SWMM56

Note:   Storage Maximum Outflow Includes Reverse Flow in SWMM 5 The SWMM 5 text output file has a Storage Volume Summary Table.  The Maximum Outflow from a storage node includes ALL of the outflow from the Storage node including both downstream link flow and reverse flow into the upstream links of the storage node.  You need to look at all of the flow out of a Storage node to find out how the maximum flow was computed during the simulation. Figure 1.  Storage Volume Summary Table Figure 2:  Total Flow Out of A Storage Node includes Reverse Flow.

Subject:   EPS and Steady State Variables in GM, FM and Pumps of InfoSewer v7 Figure 1:  InfoSewer Output Variables

Subject:   Area Types in SWMM 5 for Links with Offsets  There are six types of link flow in SWMM 5: 1.    Dry Conduit at both Ends 2.    Upstream End is Dry 3.    Downstream End is Dry 4.    Subcritical Flow 5.    SuperCritical Flow 6.    Free Fall at Upstream End 7.    Free Fall at Downstream End Figure 1.  Six types of Link Area Allocation Figure 2.  Example Link Area Type in SWMM 5

Cloud Movement Source:  http://www.atlanticvortex.com/EN/FAQ.htm

Subject:   Force Main Friction Loss in SWMM 5 You can model Force Mains in SWMM 5 using either Darcy Weisbach or Hazen Williams as the full pipe friction loss method (see Figure 1 for the internal defintion of full flow).   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 SWMM 5).  Force Main Friction Loss in SWMM 5. Figure 1.   How the full pipe condition is defined in SWMM 5 Figure 2:   Friction equations used in SWMM 5 for a Force Main. Figure 3:   Regions of Friction loss equations in SWMM 5.

Subject: Capacity Limited Links in SWMM 5 The table in the text report file of SWMM 5 called “Conduit Surcharge Summary” has a column entitled “Hours Capacity Limited” Here is how a link is defined as Capacity Limited in SWMM 5. Two factors have to be present: 1. The upstream end of the link has to be full and 2. The HGL Slope has to be greater than the Slope of the Link

Subject: What is the Area of a Node in SWMM 5? The minimum area of a node is the default area of the node, which is the user defined minimum surface area or 12.566 square feet if the user does not define the surface area of the node. The surface area of a node is usually the half of the surface area of all of the connecting conduits but if the link is dry then the sum of all of the surface areas may be less than the default surface area. If you look at a scatter plot of the area versus the depth then you will see that it always has the minimum surface area.

Subject: What is Node Convergence in SWMM 5? If a link has converged within two iterations then the hydraulic computations will be bypassed for the link in new iterations. A link is deemed converged if BOTH the upstream and downstream node depth has converged between successive iterations as long as two iterations have occurred during the time step. The nodes are considered converged if the depths between successive iterations is less than the stop tolerance of the program (the default stop tolerance is 0.005 feet). The new node depths are ALWAYS computed for each iteration but the links connected to the converged nodes may bypass computations and save on simulation time. Note: If the nodes ever become non converged after 2 iterations then the link flows will be computed.

Subject: What is Link Bypass in SWMM 5? If a link has converged within two iterations then the hydraulic computations will be bypassed for new iterations. A link is deemed converged if BOTH the upstream and downstream nodes depth has converged between successive iterations as long as two iterations have occurred during the time step. This is simulation savings step as it my eliminate up to 75 percent of the computational time in a SWMM 5 simulation. The image below shows that for some links the flow in the link is converged within 2 iterations whereas for others it may take 3 or 4 iterations. Overall, 37 percent of the link computations are bypassed during the simulation of this particular hydraulic network .

