Page 285 - Fair, Geyer, and Okun's Water and wastewater engineering : water supply and wastewater removal

JWCL344_ch07_230-264.qxd 8/2/10 8:44 PM Page 245

7.7 Automated Optimization 245

• 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 hours. 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 win-
dow. 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 com-
pany 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 0.5/day.
The network model may be entered in WaterGEMS using the layout in Fig. 7.8 and the data in
Tables 7.3 and 7.4.
The tank is circular with a diameter of 15.0 m. The minimum elevation is 99.0 m. The maxi-
mum elevation is 104.0 m, and the initial elevation is 103.4 m. The base elevation is 98.0 m, and the
3
inactive volume is 10.0 m . The elevation of the pump is 70.0 m and it is initially on.
Part 1: Perform an age analysis on the system using a duration of 7 days and a time step of
1 hour. Determine the youngest and oldest water in the distribution system and the
storage tank. Explain why water age varies.
Part 2: Perform a constituent analysis using the same duration and time step as in part 1.
Determine the range of concentrations in the system and the storage tank. Explain the
behavior of the system with regard to chlorine.
Part 3: Are the simulation results consistent with the known behavior of chlorine?
Part 4: Why is it necessary to run the model for such a long period of time? Do you feel seven
days is too long or too short a time period to test the model? Why?