1. In an area of 200 hectare, water table drops by 4m. If the porosity is 0.35 and the specific retention if 0.15, change in volume of storage in the aquifer is

1. 1. 160 m³

   
   
   

   2. 1.6 × 106 m³

   
   
   

   3. 8 × 106 m³

   
   
   

   4. 1.6 × 103 m³

   
   
   

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1. View Hint View Answer Discuss in Forum

   Porosity, η = Specific yield + Specific reference
   ⇒ η = S_y + S_R
   ⇒ 0.35 = S_y + 0.15
   S_y = 0.2
   

   Sy =	Volumeof water extracted
   	Unit Volume of aquifer

   
   

   ⇒ 0.2 =	Volumeof water extracted
   	200 × 104 × 4

   
   ∴ Change in volume = 0.2 × 200 × 10⁴ × 4
   = 1.6 × 10⁶ m³

   Correct Option: B

   Porosity, η = Specific yield + Specific reference
   ⇒ η = S_y + S_R
   ⇒ 0.35 = S_y + 0.15
   S_y = 0.2
   

   Sy =	Volumeof water extracted
   	Unit Volume of aquifer

   
   

   ⇒ 0.2 =	Volumeof water extracted
   	200 × 104 × 4

   
   ∴ Change in volume = 0.2 × 200 × 10⁴ × 4
   = 1.6 × 10⁶ m³

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2. The direct runoff hydrograph of a storm obtained from a catchment is triangular in shape and has a base period of 80 hours. The peak flow rate is 30 m³/sec and catchment area is 86.4 km². The rainfall excess that has resulted the above hydrograph is

1. 1. 5 cm

   
   
   

   2. 8 cm

   
   
   

   3. 10 cm

   
   
   

   4. 16 cm

   
   
   

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1. View Hint View Answer Discuss in Forum

   Volume of run off = Area of hydrograph
   

   =	1	× 30 × (80 × 60 × 60)
   	2

   
   = 4320000 m³/s
   
   Area of catchment = 86.4 km² = 86.4 × 10⁶ m²
   Rainfall excess = run off
   

   =	Volume of run off
   	Area of catchment

   
   

   =	4320000	= 0.05 m
   	86.4 × 106

   Correct Option: A

   Volume of run off = Area of hydrograph
   

   =	1	× 30 × (80 × 60 × 60)
   	2

   
   = 4320000 m³/s
   
   Area of catchment = 86.4 km² = 86.4 × 10⁶ m²
   Rainfall excess = run off
   

   =	Volume of run off
   	Area of catchment

   
   

   =	4320000	= 0.05 m
   	86.4 × 106

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3. The parameters in Horton’s infiltration equation [f(t) = f_c + (f_o – f_c)^e–kt] are given as, f_o = 7.62 cm/ hour, fc = 1.34 cm/ hour and k = 4.182/hour. For assumed continuous ponding the cumulative infiltration at the end of 2 hours is

1. 1. 2.68 cm

   
   
   

   2. 1.50 cm

   
   
   

   3. 1.34 cm

   
   
   

   4. 4.18 cm

   
   
   

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1. View Hint View Answer Discuss in Forum

   ƒ_t = ƒ_c + (ƒ₀ – ƒ_c) e^–kt
   ƒ_t = 1.34 + (7.62 – 1.34) e^–4.182×t
   = 1.34 + 6.28 e^–4.82t
   2 hours of infiltration
   ⇒ ∫²₂ƒ_tdt ∫²₀(1.34 + 6.28.e^–4.182t)dt
   

   = 1.34 × 2[t]²0 +	6.28	[e-4.182t]²0
   	-4.182

   
   

   = 1.34 × 2 -	6.28	(e-4.182×2 - e-4.182×0)
   	-4.182

   
   = 4.18 cm

   Correct Option: D

   ƒ_t = ƒ_c + (ƒ₀ – ƒ_c) e^–kt
   ƒ_t = 1.34 + (7.62 – 1.34) e^–4.182×t
   = 1.34 + 6.28 e^–4.82t
   2 hours of infiltration
   ⇒ ∫²₂ƒ_tdt ∫²₀(1.34 + 6.28.e^–4.182t)dt
   

   = 1.34 × 2[t]²0 +	6.28	[e-4.182t]²0
   	-4.182

   
   

   = 1.34 × 2 -	6.28	(e-4.182×2 - e-4.182×0)
   	-4.182

   
   = 4.18 cm

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4. During a 6-hour storm, the rainfall intensity was 0.8 cm/hour on a catchment of area 8.6 km². The measured runoff volume during this period was 2,56,000 m³. The total rainfall was lost due to infiltration, evaporation, and transpiration (in cm/hour) is

1. 1. 0.80

   
   
   

   2. 0.304

   
   
   

   3. 0.496

   
   
   

   4. sufficient information not available

   
   
   

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1. View Hint View Answer Discuss in Forum

   Rainfall, P = i × t = 0.8 × 6 = 4.8 cm
   Run off depth,
   

   R =	Volume of run off
   	Catchment area

   
   

   =	25600
   	8.6 × 106

   
   = 0.02976 m
   = 2.97 m
   

   Total loss =	P - R	=	4.8 - 2.97	= 0.34 cm/h
   	r		6

   Correct Option: B

   Rainfall, P = i × t = 0.8 × 6 = 4.8 cm
   Run off depth,
   

   R =	Volume of run off
   	Catchment area

   
   

   =	25600
   	8.6 × 106

   
   = 0.02976 m
   = 2.97 m
   

   Total loss =	P - R	=	4.8 - 2.97	= 0.34 cm/h
   	r		6

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5. An isohyet is a line joining points of

1. 1. equal temperature

   
   
   

   2. equal humidity

   
   
   

   3. equal rainfall depth

   
   
   

   4. equal evaporation

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: C

   NA

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