1. CHAPTER 3: Water Distribution Systems & networks
University of Palestine
Engineering Hydraulics
2nd semester
CHAPTER 3: Water Distribution Systems & networks

2. Water Distribution Systems & networks
Content
Water Distribution Systems
Design of Water Distribution Systems
Pipe Network Analysis

3. Water Distribution Systems
Water Distribution Systems & networks
Part A
Water Distribution Systems

4. Water Distribution Systems
Introduction
To deliver water to individual consumers with appropriate
quality, quantity, and pressure in a community setting requires
an extensive system of:
Pipes.
Storage reservoirs.
Pumps.
Other related accessories.
Distribution system: is used to describe collectively the facilities used to supply water from its source to the point of usage .

5. Methods of Supplying Water
Water Distribution Systems
Methods of Supplying Water
Depending on the topography relationship between the source of supply and the consumer, water can be transported by:
Canals.
Tunnels.
Pipelines.
The most common methods are:
Gravity supply
Pumped supply
Combined supply

6. Water Distribution Systems
Gravity Supply
The source of supply is at a sufficient elevation above the distribution area (consumers).
so that the desired pressure can be maintained
HGL or EGL
Source
(Reservoir)
(Consumers)
Gravity-Supply System

7. Advantages of Gravity supply
Water Distribution Systems
Advantages of Gravity supply
HGL or EGL
Source
No energy costs.
Simple operation (fewer mechanical parts, independence of power supply, ….)
Low maintenance costs.
No sudden pressure changes

8. Water Distribution Systems
Pumped Supply
 Used whenever:
The source of water is lower than the area to which we need to distribute water to (consumers)
The source cannot maintain minimum pressure required.
 pumps are used to develop the necessary head (pressure) to distribute water to the consumer and storage reservoirs.
HGL or EGL
(Consumers)
Source
(River/Reservoir)
Pumped-Supply System

9. Disadvantages of pumped supply
Water Distribution Systems
Disadvantages of pumped supply
Complicated operation and maintenance.
Dependent on reliable power supply.
Precautions have to be taken in order to enable permanent supply:
Stock with spare parts
Alternative source of power supply ….
HGL or EGL
(Consumers)
Source
(River/Reservoir)

10. Combined Supply (pumped-storage supply)
Water Distribution Systems
Combined Supply (pumped-storage supply)
Both pumps and storage reservoirs are used.
This system is usually used in the following cases:
1) When two sources of water are used to supply water:
Pumping
Source (1)
Gravity
HGL
HGL
Pumping station
City
Source (2)

11. Combined Supply (Continue)
Water Distribution Systems
Combined Supply (Continue)
2) In the pumped system sometimes a storage (elevated) tank is connected to the system.
When the water consumption is low, the residual water is pumped to the tank.
When the consumption is high the water flows back to the consumer area by gravity.
Low consumption
High consumption
Elevated tank
Pumping station
Pipeline
City
Source

12. Combined Supply (Continue)
Water Distribution Systems
Combined Supply (Continue)
3) When the source is lower than the consumer area
A tank is constructed above the highest point in the area,
Then the water is pumped from the source to the storage tank (reservoir).
And the hence the water is distributed from the reservoir by gravity.
Pumping
HGL
Gravity
HGL
Reservoir
Pumping Station
City

13. Distribution Systems (Network Configurations )
Water Distribution Systems
Distribution Systems (Network Configurations )
In laying the pipes through the distribution area, the following configuration can be distinguished:
Branching system (Tree)
Grid system (Looped)
Combined system

14. Branching System (tree system)
Water Distribution Systems
Branching System (tree system)
Source
Submain
Main pipe
Dead End
Branching System
Advantages:
Simple to design and build.
Less expensive than other systems.

15. Water Distribution Systems
Disadvantages:
Source
Dead End
The large number of dead ends which results in sedimentation and bacterial growths.
When repairs must be made to an individual line, service connections beyond the point of repair will be without water until the repairs are made.
The pressure at the end of the line may become undesirably low as additional extensions are made.

