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

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.

Example Groundwater Model in SWMM 5

Subject:   Example Groundwater Model in SWMM 5

The attached model shows three ways in which the groundwater model of the SWMM 5 subcatchments interact with the node depths of the hydraulic network.  The hydraulic network interaction can be either:

1.       At a fixed water surface elevation,
2.       At a time varying water surface elevation based on the inflow and geometry of the node and
3.       At a threshold node water surface elevation.

Example SWMM 5 Snowmelt Model

Subject: Example SWMM 5 Snowmelt Model

Attached is a simple sample snowmelt model in SWMM 5 that has built in snowfall and temperature in a one subcatcment model with snowmelt.   You define the separation of precipitation into snowfall and rainfall by setting a base temperature in the Snow Pack Editor.   The precipitation that falls with when the air temperature is below the base temperature is stored in a snow pack where it eventually will melt when the temperature rises or is moved via plowing.  You can have an initial snow cover, final snow cover and runoff from the melting snow long after the snowfall occurs.

SWMM 5 Leaping Weir Example

Subject:  SWMM 5 Leaping Weir Example

The attached example shows one way how SWMM 5 RTC Rules can be used to have the low flow go down a leaping weir orifice and the high flow go over the weir to the downstream section of the sewer. 

SWMM 5 Precipitation Options

Subject:  SWMM 5 Precipitation Options

You can have design storms, monitored storms of any length of the time from minutes to centuries, use intensity, volume or cumulative precipitation, use both rainfall and snowfall in the same rain gage depending on temperature, use both time series or external files for the rain gage and have unlimited rain gages with the limitation of one rain gage per subcatchment . 

How is the St Venant Equation Solved for in the Dynamic Wave Solution of SWMM 5?

Subject:   How is the St Venant Equation Solved for in the Dynamic Wave Solution of SWMM 5?

An explanation of the four St. Venant Terms in SWMM 5 and how they change for Gravity Mains and Force Mains. The HGL is the water surface elevation in the upstream and downstream nodes of the link. The HGL for a full link goes from the pipe crown elevation up to the rim elevation of the node + the surcharge depth of the node.  The four terms are:

dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) / Link Length or

dq2 = Time Step * Awtd * (HGL) / Link Length

Qnew = (Qold – dq2 + dq3 + dq4) / ( 1 + dq1)

when the force main is full dq3 and dq4 are zero and

Qnew = (Qold – dq2) / ( 1 + dq1)

The dq4 term in dynamic.c uses the area upstream (a1) and area downstream (a2), the midpoint velocity, the sigma factor (a function of the link Froude number), the link length and the time step or

dq4 = Time Step * Velocity * Velocity * (a2 – a1) / Link Length * Sigma

the dq3 term in dynamic.c uses the current midpoint area (a function of the midpoint depth), the sigma factor and the midpoint velocity

dq3 = 2 * Velocity * ( Amid(current iteration) – Amid (last time step) * Sigma

dq1 = Time Step * RoughFactor / Rwtd^1.333 * |Velocity|

The weighted area (Awtd) is used in the dq2 term of the St. Venant equation:

dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) / Link Length

The four terms change at each iteration and time step to determine the new flow (Figure 1) based on the two equations:

Denom = 1 + dq1 + dq5

Q = [Qold – dq2 + dq3 + dq4] / Denom

If you look at a table of the values you will see that the terms add up to zero when the flow is constant and to delta Q or the change in Q when the flow is NOT constant (Figure 2).

Figure 1.  The four terms define the new flow at each iteration in the dynamic wave solution of SWMM5

Figure 2.   The magnitude of the four terms determine the flow at the new iteration and ultimately the new Time Step.  If the flow is constant then the value of the term is constant.

Link Iterations in the SWMM 5 Dynamic Wave Solution

Subject:   Link Iterations in the SWMM 5 Dynamic Wave Solution

 

Each of the links in the SWMM 5 network can use up to 8 iterations to reach convergence during a time step in the dynamic wave solution of SWMM 5.  The rules governing the number of iterations are:

 

1.       A minimum of 2 iterations per time step with the 1^st iteration NOT using the underrelaxtion parameter of 0.5 (Figure 1)

2.       If both the downstream and upstream nodes are converged then the link drops out of the iteration process during the time step (Figure 2)

3.       The number of iterations for each link can vary over the simulation from 2 to 8 depending on how fast the flow is changing.

 

Figure 1.  A minimum of two and up to eight iterations per time step in the SWMM 5 dynamic wave solution.

Figure 2.  The number of iterations for each link vary through out  the simulation with less iterations being used for constant flows.

