chapter 3 - Water Distribution System.pptx

water supply

1. IN TR OD UC TI ON TO W AT ER SUPPLY ENGINEERING

2. INTRODUCTION TO WATER SUPPLY CHAPTER THREE WATER DISTRIBUTION SYSTEM

3. INTRODUCTION W ater from the source is to be stored temporarily and supplied to the consumers through the network of pipelines called distribution system . The distribution system Consists: pumps , reservoirs , pipe fittings , instruments for measurement of pressures , flow leak detectors etc. The cost of distribution is about 40-70 % of total cost of the entire scheme. Its efficiency depends upon proper planning , execution and maintenance . The purpose of distribution system is to deliver potable water to consumer with appropriate quality, quantity & pressure. 3

4. Requirements of Good Distribution System Water quality should not get deteriorated in the distribution pipes. The supplying water should have sufficient pressure at all places. It should be designed that the supply should meet peak hourly demand. The layout should be such that no consumer would be without water supply, even when repairs of any section. It should safe against any future pollution. All the distribution pipes should be preferably laid one meter away or above the sewer line. The system should be economical and easy to maintain and operate . 4

5. METHODS OF SUPPLYING WATER The water may be supplied to the consumers by these two systems: Continuous System This is the best system and water is supplied for all 24 hours. This system is possible when there is adequate quantity of water to supply. Intermittent System If plenty of water is not available, the supply of water is divided into zones and each zone is supplied with water for fixed hours in a day or on alternate days. As the water is supplied after intervals . 5

6. METHODS OF WATER DISTRIBUTION Gravity System This method is suitable when the source of supply such as lake, river or impounding reservoir is at sufficiently higher than city. The water flows in the mains due to gravitational forces. As no pumping is required therefore it is the most reliable system for the distribution of water as shown in the Figure below 6

7. METHODS OF WATER DISTRIBUTION Gravity System 7

8. METHODS OF WATER DISTRIBUTION Pumping System Treated water is directly pumped into the distribution main without storing. This is also called pumping without storage system. High lifts pumps are required. If power supply fails, complete stoppage of water supply. The method is not general used. 8

9. METHODS OF WATER DISTRIBUTION Pumping System 9

10. METHODS OF WATER DISTRIBUTION Combined Gravity and Pumping System Treated water is directly pumped into the distribution main without storing. This is also called pumping without storage system. High lifts pumps are required. If power supply fails, complete stoppage of water supply. The method is not general used. 10

11. METHODS OF WATER DISTRIBUTION Combined Gravity and Pumping System This is also known as dual system . The pump is connected to the mains as well as elevated reservoir. In the beginning when demand is small the water is stored in the elevated reservoir, but when demand increases the rate of pumping increases, the flow in the distribution system comes from the both the pumping station as well as elevated reservoir . As in this system water comes from two sources one from reservoir and second from pumping station, it is called dual system 11

12. METHODS OF WATER DISTRIBUTION Combined Gravity and Pumping System It is the most common system, Treated water is pumped and stored in an elevated distribution reservoir, Then supplies to consumer by action of gravity. The excess water during low demand periods get stored in reservoir and get supplied during high demand period. Economical , efficient and reliable system. 12

13. METHODS OF WATER DISTRIBUTION Combined Gravity and Pumping System 13

14. LAYOUTS OF DISTRIBUTION NETWORK The distribution pipes are generally laid below the road pavements, and as such their layouts generally follow the layouts of roads . There are general, four different types of pipe networks; Dead End System  Radial System  Grid Iron System  Ring System. The distribution system of Pipe networks consist; Primary mains : from water stations to various districts of the city . Secondary lines or Sub-mains : run from one primary main to another . Small distribution mains or branches : supply water to every consumer. 14

15. LAYOUTS OF DISTRIBUTION NETWORK Dead End System This system is suitable for irregular old towns or cities having no different pattern of roads. In this system water flows in one direction only into sub-mains and branches . 15

16. LAYOUTS OF DISTRIBUTION NETWORK Dead End System Disadvantage Due to many dead ends, stagnation of water occurs in pipes causing contamination. During repairs of pipes or valves at any point the entire downstream end are deprived of supply 16

17. LAYOUTS OF DISTRIBUTION NETWORK Radial System This is a zoned system, where the area is divided into different zones. The water is pumped into the distribution reservoir kept in the middle of each zone. 17

18. LAYOUTS OF DISTRIBUTION NETWORK Radial System Advantages It gives quick service Calculation of pipe size is easy ensures high pressure and efficient water distribution 18

19. LAYOUTS OF DISTRIBUTION NETWORK Grid Iron System It is suitable for cities with rectangular layouts, where the water mains and branches are laid in rectangles. 19

20. LAYOUTS OF DISTRIBUTION NETWORK Grid Iron System Advantages Water is kept in good circulation due to the absence of dead ends. In the cases of a breakdown in some section, water is available from some other direction. Disadvantage Exact calculation of sizes of pipes are not possible due to provisions of valves on all branches. High cost of construction; due to more pipelines and shut-off valves. Also the design is difficult. 20

21. LAYOUTS OF DISTRIBUTION NETWORK Ring System This system also follows the grid iron system. Water can be supplied to any point from at least two directions. Not problematic if a pipe is damaged. 21

22. DISTRIBUTION RESERVOIRS These also called service reservoirs, are the storage reservoirs whose function are: To absorb the hourly variations in demand. To maintain constant pressure in the distribution main. Water stored can be supplied during emergencies. Depending upon the elevation with respect to ground, it may be classified into: Surface reservoirs Elevated reservoirs 22

23. DISTRIBUTION RESERVOIRS 23

24. DISTRIBUTION RESERVOIRS Investigation for Reservoir Planning: Topographic Surveying Geological Investigation Hydrological Investigation Design Capacity of Reservoirs: - The three major components of service storage are: Equalizing or operating storage Fire reserve Emergency reserve 24

25. DISTRIBUTION RESERVOIRS Volume of Reservoir; The safe yield from a reservoir > demand Safe yield; is the maximum quantity of water that can be guaranteed during a critical dry period. Methods to determine the storage volume of reservoirs are; - Analytical Method - Mass Curve Method 25

26. DISTRIBUTION RESERVOIRS Analytical Method: is by finding out maximum cumulative surplus when pumping rate is higher than demand rate and adding to this maximum cumulative deficit when the pumping rate is lower than the demand rate of water. M ass Curve Method: is the plot of accumulated inflow (supply ) or outflow (demand ) versus time. The mass curve of supply is , therefore, first drawn and is superimposed by the demand curve. 26

27. DISTRIBUTION RESERVOIRS Volume of Reservoir; The total reservoir storage can finally be worked out by adding all the three storages operating storage emergency storage (Breakdown Storage): it is about 25% of the total storage capacity of reservoirs fire storage: 5 to 10% of the total storage is sufficient to meet the requirement 27

28. THANKS ……. 28