L-37 Distribution of WaterPart-I

Environmental Engineering

Unit-IV

Prof S S Jahagirdar

Contents• Water distribution systems, method of

distributing water, system configuration, appurtenances, basic system requirements, hydraulic analysis head balance method, quantity balance method, equivalent pipe concept, Newton – Raphson and linear theory methods.

Requirements of Good Distribution System

1.Water quality should not get deteriorated in the distribution pipes.

2.It should be capable of supplying water at all the intended places with sufficient pressure head.

3.It should be capable of supplying the requisite amount of water during fire fighting.

4. The layout should be such that no consumer would be without water supply, during the repair of any section of the system.

5.All the distribution pipes should be preferably laid one meter away or above the sewer lines.

6.It should be fairly water-tight as to keep losses due to leakage to the minimum.

Classification of distribution system

•Depending on topography of town water may be distributed by

1. Pumping

2. Gravity

3. Combination of pumping and gravity

1. Pumping system

• The treated water is directly pumped into a distribution main without storing at high level reservoirs.

• High lift pumps are provided.

• Pumps are required to be operated at variable speed because of fluctuating demand

• Continuous attendance is required to regulate the pump.

• Additional pumps are provided as standby.

• Due to load shading water supply may get hampered.

• In such case pumps are operated by using generators.

2. Gravity system

• Gravity force is used to distribute water from ESRs to users.

• Pumping is eliminated

• For proper working sufficient head should be available.

• In case of fires water is to be pumped by using pumps into distribution system

3. Combination of pumping and gravity

• Water after treatment is pumped to ESRs and supplied to users under gravity.

• To fill the ESRs pumps can be operated at constant speeds.

• This reduces wear and tear of pumps and reduces maintainace cost.

• Special supervision is not required.

• Fire demand is satisfies efficiently.

• Water is available in case of load shading or failure of pumps

Layouts of Distribution Network

1. Dead End System

2. Grid Iron System

3. Ring System

4. Radial System

1. Dead End system

Advantages:1.Relatively cheap.2.Simple, economical and can be extended according to growth3.No. of valves are less4.Determination of discharges and pressure easier due to less number of valves.

Disadvantages1.Due to many dead ends, stagnation of water occurs in pipes.2.Particular area is affected in case of repairs.3.System fails in maintaining satisfactory pressure at remote parts.4.Discharge available for fire fighting will be limited.5.Large no. of scour valves are required and periodically need to be opened

2. Grid Iron or Reticulation System:It is suitable for cities with rectangular layout, where the water mains and branches are laid in rectangles.

Advantages:1. Water is kept in good circulation due to the

absence of dead ends.

2. In the cases of a breakdown in some section, water is available from some other direction.

3. Enough water is available in the streets for fire fighting.

4. No stagnation of water as there is free circulation of water in the system

Disadvantages1. Large no of cutoff valves are provided.

2. Exact calculation of sizes of pipes is not possible due to provision of valves on all branches.

3. Analysis of distribution network is difficult and time consuming.

4. Cost of laying water pipes is more

3. Ring or Circular System:

• The supply main is laid all along the peripheral roads and sub mains branch out from the mains.

• Thus, this system also follows the grid iron system with the flow pattern similar in character to that of dead end system. So, determination of the size of pipes is easy.

• Can be used for well developed and well planned cities.

• Possesses same advantages and disadvantages of grid iron system.

• For fire fighting large quantity of water is available

4. Radial System:

• The area is divided into different zones.

• The water is pumped into the distribution reservoir kept in the middle of each zone and the supply pipes are laid radially ending towards the periphery.

Advantages:

1. It gives quick service.

2. Calculation of pipe sizes is easy.

3. Head loss is less

Theory QuestionsQ1. Explain following types of layouts of distribution

system with sketch

i. Dead end system

ii. Grid iron system

iii. Radial system

iv. Ring system

Q2. Discuss types of distribution system