Page 261 - Water Engineering Hydraulics, Distribution and Treatment

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Problems/Questions
Junction data for Problem 7.8
3. From the above table and graphs of demand, age, and concen-
Table 7.30
tration versus time generated within WaterGEMS, determine
Junction
Demand (L/min)
Elevation (m)
the following correlations:
(a) Age and chlorine concentration;
151
73
J-1
J-2
227
67
(b) Demand and chlorine concentration at a junction;
J-3
81
229
(c) Demand and water age at a junction.
J-4
219
56
4. Why is it necessary to run the model for such a long time? Do
67
J-5
215
you feel that 300 h is too long or too short a time period for
73
J-6
219
testing the model? Why?
J-7
55
215
A planning commission has indicated a new industry may
7.9
180
84
J-8
be connected to the water system described in Problem 7.8. You
88
J-9
151
are to determine the pipe diameters in the network to minimize
the installation cost assuming all the pipes are ductile iron. Use
the Darwin Designer module to determine the total cost and size
Table 7.31 Pipe data for Problem 7.8
each pipe for each of the following conditions. Use the pipe cost
Pipe Length (m) Diameter (mm) Roughness information from Problem 7.4 for the ductile-iron pipe.
I. Size the pipes using a demand multiplier (peaking factor) of
P-1 300 200 130
3.2. The pressure must remain between 170 and 550 kPa during
P-2 305 200 130
peak demand. Exclude pipes P-7 and P-8 in your analysis when
P-3 300 200 130
determining the pipe sizes. (Hint: You will need to specify an
P-4 200 200 130
additional demand of zero (0 L/min) with the default pressure
P-5 300 300 130
constraints at the junctions or a fatal error will occur.)
P-6 200 200 130
II. It is expected that a new industry with an expected additional
P-7 1 300 130
demand of 2,000 L/min with a required minimum pressure of
P-8 5,000 300 130
260 kPa will be added to the system. It could be tapped into
P-9 300 300 130
the network at either junction 6, 7, or 8. Size the pipes for the
P-10 500 200 130
conditions in part I along with the industry added to all proposed
P-11 500 200 130
junctions. You will need to analyze the network three times, once
P-12 500 200 130
for the industry at J-6, again with the industry at J-7, then finally
P-13 150 150 130
with the industry at J-8.
P-14 200 200 130
1. Indicate which option(s) would work best.
2. Which junction should the industry be tapped into to be the
The cylindrical tank has a diameter of 15 m. The base and least costly and what is the expected cost?
minimum elevations are 99 m. The maximum elevation is 104 m
3. What is Table 7.32 Results Table for Problem 7.8 the size of
and the initial elevation is 103.4 m.
each pipe for the best solution at the least costly option with
1. Perform an age analysis on the system using a duration of the industry added?
300 h and a time step of 2 h. Fill in the results in Table
4. What is the calculated minimum pressure at the industry for
7.32, indicating the maximum water age at each junction and
the best solution?
tank after the system reaches equilibrium (a pattern of average
water age vs. time becomes evident). What point in the system 7.10 Find and help a city or town in your local area, which has
generally has the oldest water? Explain why the water is oldest at least one of the following engineering problems facing their
at this location. water supply system, such as (a) low water pressure in certain
locations during peak water demand periods or high fire demand;
2. Perform a constituent analysis using the same duration and
(b) unknown Hazen–William formula coefficients for some of their
time step as in part 1. Fill in the results in Table 7.32, indicating
pipes; (c) planned new subdivision developments in the city/town;
the minimum chlorine concentration for each junction and
(d) proposed new pump station, valve station, and/or interconnec-
tank after the system has reached equilibrium (a pattern of
tion of major pipelines; (e) proposed elimination of dead-end pipes;
concentration vs. time becomes evident). What point in the (f) optimization of a new water storage tank’s location; (g) determi-
system has the lowest chlorine concentration? Explain why nation of a new water storage tank’s elevation; (h) interconnection
the chlorine residual is lowest at this location.
of the city/town’s water supply system with another city/town’s
water supply system during an emergency situation; (i) frequent
Table 7.32 Results table for Problem 7.8
pipe breaks due to excessive water pressures in certain areas;
Junction J-1 J-2 J-3 J-4 J-5 J-6 J-7 J-8 J-9 T-1 (j) the planned lining of old pipes for structural and hydraulic
(C value) improvements; (k) planned by-passing of major water
Age (h) facilities (such as water reservoir, water storage tower, and trans-
Chlorine mission pipeline) for renovation, replacement, or elimination; (l)
concentration planned partial empty (1/2) of water storage tower in order to reduce
(mg/L)
chlorination detention time for reducing DBP concentrations; (m)