Reservoir vs Dam is a common topic in civil engineering, yet many people confuse the two terms. While a dam is a structural barrier constructed across a river to control water flow, a reservoir is the stored body of water created behind the dam. Understanding the difference between dam and reservoir is essential for grasping water resource management concepts. This article explains the types of reservoirs, their classification, and the functions of reservoir systems in irrigation, hydropower generation, flood control, and water supply. It also discusses the types of dams and reservoirs and highlights the purpose of dams and reservoirs in sustainable development and comparison of dams vs reservoirs. By clarifying these concepts, engineers and students can better understand modern water infrastructure systems. The Reservoir is located on the upstream side of dams and prevents floods by managing the water flow apart from serving as a storage basin.
What is a dam ?
A dam is a man-made structure built across a river or stream to control, store, or divert water. Engineers construct dams to create reservoirs for irrigation, hydropower generation, drinking water supply, and flood control. Different types of dams, such as gravity, arch, and earth dams, serve specific site conditions and purposes. Dams play a vital role in water resource management and support sustainable development by regulating water flow and ensuring reliable water availability.
For more details please read :
- Types of Dams – 3 Classification Criteria Explained.
- Components of a bridge – Types and Functions Explained
- Components of a dams-12 Dam Components explained.
What is a reservoir ?
A reservoir is a natural or artificial water storage area created to collect and store water for various uses. In most cases, engineers form a reservoir by constructing a dam across a river, allowing water to accumulate behind it. Reservoirs play a crucial role in water resource management by supplying water for irrigation, drinking purposes, industrial use, and hydropower generation. They also help in flood control by regulating excess water during heavy rainfall. There are different types of reservoirs based on purpose and location, including storage and detention reservoirs. Proper reservoir management ensures sustainable water supply, environmental balance, and long-term infrastructure efficiency.
Functions of Reservoirs
Reservoirs play a vital role in modern water resource management by storing and regulating water for multiple uses. They support irrigation, drinking water supply, hydropower generation, and flood control. By managing seasonal variations in rainfall and river flow, reservoirs ensure reliable water availability and reduce the impact of droughts and floods. Reservoirs are man made lake or a fresh water body that plays an important role a lot of ways as listed below.
- Water supply
- Flood control
- Environmental management
- Hydroelectric power management
- Navigation
- Irrigation
- Development of fish and wildlife
- Soil conservation
Types of reservoirs
Reservoirs are classified based on their purpose, location, and operational characteristics. Different types of reservoirs serve specific functions such as water storage, flood control, and distribution. Understanding the types of reservoirs helps engineers design efficient water management systems and ensure reliable supply for irrigation, hydropower, and domestic needs.
Reservoirs are broadly classified based on purpose and location
Classification Based on Purpose
- Storage Reservoir
- Detention (Flood Control) Reservoir
- Distribution / Service Reservoir
Storage Reservoir
A storage reservoir stores excess water during periods of high rainfall or river flow for use during dry seasons. Engineers use storage reservoirs to ensure a reliable water supply for irrigation, drinking water, hydropower generation, and industrial needs. They help regulate seasonal variations and support long-term water resource management.
Detention (Flood Control) Reservoir
A detention (flood control) reservoir temporarily stores excess runoff during heavy rainfall or flood events and releases it gradually to downstream areas. Unlike storage reservoirs, it does not retain water for long-term use. Its main purpose is to reduce flood peaks, protect infrastructure, prevent riverbank overflow, and minimize damage to urban and agricultural areas.
Distribution / Service Reservoir
A distribution or service reservoir stores treated water within a water supply system to ensure continuous and regulated distribution to consumers. It helps maintain adequate pressure in pipelines and balances daily fluctuations in demand. Service reservoirs are commonly located at elevated points to allow gravity flow, improving efficiency and reliability of municipal water supply networks.
Classification based on locations
- Valley dammed reservoirs
- Bank-side reservoirs
- Service reservoirs
Valley dammed reservoirs
Valley dammed reservoirs are located between mountain valleys where there is an existing water body. A dam is built in the narrowest portion for holding the water. A valley-dammed reservoir forms when engineers construct a dam across a river valley, allowing water to accumulate naturally behind the structure. This type of reservoir is commonly used for large-scale water storage, irrigation, hydropower generation, and flood control. It takes advantage of natural topography, making it efficient and suitable for major water resource projects.