Making a Model in SWMM 5/Pathways

Making a Model in SWMM 5

Runoff Routing Options Example in SWMM 5 and InfoSWMM

Subject:   Runoff Routing Options Example in SWMM 5

There are six options for runoff routing in SWMM 5:

·         All Runoff to an Outlet Node
·         All Runoff to another Subcatchment
·         All Runoff to the Pervious Area of the Subcatchment or other Subcatchment
·         All Runoff to the Impervious Area of the Subcatchment or other Subcatchment
·         Partial Runoff to the Pervious Area of the Subcatchment or other Subcatchment
·         Partial Runoff to the Impervious Area of the Subcatchment or other Subcatchment

 The attached example SWMM 5.0.022 file has three catchments in a chain, the 1^st Subcatchment Routes to the Pervious area of the 2^nd Subcatchment and the 2^nd Subcatchment routes the runoff to the Impervious area of the 3^rd Subcatchment which routes all runoff to an outlet node.

DownLoad File

Welcome to the Curated Web

Welcome to the Curated Web

from http://www.nirandfar.com/2012/01/where-is-web-going.html

Create Watersheds Using InfoSWMM Subcatchment Manager

Subject:  Create Watersheds Using InfoSWMM Subcatchment Manager

  

The Subcatchment Manager of InfoSWMM will  help calculate most of the  physical parameters associated with a Watershed or Subcatchment in SWMM 5 from a Digital Elevation Data (Step 1).  The Subcatchments area created from a Flow Direction Raster (Step 2) and a Flow Accumulation Raster (Step 4) after filling in any Sinks in the DEM (Step 3).  The created watersheds (Step 5).   The physical parameters estimated from the DEM are shown in Figure 1.

Figure 1.  Physical Data Estimated from a DEM using the Subcatchment Manager in InfoSWMM.

Step 1.  Find, Create or Otherwise Locate a TIN, DEM or DTM for the project area with elevation data that you can  use with the InfoSWMM Subcatchment Manager.

Step 2.   Create a Flow Direction Raster using the Watershed Command.

Step 3.   Check to see if there are Sinks in the Elevation Data that have to be filled using the Filled Sink Command.

Step 4.   Create a Flow Accumulation Raster

Step 5.   Create the Watersheds from the Flow Direction and Flow Accumulation Rasters.

Three Flow Divider Link Example in SWMM 5

Subject:  Three Flow Divider Link Example in SWMM 5

You can have more than 2 downstream OUTLET Type links in the SWMM 5 dynamic wave solution.  Each link, Under5, Over5 and ReturnFlow is an OUTLET Link with a rating curve depth/flow table.  Depending on the depth in the storage node DIVIDER, the flow is computed from the table for links Under5, Over5 and ReturnFlow.

Output Statstics Manager to find negative flows in InfoSWMM

Subject:  Output Statstics Manager to find negative flows in InfoSWMM

Output Statstics Manager to find negative flows with these parameters:

1.       Pipe Features
2.       Use a Domain with your force mains
3.       Select Flow
4.       Event Dependent
5.       Total – NOT Mean or Peak to  find the negative and positive flows
6.       Large NEGATIVE Flow Threshold
7.       Large NEGATIVE Volume Threshold
8.       Zero for Interevent Time to pick up all values
9.       You will get a table that shows you the minimun flows, and a histogram of the flows

Drawing features to show multiple attributes in InfoSWMM and InfoSewer

Subject:   Drawing features to show multiple attributes in InfoSWMM

Your network data usually has a number of different attributes that describe the features it represents (Figure 3). While you'll commonly use one of the attributes to symbolize the

data—for example, showing one quantity in the InfoSWMM Map Display —you may sometimes want to use more than one.   One way to show multiple attributes inInfoSWMM is to copy layers and then use the Layer Properties to color, map or otherwise display the multivariable data (Figure 1).  For example, Figure 2 shows the important Subcatchment parameters of Slope, Imperviousness and Width as graduated colors, dots and a pie shape, respectively.

Figure 1.  Use the Symbology Tab to select the attribute you want to show and the way to show the attribute.

Figure 2.   The Subcatchment slope is shown in graduated colors, the percent impervious in scattered dots a a measels map and the Subcatchment Width is shown in a pie graph with the size of the pie a function  of the total  width.

Figure 3.  Physical Data Estimated from a DEM using the Subcatchment Manager in InfoSWMM.

Flow Dividers in SWMM 5 Dynamic Routing

Note:  Flow Dividers in SWMM 5 Dynamic Routing

You can  have flow dividers in SWMM 5 dynamic routing by using Storage Nodes for the dividers, OUTLET links for the downstream links and minimizing downstream HGL effects. The needed components are:

1.   A Storage Node for the divider node as a OUTLET Link does not have a Surface Area,
2.   Two or More OUTLET Links as the downstream diversion and cutoff links,
3.   Two or More Rating Curves to divide the flow up based on either depth or head,
4.   Pumps, Outfalls or Steep Sloped Links Downstream of the diversion and cutoff links to minimize downstream HGL  effects

The Keep and Dampen options and their effect on the four main terms of the St Venant equation in SWMM5

Note:  The Keep and Dampen options and their effect on the four main terms of the St Venant equation. 

