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2073 Chaitra · 8 marks

Average demand, village survey 2013, design 25 years

Short answer

Design year 2041, n=28, population 1897. Using Nepal rural rates, net demand is 100744 l/d; adding 15% losses gives 115855 l/d = 115.86 m3/d = 1.34 l/s.

The survey data collected for a water supply scheme in a village of Nepal is given below:

Survey year = 2013; Base period = 3 years; Design period = 25 years; Population = 1250; Cows = 200; Goats = 500; Chicken = 5000; Annual population growth rate = 1.5%; Day scholar students in a school = 100; Boarder students in a school = 10; No. of Health post = 1; No. of tea shop = 1; No. of VDC office = 1.

Neglect demand for fire fighting. Calculate average water demand for the design year.

Survey year 2013; base period 3 years and design period 25 years: design year 2041, $n = 28$ years after the survey.

Design population

P_{2041} = 1250\times(1.015)^{28} = 1{,}897

Water demand

Design values assumed (Nepal rural water supply practice): domestic 45 lpcd (public taps); day scholar 5 l/d; boarder 45 l/d; office staff 45 l/d with 10 staff per office; big animal (cow, buffalo) 45 l/d; small animal (goat, pig) 5 l/d; poultry 0.2 l/d; health post 1000 l/d; tea shop 500 l/d; losses and wastage 15% of net demand; maximum day factor 1.5 and peak hour factor 3. Fire demand is neglected.

Demand	Quantity	Rate	Demand (l/day)
Domestic (45 lpcd)	1,897	45 l/c/d	85,344
Day scholars	100	5 l/c/d	500
Boarders	10	45 l/c/d	450
Cows	200	45 l/d	9,000
Goats	500	5 l/d	2,500
Chickens	5,000	0.2 l/d	1,000
Health post	1	1000 l/d	1,000
Tea shop	1	500 l/d	500
VDC office (10 staff)	10	45 l/staff	450
Net demand			100,744

Losses and wastage $= 15\%$ of net demand $= 15{,}112$ l/day

Q_{avg} = 100{,}744 + 15{,}112 = 115{,}855\ \text{l/day} = 115.86\ \mathrm{m^3/day} = 1.34\ \text{l/s}

Answer: Design population = 1,897; average water demand = 116 m $^3$ /day (1.34 l/s).

✓ Answer checked by Claude Opus 5.5 (high effort)

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