Calibrating a model based on hydrant flow tests

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


How can I set up Darwin Calibrator to calibrate a hydraulic model based on hydrant flow tests?


First, ensure that the hydrant test data was properly recorded. You can then enter the data into Darwin Calibrator as field data snapshots, enter demand adjustments to tell Calibrator to flow the hydrant during calibration, then set up a Calibrator run to adjust model parameters until the results match the observed values. For more tips on Calibrator, see: Water Model Calibration Tips

Collecting the hydrant test data

More than one hydrant is needed to perform a hydrant flow test. One hydrant is the residual hydrant, where pressure is measured, and the other is the hydrant(s) that is flowed (opened) and where flow is measured.

See also: One Hydrant vs. Two Hydrant Flow Test

Under Static conditions when the flowed hydrant is closed, the pressure at the residual hydrant is the Static Pressure. When one or more of the flowed hydrants are open, the pressure at the residual hydrant is the Residual Pressure.

Following the ISO and AWWA guidelines, the static and residual pressures must not be read at the flowed hydrant. The location where static pressure was measured won't cause a problem because there was no head loss in the hydrant lateral under static conditions. But the head loss in the flowed hydrant would completely skew measurements of residual pressure. If you were try to use it, you would end up calibrating the lateral which is not what you are interested in. When performing a hydrant flow test, what you really want to know what the residual pressure is in the main.

Additional tips:

  • Make your comparisons (between the measured data and model results) in terms of HGL, not pressure units. HGL for static pressure shows you the direction of flow and makes it much easier to identify outliers. You can always convert back to pressure units in your final report.
  • If you have data loggers recording pressure, place them at key locations in your system during the flow tests. This will give you great insights in case you have an inadvertently closed valve.
  • See more information on this subject in chapter 5.2 of Advanced Water Distribution Modeling and Management 
  • Watch the below video on hydrant testing:

Entering the data into Calibrator

An example of this can be seen in the included Example5 model, found in the Samples folder within the WaterGEMS installation folder.

Enter each test as a field data snapshot, with the hydrant flows as demand adjustments and the residual pressures as observed targets. Below outlines the process:

1) Create a new calibration study and select the correct representative scenario

2) In the Calibration study, create a new field data snapshot for each hydrant test

3) For each snapshot, enter the appropriate time and date that the test occurred. In the Observed Target tab at the bottom, enter the observed "residual" pressure at the appropriate locations during the time when
the hydrant was flowed.

4) In the Boundary Overrides tab, enter the status of elements in the model during that particular test, such as the level in a tank, status of a pump or valve, etc.

5) In the Demand Adjustments tab, enter the residual flow at the hydrant when it was opened.

6) In the roughness groups tab at the top, define groups of similar pipes that tend to have the same roughness (see documentation for more guidance on this), which Darwin will have the freedom of adjust as a
group (apply the same multiplier to all pipes in the group) For tips, see the WaterGEMS Help documentation.

7) If there are demands in the model that are uncertain, enter them in the Demand Groups tab. Darwin will be able to adjust the demand as part of the calibration process.

8) If there are elements whose status is uncertain (such as possibility of stuck valves), enter those in the Status Elements tab. Darwin will have the freedom to adjust these as part of the calibration.

9) Create a new optimized calibration under the calibration study

10) In the Roughness tab, select the roughness groups to consider and enter the range of multipliers, to define the range that Darwin can adjust them.

11) In the Demand tab, select any demand adjustment groups that will be active, and their range.

12) In the Status tab, select the elements that Darwin will be able to adjust as part of the calibration

13) In the field Data tab, select which hydrant flow tests to consider in the calibration.

14) Compute the calibration run, review the results, adjust as necessary, then when done, click the export to scenario button.

See Also

Using Darwin Calibrator