The average surface area of a reservoir in the month of

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The average surface area of a reservoir in the month of June is 20 km². In the same month, the average rate of inflow is 10 m³/s, outflow rate is 15 m³/s, monthly rainfall is 10 cm, monthly seepage loss is 1.8 cm and the storage change is 16 million m³. The evaporation (in cm) in that month is:

1. 46.8
2. 136.0
3. 13.6
4. 23.4

Correct Option: B

Surface area = 20 km²
Inflow = 10 m³/s (Q_i) ↓
Rainfall = 10 cm (Q_R) ↓
Outflow = 15 m³/s (Q_o) ↑
Seepage loss = 1.8 cm. (Q_s) ↑
Evaporation loss = ? (Q_E) ↑
Storage change = inflow – outflow = 16 × 10⁶ m³
⇒ 16 × 10⁶ = Q_i +Q_R – (Q_o + Q_s + Q_E)
= (10 × 86400 × 30) + (0.1 × 20 × 10⁶) – [(15 × 86400 × 30) + (1.8 ×10^-2 × 20 ×10⁶) + Q_E]
⇒ 16 × 10⁶ = (2.592 × 10⁶ + 2 × 10⁶) – (12.96 × 10⁶ + .36× 10⁶ + Q_E)

⇒ Q_E =	27.32 × 10⁶	= 1.366 m
	20 × 10⁶

= 136.6 cm
Maximum bending stress occurs when wheel load is equidistant from the centre of the beam. The figure shows the position of wheal loads at maximum bending stress condition.