Conducting Flushing Studies in WaterGEMS and WaterCAD

Product(s): WaterGEMS, WaterCAD
Version(s): CONNECT Edition, V8i SELECTSeries 6
Area:  Modeling


Starting in the SELECTseries 6 release of WaterGEMS and WaterCAD, 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 versions of WaterGEMS/CAD before V8i SELECTSeries 4, flushing was controlled in a flushing alternative.

For the CONNECT Edition release of WaterGEMS and WaterCAD, the Flushing model can be accessed by going to the Analysis tab, then selecting Flushing > Flushing. For the V8i releases starting with the SELECTseries 4 release, you can access this by going to 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.

Starting with WaterGEMS/WaterCAD, the following criteria is now available: 

  • "Target Shear Stress" along with the Target Velocity. This field can be used as a requirement to test the flushing event run. 
  • “Safety Factor (Flushing Time, Volume)” field has been added to the flushing area options screen to identify recommended flushing time/volume.
  • “Boundary Valves” to select valves to close during a flushing area: Pipes, isolation valves and valve nodes.

For more information on using Flushing in SELECTseries 4 and 5, see this article.

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.

Note that any demands from other elements such as junctions and customer meter elements will be accounted for during the flushing run. Meaning, a flushing run will not have only a demand on the flushing node - it will use the baseline scenario's base conditions (including demands), and flush the hydrant(s) along with those other conditions (such as demands, controls, etc).

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
  • Duplicate: to duplicate any area or event
  • Compute:  starts analysis of highlighted study, area or event. Also opens flushing area table or flushing results browser
  • Report:  opens up a preview of flushing field report of study, area or event
  • Zoom:  zooms to extent of selected study, area or event
  • Highlight:  highlights elements in selected study, area or event
  • Highlight Results: highlights the pipes associated with the flushing area
  • Options:  enables user to set default colors and extent of view in conventional flushing
  • Help:  opens flushing help
  • The expand button in the down corner,  expands or collapses selected node
  • Right click on any event or area to shift it up or down

Within a flushing area, the user defines the representative scenario, target velocity and shear stress, pipe set, method to determine flow (emitter or flow), boundary valves 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.
  • Safety Factor (Flushing Time, Volume): Safety factor to calculate the "Recommended Flushing Volume", and "Recommended Flushing Time”  in the Flushing Results Browser
  • 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 useful 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). You can also choose to replace any baseline demands already on the flowing element, or add to them (though typically you would not have any base demands on hydrant node elements). Note that any demands from other elements such as junctions and customer meter elements, will be accounted for during the flushing run. Meaning, a flushing run will not have only a demand on the flushing node - it will use the baseline scenario's base conditions (including demands), and flush the hydrant(s) along with those other conditions (such as demands, controls, etc).
  • Boundary Valves: You can now select valves to close during a flushing area: Pipes, isolation valves and valve nodes. These elements will be closed during all events in the respective flushing area. This can be useful if you have valves that will close off a larger section of the model during multiple flushing events in that area.
  • 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 needed areas. To change the order of the events or areas, use the shift-up and shift-down buttons.

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.

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 user to enter a text description of the area.


UDF Events:

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.

Quick Pipe Run Creation Tools

Prior to WaterGEMS and WaterCAD V8i SELECTseries 6, the unidirectional flushing event element selection only allowed you to select one pipe at a time to add pipes to the flushing event pipe list. The Add Pipe Run Elements tool now has the ability to pick a node and add pipes in the shortest path between the selected node and the nearest end nodes of pipes already selected.

An Undo button has also been added to let the user undo the last element selection. Undo works for all types of element selections, including adding pipes in a path, adding single pipe, adding operational open element, adding operational close element and removing an element.

The Highlight Previous button will highlight the previous event's elements.

Auto-isolate feature

With the new Auto-isolate feature you can quickly identify candidate isolation valves to close off the selected pipe run, which will save you time when compared to manually picking valves to close with the third button. Be sure that no demand nodes are isolated using this tool.

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 user to enter a text description of the area.

In creating a UDF event,

  • Use the third button to add the pipe run elements.
  • 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.

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.

The new fields have been added to the flushing results browser which are Time (recommended flushing) and Volume (recommended flushing), which are calculated by multiplying the "Safety Factor" by the related "minimum" value.

Note that the minimum flushing time and volume ("Time (Minimum Flushing)" and "Volume (Minimum Flushing)") are calculated based on the volume of water in the pipe run. This is taken as the volume that must be flushed and the time to flush that volume is used as the minimum time of flushing. A pipe run should consist of pipes in series from the flowed hydrant. Pipes in a pipe run should also be part of the pipe set for an area. 

