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Water Distribution Systems – Part 1

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1 Water Distribution Systems – Part 1
Lecture 2 Dr. Jawad Al-rifai

2 Contents Methods of Distributing Water Capacity Requirements
System Losses Population Forecast Water Demand Fire Demand Pressure Design Period Work Examples Storage Reservoirs Elevated Reservoirs Work Example Contents

3 Water Distribution Systems (WDS)
The objective of WDS is to deliver water to individual consumers with appropriate quality, quantity and pressure. The distribution system describes collectively the facilities used to supply water from its source to the point of usage. This may include extensive system of pipes, storage reservoirs, pumps and related appurtenances. The proper functioning of a water distribution system is critical to providing sufficient drinking water to consumers as well as providing sufficient water for fire protection

4 Average day demand. The total annual quantity of water production for an agency or municipality divided by 365. Maximum day demand. The highest water demand of the year during any 24-h period. Peak hour demand. The highest water demand of the year during any 1-h period. Peaking factors. The increase above average annual demand, experienced during a specified time period. Peaking factors are customarily used as multipliers of average day demand to express maximum day and peak hour demands. Distribution pipeline or main. A smaller diameter water distribution pipeline that serves a relatively small area. Water services to individual consumers are normally placed on distribution pipelines. Distribution system pipelines are normally between 150 and 400 mm (6-16 in.). Transmission pipeline or main. A larger-diameter pipeline, designed to transport larger quantities of water during peak demand-periods. Water services for small individual consumers are normally not placed on transmission pipelines. Transmission mains are normally pipelines larger than 400 mm (16 in.). Definitions

5 Methods of Distributing Water
Depending on the topography between the source and the consumer the following may be used to transport water to consumers with adequate pressure: Gravity – when the source is at a sufficient elevation above the consumer to produce the desired pressure. Highly economical Pumping – Pumps are used to develop the necessary head (pressure) to distribute to consumers and storage reservoirs Pump-Storage System- storage reservoirs are used to maintain adequate pressure during periods of high demand and emergency (fires & power failures). During low consumption, water is pumped and stored in the storage reservoir.

6 Capacity Requirements
When designing a water –supply system, a major consideration is the population to be served, the fire flows needed and the proximity to the source. Categories of water demand are given in the table and can vary from city to city or country to country. Residential – Typical for third world lpcd Bath – 55 L Washing Cloths – 20 L WC – 30 L Washing House – 10 L Washing Utensils – 10 L Cooking – 5 L Drinking – 5 L

7 Capacity Requirements - Water Demand
Demand vary throughout the 24hr period and can range - from 25-40% of the avg daily demand between to 6.00am - to as high as 150 to 175% during morning and evening peak Demand also vary from year to year; season to season; day to day and house to house

8 Capacity Requirements - Water Demand
The range of demand conditions expected within a distribution are specified by demand factors or peaking factors. See Table NOTE: Max daily demand – demand on the day of the year that uses the most water = 1.8 x Avg daily demand Max hourly demand – the demand during the hour that uses the most water = 3.25 x avg daily demand

9 System Losses Leaking and overflow from reservoir
Leaking from main and service pipelines Leaking and losses on premises Leaking from public taps In a well maintained system losses are about 20%. Partially maintained systems are about 50%

10 Capacity Requirements –
In water-supply projects the water demand at the end of the design life of the project forms the basis for design. Design flow rate =population (at the end of service life) x per capita water demand


12 Design Periods Design period: Time periods for which the system or components is to be adequate (useful life) The design periods of water & wastewater facilities depends on several factors including : Point of diminishing returns: (Repair and maintenance vs cost of new facility) Ease of replacement and expansion Likelihood of obsolescence by technological advances Future needs (expected growth) Cost and interest rate

13 Design Period-Drinking Water Systems
(1)Allow for expansion

14 Design Period Wastewater Systems
(1)Allow for expansion

15 Population Projection

16 Population Projection


18 Work Example – Population Forecast





23 Work Example –water Demand
A community have a population of 225,000 persons with the average daily demand 600L/capita/day. 1- Calculate the water demand; giving the following data Maximum daily demand factor is 1.8 Max. peak hour demand factor is 2.7 Fire demand should be calc for 10 hrs 2- Based on your calculation, Should we include a storage reservoir in our design and if yes, estimate the size of the reservoir

24 Work Examples – Water Demand

25 Work Examples – Water Demand

26 Work Examples – Water Demand

27 Work Examples – Water Demand

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