Cocchi 1
Franklin Cocchi
Writ 340
Martha J. Townsend
December 11, 2013
Ensuring Water Distribution
Abstract
There are a number of different strategies water utilities use to ensure customers
are reliably provided with water. The first component of ensuring water reliability is
involved with the actual engineering of a water distribution network. From there, water
utilities can implement day-to-day strategies such as increasing flow rates to ensure
continued water availability. This strategy, however, is merely a temporary remedy until
something like a pipe can be physically repaired in the system. When a more serious
situation, such as an earthquake, disrupts a system, typical strategies are likely to fall short,
so simulating disasters like earthquakes can provide water utilities with a better postearthquake plan, or help them strengthen critical areas. Consumers have come to expect
water will be available at all times, so utilities constantly update and adapt their water
distribution network to meet this expectation.
Introduction
Water: for some it is a favorite beverage, and for others, simply a component
necessary to take a shower. These two water uses, in addition watering plants and fighting
fires, require a distribution system to get water from its origin (ground water, rivers, lakes,
etc.) directly to the consumer. As long as customers pay their utilities (potentially the most
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important factor in ensuring water service), most individuals in the United States have
access to water with virtually no disruptions of service. The Tucson Metropolitan area of
Arizona, for example, has a reliability rate of 96.32% [1, pp. 148]. Water reliability requires
having water available and having that water above a minimum psi. In this same area,
water is actually available over 99.9% of the time [1, pp.148], showing most users will only
suffer from pressure drops. Disruptions in service often come from pipe bursts, such as the
one seen in Figure 1, or unforeseen
Figure 1: Pipe Break in a Water Network
spikes in water demand, but there
are a number of strategies municipal
water companies can implement to
ensure water is available in the
nearest faucet. These strategies
include optimal design of the
distribution network, short-term
adjustments to water supplied,
improved distribution system
Source: [2]
monitoring, and disaster simulation.
Planning Ahead
Ensuring water distribution starts with the initial laying of pipe to produce the
distribution system. If the distribution network focuses on reliability alone, it is likely to be
uneconomical [3, pp. 13], requiring engineers select a network that establishes a tradeoff
between minimizing cost and maximizing reliability. Figure 2 shows three different
situations: two extremes and an example optimized design. In actual distributions, the
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shape of the system will vary; this figure is based on a rectangular grid to simplify
comparing the different implementable strategies. In Figure 2, (a) would require the least
pipe, making it the most cost efficient. Its biggest problem, however, is that if one pipe
breaks, depending on the break location, most of the system could end up immediately
failing. In Figure 2, (c) is far less likely to fail because there are multiple paths water can
travel to reach a potential consumer in the event of a rupture, although the liberal use of
pipe makes it far more expensive to implement. In Figure 2, (b) represents the trade off
between minimizing the cost and maximizing the reliability. If one pipe breaks, water still
has an additional path to its source, even though it may be less direct. An actual, optimal
water network can be designed by combining these two principles. With proper analysis,
water utilities can ensure the system has enough reliability through redundant paths to
make sure only fractions of the distribution system may fail. As one can note from the
figure, a system consisting of many loop and few branches (c) will be more reliable than
one with many branches (a) [1, pp. 140], but is likely to be extremely impractical. Most
systems today will have some form of efficient pipe layout, depending on their specific
distribution area and any potential limitations associated with their respective area.
Figure 2: Cost Efficiency and Reliability of Distribution Network
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Ensuring Adequate Availability
Failure in the distribution system may result in the complete loss of water service
for a utility customer, although it is more likely this failure will result with sub-par water
pressure. While the pipe failure itself may result in a loss of pressure, the municipal water
company often isolates a leak until the leak can be fixed. In some situations, this isolation
results with lower water pressures in neighboring areas of the system because there are
fewer pipes for water
Figure 3: Adaptive Pumping Strategy
to flow through [4, pp.
529]. If the utility
reacts by using
additional pumps to
increase the system’s
pressure, the pressure
surrounding the
isolated area can be
Modified From: [4, p. 528]
maintained and the disruption in service can be ended as early as the utility can detect and
react to the change [4, pp. 529]. With this remedy, the time the system experiences sub-par
flow is far shorter in comparison to simply waiting until the pipe was fixed. Figure 3 shows
the improvement resulting from using additional pumps as a temporary fix compared with
simply waiting for a repair to be completed. The flow rate is temporarily higher than
normal because there is a relatively unrestrained flow until the problem area is isolated.
From this time until the time the break is fixed, the utility can use extra pumps to increase
the pressure in the system and can maintain an almost normal quality of service. This extra
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pressure can be as important as the difference between a fire hydrant working or not, or
simply ensuring sprinklers cover their intended watering area. Regardless, maintaining a
standard flow rate at all times is an important component for water reliability. Although
most current distribution systems may not have an adaptive system, relying only on only
predefined pump operation schedules [4, pp. 531], it is likely to see greater
implementation.
