Water distribution systems

WATER DISTRIBUTION SYSTEMS

The function of carrying water from treatment plant to individual homes is accomplished by a well planned distribution system. A distribution system consists of :

• pipelines of various sizes
• valves for controlling flow in pipes
• hydrants for providing connections with water mains for releasing water during fires
• meters for measuring discharges
• service connections to individual homes
• pumps for lifting and forcing water in distribution pipes
• distribution or service reservoirs, etc

A distribution system should:

• supply water at all intended places with sufficient pressure head
• supply requisite amount of water for fire fighting on need basis
• be cost effective implying least capital construction cost since it accounts for 70% of the total cost of the scheme
• be simple, easy to operate and repair thus RMO cost and trouble to a minimum
• be safe against any future pollution of water. This can be achieved by keeping water pipelines away from sewerage and drainage lines
• be safe by not causing damage to life and property by bursting of pipelines
• be fairly water-tight by keeping losses due to leakage to a minimum

ARRANGEMENT OF DISTRIBUTION PIPES

A distribution pipe consists of :

• Supply mains
• Sub mains
• Branches and
• Laterals

These are made of cast iron and jointed by means of

• Spigot and socket joints
• Service connections are made-up of galvanised cast iron pipes
• Water mains and sub mains are laid sloping from high level to low level areas to take maximum advantage of available head
• Sluice valves are placed along straight length of pipes and junction and branching off points
• Drain valves are placed at all low points in the distribution system in order to drain water from pipes to carry-out repairs
• Air valves are placed at high points to remove air during filling operations. They are also used for admitting air while emptying the pipe.
• Sometimes, distribution mains emerge directly from the treatment plant.
• Large cities are divided into various zones and each zone may be served by a separate (different)  distribution reservoir
• Sizes of distribution pipes depend on:
• amount of flow to be carried and
• permissible loss in pressure head
• Distribution pipes are normally laid on one side of the road and streets usually below footpaths and 2m vertically above and 3m away from sewers

LAYOUT OF DISTRIBUTION NETWORKS

• Distribution pipes are normally laid below road pavements and thie layout follows roads.
• There are FOUR different types of pipe networks. They are:
• Dead end system
• Grid iron system
• Ring system and
• Radial system
• Dead-end system
• This system is also called the Tree system
• This system has one main supply line from which a number of sub-main pipes emerge generally at right angles
• Each submain then divides into several branch pipes called laterals
• From laterals, service connections are given to consumers
• This type of distribution network is adopted for older towns which have developed in a haphazard manner without properly planned roads
• This system results in the formation of a number of dead ends
• It is suitable for localities which expand irregularly and where water pipes have been laid at random due to absence of full fledged road network.

Advantages

• Distribution network can be solved easily and accurately to determine discharges and pressure at different points in the system
• Lesser number of sluice valves (cut-off valves) are required in this system
• Shorter pipe lengths are needed and laying of pipes is easier
• It is cheap and simple and can be extended or expanded easily.

Disadvantages

• Water can reach a point only through one route. Any damage or repair in any pipeline will completely stop the water supply in the area being fed by the pipe.Any damage in a main pipe or sub-main pipe, considerable areas may get affected
• There are numerous dead-ends in this system that prevent free circulation of water
• Stagnation may cause degradation in water quality
• Removal of stale water periodically al all dead ends by providing scour valves at all dead ends is accomplished by providing scour valves at all dead ends
• This causes greater wastage of treated water along with necessary careful attendance at each valve
• Since discharge reaches a point from only one direction supplies during fire-fighting cannot be increased by diverting supplies from any other side.

• Grid iron system

This system is known as interlaced system or reticulation system. In this system, the mains, sub-mains and branches are all interconnected with each other. Hence this system is suitable for well planned towns and cities. It has been used in Chandigarh. The Grid-Iron system can be applied to dead end system by closing the loop.

FIGURE

The advantages of this system are

• Reduced size of pipe since water reaches different places through more than one route
• In case of repairs, a small area will be devoid of water as water can reach other points using altrnate routes
• Due to inter-connections, dead ends are completely eliminated and water remains in continuous circulation and is not polluted due to stagnation
• During fire, more water can be diverted by manipulating cut-off valves.

The disadvantages of this system are

• The system requires more length of pipe lines and larger number of sluice valves
• Construction cost is higher
• Design is difficult

• Ring system

This system is also called circular system. The distribution area is divided into rectangular or circular blocks and the main water pipes are laid on the periphery of these blocks. It is suitable for towns and cities having well planned roads. It can be used to enhance the capacity of a grid iron system by placing it as a loop feeder placed centrally around a high demand area. This system has the same advantages and disadvantages as that of the grid iron system

FIGURE

• Radial system

If a city or town has a radial system of roads emerging from different centers, the pipes are laid along the roads with distribution reservoirs located at the center. In this system, water is taken from the water mains and pumped to distribution reservoirs located at various central locations. The water is supplied to various points using radially laid distribution pipes. This ensures high pressure and efficient water distribution. The calculation for this design are simple

FIGURE