Flushing in WaterGEMS/CAD

  Applies To 
  Product(s): Bentley WaterGEMS/WaterCAD
  Version(s): 08.11.04.XX, 08.11.05.XX
  Area:  Modeling
  Original Author: Terry Foster, Bentley Technical Support Group


This technote applies for Flushing in SELECTseries 4 and SELECTseries 5 versions of WaterGEMS and WaterCAD.

There is a separate technote on Flushing in WaterGEMS/CAD Select Series 6 +, below is the link to that.




The Flushing tool has greatly been improved.  The new flushing module is easy to setup, easy to run (you can run a selected event or all events), and easy to generate printer ready reports. Both conventional and unidirectional flushing can be arranged under certain area or study. 
In earlier builds of WaterGEMS/CAD, flushing was controlled in the flushing alternative.  Flushing is now under the Analysis menu (Analysis > Flushing Manager).  If a user opens a project created in an earlier build, the data in the flushing alternative will be transferred to the flushing manager.

There has been a new criteria added "Target Shear Stress" along with the Target Velocity. This field can be used as a requirement to test the flushing event run. 

Reasons to Flush

  • Operating hydrant to assure that the hydrant will operate properly when called on in an emergency
  • Removing stale water
  • Increasing disinfectant residual
  • Removing dissolved material
  • Removing settled solids
  • Removing attached solids
  • Removing bio-films
  • Removing contaminants after a contamination event


  • Movement of dissolved matter (includes disinfectant and taste and odor) - Velocity and shear stress are inconsequential.
  • Removal of settled and loosely attached material (includes color and turbidity) - Very small increases in shear stress are all that is required.
  • Removal of attached material (includes bio-films and attached solids) - More substantial threshold shear stress must be met.

Work Flow for Modeling Flushing

  • Start with a calibrated model
  • Start Flushing Manager
  • Create Study
  • Create Area/Set up Options
  • Create Events
  • Compute Study Area or Event
  • Create Area/Set up Options

To perform an analysis of a set of flushing events (i.e. a flushing area), the user must create flushing events.  Upon opening the flushing manager initially, there will be a default study, "Flushing Study" which will have one area called "Base Flushing" in the left pane.

The user creates new studies or areas by right-clicking on the study node in the left pane.  By right-clicking on the area a new event can be created.

Identifying the Buttons Left to Right


  • New:  creates new study, area or event depending on which node is highlighted
  • Delete:  deletes the highlighted study, area or event
  • Rename:  to edit the name of the highlighted study, area or event
  • Compute:  starts analysis of highlighted study or area
  • Flushing Browser:  opens the flushing results browser
  • Report:  opens up a preview of the operator report
  • Move Up:  moves selected area or event up the list
  • Move Down:  moves selected area or event down the list
  • Zoom:  zooms to extent of selected study, area or event
  • Highlight:  highlights elements in selected study, area or event
  • Expand/Collapse:  expands or collapses selected node
  • Options:  enables user to set default colors and extent of view in conventional flushing
  • Help:  opens flushing help

Within a flushing area, the user defines the representative scenario, target velocity and shear stress, pipe set, method to determine flow (emitter or flow) and auxiliary output if desired.  It is a good idea to create a selection set corresponding to the pipe set before entering the flushing manager.


  • Representative Scenario:  This establishes the boundary conditions (tank levels, pump status, demands) for the area.
  • Output Scenario:  This is created automatically the first time the area is computed.
  • Target Velocity:  The velocity that should be exceeded for the flushing to be considered successful for that pipe.
  • Target Shear Stress:  The user may specify a Target Shear Stress or a Tar Velocity, or in addition to a Target Velocity.  Both defaults are zero.
  • Pipe Set:  By clicking on the ellipsis button the user can select the pipes or a selection set.
  • Nodes of Interest:  Auxiliary results are saved to these.  They are usful for monitoring low pressure during flushing.  This is an optional field.
  • Flushing Flows:  The user can specify either emitter coefficient for the hydrant or junction being flowed or the actual flow rate.  Because the flow rate depends on pressure and the user usually does not know the flow rate ahead of time, it is usually more accurate to specify an emitter coefficient.  Do not specify both an emitter coefficient and a flow.  Typical values are 250 gpm/psi^0.5 (20 L/s/m^0.5).
  • Auxiliary Output:  The user can save values for all elements from each event.  However, in most cases the user is not interested in values far from flushing.  Therefore, the user must specify conditions for element data to be saved and available for display for individual events.  If the box, "Includes nodes with Pressure less than?" is checked, properties for elements with pressure less than the specified value are saved for display.  If the box, "Include pipes with velocity greater than?" is checked, properties of pipes with high velocity are saved.  This makes it possible to use color coding to display results of flushing without saving a great deal of unneeded values.

The user then creates events within an area.  It is assumed that the flushing events are conducted in the order in which they are listed.  The key to order is usually to flush from clean water into un-cleaned areas.

