1. CE 3372 Water Systems Design
Lecture 008: Demand Estimation

2. Outline Distribution Systems Estimating Water Demand
Network Design Principles
Components
Fire flow
Estimating Water Demand
USGS Circular 1200
Plumber Estimate
Rural Estimate
TCEQ equations

3. Network Design Principles
Water Supply System
Includes water supply
Treatment
Facilities
Pumping facilities
Transmission lines
Local distribution network
What is a water supply system?

4. Water Supply system
Distribution network - Consists of items designed to convey potable water at adequate pressures and discharges
Pipes
Fittings
Valves
Other appurtenances
Why are adequate discharges necessary? To cover the range of flows due to the fluctuation in demand
Pressures? Necessary for firefighting, general service to residents, and economic considerations such as leakage and energy losses
The pipes/fittings/etc. will be entered into the model. Valves as minor losses.

5. DESIGN Who? Design parameters and regulations?
Personnel within the water company
Engineers / Consultants
Design parameters and regulations?
State board of health
Local city/county health departments
EPA, AWWA, ANSI

6. DESIGN REQUIREMENTS Pressure Velocity Age Chlorine concentration
Fire Flow
This slide was added to the Water Distribution Lecture
Engineers have to estimate: amount of water needed for service area + average and maximum daily demand
Pressure – will ensure that the beneficiaries will receive water at EVERY house/point considered
Velocity – In pipe, determines if the proposed network is too big and expensive to build (low velocities) or too small and too expensive to operate (high velocities)
Age – Time water spends in the network meaning the quality deteriorates as the residence time increases
Chlorine Concenration – Will ensure the water is drinkable
FIRE FLOW REQUIREMENTS! Usually controlling criteria in design of dist piping and storage
amount of water req to fight a fire (even if only a few hours) puts a strain on system

7. Pressure
Pressures
Must be high enough to..
overcome head losses in the system.
But not too high to...
prevent damage to fittings and other appurtenances.
Pressure Zones – Set pressurized areas (min and max) within the system by storage, boosters, or pressure control valves.
Can also be due to varying pipe size and topography
May be generated to ensure reliability in meeting fluctuation demands.
System pressures are adapted to requirements.
Hilly areas – booster pumping
Minimum pressures vary state to state
Established by the state’s Health Department / other agency
Fire Marshall may establish additional requirements.
Pressure zones – provide min and max pressures in the zone (could be a set force main)
Boosters are pump stations within the distribution network used to maintain a minimum pressure
The minimum pressure(20 psi) is a safety requirement to prevent potential back flows from house fixtures, and still have enough energy to push water up three stories.
Average for residential 40-60psi

8. Fire flow Fire Flow Parameters
Each municipality establishes own parameters based on local cond.
Insurance Services Offices (ISO) - Most used “Guide for Determination of Required Fire Flow”
Recommends criteria for
Establishing insurance rates
Classifying municipality. with reference to their fire defenses and physical cond.
Q = required fire flow in gpm
C = coefficient related to the type of construction
A = total floor area in ft2 (excludes basements)
Fire flow tests
Before new projects get approved for construction by the fire marshals office.
Flow tests are performed to determine fire flow capacity and adequacy of system

9. Fire flow Fire Flow Parameters
City of Houston IDM has specific instructions for locating hydrants and required fire flow to these hydrants
Other municipalities will have similar guidelines
Fire flow tests
Before new projects get approved for construction by the fire marshals office.
Flow tests are performed to determine fire flow capacity and adequacy of system

10. Water supply system Hydraulic Characteristics Service Characteristics
Pressures and discharges are a functions of HC
Length
Size
Condition of pipe
Service Characteristics
Demand as it relates to:
Present and projected population
Economic base
Fire flow
Climate
Q=VA
Pv=nrt
Driving in a car in traffic is high pressure
Service and hydraulic changes – design must incorporate allowances for changes
Changes can be relocating or replacing existing water line, increase pipe sizes, etc.

11. WATER utility Water utility company Companies exist in two forms
…who is responsible for the water quality and operation of the distribution system.
Companies exist in two forms
public entity that
..“exists for the health, safety, and welfare of the public”
privately owned utility that
..provides water for profit

12. Water supply system Gravity Pump Pump with Storage Dependable
Source of supply must be located well above the city
High-pressure demand for fire-fighting may require pumper trucks
Pump
Least Desirable
Pressures vary substantially with variations in flow
Provides no reserve if power failure
Pump with Storage
Most common
Water supplied at approximately uniform rate
Flow in excess of consumption stored in elevated tanks

13. Pipe System Primary Mains (Arterial Mains)
Form basic structure of the system
Carry flow from pumping station to elevated storage tanks
Carry flow from elevated storage tanks to service areas
Laid out in interlocking loops
Mains not more than 1 km (3000 ft) apart
Valved at intervals of not more than 1.5 km (1 mile)
Smaller lines connecting to them are valved

14. Pipe System Secondary Lines
Form smaller loops within the primary main system
Run from one primary line to another
Spacings of 2 to 4 blocks
Provide large amounts of water for fire fighting with out excessive pressure loss