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. 

An example of how this might work would be to toggle "Include nodes with pressure less than" and enter a value, such as 40 psi. You can then set up a color coding for all junctions based on pressure. After opening the Flushing Results Browser, you can highlight one of the flushing events. Only the nodes where the pressure was less than 40 psi were color coded (nodes near the pipe run are also color coded, but may have a different color based on the color coding you have set up). All other nodes were set to the default color. If you select a different flushing event, different elements were highlighted. This allows the user to get a visual representation of what is happening during different events.

You can also set up Nodes of Interest, which is an optional collection of nodes that you may deem important in the model. If you choose to include Nodes of Interest, these will also be color coded, even if the pressure doesn't fall below the pressure in the auxiliary. In addition, the node of interest with the lowest pressure for a given run will be included in the Flushing Results Browser. If no Nodes of Interest are included, "N/A" will be listed there instead.

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 Response
"The pipe set for this area must contain at least one pipe.  Refer to the "Pipe Set" field on the flushing area [Options] tab.". Error Specify pipe set
At least one flushing event element is not active during the flushing run. Warning 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 Information 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 Warning Check for gaps in the pipe run
You should provide a non-zero flushing flow value.  Refer to the "Flushing Flows" field on the flushing area [Options] tab. Warning  Check the area Flowing Emitter Coefficient and Flowing Demand 



Starting in the SELECTseries 6 release, new flushing options have been added, such as options to change the color of closed operational elements, elements satisfying flushing target, elements which fails flushing target. Also Symbol size and line width multiplier can also be defined through flushing options. 


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 filed 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.".

Field Report

Starting with V8i SELECTseries 6 (including CONNECT Edition), the flushing Field Report has been reduced from three to two pages per hydrant.

Include Reopen, Reclose, Close (Prior), and Open (Prior) result options, based on the status of a valve in a previous event

The flushing report's event elements table and operator's field report now provides context on valve/pipe status based on the prior event so the valve that was closed in the prior event, that should remain closed in the current event, doesn't have to be operated again and so the valves can return to the correct state when completing an event. Some of these rows in the Event Elements table are virtual and can't be deleted. These rows indicate steps that need to be performed to restore valves to their original state after the prior event. If valve is not to be re-opened/re-closed, select in drawing to change.

Before V8i SS6, the operator’s field report used to be 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

Export Flushing Area Summary Table

Starting with the CONNECT Edition release of WaterGEMS and WaterCAD, you can now export the Flushing Area Summary Table for a given flushing run. The table is exported into a CSV format, which can be opened in Excel, and will include element labels and results. While the table currently used in the Flushing module allows for the operator to include notes, this export feature allows you to have additional flexibility for presenting your data. Once the data is exported, you can format the Excel file to your specifications.


Crash while clicking various command buttons in the Flushing Manager dialog

A crash occurs when duplicating or adding an event, or sometimes when clicking various buttons (Expand All/Collapse All) with the following details:

System.InvalidOperationException: Operation is not valid because it results in a reentrant call to the SetCurrentCellAddressCore function.

Or Haestad.SQLite.SQLiteException: 18: string or blob too big

This is a known issue with versions and and is resolved by upgrading to version and applying the latest cumulative patch set for version (contact Support for help), or for version by installing the latest Cumulative Patch (WaterGEMS_10.04.00.108_en_Patch02.msp).

"Reference to deleted..." error occurs on compute

When computing a flushing event, the following error occurs:

Reference to a deleted or inactive element of interest

For the solution, see: Error when running Flushing analysis: Reference to a deleted or inactive element of interest

Flushing Field Report can only accept 13 rows for valve operations

See: Customizing the Flushing Field Report

Discrepancy between reported status in Flushing Report and Flushing Area Summary Table

There is a known issue in WaterGEMS and WaterCAD CONNECT Edition Update 3 where the reported status for a hydrant in the Flushing Report and the Flushing Area Summary Table is different. The data in the Flushing Report will display correctly, but the Flushing Area Summary Table will show a different, incorrect value. This has been resolved with a patch for WaterGEMS and WaterCAD version Please contact Technical Support for the patch. Note that this fix will be available in all later versions of WaterGEMS and WaterCAD; no patch will be required for these later versions.

See Also

Flushing in V8i SS4

Changing the order of Flushing Events or Flushing Areas

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