Question

Using arithmetic growth method with 2011 as base year, estimate the daily domestic water demand in 2041 (million litres per day), given the population data and 175 LPCD consumption. 

Hint:

In arithmetic growth forecasting, the average past decadal increase is added linearly for each future decade.

Answer 1

Correct Answer: 53 - 56

Step 1: Compute decadal population increases. \[ \Delta P_{1981-1991} = 195{,}850 - 180{,}750 = 15{,}100 \] \[ \Delta P_{1991-2001} = 215{,}300 - 195{,}850 = 19{,}450 \] \[ \Delta P_{2001-2011} = 245{,}450 - 215{,}300 = 30{,}150 \] Average decadal increase: \[ \Delta P_{\text{avg}} = \frac{15100 + 19450 + 30150}{3} = 21500. \]

Step 2: Forecast population in 2041. Number of decades from 2011 to 2041: \[ 3 \text{ decades}. \] Thus, \[ P_{2041} = 245{,}450 + 3 \times 21{,}500 = 245{,}450 + 64{,}500 = 309{,}950. \]

Step 3: Convert population to water demand. Per capita demand = 175 L/day \[ \text{Total L/day} = 309{,}950 \times 175 = 54{,}241{,}250. \] Convert to MLD: \[ \text{MLD} = \frac{54{,}241{,}250}{10^6} = 54.24. \]

Final Answer: \[ 54.24\ \text{MLD} \]