Bank-side reservoirs
A bank-side reservoir is constructed adjacent to a river rather than directly across it. Water is diverted or pumped from the river into the reservoir for storage. This type of reservoir helps regulate water supply, reduce sediment entry, and maintain controlled storage levels. Bank-side reservoirs are commonly used for municipal and industrial water supply systems. Bank side reservoirs are made by diverting water from rivers and streams to an existing reservoir. These reservoirs can be located in different geographical locations.
Service reservoirs
A service reservoir is a storage structure used in water supply systems to hold treated water before distribution to consumers. It ensures continuous supply, maintains adequate pressure in pipelines, and balances fluctuations in daily demand. Service reservoirs are often located at elevated positions to allow gravity-based distribution and improve overall system efficiency. Service reservoirs are man made reservoirs located above the ground or below the ground. The huge water towers/ water tanks and sumps are service reservoirs.
Reservoir Components and Terms
Reservoir components and terms define water levels, storage zones, and operational limits that control storage capacity, flood management, and water supply reliability in dam and reservoir engineering systems.
Main Reservoir Components & Terms
- Maximum Pool Level (MPL)
- Normal Pool Level (NPL)
- Minimum Pool Level (MinPL)
- Useful (Live) Storage
- Dead Storage
- Surcharge Storage
- Gross Storage
- Reservoir Yield
- Spillway Level
- Intake Level
Maximum Pool Level (MPL)
Maximum Pool Level is the highest water level a reservoir can safely reach under designed conditions. Water should not rise above this level except during extreme floods. It defines the upper storage boundary and protects the dam from overtopping and structural stress.
Normal Pool Level (NPL)
Normal Pool Level is the regular operating water level maintained in a reservoir under standard conditions. It represents the top of useful storage and ensures stable water supply for irrigation, hydropower, and municipal needs.
Minimum Pool Level (MinPL)
Minimum Pool Level is the lowest operational water level from which water can be withdrawn. Below this level, outlets cannot function effectively. It separates useful storage from dead storage in reservoir design.
Useful (Live) Storage
Useful storage is the volume of water between the Normal Pool Level and Minimum Pool Level. This water is available for irrigation, water supply, and power generation. It forms the active and operational storage zone of the reservoir.
Dead Storage
Dead storage lies below the Minimum Pool Level. This water cannot be drained by gravity through outlets. It mainly accommodates sediment deposition and prevents silting from affecting live storage capacity.
Surcharge Storage
Surcharge storage is the temporary water volume stored between the Normal Pool Level and Maximum Pool Level during flood conditions. It helps control floods by temporarily holding excess inflow before safe discharge through the spillway.
Gross Storage
Gross storage is the total volume of water between the reservoir bed and Maximum Pool Level. It includes live storage, dead storage, and surcharge storage combined.
Reservoir Yield
Reservoir yield is the quantity of water a reservoir can supply over a specified period under given conditions. It depends on inflow, storage capacity, evaporation losses, and operational policy.
Reservoir Planning
Reservoir planning involves technical evaluation of site conditions, geology, hydrology, and storage requirements to ensure safe construction, optimal water storage, and long-term operational efficiency in dam and reservoir projects.
Key Factors in Reservoir Planning
- Topography
- Groundwater Conditions
- Permeability of Foundation
- Hydrological Investigation
- Geological Investigation
- Catchment Characteristics
- Sedimentation Study
- Environmental and Social Impact
Topography
Topography plays a crucial role in reservoir site selection. Engineers prefer broad natural valleys, either U-shaped or V-shaped, as they allow efficient water storage with minimum dam length. Flat plains are generally unsuitable because they require larger embankments and result in excessive submergence and higher construction costs.
Groundwater Condition
Groundwater investigation determines the relationship between the water table level and reservoir water level. If the reservoir level is significantly higher than the groundwater table, seepage losses may occur. Ideally, balanced groundwater conditions reduce loss and prevent uplift pressure or instability in the foundation.
Permeability
Permeability refers to the ability of soil or rock to allow water to pass through it. Highly permeable foundations can lead to seepage and structural instability. Therefore, detailed geotechnical investigation is required to assess permeability and decide on grouting or cutoff measures.
Hydrological Investigation
Hydrological investigation studies rainfall, runoff patterns, flood frequency, and inflow data. Engineers calculate storage capacity, maximum discharge rate, and probable maximum flood. This analysis ensures adequate reservoir capacity and safe spillway design to manage extreme flood events.
