Water quality simulation#

Water quality simulations can only be run using the EpanetSimulator.

After defining water quality options and sources (described in the Water quality options and Sources sections below), a hydraulic and water quality simulation using the EpanetSimulator is run using the following code:

>>> import wntr 

>>> wn = wntr.network.WaterNetworkModel('networks/Net3.inp') 
>>> sim = wntr.sim.EpanetSimulator(wn)
>>> results = sim.run_sim()

The results include a quality value for each node (see Simulation results for more details).

Water quality options#

Three types of water quality analysis are supported. These options include water age, tracer, and chemical concentration.

Water age: A water quality simulation can be used to compute water age at every node. To compute water age, set the ‘quality’ option as follows:
```
>>> wn.options.quality.parameter = 'AGE'
```
Tracer: A water quality simulation can be used to compute the percent of flow originating from a specific location. The results include tracer percent values at each node. For example, to track a tracer from node ‘111,’ set the ‘quality’ and ‘tracer_node’ options as follows:
```
>>> wn.options.quality.parameter = 'TRACE'
>>> wn.options.quality.trace_node = '111'
```
Chemical concentration: A water quality simulation can be used to compute chemical concentrations given a set of source injections. The results include chemical concentration values at each node. To compute chemical concentrations, set the ‘quality’ options as follows:
```
>>> wn.options.quality.parameter = 'CHEMICAL'
```
The initial concentration is set using the initial_quality parameter on each node. This parameter can also be set using the [QUALITY] section of the INP file. The user can also define sources (described in the Sources section below).
To skip the water quality simulation, set the ‘quality’ options as follows:
```
>>> wn.options.quality.parameter = 'NONE'
```

Additional water quality options include viscosity, diffusivity, tolerance, bulk reaction order, wall reaction order, tank reaction order, bulk reaction coefficient, wall reaction coefficient, limiting potential, and roughness correlation.

When creating a water network model from an EPANET INP file, water quality options are populated from the [OPTIONS] and [REACTIONS] sections of the EPANET INP file. All of these options can be modified in WNTR and then written to an EPANET INP file. More information on water network options can be found in Options.

Sources#

Sources are required for CHEMICAL water quality analysis. Sources can still be defined, but will not be used if AGE, TRACE, or NONE water quality analysis is selected. Sources are added to the water network model using the add_source method. Sources include the following information:

Source name: A unique source name used to reference the source in the water network model.
Node name: The injection node.
Source type: Options include ‘CONCEN,’ ‘MASS,’ ‘FLOWPACED,’ or ‘SETPOINT.’
- CONCEN source represents injection of a specific concentration.
- MASS source represents a booster source with a fixed mass flow rate.
- FLOWPACED source represents a booster source with a fixed concentration at the inflow of the node.
- SETPOINT source represents a booster source with a fixed concentration at the outflow of the node.
Strength: Baseline source strength (in mass/time for MASS and mass/volume for CONCEN, FLOWPACED, and SETPOINT).
Pattern: The pattern name associated with the injection.

For example, the following code can be used to add a source, and associated pattern, to the water network model:

>>> source_pattern = wntr.network.elements.Pattern.binary_pattern('SourcePattern',
...       start_time=2*3600, end_time=15*3600, duration=wn.options.time.duration,
...       step_size=wn.options.time.pattern_timestep)
>>> wn.add_pattern('SourcePattern', source_pattern)
>>> wn.add_source('Source', '121', 'SETPOINT', 1000, 'SourcePattern')

In the above example, the pattern is given a value of 1 between 2 and 15 hours, and 0 otherwise. The method remove_source can be used to remove sources from the water network model.

In the example below, the strength of the source is changed from 1000 to 1500.

>>> source = wn.get_source('Source')
>>> print(source)
<Source: 'Source', '121', 'SETPOINT', 1000, SourcePattern>

>>> source.strength_timeseries.base_value = 1500
>>> print(source)
<Source: 'Source', '121', 'SETPOINT', 1500, SourcePattern>

When creating a water network model from an EPANET INP file, the sources that are defined in the [SOURCES] section are added to the water network model. These sources are given the name ‘INP#’ where # is an integer representing the number of sources in the INP file.