What is the design period?

Years for which a scheme is designed to serve the growing population

Time between survey and start of operation

What does the base period represent?

Time between survey year and start of operation (design, approval, construction)

Years between design year and demolition

How is the fire demand estimated?

4637 sqrt(P)(1 - 0.01 sqrt(P)) l/min, P in thousands

2075 Chaitra · 8 marks

Design period, base period, demand types

Short answer

Design period is years until extension; base period is 2–5 years from survey to operation. Peak hour demand (~2.7 × average daily demand) sizes distribution pipes. Demand types: domestic (45–135 lpcd), institutional, industrial, livestock, public, fire, and losses. Factors: climate, town size, living standard, industry, water cost, metering, pressure, and supply continuity.

What is meant by design period, base period and peak hour demand? Describe the various types of water demand and discuss the factors which affect the rate of demand in a water supply scheme.

Design period

The number of years for which a water supply scheme is designed to serve the growing population before it must be extended or replaced. It is counted from the base year to the design year and depends on the life of the component, the cost of capital, the ease of expansion and the growth rate. Typical values: intake and pipes 20 to 30 years, treatment plant 15 to 20 years, pumps 10 to 15 years, reservoirs 30 to 50 years. For rural schemes in Nepal it is commonly 15 to 20 years.

Base period

The time between the survey (data collection) year and the start of operation of the scheme (it covers design, approval and construction). Typical value: 2 to 5 years. The base year = survey year + base period, and the design year = base year + design period.

Peak hour demand

The maximum rate of demand in any hour of the day; this rate is used to design the distribution system. Peak hour demand $\approx 1.5\times$ maximum daily demand $\approx 2.7\times$ average daily demand.

Types of water demand

Type	Examples	Usual rate
Domestic	Drinking, cooking, bathing, washing, flushing	45 lpcd (rural) to 135 lpcd (urban)
Institutional and public	Schools, offices, hospitals, hotels, public standposts	5 to 45 l/head/day; hospitals 340 l/bed/day
Commercial and industrial	Shops, factories, cinemas, markets	Depends on the type
Livestock	Cows, buffaloes, goats, poultry	45 l/day per big animal, 5 l/day per small animal
Public use	Road washing, parks, fountains, sewer flushing	About 5 percent of the total
Fire demand	Fire fighting	$4637\sqrt P\,(1-0.01\sqrt P)$ l/min, P in thousands
Losses and wastage	Leakage, theft, faulty meters	15 to 20 percent

Factors affecting the demand

Climate, size and nature of the town, standard of living, industry and commerce, quality and cost of water (tariff), metering, supply pressure, continuous or intermittent supply, leakage control, and the habits and culture of the people.

✓ Answer checked by Claude Opus 5.5 (high effort)

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