Distribution System - Layout (Water Storage)

DISTRIBUTION SYSTEM - LAYOUT

The different types of distribution networks are:

1. Dead end system

2. Grid iron system

3. Ring system (circular)

4. Radial system

 

1. Dead-end system (Tree system)

• There is one main supply pipe, from which a number of submain pipes take off at right angles.

• Each submain divides into several branch pipes (Laterals)

• From lateral, service connection are given to consumers.

• Used for older towns with irregular expansion, without properly planned roads.

• Water pipes are randomly laid which leads to formation of number of dead ends.

• As there are no cross connections between the branches, submains and laterals etc. sediment accumulation and water stagnation occurs in the dead ends.

Advantages:

• Distribution network can be easily solved. Discharges and Pressures at different points can be easily and accurately calculated.

• Requires lesser number of cut-off valves (sluice valves)

• Shorter pipe lengths are needed and laying of pipes is easier.

• Cheap, simple, can be extended/expanded easily.

Fig. 3.7 Dead End or Tree system

Disadvantages:

• Damage or repair in any pipeline completely stops water supply to that area. Greater inconvenience to consumers.

• Numerous dead ends. Stagnation of water leads to degradation of water quality.

• Periodic removal of stale water at dead ends is required by providing scour valves. Greater wastage of treated water.

• Supply is only in one direction. Supplies for fire fighting cannot be increased by diverting supplies from other side.

 

2. Grid-Iron system / Interlaced / Reticulation system

• Mains, sub-mains and branches are all inter-connected with each other. In a well-planned city/town, roads are properly developed and the pipelines can follow a grid-iron pattern.

• This system is suitable for well planned cities like Chandigarh.

• There are no dead ends and water remains in continuous circulation.

Advantages:

• Since water reaches different places from different routes, the discharge, friction loss, and pipe size are reduced.

• During repairs very small area is affected. Some supply will still reach the area from other route.

• Due to the inter-connections, dead ends are eliminated. Water remains in continuous circulation, which prevents stagnation, pollution and sediment deposits.

• During fire, more water can be diverted towards the affected area by closing the cut off valves.

Disadvantages:

• Requires more pipe length and large number of sluice valves (cut off valves).

• Costlier construction

• Design is difficult and costlier. Calculations for determing the pipe size, discharge, velocities and pressures are tedious and may require design experts and computers.

 

3. Ring System/ Circular system

• A closed ring either circular or rectangular, of the main pipe is formed around the area to be served. The distribution area is divided into rectangular or circular gniadlo blocks. The main pipes are laid on the periphery of these blocks.

• Suitable for Towns and Cities having well planned roads.

• Used in combination with grid iron system to increase the capacity and pressures (zovla at various points.

• Advantages and Disadvantages of this system are same as grid iron system.

4. Radial system (Reverse of circular)

• Suitable for city or town having radial roads emerging from different

• The distribution reservoirs are placed at these centres.

• Water from the water mains is pumped into the distribution reservoirs placed at different centres. Water is then supplied through radially laid distribution pipes.

• This method ensures high pressures and efficient water distribution.

• The calculations for design of pipe sizes are also simple.

 

Methods of Distribution

• The main objective of distribution system is to develop adequate water pressure at the consumer's taps.

• Depending upon the level of the source and the distribution area, topography of the area and other local conditions; water distribution is done in the following ways:

1. Gravitational system

2. Pumping system

3. Combined gravity and pumping system.

 

1. Gravitational system

• This system is adopted when the source (lakes or reservoirs) are at high leve and the distribution area or consumers are at low level.

• Water flows from high level to low level under gravity.

• Economical and reliable system, since no pumping is required.

• Economical and reliable system, since no pumping is required..

• However, sufficient head should be available to maintain adequate pressure a the consumer's end after allowing frictional losses in pipes.

•  Suitable for cities located at the foothills.

Example :Mumbai city is supplied from lakes situated in the hills.

• Leakage and wastages are minimum.

• Size of pipes is reduced for a given discharge.

• Pumping is required only during fires to increase pressure.

 

2. Pumping System (Pumping without storage system)

• Treated water (without storage) is directly pumped into the distribution mains.

• High lift pumps are required to be operated at variable speeds to meet the water demand.

• Continuous supervision is required at pumping station.

• During power failures, there will be complete stoppage of supply.

• During fires, large volume of water can be forced at high pressure. But, in case there is a fire during power breakdown, it will be a disaster.

 

3. Combined Gravity and Pumping System

• The treated water is pumped at a constant rate and stored into an elevated disribution reservoir.

• From the elevated reservoir, water is distributed to the consumers, by gravity.

• The system is also called as pumping with storage system; which combines gravity flow and pumping.

• The excess water during low demands is stored in the reservoir and is supplied during high demand periods.

• The pumps are operted at constant speeds at their rated capacities which increases efficiency and reduces wear and tear. Supervision is also not required.

This system is universally adopted, because of the following advantages:

• The reserve water in the distribution reservoir can be supplied for fire fighting. Pressure required for fire fighting can be achieved by closing down supply to some localities or by using pumps. (mm)

• The pumps operate at uniform rate at their rated capacities, which increases their efficiency and reduces wear and tear.

• Supervision is not required for operating the pumps.

• Reliable system. Water can be supplied from storage reservoirs during power or pump failure.

• Cheap, efficient, reliable and universally adopted.