Conventional events are made up of the hydrant (or junction) to be flowed.  These events have an advantage of being very easy to set up a large number of conventional events in essentially one step.  The user will see the Selection dialog where individual junctions or hydrants are selected.  Junctions or hydrants can be selected by polygon or they can be selected based on a selection set that has been previously defined.  If not all the nodes in a polygon are to be flowed, it can be helpful to have a selection set done already.

For UDF events, they must be created one at a time because the user must select flowed elements, controlled elements, and optionally the pipe run to be flushed.  In this case a special form of the select dialog is opened.

The events tab enables the user to get a quick view of the events that are contained in the area, and if desired, make events active or inactive for the next run.  The notes tab enables the uwer to enter a text description of the area.

In creating a UDF event, use the second button to select the operational elements (hydrant, junction, valve).  If a hydrant or junction is selected, it is considered to be flowed.  If an isolation valve or control valve is selected these are considered to be closed.  If a pipe element is selected the default is that the pipe is closed.  If the user selects the third button to select the pipes will be a part of the pipe run.

In creating a UDF event, use the third button to add the pipe run elements.

Once an event is created, if the event is expanded in the left pane, there is one row for each element that is flowed, closed, or part of a pipe run.

The element label and type are properties of the element selected and the status is an editable field (unless it is a flushing element such as a hydrant) indicating if the element is open/closed, flowed, or part of a pipe run.  The flow emitter or flows specified in an area tab can be overwritten by checking the Specify Local Flows check box for that element and inserting a different flow or emitter.

Note fields are very important if the results of the flushing analysis are to be given to operators to locate elements to operate.  The notes may included an address for a hydrant or at a location of a valve that needs to be closed.

Flushing Results Browser

The flushing results browser contains the results of a flushing run listed by event.  The content of the browser corresponds to the current scenario.  If it is not a flushing output scenario, no events would be displayed.  The scenario can be switched to the flushing browser in the main drawing or by picking the button next to the output scenario selection in the right panel of the flushing manager.

Before opening the browser it is helpful to set up color coding and annotations that will highlight the flushing events.  Usually color coding pipes by velocity or shear stress, and junctions or hydrants by demand, will be the most useful.

Conventional Results

UDF Results

Toolbar Buttons on Flushing Results Browser

  • Zoom:  zooms to extent of flushing event
  • Highlight:  highlights elements in flushing event.  In highlighting, the pipe run color will override element symbology color coding.
  • Reset:  cancels out the selected event and displays results for representative scenario
  • Report:  opens preview of flushing browser report
  • Help:  opens flushing help

Flushing Area Report (Flex Table)

While the Flushing Results Browser displays flushing results on an event basis, the flushing area results flex table presents the results on a pipe basis listing whether the pipe met the flushing target and which event was the most effective in flushing that pipe.

With the current scenario set to a flushing output scenario, open the flushing flex table.  By default, the table will open with all pipes.  If the model is large it is helpful to make a selection of elements and pick "Open on Selection" when opening the flex table.

Flushing Notifications


Message Text

Message Category


Pipe set not specified.


Specify pipe set

At least one flushing event element is not active during the flushing run.


Elements must be active to affect flushing results.  Have you deleted any pipes since pipe set was created?

At least one run pipe is not included in flush pipe set


Ideally, pipes in a run should be included in pipe set.

At least one run pipe is closed during the flushing run


Pipes in run should not be closed.

At least one event contains a pipe run that is not continuous


Check for gaps in the pipe run.



The user can identify the extent of the drawing that will appear in the optional reports.

Default Report Options

User Defined Report Options


Before opening the operator's report button, the modeler should:

1. Set up the desired background layer

2. Decide the extent of the view to display and if additional views are desired, set up those views.

3. Include detailed notes to help the operators locate the elements (e.g. an operator may not know where H-21 is located but will know "Hydrant in front of 31 Elm St.".

Operator Report

The operator report consists of three types of pages for each event:

1.  Text description of the event indicating which elements to operate

2.  Drawing of the event

3.  Form which flushing operator can complete to describe results of flushing for feedback (optional).

In addition to the default drawing of the event, the user can create "Secondary Views" which may for example, zoom into details of a complex intersection.  To do this, right-click on Report Views in the left pane and select Add Secondary View.  Draw a box around the extents of the secondary view and click Select New Report View.

The view that appears when the report is open is called a Preview.  With this preview, it is possible to:

  • Change page set
  • Print
  • Export to a variety of file formats including .pdf and text file
  • Transmit via email

The report can be saved and it is possible to zoom and pan within the document.

Example of a Conventional Report


Example of a UDF Operator Report


External Links

  • Created by
  • When: Tue, Jun 18 2013 1:32 PM
  • Last revision by Bentley Colleague
  • When: Wed, Jun 30 2021 1:21 AM
  • Revisions: 14
  • Comments: 0