16. Grid System (Looped system)
Water Distribution Systems
Grid System (Looped system)
Grid System
Advantages:
The grid system overcomes all of the difficulties of the branching system discussed before.
No dead ends. (All of the pipes are interconnected).
Water can reach a given point of withdrawal from several directions.

17. Water Distribution Systems
Disadvantages:
Hydraulically far more complicated than branching system (Determination of the pipe sizes is somewhat more complicated) .
Expensive (consists of a large number of loops).
But, it is the most reliable and used system.

18. Water Distribution Systems
Combined System
Combined System
It is a combination of both Grid and Branching systems
This type is widely used all over the world.

19. Design of Water Distribution Systems
Water Distribution Systems & networks
Part B
Design of Water Distribution Systems

20. Design of Water Distribution Systems
A properly designed water distribution system should fulfill the following requirements:
Main requirements :
Satisfied quality and quantity standards
Additional requirements :
To enable reliable operation during irregular situations (power failure, fires..)
To be economically and financially viable, ensuring income for operation, maintenance and extension.
To be flexible with respect to the future extensions.

21. Design of Water Distribution Systems
The design of water distribution systems must undergo through different studies and steps:
Design Phases
Preliminary Studies
Network Layout
Hydraulic Analysis

22. Design of Water Distribution Systems
Preliminary Studies:
Must be performed before starting the actual design:
4.3.A.1 Topographical Studies:
Contour lines (or controlling elevations).
Digital maps showing present (and future) houses, streets, lots, and so on..
Location of water sources so to help locating distribution reservoirs.

23. Design of Water Distribution Systems
Water Demand Studies:
Water consumption is ordinarily divided into the following categories:
Domestic demand.
Industrial and Commercial demand.
Agricultural demand.
Fire demand.
Leakage and Losses.

24. Design of Water Distribution Systems
Domestic demand
It is the amount of water used for Drinking, Cocking, Gardening, Car Washing, Bathing, Laundry, Dish Washing, and Toilet Flushing.
The average water consumption is different from one population to another. In Gaza strip the average consumption is 70 L/capita/day which is very low compared with other countries. For example, it is 250 L/c/day in United States, and it is 180 L/c/day for population live in Cairo (Egypt).
The average consumption may increase with the increase in standard of living.
The water consumption varies hourly, daily, and monthly

25. Design of Water Distribution Systems
The total amount of water for domestic use is a function of:
Population increase
How to predict the increase of population?
Use
Geometric-increase model
P0 = recent population
r = rate of population growth
n = design period in years
P = population at the end of the design period.
The total domestic demand can be estimated using:
Qdomestic = Qavg * P

26. Industrial and Commercial demand
Design of Water Distribution Systems
Industrial and Commercial demand
It is the amount of water needed for factories, offices, and stores….
Varies from one city to another and from one country to another
Hence should be studied for each case separately.
However, it is sometimes taken as a percentage of the domestic demand.

27. Design of Water Distribution Systems
Agricultural demand
It depends on the type of crops, soil, climate…
Fire demand
To resist fire, the network should save a certain amount of water.
Many formulas can be used to estimate the amount of water needed for fire.

28. Design of Water Distribution Systems
Fire demand Formulas
QF = fire demand l/s
P = population in thousands
QF = fire demand l/s
P = population in thousands
QF = fire demand flow m3/d
A = areas of all stories of the building
under consideration (m2 )
C = constant depending on the type of
construction;
The above formulas can be replaced with local ones
(Amounts of water needed for fire in these formulas are high).

29. Design of Water Distribution Systems
Leakage and Losses
This is “ unaccounted for water ”(UFW)
It is attributable to:
Errors in meter readings
Unauthorized connections
Leaks in the distribution system

30. Design of Water Distribution Systems
Design Criteria
Are the design limitations required to get the most efficient and economical water-distribution network
Pressure
Pipe Sizes
Design Period
Velocity
Head Losses
Average Water Consumption

31. Design of Water Distribution Systems
Velocity
Not be lower than 0.6 m/s to prevent sedimentation
Not be more than 3 m/s to prevent erosion and high head losses.
Commonly used values are m/sec.