While this temporary fix can maintain water distribution to a relatively normal
position, it can only be implemented after the break is both detected and isolated.
Typically, water variables such as pressure, flow, and water quality are only collected at
inlets and outlets of a distribution system. Traditional monitoring at only these two points
may be effective in noticing a pressure drop resulting from a break, but makes it difficult to
pinpoint specific problem areas [5, pp. 64]. By adding additional monitoring sub-stations
at various points along the water system, water utilities can isolate problem areas far more
quickly. Adding additional monitoring stations is not cheap, however, since the technology
is relatively recent, costing a municipality as much as $20,000 for each additional station
[5, pp. 65]. With a number of monitoring sub-stations along the network, the location of a
pressure drop can be found almost instantaneously by monitoring the time it takes the
pressure drop to traverse the various sub-stations [5, pp. 72]. This process is depicted in
Figure 4. Sensor node 1 is the closest to the break, so it notices the pressure difference at an
earlier time than the nodes 2 and 3. Using the known pipe length between the nodes in
combination with the time the pressure drop took to travel, the break location can be
quickly isolated. Existing distribution technicians can use this information to quickly make
more informed repair and recovery decisions. Isolating the break more quickly will allow
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the water utility to make adaptive measures such as increasing the amount of water
pumped into the system, as noted in the previous section, in addition to being able to repair
the damage faster. Both improvements result in a further reduced disruption of service for
water customers.
Figure 4: Tracing Pressure Drop Through Water System
Source: [5, pp. 71]
While these strategies help reduce disruptions of service resulting from relatively
minor incidents, their effectiveness may fall short with disruptions resulting from disaster
events like earth quakes. Since many water pipes are buried under ground, the abrupt shift
resulting from an earthquake can rupture many water pipes simultaneously. While it is
impossible to know the precise pipes that will break after an earthquake, utilities can
reduce the ensuing disruptions in service by running disaster simulations to explore
restoration strategies [6, pp. 199]. GIRAFFE (Graphical Interactive Response Analysis for
Flow Following Earthquakes) is one specific software that has been recently developed and
used for earthquake damage simulation [7, pp. 1]. Simulations with software such as
GIRAFFE is fairly extensive and takes virtually every real-life condition into account, in
addition to the various water system components (pipes, reservoirs, water tanks, wells,
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etc.) [6, pp. 200]. These conditions include, but are not limited to ground shaking, ground
failure (permanent ground displacement), pipe material, diameter [7, pp. 2], and the
availability of work crews [6, pp. 200]. Once the earthquake is accurately simulated, a
water system can be upgraded and utilities can develop emergency planning to reduce
predicted damage and service losses before the actual earthquake ever occurs [7, pp. 1].
While each water municipality may have different available options, the Los Angeles
Department of Water and Power has three different strategies for emergency service.
These are maximizing the groundwater pumped, connecting raw emergency storage
reservoirs, and rationing water use [6, pp. 201]. One of these, or a combination of the three,
may be needed, depending on the severity of the damage caused by the disaster. These
precautions are necessary so customers are not left without water for long periods of time,
in addition to being important for emergency services like firefighting post-earthquake
blazes.
Conclusion
There is far more behind ensuring the water we use on a daily basis is available than
many individuals realize. Our water and the distribution system that delivers water to our
homes is engineered to ensure a maximum level of service for this seemingly basic need.
While our distribution system has improved by leaps and bounds from the aqueducts of the
roman era, there is always room for progress in ensuring water’s consistent availability.
Most of us have come to depend on this availability, whether it be for a morning shower or
a toilet flush. Having water available at all times has become a convenience that would be
difficult to live without, and water distribution systems are constantly being developed so
you don’t have to.
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In the future, some of these developments are likely to see more wide-spread
implementation while other concerns will rise. It is likely there will be an increased amount
of monitoring stations along water networks. While the monitoring technology presented
earlier in the paper exists, it is rather new and expensive, so it has yet to see widespread
implementation. In addition, utilities would like a better understanding of how their pipes
affect water quality [8, pp. 121]. Not only would the additional monitoring stations aid in
damage location, they could also be used to monitor a variety of water variables,
potentially allowing utilities to get a greater understanding of how their distribution
system affects quality. Finally, there is likely to be an increasing emphasis on maintaining
and rehabilitating existing water distribution infrastructure [8, pp. 121]. Many distribution
systems are aging and it is simply not cost effective to entirely replace components. While
there has been much progress in the way of water distribution, future developments will
ensure water is available at an ever-increasing amount.
Biography
Franklin Cocchi is a USC student studying Electrical Engineering with an expected
graduation in May 2015. He is interested in pursuing a career in the power industry and
plans to return to USC to obtain a Master’s degree in the field.
Contact Information
Franklin Cocchi
Phone: 562-810-0941
Email: Cocchi@usc.edu
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References
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[3]
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[8]
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