Subject: Time Step Critical Elements in SWMM 5 The time step critical elements in the SWMM 5 report text output file tells you which elements were controlling the time step during the simulation. If no element was controlling the time step then the program will just use the maximum time step. For example, if the maximum time step was 10 seconds and the average time step was 9.8 then only a few time steps were set by a link or node that needed a smaller than maximum time step (Figure 1). If the maximum time step for the same simulation was 30 seconds then many links and nodes will set the time step (Figure 2). Figure 1. Most of the time the simulation used the maximum time step of 10 seconds so only a few links were time step critical. Figure 2. Most of the time the simulation used less than the maximum time step of 30 seconds so many links were time step critical.

Subject: Pump Power Usage in SWMM 5 The pumping summary table (Figure 1) includes a column that tells the user how much power was consumed by the pump in kilowatts by the head loss or head gain of the water flowing through the pump. The power usage equations are shown in Figure 2. Figure 1. Pump Summary Table in SWMM 5.0.021 Figure 2. Pump Power Equations in SWMM in which dt is the time step.

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 4. The water surface slope term or dy/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 di

Subject: The number of Hydraulic Iterations in Various Versions of SWMM 5. The maximum number of iterations was 4 before SWMM 5.0.021 and 8 iterations after SWMM 5.0.021. In InfoSWMM and H2OMAP SWMM you can have a a minimum of 2 iterations or a maximum of 8 iterations for compatibility to SWMM 5 and backwards compatibly with your earlier InfoSWMM models. .

Subject: Time Step Selection in SWMM 5 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 ma

Subject: Pump Priorities in SWMM 5 The Startup and Shutoff depths are evaluated 1 st followed by any Control Rules. The priority value is just to decide between two or more control rules that are both active at the current time step. The rule with the highest priority will be used or in the case of two rules with the same priority the last control rule evaluated will be used during the current time step.

Subject: Node Surcharge Summary in SWMM 5 Surcharging occurs in SWMM 5 when water rises above the crown of the highest conduit. The RPT file of SWMM 5 lists the surcharging in hours in the Node Surcharge Summary Table (Figure 1) using the definitions for surcharging shown in Figure 2. Figure 3 shows the relationship between the output columns of the table. Node surcharging occurs at a node if: 1. The node cannot pond and the node depth is above the highest pipe crown elevation connected to the node, or 2. The node can pond and the node depth is above the highest pipe crown elevation connected to the node and 3. The node depth is below the full depth of the node. Node Flooding occurs if the water surface elevation is at the rim or above the rim elevation of the node. Figure 1: Node Surcharge Summary Table Figure 2: Definition of Surcharging at a Node in SWMM 5. Figure 3: The definition of the Height above Crown and Depth below Rim columns in the Node Surcharge Table.

Note: There is a function called ForceMain in SWMM5/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 . f = forcemain_getFricFactor(xsect.rBot, d/4.0, 1.0e12); return sqrt(f/185.0) * pow(d, (1./6.)); double forcemain_getFricFactor(double e, double hrad, double re) //// Input: e = roughness height (ft) // hrad = hydraulic radius (ft) // re = Reynolds number // Output: returns a Darcy-Weisbach friction factor // Purpose: computes the Darcy-Weisbach friction factor for a force main // using the Swamee and Jain approximation to the Colebrook-White equation. { double f; if ( re < 10.0 ) re = 10.0; if ( re <= 2000.0 ) f = 64.0 / re; else if ( re < 4000.0 ) { f = forcemain_getFricFactor(e, hrad, 4000.0); f = 0.032 + (f - 0.032) * ( re - 2000.0) / 2000.0; } else { f = e/3.7/(4.0*hrad); if ( re < 1.0e10 ) f += 5.7

Subject: Link Surcharging Definitions in SWMM 5 The report or RPT text output file of SWMM 5 contains a table that lists the Surcharged Conduits during the simulation (Figure 1). The 5 columns in the table are: Hours Both Ends Surcharged Hours Upstream End Surcharged Hours Downstream End Surcharged Hours Above Full Normal Flow Hours Capacity Limited .the five columns are defined in Figure 2. Notice that if the midpoint of the link is full then the link and both end of the link are considered to be surcharged. If the midpoint is NOT full then the cross sectional area of the ends of the link determine wheter the ends of the link are considered surcharged. The end of a link can be considered surcharged based on either the depth at the midpoint or the cross sectional area at the end of the link. Figure 1: The SWMM 5 Conduit Surcharge Table F igure 2: The SWMM 5 Conduit Surcharge Table Definitions, the numbers in the 3 rd column correspond to the columns in the Conduit Surcharge Ta

