1. Gravity Water Supply Design

2. Population Projection
Example from Agua Para el Pueblo (Honduras)
Count the houses
Assume 6 people per house
Assume linear growth for design period
N = design period
K = growth rate

3. Water Demand
Assume a per capita demand (this might be based on a governmental regulation)
Multiply per capita demand by the future population to get design average demand
Multiply average demand by scaling factors to get maximum day demand and maximum hour demand

4. Distribution Storage Tank Size
Based on 8 hours of storage at average demand
These systems aren’t designed for fire protection

5. Design Flows Transmission Line Design flow
Perhaps based on maximum daily demand or on maximum hourly demand
Distribution system design flows
Take peak hourly flow at the end of the system design life
Divide that flow by the current number of houses to get a flow per house
The flow in each pipe is calculated based on the number of houses downstream

6. Pipe Diameters How are pipe sizes chosen? Energy Equation
An equation for head loss
Requirement of minimum pressure in the system

7. head (w.r.t. reference pressure)
EGL (or TEL) and HGL
elevation
head (w.r.t. datum)
pressure
head (w.r.t. reference pressure)
velocity
head
The energy grade line must always slope ___________ (in direction of flow) unless energy is added (pump)
The decrease in total energy represents the head loss or energy dissipation per unit weight
EGL and HGL are coincident and lie at the free surface for water at rest (reservoir)
If the HGL falls below the point in the system for which it is plotted, the local pressures are _____ ____ __________ ______
downward
lower than reference pressure

8. Energy equation Energy Grade Line velocity head Hydraulic G L
pressure head
static head z
elevation
pump
z = 0
datum

9. Transmission Line Design
Spring box
Air release valves
EGL
HGL
Distribution Tank

10. Hydraulic Grade Line Minimum
Avoid having the HGL below the point in the system for which it is plotted (negative pressure)
Air will accumulate at intermediate high points in the pipeline and the air release valve won’t be able to discharge the air if the pressure is negative

11. Methods to Calculate Head Loss (Mechanical Energy Loss)
Moody Diagram
Swamee-Jain
Hazen-Williams

12. Moody Diagram 0.10 0.08 0.06 0.05 0.04 friction factor 0.03 0.02 0.01
0.015
0.04
0.01
0.008
friction factor
0.006
0.03
0.004
laminar
0.002
0.02
0.001
0.0008
0.0004
0.0002
0.0001
0.01
smooth
1E+03
1E+04
1E+05
1E+06
1E+07
1E+08 Re

13. Swamee-Jain Each equation has two terms. Why? 1976 limitations
/D < 2 x 10-2
Re >3 x 103
less than 3% deviation from results obtained with Moody diagram
easy to program for computer or calculator use
Each equation has two terms. Why?

14. Pipe roughness Must be dimensionless! pipe material pipe roughness e
(mm)
glass, drawn brass, copper
0.0015
commercial steel or wrought iron
0.045
Must be dimensionless!
asphalted cast iron
0.12
galvanized iron
0.15
cast iron
0.26
concrete
rivet steel
corrugated metal 45
0.12
PVC

15. Pipeline Design Steps
Find the minimum pipe diameter that will keep the HGL above the pipeline
Round up to the next real pipe size
Calculate the location of the HGL given the real pipe size
If an intermediate high point constrained the design then investigate if a smaller size pipe could be used downstream from the high point.

16. Minor Losses
Most minor losses (with the exception of expansions) can not be obtained analytically, so they must be measured
Minor losses are often expressed as a loss coefficient, K, times the velocity head.
High Re

17. Entrance Losses vena contracta
Losses can be reduced by accelerating the flow gradually and eliminating the
vena contracta

18. Head Loss in Valves Function of valve type and valve position
The complex flow path through valves can result in high head loss (of course, one of the purposes of a valve is to create head loss when it is not fully open)
What is the maximum value of Kv? ______

19. Solution Technique: Head Loss
Can be solved explicitly

20. Solution Technique 1: Find D
Assume all head loss is major head loss
Calculate D using Swamee-Jain equation
Calculate minor losses
Find new major losses by subtracting minor losses from total head loss

21. Solution Technique 2: Find D using Solver
Iterative technique
Solve these equations
Use goal seek or Solver to find diameter that makes the calculated head loss equal the given head loss.
Spreadsheet

22. Exponential Friction Formulas
Commonly used in commercial and industrial settings
Only applicable over _____ __ ____ collected
Hazen-Williams exponential friction formula
range of data
C = Hazen-Williams coefficient

23. Head loss: Hazen-Williams Coefficient
C Condition
150 PVC
140 Extremely smooth, straight pipes; asbestos cement
130 Very smooth pipes; concrete; new cast iron
120 Wood stave; new welded steel
110 Vitrified clay; new riveted steel
100 Cast iron after years of use
95 Riveted steel after years of use
60-80 Old pipes in bad condition

24. Hazen-Williams vs Darcy-Weisbach
Both equations are empirical
Darcy-Weisbach is dimensionally correct, and ________.
Hazen-Williams can be considered valid only over the range of gathered data.
Hazen-Williams can’t be extended to other fluids without further experimentation.
preferred

25. Air Release Valve http://www.apcovalves.com/airvalve.htm

26. Pipes

27. Additional PVC Pipe Schedules
Presión de Trabajo
RD kg/cm psi
RD kg/cm psi
RD kg/cm psi
RD kg/cm psi

28. Surveying
Vertical angle q Dx r Dz

29. Surveying using Stadia
Vertical angle q Dx r Dz b c
The reading is on a vertical rod, so it needs to be corrected to the smaller distance measured perpendicular to a straight line connecting the theodolite to the rod. a

30. Horizontal Distance Trig identity
M is the Stadia multiplier (often 100)
c is the Stadia reading

31. Vertical Distance
Trig identities

32. Pipe Length (along the slope)