Page 244 - Water Engineering Hydraulics, Distribution and Treatment

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Chapter 7
Water Distribution Systems: Modeling and Computer Applications
Running the Model
To run the model, first click the Compute button on the main toolbar. Arrows should appear on your layout screen indicating

the flow direction in each pipe. If you click on any of the objects, you will see the results in the dialog. You could look at the
results for all similar objects by opening the Flex Tables button. For example, if you want to look at flows in all the pipes, select
the Pipe Table. To examine the flow through the system over a 24-h period, select the Calculation Options under the Analysis
menu. Double-click the Base Calculation Options,theninthe Time Analysis Field select EPS. Set the start time to 12:00:00
a.m. and the duration to 24 h. The Hydraulic Time Step of 1 h will provide sufficient output for the purpose of this tutorial.
Click the Compute button.
The software provides a couple of different ways to determine whether your model meets the target demand: scroll through the

Calculation Summary and check to see if there are any disconnected node warnings. When the level in tank T-1 drops to the
minimum tank elevation of 99 m (tank level of 9 m), the tank closes off, preventing any more water from leaving. This closure
will cause the linen factory to be disconnected from the rest of the system (i.e., it will not get the required 20 L/s).
OR
Close the Calculation Summary window and select the Linen Factory junction. To create a graph of the pressure at this node,
click the Graphs button in the main toolbar. Create a Line-Series Graph from the New button in the Graphs dialog. Select the
Pressure box in the Graph Series Options window, then close the options window. You should see the calculated pressure at
the Linen Factory and notice that it never reached zero (no water pressure).
Answer
As you will see for this problem, all the pressures at the linen factory hover around 465 kPa, and no disconnected nodes are detected.
Therefore, the pumping station can support the factory’s 20 L/s demand for a 24-h period.
Solution to Part 2:
Add another demand to the Linen Factory node. To do this, double-click the Linen Factory junction and enter into the Demand

Collection field a second fixed demand of 108 L/s in the row below the 20 L/s demand after clicking the Ellipse button. Close
the dialog editor.
Select the Calculation Options under the Analysis menu, and then double-click the Base Calculation Options. You only need

to run this model for 6 h, so change 24 to 6 in the Duration field. Click Compute to run the model.
As you scroll through the results, you will see warning messages (yellow or red indicators instead of green) indicating a

disconnected node at the linen factory after 3 h. Close the User Notifications window. Select the tank and create a Line-Series
Graph of the water level in the tank by selecting Level (Calculated) in the Graph Series Options window. The graph indicates
that the water level in the tank reaches the minimum level of 9 m at 3:37:30 and cannot supply water to the linen factory.
Answer
If there were a fire at the factory, the existing system would not be adequate.
Solution to Part 3:
Answer
PUMP-3 could be manually switched on at the beginning of the fire to supply the flow necessary to fight the fire at the linen factory.
To do this, delete the pump controls for PUMP-3. Then PUMP-3 will be always on during the model simulation.

EXAMPLE 7.2 WATER QUALITY
This example demonstrates the use of WaterGEMS to simulate water quality in a water distribution system. The Scenario Manager
module is used to facilitate different types of analysis on the same network (within the same project file).

Problem Statement
A local water company is concerned with the water quality in its distribution network. The company wishes to determine the age
and chlorine concentration of the water as it exits the system at different junctions. The water surface at the reservoir is 70 m.
Chlorine is injected into the system at the source of flow, R-l (see Fig. 7.8), at a concentration of 1 mg/L. It has been determined
through a series of bottle tests that the average bulk reaction rate of the chlorine in the system (including all pipes and tanks) is
approximately 30.5 per day.