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CIE 424 Water Distribution & Treatment

Water Distribution Systems

CIE 424 Water Distribution & Treatment

Methods of distributing water

Gravity Supply

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CIE 424 Water Distribution & Treatment

Methods of distributing waterPumped Supply

CIE 424 Water Distribution & Treatment

Methods of distributing waterPumped-storage supply

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CIE 424 Water Distribution & Treatment

CIE 424 Water Distribution & Treatment

Distribution Reservoirs

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CIE 424 Water Distribution & Treatment

Types of Reservoirs

Capacity of storage reservoirs

CIE 424 Water Distribution & Treatment

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CIE 424 Water Distribution & Treatment

Ex. 13

CIE 424 Water Distribution & Treatment

Solution

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CIE 424 Water Distribution & Treatment

CIE 424 Water Distribution & Treatment

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CIE 424 Water Distribution & Treatment

CIE 424 Water Distribution & Treatment

Tank Levels The most significant decision about a tank

in terms of distribution system design is its overflow elevation.

This elevation and the minimum, average-day, bottom of the tank will determine the size and boundary of the pressure zone that can be served from the tank, as well as the layout of the transmission mains and the required pumping head

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CIE 424 Water Distribution & Treatment

Volume For small systems not providing fire protection, the minimum

storage capacity shall be equal to the average daily consumption. A historically more conservative rule-of-thumb is to provide capacity equal to two to three days average daily consumption.

This may be excessive with the recognition that a long storage time results in increased formation of disinfection byproducts, as well as decay of chlorine residual.

For those communities that elect to provide fire protection, the sizing of the tank requires a more complex evaluation. For the purpose of this evaluation, the volume of the storage tank may be conceptually divided into three layers:

1. Domestic water demand is fed to the distribution system from the top 3 to 5 m. As the water level drops, the tank controls open, and the high service pumps start pumping to fill the tank. This is called equalization storage.

2. The next layer, amounting to 30 to 50 percent, is reserved for fire demand.

3. The bottom layer is termed emergency storage. It can still supply a minimum pressure of 140 kPa.

CIE 424 Water Distribution & Treatment

Fire Storage. Fire storage requirements are based on the need for water to supplement the capacity of the water supply. If the capacity of the water supply is such that it can provide fire flow while still meeting maximum daily demand, no fire storage is required. This is sometimes the case in extremely large systems where fire demands are a tiny fraction of maximum daily demands.

Emergency Storage. No formula exists for determining the amount of emergency storage required. The decision will have to be made on a judgment about the perceived vulnerability of the utility’s water supply. If a utility has several sources and treatment facilities with an auxiliary power supply (or power supplied from several sources), the need for emergency storage is small. Some storage should be available to handle a catastrophic pipe break that cannot be isolated easily. If a utility has a single source without auxiliary power and a relatively unreliable distribution system, a significant volume of emergency storage is prudent.

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CIE 424 Water Distribution & Treatment

Combination Equalization, Fire, and Emergency Storage. The volume of effective storage required should be based on a combination of qualization, fire, and emergency storage. Some engineers use the sum of the three types of storage, whereas others base design on the sum of equalization storage plus which is larger fire or emergency storage. The logic in such cases is that the fire is not likely to occur at the same time as a critical pipe break or power outage. The total storage can be summarized by equalization+maximum (fire, emergency). The most economical tanks are constructed in standard sizes, so the number above is rounded (usually upward) to a standard size.

CIE 424 Water Distribution & Treatment

Hourly demand

Hourly demand

Cumulative demand

Time (hr) % of the average

Hourly demand

Average hourly

demand – hourly

demand

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CIE 424 Water Distribution & Treatment

Reservoir full

v

v

v

v

v

CIE 424 Water Distribution & Treatment

Reservoir full

Reservoir empty

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CIE 424 Water Distribution & Treatment

Ex. 14

Time Demand (l/s)12h00 AM - 5h00 AM 255h00 AM - 7h00 AM 357h00 AM - 9h00 AM 1959h00 AM - 4h00 PM 854h00 PM - 8h00 PM 115

8h00 PM – 12h00 AM 64

The 24-hours consumption of a village X is as follows:

A reservoir is used in the water distribution . Assuming a daily demand of 500 l/per.d for this residential village, determine the volume of this reservoir (equalization storage). The volume of water required for fire protection is equal to 10% of the total volume.