1. Concept Explanation (Exam-Focused)
Reservoir
A reservoir is a large artificial lake formed by constructing a dam across a river to store water for future use.
In simple words:
Reservoir = Storage of water for controlled use.
Objectives of a Reservoir (Highly Repeated)
• Irrigation
• Water supply (domestic & industrial)
• Hydroelectric power generation
• Flood control
• Navigation
• Recreation & fisheries
Classification of Reservoirs
1. Based on Purpose
• Irrigation reservoir
• Power reservoir
• Flood control reservoir
• Multipurpose reservoir
2. Based on Location
• Valley reservoir – formed in a river valley
• Bank reservoir – formed by excavating land near river
Types of Reservoir Storage (Most Important Area)
1. Dead Storage
The portion of water below the lowest outlet level, which cannot be used by gravity.
Purpose:
• Sediment deposition
• Maintain minimum water level
2. Live Storage (Useful Storage)
The water stored between minimum drawdown level and full reservoir level.
This is the usable storage.
3. Surcharge Storage
The water stored above full reservoir level up to maximum flood level.
Used only during floods.
4. Bank Storage
Water stored in river banks and surrounding soil due to seepage.
Storage Zone Diagram (Exam Concept)
2. Important Formulas (With Units)
Reservoir Storage Capacity
Storage=Area×DepthStorage = Area \times DepthStorage=Area×Depth
Unit: m³ or ha-m
Reservoir Yield
Yield=Total available storageTimeYield = \frac{Total\ available\ storage}{Time}Yield=TimeTotal available storage
Unit: m³/s
Storage Efficiency
ηs=Useful storageTotal storage×100\eta_s = \frac{Useful\ storage}{Total\ storage} \times 100ηs=Total storageUseful storage×100
🔥 Frequently used in numericals
3. Short Notes / One-Liners
• Dead storage cannot be used for irrigation
• Live storage is also called useful storage
• Surcharge storage is for flood control
• Bank storage increases groundwater
• Multipurpose reservoirs are most economical
• Sedimentation reduces reservoir capacity
• Valley reservoirs are most common
• Reservoir planning ensures water security
4. PYQ Patterns
Common Trends:
Define live, dead and surcharge storage
Identify correct storage zone
Match reservoir type with purpose
Simple storage numericals
Typical Traps:
• Confusing live and dead storage
• Assuming surcharge is usable
• Forgetting unit conversion (ha-m to m³)
• Mixing bank storage with live storage
5. Solved Examples
Example 1 (Conceptual)
Which storage is used for irrigation?
Live storage
Example 2 (Numerical – SSC JE Level)
Area of reservoir = 500 ha
Average depth = 4 m
Storage=500×4=2000 ha-mStorage = 500 \times 4 = 2000 \text{ ha-m}Storage=500×4=2000 ha-m
Example 3 (Storage Efficiency)
Total storage = 3000 ha-m
Live storage = 2100 ha-m
ηs=21003000×100=70%\eta_s = \frac{2100}{3000} \times 100 = 70\%ηs=30002100×100=70%
6. MCQs (50 Exam-Level)
Q1. A reservoir is mainly used for:
A) Storing soil
B) Storing water
C) Storing crops
D) Storing sediment
✅ Answer: B
Q2. Dead storage is provided mainly for:
A) Irrigation
B) Flood control
C) Sedimentation
D) Power generation
✅ Answer: C
Q3. Live storage is also called:
A) Gross storage
B) Useful storage
C) Surcharge storage
D) Bank storage
✅ Answer: B
Q4. Surcharge storage is used during:
A) Drought
B) Normal flow
C) Flood
D) Summer
✅ Answer: C
Q5. Which storage is below lowest outlet?
A) Live
B) Dead
C) Bank
D) Surcharge
✅ Answer: B
Q6. Bank storage is:
A) Stored in dam
B) Stored in canals
C) Stored in soil near river
D) Stored in tanks
✅ Answer: C
Q7. The most economical reservoir is:
A) Flood control
B) Power
C) Irrigation
D) Multipurpose
✅ Answer: D
Q8. Valley reservoirs are formed by:
A) Excavation
B) Constructing dam across river
C) Pumping wells
D) Digging pits
✅ Answer: B
Q9. Which storage is not directly usable?
A) Live
B) Dead
C) Bank
D) None
✅ Answer: B
Q10. Which is not an objective of reservoir?
A) Irrigation
B) Water supply
C) Flood control
D) Soil testing
✅ Answer: D
Q11. Sedimentation reduces:
A) Dam height
B) Storage capacity
C) River length
D) Rainfall
✅ Answer: B
Q12. Reservoir yield is expressed in:
A) ha
B) m
C) m³/s
D) %
✅ Answer: C
Q13. Which storage lies above FRL?
A) Dead
B) Live
C) Surcharge
D) Bank
✅ Answer: C
Q14. The full reservoir level (FRL) separates:
A) Dead and live storage
B) Live and surcharge storage
C) Dead and bank storage
D) Bank and surcharge storage
✅ Answer: B
Q15. Which reservoir is constructed near river banks?
