Flushing Simulation
Learn how the new Flushing Simulation module in WaterCAD and WaterGEMS can help you optimize flushing programs with multiple conventional and unidirectional flushing (UDF) events in a single run.
The new Bentley SELECT Update (SU3) for WaterCAD and WaterGEMS includes, among other new features and enhancements, a Flushing Simulation module that will help utilities and municipalities plan, analyze, and optimize flushing programs to control and improve water quality in their water distribution systems. The new module is included with both WaterCAD and WaterGEMS ad no additional cost. Bentley SELECT subscribers can immediately download this new update to start optimizing flushing programs in their water distribution infrastructure.
The importance of Flushing Simulation
Water distribution system flushing is an important tool for controlling water quality throughout the network. Flushing stirs up and removes sediments from mains and removes poor quality water from the system, replacing it with fresh water from the source. Flushing is usually accomplished by opening one or more hydrants in a planned pattern. The usual rule of thumb for flushing is to always flush with clean water behind you, meaning that hydrants should be operated to pull the freshest water into the area being flushed.
Flushing programs usually start at the source and move out through the system. Unfortunately, operators conducting the flushing program cannot see what is occurring in the mains, or measure parameters like velocity or flow rate in pipes. Water distribution models provide a way to look into the pipes and obtain an indication of how a flushing program will work.
Flushing Simulation in WaterCAD and WaterGEMS
The new Flushing Simulation module – included at no additional cost in both WaterCAD and WaterGEMS – can be used to simulate the effect of flushing water distribution systems. The implementation of the new module is oriented toward increasing velocity in mains to flush out solids and stale water, with the primary indicator of the success of flushing being the maximum velocity achieved in any pipe during the flushing operation.
There are two types of flushing that can be simulated using the new module:
- Conventional Flushing: Consists of opening up hydrants one at a time without any isolation valve operation.
- Unidirectional Flushing (UDF): Consists of one or more hydrants while isolation valves (or pipes) may be closed to control the direction of flow.
Depending on the target velocities and layout of the system, conventional flushing is often adequate. Unidirectional flushing will improve velocity although it requires additional labor and input data. A recommended workflow is to first simulate conventional flushing strategies and then identify areas which are not adequately flushed and require unidirectional flushing. If a secondary goal is to test the operation of every hydrant, then conventional flushing is usually adequate, while if valve exercising is also a goal, unidirectional flushing becomes more attractive.
The following is a summarized Flushing Simulation workflow using WaterCAD or WaterGEMS:
1. Start with a calibrated model with all meaningful pipes included
For flushing analysis, it is recommended to start from an all-pipe model. Ideally, the model should contain every hydrant and isolating valve at its exact location. This is especially important for UDF because the location of a hydrant relative to the closed valves is very important.
2. Input data:
Using the Flushing Alternative, the modeler needs to specify a target velocity, the group of pipes to be evaluated (selection set or all pipes), and global or local flow emitter coefficients. Hydrant flows may be specified directly in flow units or as an emitter coefficient. Because hydrant flow is a function of pressure and the user does not usually know the pressure at the hydrant beforehand, it is more accurate to specify the emitter coefficient.
3. Specify constraints and reporting options:
The user can specify constraints such as a minimum system pressure so flushing will not allow the pressure to drop below a value specified by the user. The modeler can also choose to report on nodes that dropped below a given minimum pressure during any flush to check if flushing will adversely affect customers.
4. Create Conventional and/or Unidirectional Flushing events
For Conventional Flushing events the user can either create events one by one or streamline the event creation process by asking the model to create a flushing event for a group of hydrants or all hydrants in the system.
Unidirectional Flushing events are more complex and additional information is required to describe the event. For each Unidirectional Flushing event the user needs to specify the elements to be flowed (in the case of a multi hydrant flush) and pick isolating valve or pipe elements to be operated during the event.
5. Running the Flushing Simulation and analyzing results
Once one or more flushing scenarios have been created, the modeler just needs to set up the calculation type option to “Flushing” and hit the Compute button in WaterCAD or WaterGEMS. The flushing results can be viewed several ways:
Customized FlexTables Flushing report: This overall summary report contains the results of all flushing runs. For each pipe the table provides key results for the flushing event such as the maximum velocity achieved, whether that velocity achieved the target velocity, and which flushing event yielded the maximum velocity in the pipe.
Flushing Results Navigator: For more in depth viewing of flushing results, the Flushing Results Navigator allows you to easily switch between flushing events to view results in color coding, the property grid, and FlexTables for that specific event. Red lines in the left drawing show the pipes that were flushed using the magenta hydrant in the UDF run. The green pipes around it are those that were closed to obtain these high velocities.
Using color-coding and advanced symbology: A good way to get an overview of flushing operations is to color code the drawing by Maximum Velocity. This will indicate which pipes reached a high velocity at a glance.
What else is new with SELECT Update 3?
In addition to the new Flushing Module, the new SELECT Update for WaterCAD and WaterGEMS includes, at no additional cost, the following new features and enhancements:
- Leak calibration: A new Darwin Calibrator enhancement that points the user in the direction of likely leaks.
- Hydropneumatic tank element: A new element that improves hydropneumatic tank EPS modeling and facilitates import from HAMMER for transient modeling).
- HAMMER Integration: A WaterCAD or WaterGEMS model is now a HAMMER model. Many new elements in WaterCAD and WaterGEMS to accommodate HAMMER such as surge tanks, air valves, and rupture discs.
- VSP suction side improvements: Variable Speed Pumps can now handle suction side controls and fixed flow settings.
- Hydrant element improvement: Additional behavior for hydrant elements has been added including lateral losses and a default emitter coefficient.
- Time series data import: For graphing of SCADA data for EPS calibration
- Compliance with new platforms: Support for ArcGIS 9.2, MicroStation 8.9.4 and AutoCAD 2008.
WaterCAD and WaterGEMS SELECT Update 3: Download instructions