32. Design of Water Distribution Systems
Pressure
Pressure in municipal distribution systems ranges from kPa in residential districts with structures of four stories or less and kPa in commercial districts.
Also, for fire hydrants the pressure should not be less than 150 kPa (15 m of water).
In general for any node in the network the pressure should not be less than 25 m of water.
Moreover, the maximum pressure should be limited to 70 m of water

33. Design of Water Distribution Systems
Pipe sizes
Lines which provide only domestic flow may be as small as 100 mm (4 in) but should not exceed 400 m in length (if dead-ended) or 600 m if connected to the system at both ends.
Lines as small as mm (2-3 in) are sometimes used in small communities with length not to exceed 100 m (if dead-ended) or 200 m if connected at both ends.
The size of the small distribution mains is seldom less than 150 mm (6 in) with cross mains located at intervals not more than 180 m.
In high-value districts the minimum size is 200 mm (8 in) with cross-mains at the same maximum spacing. Major streets are provided with lines not less than 305 mm (12 in) in diameter.

34. Design of Water Distribution Systems
Head Losses
Optimum range is 1-4 m/km.
Maximum head loss should not exceed 10 m/km.

35. Design Period for Water supply Components
Design of Water Distribution Systems
Design Period for Water supply Components
The economic design period of the components of a distribution system depends on
Their life.
First cost.
And the ease of expandability.

36. Average Water Consumption
Design of Water Distribution Systems
Average Water Consumption
From the water demand (preliminary) studies, estimate the average and peak water consumption for the area.

37. Design of Water Distribution Systems
Network Layout
Next step is to estimate pipe sizes on the basis of water demand and local code requirements.
The pipes are then drawn on a digital map (using AutoCAD, for example) starting from the water source.
All the components (pipes, valves, fire hydrants) of the water network should be shown on the lines.

38. Water Distribution Systems & networks
Part C
Pipe Network Analysis

39. Pipe Network Analysis
Pipe Network Analysis

40. Pipe Networks Pipe Network Analysis
A hydraulic model is useful for examining the impact of design and operation decisions.
Simple systems, such as those discussed in last chapters can be solved using a hand calculator.
However, more complex systems require more effort even for steady state conditions, but, as in simple systems, the flow and pressure-head distribution through a water distribution system must satisfy the laws of conservation of mass and energy.

41. Pipe Networks Pipe Network Analysis
The equations to solve Pipe network must satisfy the following condition:
The net flow into any junction must be zero
The net head loss a round any closed loop must be zero. The HGL at each junction must have one and only one elevation
All head losses must satisfy the Moody and minor-loss friction correlation

42. Pipe Network Analysis
Node, Loop, and Pipes
Pipe
Node
Loop

43. Hydraulic Analysis Pipe Network Analysis
After completing all preliminary studies and layout drawing of the network, one of the methods of hydraulic analysis is used to
Size the pipes and
Assign the pressures and velocities required.

44. Hydraulic Analysis of Water Networks
Pipe Network Analysis
Hydraulic Analysis of Water Networks
The solution to the problem is based on the same basic hydraulic principles that govern simple and compound pipes that were discussed previously.
The following are the most common methods used to analyze the Grid-system networks:
Hardy Cross method.
Sections method.
Circle method.
Computer programs (Epanet,Loop, watercad...)

45. Pipe Network Analysis
Hardy Cross Method
This method based on:
1- A distribution of flows in each pipe is estimated such that the total inflow must be equal to the outflow at each junction throughout the network system
The interflow in the network has +ve sign
The outflow from the network has -ve sign

46. 2- Neglect Minor loss 3- In each loop
Pipe Network Analysis
2- Neglect Minor loss
3- In each loop
4- If the direction of flow is clockwise it take +ve sign, otherwise it take –ve sign
5- If the flow is correct other wise, the assumed flow must be corrected as the flowing:

47. Pipe Network Analysis
Neglect terms contains
For each loop

48. 6- After calculation correct Qo and check
Pipe Network Analysis
6- After calculation correct Qo and check