The four terms are are used in the new flow for a time step of Qnew:

Qnew = (Qold – dq2 + dq3 + dq4) / ( 1 + dq1)

when the force main or gravity main is full dq3 and dq4 are zero and  Qnew = (Qold – dq2) / ( 1 + dq1)

The dq4 term in dynamic.c uses the area upstream (a1) and area downstream (a2), the midpoint velocity, the sigma factor (a function of the link Froude number), the link length and the time step or

dq4 = Time Step * Velocity * Velocity * (a2 – a1) / Link Length * Sigma

where Sigma is a function of the Froude Number and the Keep, Dampen and Ignore Inertial Term Options.  Keep sets Sigma to 1 always and Dampen set Sigma based on the Froude number, Ignore sets Sigma to 0 all  of the time during the simulation

the dq3 term in dynamic.c uses the current midpoint area (a function of the midpoint depth), the sigma factor and the midpoint velocity.

dq3 = 2 * Velocity * ( Amid(current iteration) – Amid (last time step) * Sigma

dq1 = Time Step * RoughFactor / Rwtd^1.333 * |Velocity|

The weighted area (Awtd) is used in the dq2 term of the St. Venant equation:

dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) / Link Length or

dq2 = Time Step * Awtd * (Head Downstream – Head Upstream) / Link Length

Normally, dq1 (Friction Loss / Maroon in the Graph) balances dq2 (Water Surface Slope Term or Green in the Graph) but often for links with a large difference between upstream and  downstream depths dq4 (Red in the Graph) can have a significant value.  If dq4 or dq3 are important then the depth of water to increases to pass the same flow using the Keep option over the Ignore.   If you have a link with a Froude number near or over 1.0 (Supercritical) then using Keep or Dampen  for the Options may result in depth differences.   The effect of Keep is to increase the "loss" terms in the St VenantEquation.   The effect of Dampen and Ignore is to decrease the sum of the "loss" terms in the St. Venant Solution and lower the simulated depth.

Surcharged Node and the Link Connection in SWMM 5

Subject:   Surcharged Node and the Link Connection in SWMM 5

A surcharged node in SWMM 5 uses this point iteration equation (Figure 1):

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/dHis 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.

Figure 1.  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. 

Figure 2.  The value of dQ/dH in a link as the roughness of the link increases.

How to Divide the Inflow at a Node in InfoSWMM

Subject:  How to Divide the Inflow at a Node in InfoSWMM

In SWMM 5 only the Kinematic Wave solution allows a flow divider at a node to divide the Inflow to node to two  downstream  links, but you can use the Inflow/Outflow Outlet type in InfoSWMM to divide the inflow based on a Inflow/Outflow Diversion Table (Figure 1).  For example, in InfoSWMM it is possible to have two downstream links from a Node that are Outlet types Inflow/Outflow so that the low flow goes down one link and the high flow goes down the other link (Figure 2 and Figure 3).   The low flow and the high flow  link  use different diversion tables in which the tables are constructed so that the flow is positive in one link and zero in the other to a dividing flow value and then zero and positive for the same two links after the dividing flow value ( 5 cfs in the example).

Figure 1.  Types of OUTLETS in InfoSWMM and SWMM 5

Figure 2.  Example low flow and high flow Outlet Links to divide the total  inflow at the upstream node at 5 cfs.

Figure 3.   The flow is divided into the low and high flow links at the dividing flow of 5 cfs.

Example SWMM 5 Model for Activated Slude

Note:   Example SWMM 5 Model for Activated Sludge

Here is one example of how to model an activated sludge tank.  The image is Wikipedia (http://en.wikipedia.org/wiki/Activated_sludge)  and is the watermark background in the SWMM 5 GUI.  There is 100 lps inflow, 20 percent recycle and 10 percent sludge drawoff.   You can adjust the amount of recycle and sludge altering the pump type 2 flows or if you want to increase the inflows – add more flow in the RawWater inflow node.

How to Make Icons and Expand the Toolbars in InfoSWMM and InfoSewer

Subject:  How to Make Icons and Expand the Toolbars in InfoSWMM and InfoSewer

You can customize the toolbars in InfoSWMM and InfoSewer by clicking on Customize and performing 4 steps:

Step 1.  Click on Customize

Step 2.  Move the tool from the Command list to the toolbar.

Step 3.  Change the Button Image for the Default Style.

Step 4.  The Toolbar now has a new Icon for the InfoSWMM command.

Step 1.  Click on Customize

Step 2.  Move the tool from the Command list to the toolbar.

Step 3.  Change the Button Image for the Default Style.

Step 4.  The Toolbar now has a new Icon for the InfoSWMM command.

Example Dual Drainage SWMM 5 model

 Example Dual Drainage SWMM 5 model

How to Edit the Subcatchment Polygons in InfoSWMM with Arc Map

Subject:  How to Edit the Subcatchment Polygons in InfoSWMM with Arc Map

You can edit the polygon boundaries of the Subcatchments in Arc GIS by using the Editor command and either editing the vertices or by using the Reshape Feature Tool to adjust the boundaries or snap to the polygon lines or vertex points.    You should start the editing session by right mouse clickining on the Subcatchment Feature layer

Vertex Editing and Reshape Feature Tool