15. Pipe System Small distribution lines
Form a grid over the entire service area
Supply water to every user and fire hydrants –Connected to primary, secondary, or other small mains at both ends
Valved so the system can be shut down for repairs
Size may be dictated by fire flow except in residential areas with very large lots

16. Water SUPPLY system Water source (Main Supply) Treatment Facility
Lake
River
Aquifer
Treatment Facility
Treats and disinfects water
Meet water quality standards
Potable water
Transmission Lines
Convey water from source – treatment facility facility – network
Pumping Facilities
Provide energy to move water
Intermediate Storage Facilities
Stabilize line pressures
Reserve for peak demand periods
Provide storage for fire flow req.
Distribution Lines
Convey water from storage – service areas
Looped(grid) and Branched Layouts
Appurtenances
Fire Hydrants. Valves, auxiliary pumps, fittings
Water Source – Larger may have multiple sources
Lakes and Res located in outlying areas – less pollution + hope of larger runoff from catchments
Rivers – water’s extracted upstream of civilization
Min supply volume of water source MUST serve present AND projected demand
Int Storage Facilities
In times of high demand, pressure in the network is decreased
Low demand, pressure is increased
Water volume fluctuates from 40-70% daily (discounting fire flow storage)
Distribution Lines
Service areas include residential/commericial/industrial areas
Appurt
Valves allow system to isolate small service areas when repairs are needed

17. Water Use Systems
Spatial and temporal distribution in support of human habitation
Water supply/treatment/distribution
Waste water collection/treatment/discharge
Capacity is based on POPULATION served
hydraulic dominated designs
We briefly went over water use systems

18. Water Use AND DEMAND Water Use Water Demand Consumptive
Municipal
Agricultural
Industrial
Mining
Non-consumptive
Hydropower
Transportation
Recreation
Water Demand
Quantity that consumers use per unit of time
Ex: Mgpd
Depends on population, climate, industry and economic factors
Water demand is what you have to estimate as an engineer include FUTURE development

19. Water DEMAND Residential Commercial Industrial
Single-family, multi-family (apartments)
Water for drinking, landscape, swimming, fires, street cleaning, etc.
Usually two demand peaks (morning and evening)
Commercial
Motels, hotels, offices, shopping centers
Usually less peak demand and less varied than residential
Industrial
Chemical plants, food processing plants, mines
Water for fabrication, cooling, petroleum refining, etc.
Water use depends on type of industr.
Also the 3 main developments

20. Assigning Demand Assign demand using network models (links and nodes)
Network models contain nodes that represent a multitude of actual connections.
While conceptually possible to model to every single connection, it is discouraged because
Model is hard to maintain
Small errors may go unnoticed
The operation of any single connection is not well known.

21. Network Types Branch No circulation Has terminals and dead-ends
Water in dead-ends is stagnant
Disinfection residual
Corrosion

22. Network Types Grid/Loop Furnishes supply from more than one direction
Water circulates
Disinfection is more effective.
Water “age” in system is younger (fresher).
In case of water main break, fewer people are inconvenienced
It’s cost that prohibits

23. Network Types Loop vs. Branch during network failure
Every link in a branch system is a single point of failure that isolates all downstream nodes.
Not with loop, only main supply line is failed

24. Estimating Flow Rate
Demand estimation is used to determine how much water a system is likely to use (for sizing reservoirs and tanks
Flow rate estimation (a plumber’s perspective) is used to determine how much capacity a system should be able to provide

25. USGS Circular 1200 Contains maps and tables by location
Useful gross estimate tool

26. USGS Circular 1200 Contains maps and tables by location
Useful gross estimate tool

27. Plumber Estimate How Much Water Can You Actually Get?
Inside home
How Much Water Can You Actually Get?
Flow Rates are measured in gallons per minute (gpm).
For our purposes, we will talk about the amount of water that you can get through a pipe at a velocity of 8 feet per second (a standard velocity used to engineer a plumbing system).
Plumbing diameter will limit the flow rate you can get – the larger the pipe, the more water you can get. A home with 1″ plumbing can use substantially more water than a home with 3/4″ plumbing.
Meter to house

28. Plumber Estimate
1. Think about the maximum number of fixtures and appliances you might operate at the same time.
2. Look at the chart to see how many gallons per minute each device requires.
3. Add up the flow rates for all the devices you selected.
You just figured out the PEAK FLOW RATE that you need.
Now, think about your continual water use, or water use that may run for more than 10 minutes. Add up the fixtures again, and you just calculated your SERVICE FLOW RATE.

29. Rural Estimate

30. TCEQ Tool(s)

31. Using the estimate Estimate need per connection to size the system;
Run a hydraulic model at these values to size pipes
Estimate demand to evaluate how the system is likely to perform in terms of pressure zones and such
Run a hydraulic model at these values to check pressures – no fire flow
Run a hydraulic model with fire flow to check minimum pressures

32. Readings
Several readings on server will be useful:

33. Next Time Introduction to EPANET How to install on PC
How to install on MAC (Experimental – Unsupported)
4-Examples (of increasing complexity)