49. Assumptions / Steps of this method:
Pipe Network Analysis
Assumptions / Steps of this method:
Assume that the water is withdrawn from nodes only; not directly from pipes.
The discharge, Q , entering the system will have (+) value, and the discharge, Q , leaving the system will have (-) value.
Usually neglect minor losses since these will be small with respect to those in long pipes, i.e.; Or could be included as equivalent lengths in each pipe.
Assume flows for each individual pipe in the network.
At any junction (node), as done for pipes in parallel, or

50. Pipe Network Analysis
Around any loop in the grid, the sum of head losses must equal to zero:
Conventionally, clockwise flows in a loop are considered (+) and produce positive head losses; counterclockwise flows are then (-) and produce negative head losses.
This fact is called the head balance of each loop, and this can be valid only if the assumed Q for each pipe, within the loop, is correct.
The probability of initially guessing all flow rates correctly is virtually null.
Therefore, to balance the head around each loop, a flow rate correction ( ) for each loop in the network should be computed, and hence some iteration scheme is needed.

51. Pipe Network Analysis
After finding the discharge correction, (one for each loop) , the assumed discharges Q0 are adjusted and another iteration is carried out until all corrections (values of ) become zero or negligible. At this point the condition of :
is satisfied.
Notes:
The flows in pipes common to two loops are positive in one loop and negative in the other.
When calculated corrections are applied, with careful attention to sign, pipes common to two loops receive both corrections.

52. Pipe Network Analysis
Note that if Hazen Williams (which is generally used in this method) is used to find the head losses, then
(n = 1.85) , then
If Darcy-Wiesbach is used to find the head losses, then
(n = 2) , then

53. Example 1 Pipe Network Analysis
Solve the following pipe network using Hazen William Method CHW =100 1 2 3 4 5
37.8 L/s
25.2 L/s
63 L/s 24
12.6
11.4 39 D L
pipe
150mm
305m 1 2
200mm
610m 3
457m 4
153m 5
25.2

54. 1 2 3 4 5

55. Pipe Network Analysis 1 2 3 4 5

56. Example 2 Pipe Network Analysis
Solve the following pipe network using Hazen William Method CHW =120

57. Iteration 1

58. Pipe Network Analysis

59. Iteration 2

60. Iteration 3

61. Example Pipe Network Analysis
The figure below represents a simplified pipe network.
Flows for the area have been disaggregated to the nodes, and a major fire flow has been added at node G.
The water enters the system at node A.
Pipe diameters and lengths are shown on the figure.
Find the flow rate of water in each pipe using the Hazen-Williams equation with CHW = 100.
Carry out calculations until the corrections are less then 0.2 m3/min.

71. General Notes Pipe Network Analysis
Occasionally the assumed direction of flow will be incorrect. In such cases the method will produce corrections larger than the original flow and in subsequent calculations the direction will be reversed.
Even when the initial flow assumptions are poor, the convergence will usually be rapid. Only in unusual cases will more than three iterations be necessary.
The method is applicable to the design of new system or to evaluation of proposed changes in an existing system.
The pressure calculation in the above example assumes points are at equal elevations. If they are not, the elevation difference must be includes in the calculation.
The balanced network must then be reviewed to assure that the velocity and pressure criteria are satisfied. If some lines do not meet the suggested criteria, it would be necessary to increase the diameters of these pipes and repeat the calculations.

72. Pipe Network Analysis Summary
Assigning clockwise flows and their associated head losses are positive, the procedure is as follows:
Assume values of Q to satisfy Q = 0.
Calculate HL from Q using hf = K1Q2 .
If hf = 0, then the solution is correct.
If hf  0, then apply a correction factor, Q, to all Q and repeat from step (2).
For practical purposes, the calculation is usually terminated when hf < 0.01 m or Q < 1 L/s.
A reasonably efficient value of Q for rapid convergence is given by;

73. Example Pipe Network Analysis
The following example contains nodes with different elevations and pressure heads.
Neglecting minor loses in the pipes, determine:
The flows in the pipes.
The pressure heads at the nodes.