Click here to download: extran_pid_3_master.inp (47 KB) Subject: PID Control in SWMM 5 for an Orifice The blog http://swmm5.blogspot.com/2010/12/pid-control-in-swmm-5-for-type-3-pump.html describes the Function getPIDSetting which returns the PID setting at each time step. The PID parameter set contains three values -- a proportional gain coefficient, an integral time (in minutes), and a derivative time (in minutes) which are kp, ki and kd, respectively. More about the theory of PID controllers can be found at http://en.wikipedia.org/wiki/PID_controller . Here is an example PID Rule that will keep the node depth at 5 feet in a SWMM 5 model by changing the Orifice Setting. The Orifice setting opens and closes the orifice over time. The example file is attached in this blog. In this particular example, you can reduce the oscillations about the 5 foot rule level by lowering the integral time and derivative time coefficients in the PID control rule. An important note is that for Weirs an

Subject: PID Control in SWMM 5 for a Weir The blog http://swmm5.blogspot.com/2010/12/pid-control-in-swmm-5-for-type-3-pump.html describes theFunction getPIDSetting which returns the PID setting at each time step. The PID parameter set contains three values -- a proportional gain coefficient, an integral time (in minutes), and a derivative time (in minutes) which are kp, ki and kd, respectively. More about the theory of PID controllers can be found at http://en.wikipedia.org/wiki/PID_controller . Here is an example PID Rule that will keep the node depth at 3 feet in a SWMM 5 model by changing the Weir Setting. The example file is attached in this blog. In this particular example, you can reduce the oscillations about the 3 foot rule level by lowering the integral time and derivative time coefficients in the PID control rule. RULE PID_Weir ; the PID controller adjusts the weir height to have a ; depth of 3 feet in Node 82309e IF NODE 82309c DEPTH <> 3 THEN WEIR WEIR1@8230

Subject: PID Control in SWMM 5 for a Type 3 Pump Figure 2 shows the code in Function getPIDSetting which returns the PID setting at each time step. The PID parameter set defines the degree of control. The PID parameter set contains three values -- a proportional gain coefficient, an integral time (in minutes), and a derivative time (in minutes) which are kp, ki and kd, respectively. More about the theory of PID controllers can be found at http://en.wikipedia.org/wiki/PID_controller and shown in Figure 3. Here is an example PID Rule that will keep the node depth at 3 feet in a SWMM 5 model. RULE PID1 ; the PID controller adjusts the flow in the pump to have a ; depth of 3 feet in Node 82309e IF NODE 82309e DEPTH <> 3 THEN PUMP PUMP1@82309e-15009e SETTING = PID 10 -1 -1 ; kp ki kd PRIORITY 1 Figure 1 : SWMM 5.0.021 Simulation Results Figure 2 : Source code for getPIDSetting in SWMM 5

Subject: Total Time Above Rim Elevation at a Node 1. Total Surcharge Time is the total time above the crown of the highest connecting pipe to a node. 2. Total Time Above Rim Elevation – this is the flooding time of the node and it includes flood time as well as ponding time. You can find this in the Junction Summary Report of InfoSWMM under the column Total Flood Time. The Total Flood Time is less than the Total Surcharge Time as the depth in the Node is higher. A node is flooded if the node depth equals the node rim elevation – the flooded time is the total time excess flow coming out the top of the manhole, A node is flooded if the node depth is above the rim elevation and you are using the Surface Ponding Option – the flooded time is the ponding time A node is flooded if the node depth equals the node surchage elevation – the flooded time is the total time excess flow coming out the top of the surcharged manhole.

Subject: SWMM 5 Controls