 8 in SWMM 5. This is not done for iteration 1.
Figure 2. if the change in the Node Depth is less than the stopping tolerance in SWMM 5 the node is considered converged. The stopping tolerance has a default value of 0.005 feet in SWMM 5.0.022.
Figure 3. The differences between the link flows and node depths are typically small (in a non pumping system) and normally converge within a few iterations unless you are using too large a time step. The number of iterations is a minimum of two with the 1^{st}iteration NOT using the underrelaxation parameter omega.

St. Venant equation – this is the link attribute data used when the St. Venant Equation is used inSWMM 5, H2OMAP SWMM and InfoSWMM. Simulated Parameters from the upstream, midpoint and downstream sections of the link are used.
Normal Flow Equation – this is the link attribute data used when the Normal Flow Equation is used in H2OMAP SWMM. Only simulated parameters from the upstream end of the link are used if the normal flow equation is used for the time step. The normal flow equation is used if the flow is supercritical or the water surface slope is less than the bed slope of the link.
Non Linear Term in the Saint Venant Equation of SWMM 5
The flow equation has six components that have to be in balance at each time step:
1. The unsteady flow term or dQ/dt
2. The friction loss term (normally based on Manning's equation except for full force mains),
3. The bed slope term or dz/dx
5. The non linear term or d(Q^2/A)/dx and
6. The entrance, exit and other loss terms.
All of these terms have to add up to zero at each time step. If the water surface slope becomes zero or negative then the only way the equation can be balanced is for the flow to decrease. If the spike is due to a change in the downstream head versus the upstream head then typically you will a dip in the flow graph as the water surface slope term becomes flat or negative, followed by a rise in the flow as the upstream head increases versus the downstream head.
You get more than the normal flow based on the head difference because in addition to the head difference you also get a push from the non linear terms or dq3 and dq4 in this graph.
Saturday, September 1, 2012
Storage Nodes in InfoSWMM and H2OMAP SWMM
Subject: Storage Nodes in InfoSWMM and H2OMAP SWMM
Figure 1 shows how to use the various constants, coefficients and exponents in the Storage or Wet Well data of H2OMAP SWMM. If you have a Wet Well or Storage Diameter you should convert the Wet Well diameters into an Area with the units of either square feet or square meters. The computed area will then be a constant or coefficient in the Attribute Browser. You would only use the exponent or a table of depth and area if the Wet Well area varies with depth.
Figure 1 shows how to use the various constants, coefficients and exponents in the Storage or Wet Well data of H2OMAP SWMM. If you have a Wet Well or Storage Diameter you should convert the Wet Well diameters into an Area with the units of either square feet or square meters. The computed area will then be a constant or coefficient in the Attribute Browser. You would only use the exponent or a table of depth and area if the Wet Well area varies with depth.
Figure 1. Options for Defining a Storage Node in H2OMAP SWMM or SWMM 5 
Thursday, August 23, 2012
How Does Horton Infiltration Work in SWMM 5?
This sketch summarizes what happens in a SWMM 5 Subcatchment for Horton Infiltration during a storm event:
1. The event starts out with the potential infiltration rate at the maximum infiltration rate but
2. Decay starts happening right away and the potential infiltration rate starts decreasing until it reaches the minimum infiltration rate (assuming the storm last long enough),
3. The actual infiltration rate is the minimum of the rainfall rate or the potential infiltration rate,
4. Using the Huff distributions for rainfall the runoff does not start happening until the rainfall rate exceeds the potential infiltration rate in these models
5. The runoff ceases after the rainfall rate becomes less than the current potential infiltration rate later in the storm,
6. The maximum infiltration volume for Horton caps the storm event infiltration at 10 mm in this example, the infiltration will cease when the cumulative infiltration reaches 10 mm.
7. Horton Iniltration is a five parameter method
a. Maximum infiltration rate in mm/hour
b. Minimum infiltration rate in mm/hour
c. Decay rate for the change from maximum to minimum infiltration rate
d. Regeneration rate for the change from minimum to maximum infiltration rate after the storm event ends and
e. A maximum infiltration volume per storm event in millimeters

Saturday, August 18, 2012
SWMM 5 Weir RTC Rules
Subject: 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.

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