A) Valley
B) Flood
C) Bank
D) Power
✅ Answer: C
Q16. Live storage is used for:
A) Sedimentation
B) Irrigation
C) Flood storage
D) Recreation only
✅ Answer: B
Q17. Which storage improves groundwater?
A) Dead
B) Live
C) Bank
D) Surcharge
✅ Answer: C
Q18. Which is a wrong statement?
A) Dead storage is useful
B) Live storage is useful
C) Surcharge is flood storage
D) Bank storage is temporary
✅ Answer: A
Q19. Gross storage includes:
A) Live only
B) Dead only
C) Live + Dead
D) Surcharge only
✅ Answer: C
Q20. Reservoir planning mainly ensures:
A) More rainfall
B) Better water management
C) Soil fertility
D) Wind control
✅ Answer: B
Q21. Which storage is minimum in drought?
A) Dead
B) Live
C) Bank
D) Surcharge
✅ Answer: D
Q22. Storage is measured in:
A) m³
B) ha-m
C) Both A and B
D) %
✅ Answer: C
Q23. Which reservoir is suitable for flood control?
A) Irrigation
B) Power
C) Flood control
D) Bank
✅ Answer: C
Q24. Which is not part of gross storage?
A) Dead
B) Live
C) Surcharge
D) Bank
✅ Answer: C
Q25. Which storage is for maintaining minimum water level?
A) Dead
B) Live
C) Bank
D) Surcharge
✅ Answer: A
Q26. Multipurpose reservoir is preferred because:
A) Cheap
B) Serves many needs
C) Easy to build
D) Requires no dam
✅ Answer: B
Q27. Which reduces effective life of reservoir?
A) Rainfall
B) Sedimentation
C) Flood
D) Bank storage
✅ Answer: B
Q28. Which storage is temporary?
A) Dead
B) Live
C) Bank
D) Surcharge
✅ Answer: C
Q29. Reservoir planning considers:
A) Topography
B) Rainfall
C) Demand
D) All of the above
✅ Answer: D
Q30. Which one is true?
A) Dead storage is useful
B) Surcharge is normal supply
C) Live storage is usable
D) Bank storage is permanent
✅ Answer: C
Q31. Which storage is below MDDL?
A) Live
B) Dead
C) Surcharge
D) Bank
✅ Answer: B
Q32. The maximum flood level (MFL) marks:
A) Dead storage limit
B) Live storage limit
C) Surcharge storage limit
D) Bank storage limit
✅ Answer: C
Q33. Reservoir yield depends on:
A) Catchment area
B) Rainfall
C) Storage capacity
D) All of the above
✅ Answer: D
Q34. Which is not a classification of reservoir?
A) Based on purpose
B) Based on location
C) Based on soil
D) Based on use
✅ Answer: C
Q35. Live storage lies between:
A) MFL and FRL
B) FRL and MDDL
C) River bed and MDDL
D) MFL and dam top
✅ Answer: B
Q36. Which storage is always conserved?
A) Live
B) Dead
C) Surcharge
D) Bank
✅ Answer: B
Q37. Bank storage mainly depends on:
A) Soil permeability
B) Rainfall
C) Dam height
D) Canal length
✅ Answer: A
Q38. Reservoir planning is part of:
A) Soil mechanics
B) Water resources engineering
C) Environmental engineering
D) Structural engineering
✅ Answer: B
Q39. Which is not an advantage of reservoirs?
A) Water supply
B) Flood control
C) Soil erosion
D) Power generation
✅ Answer: C
Q40. Which storage is used only in emergency?
A) Dead
B) Live
C) Surcharge
D) Bank
✅ Answer: C
Q41. Reservoirs increase:
A) Rainfall
B) Groundwater recharge
C) Wind speed
D) Temperature
✅ Answer: B
Q42. The lowest level of water for use is called:
A) FRL
B) MFL
C) MDDL
D) Dam crest
✅ Answer: C
Q43. Which storage ensures long-term sustainability?
A) Live
B) Dead
C) Surcharge
D) Bank
✅ Answer: B
Q44. Which is not considered while reservoir planning?
A) Catchment yield
B) Water demand
C) Crop pattern
D) Soil bearing capacity of building
✅ Answer: D
Q45. Reservoirs are mainly planned for:
A) Storing rainwater
B) Regulating river flow
C) Reducing wind
D) Reducing temperature
✅ Answer: B
Q46. Which storage is above FRL and below MFL?
A) Dead
B) Live
C) Surcharge
D) Bank
✅ Answer: C
Q47. Which is a limitation of reservoirs?
A) Water supply
B) Flood control
C) Submergence of land
D) Power generation
✅ Answer: C
Q48. Gross storage excludes:
A) Live storage
B) Dead storage
C) Bank storage
D) None
✅ Answer: C
Q49. Reservoir planning mainly balances:
A) Supply and demand
B) Soil and water
C) Cost and labour
D) Rainfall and wind
✅ Answer: A
Q50. The ultimate aim of reservoir planning is:
A) Bigger dams
B) More canals
C) Optimum water utilization
D) More rainfall
✅ Answer: C