Water resources project analysis of water

distribution system and its maintainance

What is a water supply network  ?• A water supply system or water

distribution system of engineered hydrologic and hydraulic components which provide water supply. 

Types of distribution systems There are basically two main layouts of a

distribution network:

• Branched configuration• Looped (or ”grid”) configuration

• Branched configuration

Branched networks are predominantly used for small-capacity community suppliesdelivering the water mostly through public standpipes and having few houseconnections, if any. Although adequate, having in mind simplicity and acceptableinvestment costs, branched networks have some disadvantages

• Looped (or ”grid”) configuration

A looped network usually has a skeleton of secondary mains that can also be in a formof branch, one loop (’ring’), or a number of loops. From there, the water is conveyedtowards the distribution pipes and further to the consumers. The secondary mains areconnected to one or more loops or rings. The network in large (urban) distributionsystems will be much more complex essentially a combination of loops andbranches with lots of interconnected pipes that requires many valves and special parts.

What does a water supply system include ?

• A drainage basin .• A raw water collection point (above or below ground) where the water

accumulates, such as a lake, a river, or groundwaterfrom an underground aquifer. Raw water may be transferred using uncovered ground-level aqueducts, covered tunnels or underground water pipes to water purification facilities.

• Water purification facilities. Treated water is transferred using water pipes (usually underground).

• Water storage facilities such as reservoirs, water tanks, or water towers. Smaller water systems may store the water in cisternsor pressure vessels. Tall buildings may also need to store water locally in pressure vessels in order for the water to reach the upper floors.

• Additional water pressurizing components such as pumping stations may need to be situated at the outlet of underground or above ground reservoirs or cisterns (if gravity flow is impractical).

• A pipe network for distribution of water to the consumers (which may be private houses or industrial, commercial or institution establishments) and other usage points (such as fire hydrants).

• Connections to the sewers (underground pipes, or aboveground ditches in some developing countries) are generally found downstream of the water consumers, but the sewer system is considered to be a separate system, rather than part of the water supply system.

water distribution system

Advantages:

• It is a very simple method of water distribution. Calculations are easy and simple to do.

• The required dimensions of the pipes are economical.

• This method requires comparatively less number of cut-off valves.

Disadvantages:

• The area receiving water from a pipe under repair is without water until the work is completed.

• In this system, there are large number of dead ends where water does not circulate but remains static.

• Sediments accumulate due to stagnation of the dead end and bacterial

• growth may occur at these points. To overcome this problem drain valves are provided

• at dead ends and stagnant water is drained out by periodically opening these valves but a large amount of water is wasted.

• It is difficult to maintain chlorine residual at the dead ends of the pipe.

• Water available for fire-fighting will be limited since it is being supplied by only one water main.

• The pressure at the end of the line may become undesirably low as additional areas are connected to the water supply system. This problem is common in many less-developed countries.

Maintainance of water distribution networks

• Here are a few of the points covering the maintainance requirements

1. pipeline Maintainance system • A pipeline maintenance system must ensure that

all required maintenance work can be carried out with ease. The system is actually determined by the scale and type of facilities, the number of employees, and other aspects, but the system must also be able to cope with operation under both normal and emergency conditions

1. Normal operation 1.1 Facility patrols and inspection Capital equipment and personnel qualified to conduct periodic patrols, inspections, servicing and surveys must be provided in order to prevent pipeline accidents from occurring.

1.2 Pipeline drawing preparation Pipeline drawings are essential for the maintenance of pipelines, and they must be absolutely correct because they are used on regular basis. This is why pipeline drawings must be prepared, and a system for their control must be established.

2. Emergency operations Pipeline leaks may cause flooding of homes, traffic accidents and traffic jams due to sunken roads, insufficient flow, and turbid water. In order to minimize such damage when a leak occurs, a system must be in place to initiate repairs immediately. As part of the system, it is a good idea to establish a stand-by system or an on-duty system organized into a cohesive unit that can respond in the event of an emergency. 3. Night and holiday dispatch A dispatch system must be established for nights and holidays since leaks can occur just as well outside business hours. In order to prepare for unexpected accidents, a mobilization plan must be set up ahead of time that designates essential restoration personnel and outlines notification arrangements so personnel can be summoned immediately and assigned to departments and sections.

4. On-call contractors In order for designated contractors to perform repair work, there must be a system of contractors, a method for designating emergencies, and annual contracts signed for handling accidents. An emergency call-out system must be established using a shift system that includes a number of companies, and a base must be set up with permanently stationed communications personnel to cope with unexpected accidents at any time, including nights and holidays. 5. Emergency water supply Water wagons and portable cans must be prepared to provide emergency supplies to areas cut off from water. Coupling to distribution pipes in surrounding areas and neighbouring cities as well as other measures are highly desirable for providing immediate water supply assistance in order to keep the area cut off from water to an absolute minimum.

6.Equipment and repair material preparation Spare pipes for repairs organized by type and diameter as well as restoration machines and equipment must be kept in a constant state of readiness. In particular, a chart showing the amount of materials stored for emergency, a chart summarizing work equipment, an emergency mobilization plan and a work division chart must be prepared and inspected periodically each year. Ideally, materials stored for an emergency will be shared by neighbouring cities

How to carry out Maintainance ??• 1. the flushing of water pipes should be carried out whereever

necessary especially in case of dead ends on lines and at places where water is supplied without filtration

• 2. the hydrants valves and various other appurtenances installed on the water mains should be checked regualrly and should be maintained in perfect running order.

• 3. the records regarding the lengths of pipes laid , lengths of pipes repaired or replaced expenditure incurred , number of fire hydrants , number of service connections and all other relevant data in connection with the distribution system should be well maintained.

• 4. the wastage of water especially of leakage through pipe joints should be brought down to minimum possible extent .

• 5. the water pipes should be cleaned periodically by use of scrapping devices.

• 6. meters installed on distribution system should be checked from time to time and the defective or unreliable meters should be immediately replaced or repaired.

Leakage control and maintainance

• There is a constant danger of leaks occurring because pipelines are exposed to various types of construction work, traffic loads, corrosion, uneven settling of the ground and earthquakes; and the pipes themselves suffer from ageing. Frequent leaks can have a major impact on the lives of citizens not only because of water shutoffs and reduced water flow, but roads and other underground facilities may be damaged or homes may be flooded. This is why it is so important to constantly patrol pipelines and inspect facilities in order to prevent leaks or to find them as quickly as possible.

Leakages in pipelines

The factors influencing leakage are ;

• soil characteristics, soil movement, traffic loading• defects in pipes, poor quality of joints• poor quality of workmanship, damage due to excavation for other purposes• pipe age and corrosion level• high pressures in the system• extreme temperatures

Corrosion of metal pipes is one of the major causes of poor operation of waterdistribution systems. It appears as a result of reaction between the water and metal. Thisinternal corrosion causes three problems:• The pipe mass is lost through oxidation to soluble iron, resulting in increased rate ofpipe bursts• The second by-product of oxidation is iron-bearing scale that accumulates on thepipe wall in the form of tubercles, causing a reduction of pipe capacity (head lossincrease)• Both soluble and particulate iron affects the water quality creating colour problems(‘brown’ or ‘red’ water)External corrosion is a result of aggressive soils and may also contribute to the pipe burst rate to a large extent.

Corrosion

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