Civilwar-Day 18-Oct 14-PWD-Water demand& population forecasting

The population of a city in the first three consecutive years is given as 6000, 8000 and 10000 respectively. What is the population of the city in the fourth continuous year, according to the geometric increase method?

• 11500
• 12000
• 12900

• 14000

Answer explanation

Geometric increase method: Growth rate = (10000/6000)^(1/2) – 1 = 0.29. Population in 4th year = 10000 × (1 + 0.29) =12900

Population is 1,00,000. The average water consumption is 200 lpcd. The capacity of distribution system is (Take fire demand 61 MLD)

• 54 MLD
• 61 MLD
• 81 MLD

• 36 MLD

Answer explanation

Average demand = 1,00,000 × 200 / 1,000,000 = 20 MLD. Adding fire demand (61 MLD) gives total =81MLD

The distribution mains are designed for

• Maximum daily demand
• Maximum hourly demand
• Average daily demand
• Maximum hourly demand of maximum day

Answer explanation

Distribution mains must handle the highest expected flow — the maximum hourly demand on the maximum day.

As compared to geometrical increase method of forecasting population, the arithmetical increase method gives

• Lesser value
• Higher value
• Equal value
• May vary as it may depend on the population figures

Answer explanation

The arithmetical increase method assumes constant increase per decade, so it generally gives lower estimates than the geometrical method.

A water lost in theft and waste contribute to how much percentage of total consumption

• 5
• 10
• 15
• 20

Answer explanation

Water loss in distribution systems due to leakage, theft, and wastage is typically around 15% of total consumption.

The average consumption of water required in factories in lpcd is .....................

• 20–30
• 30–45
• 10–15
• 70–80

Answer explanation

Industrial or factory water consumption typically ranges from 30 to 45 liters per capita per day (lpcd).

Consider the following statements

1. The arithmetical increase method is suitable for new cities.

2. The decreasing growth rate method is used where the rate of growth shows a downward pattern.

3. The geometrical increase method is used for older cities.

Which of the following above statements is/are correct?

• 1,2,3
• 1 and 3
• Only 2
• 2 and 3

Answer explanation

Only Statement 2 is correct — the decreasing growth rate method applies when a city’s population growth is slowing, while the arithmetical and geometrical methods are suited to old and new/fast-growing cities respectively.

Compute the 'fire demand' for a city of 2 lac population by Freeman's formula

• 80 MLD
• 49.07 MLD
• 64.58 MLD
• 102.84 MLD

Answer explanation

Freeman’s formula: Q = 1136 × P⁰·⁵. For P = 2 lac (0.2 million), Q = 1136 × √0.2 ≈ 508. MLD = 49.07.

The population of a city at previous consecutive census years was 400000, 558500, 776000 and 1098500. The anticipated population at the next census to the nearest 10000 by Arithmetical increase method would be

• 1340000

• 507900

• 676000

• 101400

Answer explanation

Arithmetical increase = (558500−400000)+(776000−558500)+(1098500−776000) = 724500/3 = 241500. Predicted = 1098500 + 241500 = 1340000

If the average daily water consumption of a city is 24,000,000 liters per day, peak hourly demand will be

• 1000 cu m/hr
• 1500 cu m/hr
• 1800 cu m/hr
• 2700 cu m/hr

Answer explanation

Given:

Average daily consumption = 24,000,000 L/day = 24,000 m³/day

Step 1:

Average hourly demand = 24,000 / 24 = 1,000 m³/hr

Step 2:

Peak hourly demand ≈ 1.8 × average hourly demand

= 1.8 × 1,000 = 1,800 m³/hr

✅ Answer: Peak hourly demand = 1,800 m³/hr