(Para 10.3 OF CPHEEO)
1.Peak Factor:
The per capita rate of water supply indicates only the average consumption of water per day per person over a period of one year. In the design of water supply distribution system, it is to be recognized that consumption varies with the season, month, day and hour. As far as the design of distribution system is concerned, it is the hourly variation in consumption that matters. The fluctuation in consumptions accounted for, by considering the peak rate of consumption ( which is equal to average rate multiplied by a peak factor) as rate of flow in the design of distribution system. The following peak factors are recommended for various population figures:
1.For population less than 50,000 3.0
2.For a population range of 50,000 to 2,00,000 2.25
3.For population above 2,00,000 2.0
4.For Small Water Supply Schemes (Where supply is effected through standposts for only 6 hours) 3.0
2. Residual Pressure:
Distribution system should be designed for the following minimum residual pressures at ferule points:
Single storey building = 7m
Two storey building = 12m
Three storey building = 17m
Distribution system should not ordinarily be designed for residual pressures exceeding 22 meters. Multistoried buildings needing higher pressure should be provided with boosters
3.Minimum Pipe Sizes
Minimum pipe sizes of 100mm for towns having population upto 50,000 and
150mm for those above 50,000 are recommended.
For dead ends, less than 100mm can be considered.
If it is a grid, less than 100mm can be used in situations where no further expansions contemplated.
4. Elevation of Reservoir
The elevation of the service reservoir should be such as to maintain the minimum residual pressure in the distribution system consistent with its cost effectiveness. The hydraulic gradient in the pipe should normally be between 1 and 4 per thousand at peak flow. A suitable combination of pipe sizes and staging height has to be determined optimization of the system. The staging height of service reservoirs is normally kept as 15-20m.
5. Minimum Pipe Size:
Minimum pipe size may be taken 100 mm.
6. Two pipes on wide roads:
For roads wider than 25 m distribution pipe may be provided on both side of road.
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Urban Infrastructure and Network Study notes for M. plan Sem-III
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