Geological Investigation
Geological studies assess rock type, fault lines, and structural stability of the foundation. Strong and stable rock formations are preferred to ensure dam safety and prevent seepage or settlement problems.
Catchment Characteristics
The size, slope, soil type, and vegetation cover of the catchment area affect runoff and sediment load. Proper assessment ensures accurate estimation of reservoir yield and long-term performance.
Sedimentation Study
Sedimentation reduces reservoir storage capacity over time. Engineers estimate sediment inflow and design dead storage accordingly to maintain useful storage capacity for the project life.
Environmental and Social Considerations
Reservoir planning must evaluate ecological impact, submergence of land, rehabilitation of displaced populations, and environmental sustainability before final approval.
Difference between dams vs reservoirs
Dams vs reservoirs is a commonly discussed topic in civil engineering and water resource management. Although closely related, dams vs reservoirs serve different purposes. A dam is a structural barrier built to control water flow, while a reservoir is the stored water body formed behind the dam for various uses.
| DAMS | RESERVOIR |
| Structural barriers built across,rivers valleys,streams etc for the purpose of storing and managing water flow. | Reservoir is a large water body formed behind the constructed dam structure across a river,stream,etc |
| Dams are reinforced concrete structures or structures made of bricks rubble etc erected across water bodies to control the water flow. | The reservoir is the water that accumulates behind the constructed dam. |
| Create site for hydro electric power generation. This can improve the industrial development and living standards of people living in that region. | Stores water for later usage, water for human consumption and excess water for agricultural and industrial uses. |
| Dams fluctuates oxygen levels and restricts migration of fishes in the river. | Reservoirs leads to the displacement of people. |
| Dams are tourist attraction sites | Helps in water transportation |
Reservoir Sedimentation
Rivers transport sediments. During heavy rainfall, sediments are carried by the water to the reservoir. Silts are accumulated due to soil erosion. These get collected in the dead storage.
Sedimentation depends on Rainfall intensity, Soil nature, Soil type, topography and vegetation. The sediment deposit replaces the water storage. Thus water supply and flood control are affected.
The sediments should be removed eventually. Hydraulic flushing, dredging, Explosive mobilization are methods adopted for sedimentation removal.
Environmental impacts of Reservoirs.
- The construction of the reservoir prompts severe effects on the environment.
- Since the water is stored, the rate of transpiration is high. This changes the moisture concentration.The climate of the surrounding area is affected. It causes natural temperature fluctuation. This causes heavy rainfall and deprives the traditional rainfall patterns.
- Reservoirs disturb the flow and composition of the rivers. The water from the downstream has high energy, it enhances the water flow by eroding the river bed.
- The change in the river composition affects the upstream and downstream habitats. The reservoirs disturb the fish and birds migration.
- Studies show that reservoirs emit greenhouse gases. Anaerobic bacterias are seen in the river bed releases carbon dioxide and methane. This occurs in tropical regions.
- They also cause troubles for people living near the reservoir site. Old and failing dams lead to disasters.
- Reservoir induced seismicity is a phenomenon of provoking earthquake by reservoirs. This happens when water sweeps into the minor cracks under the bed.
Key Takeaways
- Reservoir vs Dam explains the structural and functional difference between a dam and the stored water body.
- A dam is a structural barrier, while a reservoir is the water stored behind it.
- Understanding the difference between dam and reservoir is essential in water resource management.
- Reservoirs support irrigation, hydropower generation, and drinking water supply.
- Flood control is a major function of reservoirs.
- There are different types of reservoirs based on purpose and location.
- Valley-dammed and bank-side reservoirs serve different site conditions.
- Storage zones include live storage, dead storage, and surcharge storage.
- Proper reservoir planning ensures long-term performance.
- Sedimentation and environmental impacts must be carefully managed.
Conclusion
Understanding Reservoir vs Dam is fundamental in civil engineering and water resource management. A dam controls and regulates river flow, while a reservoir stores water for irrigation, hydropower generation, flood control, and drinking purposes. Knowing the difference between dam and reservoir helps engineers design efficient and sustainable water infrastructure systems. Various types of reservoirs serve specific functions, and proper planning ensures long-term storage capacity and safety. Reservoir components such as live storage, dead storage, and surcharge storage play a critical role in performance. With increasing water demand and climate variability, the purpose of dams and reservoirs becomes even more significant in achieving sustainable development and reliable water management systems.
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