Page 235 - Water Engineering Hydraulics, Distribution and Treatment

Chapter7
Water Distribution Systems: Modeling and
Computer Applications
7.1 WATERGEMS SOFTWARE 3. Master planning
This chapter deals primarily with the topic of pressure pip- 4. Construction and operation costs
ing as it relates to water distribution systems. If designed 5. Operational studies
correctly, the network of interconnected pipes, storage tanks, 6. Rehabilitation studies
pumps, and regulating valves provides adequate pressure,
7. Vulnerability studies
adequate supply, and good water quality throughout the sys-
tem. If incorrectly designed, some areas may have low pres- 8. Water quality studies
sures, poor fire protection, and even present health risks.
WaterGEMS (Haestad Methods Water Solutions by The WaterGEMS program, in addition to other useful
Bentley) is used in this chapter as a tool to illustrate the software, is available free to users of this book. Educational
application of various available software programs that can versions of the software can be accessed online or from the
help civil and environmental engineers design and analyze CD that accompanies this textbook.
water distribution systems. It is also used by water utility
managers as a tool to aid in the efficient operation of distri-
bution systems. This software can be used as a stand-alone
7.2 WATER DEMAND PATTERNS
program, integrated with AutoCAD, or linked to a geograph-
ical information system (GIS) via the GEMS component. Using a representative diurnal curve for domestic water
WaterGEMS is used primarily for the modeling and anal- demand (Fig. 7.1), we see that there is a peak in the diurnal
ysis of water distribution systems. Although the emphasis is curve in the morning as people take showers and prepare
on water distribution systems, the methodology is applicable breakfast, another slight peak around noon, and a third peak
to any fluid system with the following characteristics: (a) in the evening as people arrive home from work and prepare
steady or slowly changing turbulent flow; (b) incompressible, dinner. Throughout the night, the pattern reflects the relative
Newtonian, single-phase fluids; and (c) full, closed conduits inactivity of the system, with very low flows compared to the
(pressure system). Examples of systems with these charac- average.
teristics include potable water systems, sewage force mains, Two basic forms are used to represent the patterns of
fire protection systems, well pumps, and raw water pumping. water demand: stepwise and continuous. A stepwise pattern
WaterGEMS can analyze complex distribution systems is one that assumes a constant level of usage over a period of
under a variety of conditions. For a typical WaterGEMS time, and then jumps instantaneously to another level where
project, you may be interested in determining system pres- it again remains steady until the next jump. A continuous
sures and flow rates under average loading, peak loading, pattern is one for which several points in the pattern are
or fire flow conditions. Extended-period analysis tools also known and sections in between are transitional, resulting in
allow you to model the system’s response to varying supply a smoother pattern. Notice that, for the continuous pattern in
and demand schedules over a period of time; you can even Fig. 7.1, the magnitude and slope of the pattern at the start
track chlorine residuals or determine the source of the water and end times are the same, a continuity that is recommended
at any point in the distribution system. In summary, you can for patterns that repeat.
use WaterGEMS for Because of the finite time steps used in the calculations,
most computer programs convert continuous patterns into
1. Pipe sizing stepwise patterns for use by the algorithms, with the duration
2. Pump sizing of each step equal to the time step of the analysis.

Water Engineering: Hydraulics, Distribution and Treatment, First Edition. Nazih K. Shammas and Lawrence K. Wang.
© 2016 John Wiley & Sons, Inc. Published 2016 by John Wiley & Sons, Inc.

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