74. Assume T= 150C

75. Assume flows magnitude and direction

76. First Iteration Loop (1) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) AB
600
0.25
0.12
0.0157
11.48
95.64 BE
200
0.10
0.01
0.0205
3.38
338.06 EF
0.15
-0.06
0.0171
-40.25
670.77 FA
0.20
-0.10
0.0162
-8.34
83.42 S
-33.73

77. First Iteration Loop (2) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) BC
600
0.15
0.05
0.0173
28.29
565.81 CD
200
0.10
0.01
0.0205
3.38
338.05 DE
-0.02
0.0189
-4.94
246.78 EB
-0.01
-3.38 S
23.35
1488.7

78. Second Iteration Loop (1) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) AB
14.20
Second Iteration
14.20
14.20
7.84
Loop (1)
14.20
Pipe L
(m) D Q
(m3/s) f hf
hf/Q
(m/m3/s) AB
600
0.25
0.1342
0.0156
14.27
106.08 BE
200
0.10
0.0186
31.48
982.60 EF
0.15
0.0174
-23.89
521.61 FA
0.20
0.0163
-6.21
72.33 S
15.65

79. Second Iteration Loop (2) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) BC
7.84
14.20
7.84
7.84
Loop (2)
7.84
Pipe L
(m) D Q
(m3/s) f hf
hf/Q
(m/m3/s) BC
600
0.15
0.0176
20.37
483.24 CD
200
0.10
0.0261
0.20
93.23 DE
0.0182
-9.22
331.23 EB
0.0186
-31.48
982.60 S
-20.13

80. Third Iteration Loop (1) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) AB
600
0.25
0.1296
0.0156
13.30
102.67 BE
200
0.10
0.0190
15.30
693.08 EF
0.15
0.0173
-28.78
570.54 FA
0.20
0.0163
-6.87
75.97 S
-7.05

81. Third Iteration Loop (2) Pipe L (m) D Q (m3/s) f hf hf/Q (m/m3/s) BC
600
0.15
0.0174
25.61
539.30 CD
200
0.10
0.0212
1.96
262.11 DE
0.0186
-6.17
274.07 EB
0.0190
-15.30
693.08 S
6.1

82. After applying Third correction

83. Velocity and Pressure Heads:
pipe Q
(l/s) V
(m/s) hf
(m) AB
131.99
2.689
13.79 BE
26.23
3.340
21.35 FE
48.01
2.717
26.16 AF
88.01
2.801
6.52 BC
45.76
2.589
23.85 CD
5.76
0.733
1.21 ED
24.24
1.372
7.09
13.79
23.85
6.52
21.35
1.21
26.16
7.09

84. Velocity and Pressure Heads:
Node
p/g+Z
(m) Z
P/g A 70 30 40 B
56.21 25
31.21 C
32.36 20
12.36 D
31.15
11.15 E
37.32 22
15.32 F
63.48
38.48
13.79
23.85
21.35
1.21
6.52
7.09
26.16

85. Example Pipe Network Analysis
For the square loop shown, find the discharge in all the pipes.
All pipes are 1 km long and 300 mm in diameter, with a friction
factor of Assume that minor losses can be neglected.

86. Solution: Pipe Network Analysis
Assume values of Q to satisfy continuity equations all at nodes.
The head loss is calculated using; HL = K1Q2
HL = hf + hLm
But minor losses can be neglected:  hLm = 0
Thus HL = hf
Head loss can be calculated using the Darcy-Weisbach equation

87. Pipe Network Analysis
First trial
Since HL > 0.01 m, then correction has to be applied.
Pipe
Q (L/s)
HL (m)
HL/Q AB 60
2.0
0.033 BC 40
0.886
0.0222 CD AD
-40
-0.886 
2.00
0.0774

88. Pipe Network Analysis Since HL ≈ 0.01 m, then it is OK.
Second trial
Since HL ≈ 0.01 m, then it is OK.
Thus, the discharge in each pipe is as follows (to the nearest integer).
Pipe
Q (L/s)
HL (m)
HL/Q AB
47.08
1.23
0.0261 BC
27.08
0.407
0.015 CD
-12.92
-0.092
0.007 AD
-52.92
-1.555
0.0294 
Pipe
Discharge (L/s) AB 47 BC 27 CD
-13 AD
-53